Post on 20-Feb-2022
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DETERMINATION OF REACTIONS AND INTEGRITY OF CEMENT-
MUDSTONE INTERFACES
A thesis submitted to The University of Manchester for the degree of Master of Science
in the Faculty of Physical Sciences
2016
JORGE ARTURO MENDOZA ULLOA
SCHOOL OF EARTH, ATMOSPHERIC AND ENVIRONMENTAL SCIENCES.
THE UNIVERSITY OF MANCHESTER
9 September 2016
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Table of contents
List of tables ........................................................................................................................ 4
List of figures ...................................................................................................................... 4
ABSTRACT ........................................................................................................................ 6
Chapter 1: Introduction ..................................................................................................... 10
1.1 Rationale .................................................................................................................. 11
1.2 Aims......................................................................................................................... 12
1.3 Objectives ................................................................................................................ 12
Chapter 2: State of the art .................................................................................................. 13
Introduction ................................................................................................................... 13
2.1 Experiments on interaction between clays and hyperalkaline solutions ................. 13
2.2 Experiment with low-pH cement ............................................................................. 18
Chapter 3: Materials .......................................................................................................... 21
Introduction ................................................................................................................... 21
3.1 Mudstones ................................................................................................................ 21
3.1.1 The Whitby Mudstone ...................................................................................... 21
3.1.2 Kimmeridge Clay Formation ............................................................................ 24
3.1.3 Holywell shale .................................................................................................. 27
3.1.4 Pyritiferous Shale .............................................................................................. 28
3.2 Cement ..................................................................................................................... 30
3.2.1 Microcement ..................................................................................................... 32
3.2.2 CEM II/A-LL 42,5N ......................................................................................... 33
3.3 Silica fume ............................................................................................................... 33
3.4 Nirex Reference Vault Backfill ............................................................................... 35
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3.4.1 Limestone flour ................................................................................................. 35
3.4.2 Hydrated lime.................................................................................................... 36
3.5 Sample formulation and nomenclature .................................................................... 37
3.6 Sample preparation .................................................................................................. 39
4 Methodology .................................................................................................................. 43
Introduction ................................................................................................................... 43
4.1 Ligth microscopy ..................................................................................................... 43
4.2 ESEM and analysis .................................................................................................. 44
4.3 EMPA analysis ........................................................................................................ 46
4.4 Cement permeability ................................................................................................ 48
4.4.1 Oscillating Pore Pressure Method ..................................................................... 48
4.4.2 Permeability procedures.................................................................................... 52
4.5 Cement Porosity ...................................................................................................... 56
Chapter 5: Results ............................................................................................................. 57
5.1 Transmitted and reflected light microscopy ............................................................ 57
5.2 ESEM analysis ......................................................................................................... 62
5.4 Permeability ............................................................................................................. 90
5.4 Porosity .................................................................................................................... 99
Chapter 6 Discussion ....................................................................................................... 101
Chapter 7 Conclusions .................................................................................................... 104
REFERENCES ................................................................................................................ 105
19657
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List of tables
Table 1: Compilation of the state of the art regarding the interaction between Clay-
bearing rocks and cement. Ref. (Dauzeres et al , 2010) ....................................................... 20
Table 2: Summary of clay rocks used in this research. ..................................................... 29
Table 3: Shorthand form of chemical compounds found in Portland cement ................... 31
Table 4: Chemical composition of the most common types of microsilica ...................... 34
Table 5: Composition of Hydrated Lime .......................................................................... 36
Table 6: Composition (wt%) of the 7 mixtures utilized in this research. .......................... 38
Table 7: The cement mixtures and clay-bearing lithologies used in the experiments ...... 38
Table 8: Resume of all samples analysis. .......................................................................... 88
Table 9: Test conditions for every sample ........................................................................ 91
Table 10: Porosity results. Porosities obtained with the Digital Helium Porosimeter .... 100
List of figures
Figure 1 Whitby Mudstone ESEM. ................................................................................... 24
Figure 2: Kimmeridge Clay ESEM. .................................................................................. 27
Figure 3: Special mould specifications and details. .......................................................... 40
Figure 4 Cement mixing procedures.. ............................................................................... 41
Figure 5 Thinsection making. ........................................................................................... 42
Figure 6: Zeiss Axioskop 50 ............................................................................................. 43
Figure 7: ESEM. ................................................................................................................ 44
Figure 8: Thin section detail. ............................................................................................. 46
Figure 9: EPROBE. ........................................................................................................... 47
Figure 10 Oscillating pore pressure readings. ................................................................... 50
Figure 11: Space solution for equation 1. ......................................................................... 52
Figure 12: Permeameter scheme.. ..................................................................................... 53
Figure 13 Cement cores for permeability tests.. ................................................................ 54
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Figure 14 DHP -100. ......................................................................................................... 56
Figure 15: OPC4 optical analysis. ..................................................................................... 58
Figure 16: PMS4 optical analysis ..................................................................................... 59
Figure 17: OPC2 optical analysis. ..................................................................................... 60
Figure 18: OPC4 SEM analysis. ....................................................................................... 64
Figure 19: OPC4 element mapping.. ................................................................................. 65
Figure 20: OPC4 Si map from SEM ................................................................................. 66
Figure 21: OPC4 SEM analysis.. ...................................................................................... 67
Figure 22: OPC4 element mapping. .................................................................................. 68
Figure 23: OPC4 Si map from SEM. ................................................................................ 69
Figure 24: OPC4 SEM analysis. s. .................................................................................... 70
Figure 25: OPC4 element mapping.). ................................................................................ 71
Figure 26 PMS3 element mapping.. .................................................................................. 73
Figure 27 OPC5 element mapping. ................................................................................... 74
Figure 28: OPC4 EPMA analysis. ..................................................................................... 79
Figure 29: OPC4 EPMA analysis.. .................................................................................... 80
Figure 30: OPC4 EPMA analysis. ..................................................................................... 81
Figure 31: OPC4 EPMA analysis. ..................................................................................... 82
Figure 32 PMS4 Ca map by EPMA analysis. ................................................................... 83
Figure 33: PMS4 Si map by EPMA analysis. ................................................................... 84
Figure 34: PMS4 Al map by EPMA analysis(Left) .......................................................... 85
Figure 35: PMS4 element map detail by EPMA analysis ................................................. 86
Figure 36: NRV5 element maps by EPMA.. ..................................................................... 87
Figure 37: MPC5 permeability results .............................................................................. 92
Figure 38: OPC permeability results ................................................................................. 93
Figure 39: PMS5 permeability results .............................................................................. 94
Figure 40: NRVB permeability results............................................................................. 95
Figure 41: PMS permeability results ................................................................................. 96
Figure 42: MPC3 permeability results .............................................................................. 97
Figure 43: Summarised permeability results. .................................................................... 98
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ABSTRACT
This research examined the cement-rock/clay interface at an initial setting stage by
undertaking a series of experiments involving setting of cement against clays and mudstone
and examining the boundaries formed in terms of mineralogy, permeability and porosity.
Reactions and integrity will be study within the context of the Deep Geological
Repositories for Nuclear Waste.
The experiments were undertaken in cement cores of around 2.5cm (for porosity and
permeability). Polished thin sections were employed to analyse the interface and look at the
reactions between cement and rock. The preparation of the samples is also described where
some special moulds and methods were developed in order to make cement core samples
that could be subject to permeability test. Environmental Electron Scanning Microscope
and Electron Probe Micro Analysis were employed in the attempt to identify the
interactions that took place in the interface between both materials (cement and rock).
Petrophysical equipment such as permeameters and porosimeters were also employed to
test cement cores and measure their flow properties. These equipment and methods are also
described.
Experiments ‘results indicated a clear Ca depletion zone near to the interface with the
rock. This alteration was found only in common cement mixtures, whereas the specially
designed mixtures did not show any alteration after 28 days of interactions with pore water.
The usage of pore water is a difference with other researches since groundwater is mainly
used. All of the cement samples investigated proved to have a very low permeability
compared with the probable host rock for the repository. A particular result regarding the
porosity of NRVB was found, where this cement shows a porosity of 44% and still keeps a
very low value for permeability meanwhile other cements mixtures shows porosity of 10 to
20%.
Cracking and shrinkage due to water loss was present in samples with high water-cement
ratios. Therefore it was not possible to relate cement alteration with a change in porosity of
permeability due to technical problems in the process of sample making (mostly cracking
and shrinkage of cement samples). This was tried to be overcome by testing partially
saturated samples (with pore water from curing) but results were not satisfactory due to
lack of consistency.
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DECLARATION
No portion of the work referred to in the thesis has been submitted in support of an
application for another degree or qualification of this or any other university or other
institute of learning.
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and in The University’s policy on Presentation of Theses
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ACKNOWLEDGEMENTS
I would like to thank my supervisors Prof. Richard Pattrick and Dr. Julian Mecklenburgh
of the School of Earth and Environmental Sciences for his expertise, guidance and support
through this research.
I would also like to thank Prof. Ernest Rutter, Dr. Rochelle Taylor and Experimental
officer Stephen May from the Rock Deformation Laboratory in SEES for all their help,
assistance, training and willingness in the use of the facilities for sample preparation and
permeability tests. Thanks as well to Dr. Jonathan Fellowes for his training and assistance
in the operation of the Environmental Scanning Electron Microscope and the Electron
Probe Micro Analyser which was a key aspect in the development of this research.
Very special thanks to Prof. Ernest Rutter and Prof. Kevin Taylor from SEES for the
provision of the rock samples used in this research.
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Chapter 1: Introduction
Cement is the most common material used in the construction of all kinds of
infrastructure and much of this construction involves the interaction of cement with many
other materials, both natural and manmade
Nowadays there is also a special concern regarding our legacy of radioactive waste and
the challenge to safe dispose of it. Among the proposals to deal with this problem the
accepted final disposal method is the deep Geological Disposal Facility (GDF) also called
Deep Geological Repository (GDR). A Deep Geological Repository is a facility, with more
than 300m depth, that provides isolation for radioactive waste deep inside a suitable rock
volume to ensure that no harmful quantities of radioactivity ever reach the surface
environment. Such isolation is provided by the natural geological barrier and the
Engineered Barrier System (EBS) which may itself comprise a variety of sub-systems or
components, like the waste form which is the nuclear waste itself, canister which might
have different systems like a copper canister or drums in some cases, buffer or backfill
surrounding the canister, seals and plugs (Apted & Ahn, 2010).
Within the many concepts of the GDR, clay-rich geological formations have been
proposed as host rock for different countries like France, Switzerland and Belgium.
Commonly, cement is used in the form of concrete to provide a rigid and strong structure
for a wide variety of purposes. In other cases cement is used in the form of mortar or grout
to work as a binder between two surfaces or to provide isolation and sealing to avoid
leaking of a fluid such as gas or oil, such as in the case of petroleum well-bores.
It is important to note that the use of cement would have to be optimized in order to
minimize the influence of cement - based materials to the surrounding environment. This
has led to the development of new low pH grouts. High pH conditions of grout materials
have been studied and found to limit uranium solubility by forming uranyl–oxides, -
hydroxides and uranate salts (Serne, LeGore, Ames, LindenmeiRr, & Richland, 1993),
however the solubility of uranium in cement waste forms has been investigated generally in
undersaturated conditions. Other studies have shown that solubility of uranium could rise at
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high pH and high carbonates levels if aerobic conditions happen to develop (Sutton,
Warwick, Hall, & Jones, 1999). Interaction of groundwater with high pH cement
(conventional cement) can lead to carbonation and then to an acceleration of the release of
uranium, increase its mobility and change the solubility of other materials that might be
used as buffer, such as bentonite by reducing swelling capacity and sorptive properties
(Gascoyne, 2002).
1.1 Rationale
Regardless the different geological disposal concepts that are currently being
investigated and developed there is the need to use cement-based materials during the
construction and operation of the repository, mostly for practical reasons, (access tunnel
floors, constraint of water ingress, backfilling and sealing of tunnels, sarcophagus for
intermediate level waste). In Deep Geological Repositories for nuclear waste disposal,
cement – based materials will be exposed to very aggressive environments. For geological
disposal, in particular, the engineered repository is expected to last for up to 100,000 years.
The very long time performance expected for these projects implies the need to deeply
understand the behavior and interactions of cements with the surroundings materials.
No suitable site has been chosen so far in the United Kingdom to function as DGR, but
clay-rich formations are likely to be seriously considered. Clay-rich formations and cement
have very contrasting chemistries. Cements will be altered and release ions (mainly OH-,
K+, Na
+ and Ca
2+), resulting in high-pH porewater ranging between 10 and 13.5 and
generating a phenomenon called hyperalkaline plume which is likely to produce
physicochemical alterations not only in the host rock, but in other repository materials such
as artificial barriers(ECOCLAY II, 2005) (Alonso, Bárcena, Alonso, Pettersson, & Bodén,
2009). Since cementitious materials are likely to be used in GDF as structural elements,
backfill or waste matrix, interaction between cement and the host rock would lead to
mineralogical alterations in both faces which could have an impact in physical and
functional properties such as permeability.
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Interactions between cement-based materials and rock interfaces take place in many
projects around the world such as tunnels, foundations, wells, etc. This research will only
focus in the interactions between cementitious materials and clay in the context of a GDF
for nuclear waste.
A brief description of the different cement mixtures that were used (such as regular
cement based grout, Nirex Reference Vault Backfill (NRVB) and other mixtures
specifically design to provide low pH that includes the addition of microsilica up to 40%) is
given in the first chapters. Litholigies involved in this research are mudstones and
claystones from England such as the Whitby Mudstone, Kimmeridge Clay, Yorkshire Clay
and Holywell Clay are also described focusing on mineralogy descriptions.
1.2 Aims
The aim of this research is to provide a more detailed and complementary knowledge
regarding to the interactions between cementitious materials and clays that might be in
interactions in the Deep Geological Repositories (DGR) for Nuclear Waste.
1.3 Objectives
The main objective of this thesis it to determine the interactions between different cement
mixes and mudstones in candidate lithologies that might host the UK´s geological facility
and determine the permeability of those different mixes.
To produce a series of samples of cement mixes containing a variety of UK mudstones
that will allow observation of the nature of cement-rock interfaces.
To determine chemical change at the interface by using optical imaging and micro-
elemental mapping.
To determine the effect of addition of microsilica to the cement on the interaction
between cement and mudstones.
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Chapter 2: State-of-the-art
Introduction
Hyperalkaline solutions are expected to be found in the GDR, mostly from cement-based
materials in contact with the host rock or other components within the repository. The
research seems to have focused first to understand the interactions between clay rocks and
hyperalkaline solutions, by undertaking experiments in batch reactor or analysing natural
analogies, like the Khushaym Matruk and Maqarin sites in Jordan that may give more
detailed information about the interactions that might take place over the years.
Low-pH cements have arisen as an option to be used in the DGR context. Some of those
cements involves the addition of silica fume (Holt, 2008).
Furthermore, there is no much information about the interactions with hyperalkaline
solutions with clay rocks from the UK. Much of the research also has focused to understand
the alteration after months or even years of interaction.
2.1 Experiments on interaction between clays and hyperalkaline solutions
Much research has been undertaken in recent years regarding to the reactions in the
cement-mudstone interface and a compilation is presented in Table 1. Experiments in batch
reactors have been undertaken to investigate the effects of high-pH solutions in clay rocks.
X- ray diffraction and Scanning Electron Microscope techniques have been applied to
analyse the effects .Most of the rock samples are clay-rich rocks such as the Opalinus Clay,
the Tournemire argillite and the Callovo - Oxfordian argillite (Adler, Mader, & Waber,
1999; Chermak, 1992, 1993; Claret, Bauer, Schafer, Griffault, & Lanson, 2002; Devol-
Brown, Tinseau, Bartier, Mifsud, & Stammose, 2007; Elie et al., 2004; Ramirez et al.,
2005).
The evolution of the pore water chemistry during degradation of commercial cement has
been investigated (Berner, 1992; Taylor, 1990) showing that pH plays an important role in
the cement degradation that takes place once the concrete is saturated with ground water.
Initially generating a aqueous solution rich in K, Na, Ca ions of pH > 13, it is followed by a
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fluid with pH dominated by equilibrium with Ca(OH)2 (pH 12.4) and finally by equilibrium
with the Calcium silicate hydrate minerals, termed hereafter as C-S-H minerals, which is
the main component of the product of the hydration of Portland cement (pH ≥ 10). This
degradation sequence found with commercial cement can be modified by using low pH
cement which would decrease the disturbing effects in clays (Glasser, 1996).
Experiments conducted in the interaction between CEM I –SR cement (Sulphate resisting
Portland Cement class I) and samples of mudstones collected at 490m depth on the
Callovo- Oxfordian Formation in the Meuse and Haute Marne Depart, in France; showed a
low carbonation that does not clog the interface between cement and mudstone. This lack
of clogging allows the diffusion of aqueous species and the consequent degradation of the
cement. The portlandite dissolution and reduction of CaO/SiO2 in the C-S-H resulted in
decalcification of the cement material (Dauzeres et al 2010).
Interactions between bentonite and concrete has also been investigated, given that
Bentonite has been envisaged as an engineered barrier in DGR, due to its extremely low
permeability, high swelling pressure to provide a good contact with host rock, small pore
sizes and reduced water activity to suppress microbial activity; and its ability to limit the
rate of transport of radionuclides (NDA, 2014). The effects of the alkaline plume caused by
concrete on bentonite has been investigated in Phases I and II of the of the project
ECOCLAY between 1997 - 2000 and 2000 – 2003(ECOCLAY II, 2005; Huertas et al.,
2000). This project contained two types of experiment, batch reactions at temperatures
ranging from 24 to 200°C mixing the Spanish reference Bentonite FEBEX and
hyperalkaline solutions (NaOH/KOH/Ca(OH)2) with pH ranging from 10 to 13.5; and
transport cell experiments where compacted FEBEX bentonite (1.5 cm thickness, dry
density of 1.2 g/cm2 ) and Ordinart Portland Cement mortar (1.5cm thickness) were
introduced in order to investigate physico-chemical changes in bentonite after the
interaction with the cement. (Cuevas et al., 2006)(Cuevas & Leguey, 2006). Cuevas found
zeolites, analcime and phillipsite formed at high temperatures at the interface, whereas
Magnesium-clay precipitated and tobermorite-type hydrated calcium silicate was found.
These results are consistent with the dissolution of montmorillonite, (primary compound of
bentonite) which can be identified by the presence of analcime and tobermorite.
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Montmorillonite dissolution allows the pH to decrease by equilibrium with C-S-H minerals
(Savage, Arthur, Watson, & Wilson, 2010).
In situ studies have been also carried out in the Boom Clay/Portland Cement interactions
at different temperatures (Read et al, 2001). Boom clay is a marine clay deposit in Belgium
consisting of clay minerals (30-60 %, mainly illite and kaolinite), quartz (15-60%), calcite
(1-5%), K-feldspar and albite (both 1-10%), pyrite (1-5%) and ≈5% organic carbon (De
Craen, Wang, Geet, & Moors, 2004) The depth of the degradation zone in the cement paste
was found to be about 100 - 150 µm after 18 months where a portlandite dissolution was
observed as well as a porosity increase. The phases precipitated included magnesium -
aluminate hydroxide, Mg3Si4O10(OH)2 (magnesium - silicate hydroxide) and a low
crystallinity gel. In the Tournemire site in France a second in situ experiment was
conducted on Tournemire argillite/concrete interactions. 4 major phases are the components
of Tournemire argillite: silicate phase (clays, quartz, feldspars, micas) (≈86%), sulphide
phase (pyrite) (≈3%), carbonated phase (calcite, dolomite) (≈10%) and organic kerogen
form (≈1%). Within the clay minerals SEM observations indicated the presence of chlorite,
kaolinite, and a mixed layer of illite/smectite. Mineralogical characterization obtained by
X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the
clay/concrete interface after interaction of 7, 15 and 125 years in samples taken from an
ancient tunnel railway which is now part of the Tournemire experimental station. Analysis
showed recrystallization of the mixed layer illite/smectite and gypsum precipitation within
the saturated zone of the clay. Chlorite and kaolinite were dissolved near the interface and
important dolomite dissolution was identified (Tinseau, Bartier, Hassouta, Devol-Brown, &
Stammose, 2006).
Experiments in batch reactors were performed in the Tournemire clay rock where clay
was used in powder or fragments with a hyperalkaline solution (NaOH and KOH solutions
with pH≈13). Aqueous chemistry and solid analysis showed dissolution of pyrite, dolomite
and organic carbon, with the precipitation of calcite. SEM analysis revealed localized
zeolites and K-feldspars precipitations but only observable by SEM analysis. . (Devol-
Brown et al., 2007).
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The impact of the porewater of cements materials on clay materials is the main
interaction investigated. In experiments often an alkaline fluid (pH=13.2) is used as an
analogy to the cement porewater (Claret et al., 2002). Samples from the Callovo-Oxfordian
formation were studied in batch reactor experiments conducted at 60 °C with alkaline
solutions in order to investigate the chemical degradation of the clay rock. Smectite
degradation and precipitation of a tobermorite - like phase were found in the clay.
Several studies have been performed also in the Opalinus Clay from Mont Terri,
Switzerland. Experiments with different types of alkaline fluids at different temperatures
were conducted: pH 13.2 (with the addition of potassium, sodium, and calcium hydroxides)
at 30 °C (Adler et al., 1999), pH 13 and 12 (sodium hydroxide NaOH and potassium
hydroxide KOH) at 150 to 200 °C (Chermak, 1992, 1993). During the high temperature
experiments zeolite - type analcime, phillipsite, (Na , K) rectorite were observed.
A series of experiment conducted at 70 °C in order to investigate the rate and reaction
mechanism of cement - pore fluids (sodium, potassium, and calcium-bearing) with silicate
minerals (quartz, feldspars, micas and clays). Results showed a C-S-H precipitation. The
rate of growth of C-S-H was limited by the rate of supply of silicon by the dissolution of
primary silicates (quartz, feldspars, micas and clays) (Savage et al 1992). Different
experiments (bulk dissolution in batch reactor and in situ atomic force microscopy)
conducted on the dissolution of montmorillonite under alkaline conditions (pH=13.3) at 30,
50 and 70 °C found that dissolution rates of individual particles is independent on the
particle size, morphology and stacking (3.39-12
, 1.75-11
and 5.81-11
mol/m2 s, respectively).
Initial concentrations of SiO2 produced by montomorillonite dissolution were high in early
stages in bulk experiments and reached a steady state after 136 hours. (Yokoyama et al
2005). Other experiments were carried out in sandstones (Braney et al 1993), where the
analysis of the evolution of minerology of alkaline fluids showed quartz and feldspar
dissolutions and phase precipitation of C-S-H and hydrated calcium alumino-silicate.
Experiments in batch reactors with smectite and kaolinite dissolutions at 35 °C and 80 °C
in potassium hydroxide solutions, with different solid-mass/solution-volume ratios, indicate
difference dissolution rates between the minerals (smectite and kaolinite), explained by
structural differences (Bauer et al 1998). Interactions between alkaline fluid and minerals
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were also investigated after a review of the experimental and modelling studies regarding to
the expected interaction between alkaline fluids and potential host rocks in a radioactive
waste repository environment. Such interactions were investigated by experiments with
Ca(OH)2 solution containing muscovite and chlorite at 85 °C. Solids were analysed by
analytical transmission electron microscopy (ATEM) showing the formation of C-S-H
phases and precipitation of local zeolites (Hodgkinson et al 1999). Another series of
experiments studied the impact of circulation of portlandite - saturated water on MX-80
bentonite or a mixture of compacted mudstone (Manois argillite) and calcareous sand for
periods of 3, 6 and 12 months at 20 and 60 °C. Results indicate low degradation of the sand
mixture that could be related to the high proportion of calcite (about 60% of the mixture)
and therefore the limit quantity of minerals susceptible to dissolution when exposed to high
pH environments. In contrast, a high degradation in the bentonite mixture was found given
by dissolution of clay particles, which increases porosity of the sample. (Cuisinier et al
2008). The effects of diffusion properties and the diffusion of alkaline cations (K+, Ca
2+,
Na+, Cs
+ and Cl
-) in presence of alkaline solution through clay materials (mudrock from
Callovo-Oxfordian layer and compacted MX-80 bentonite) was also studied. Results
showed Cl- diffusion coefficient to be one to two orders of magnitude lower than the rest of
the cations which leads to the conclusion that assigning single diffusion coefficient to all
the dissolved species for a given material is yet a debate. (Melkior et al 2004, 2007). The
effects of different pH solutions ranging from 10 to 12 on (Na, Ca) smectite were
examined. Results showed that the use of KOH solution causes a partial substitution of
calcium by potassium and a significant replacement of sodium by potassium. (Na, Ca)
smectites were partially replaces by zeolites (merlinoite), feldspars and a C-S-H type
tobermorite-like phase in the presence of potassium carbonates (K2CO3). At higher
temperatures the precipitation of quartz was observed (Mosser et al 2004). The effect of
montmorillonite dissolution in compacted bentonite exposed to an alkaline solution was
also investigated, resulting in an increase in porosity caused by the dissolution of
montmorillonite. (Nakayama et al 2004).
Alteration of cement materials by clay solutions like groundwaters has been less studied.
Experiments with CEM I paste and a clay solution representing the Callovo-Oxfordian
Formation showed the degradation processes associated with an exogenous calcite crust
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formed in the initial surface of the cement paste were inhibited by this precipitation
(Dauzeres et al 2009). Other experiments were undertaken with different aqueous fluids
and different cement materials (Albert et al, 2002; Kamatil et al, 2008; Planel et al, 2006;
Badouix et al, 2000; Kurashige 2007). The evolution of calcium leaching compared with
the precipitation of calcium carbonate was observed by (Kurashige, Hironaga, & Niwase,
2007), when working with hydrogenocarbonates and chloride - charged water.
Clay/concrete interactions have been simulated using chemistry-transportation coupled
models in several studies. Simulation of the short term interactions (15 years) at the
mudstone and concrete interface were undertaken (Windt et al 2008). Long term interaction
(100,000 years) simulation using HYTEC (Windt et al 2004) or ALLIANCES was also
undertaken (Montarnal et al 2007). Simulation of the effects of an alkaline plume in a clay
barrier was also modelled using PHREEQC (Gaucher et al 2004), PRECIP (Savage et al
2002) or KINDIS (Vieillard et al 2004). Modelling on the interactions between a fractured
marl and a high-pH plume (Soler et al 2003) and between cement - pore solutions and a
crystalline rock were also studied (Savage et al 1993).
2.2 Experiment with low-pH cement
The impact of low-pH cement on Friedland Ton (70% montmorillonite and 30%
muscovite) was conducted with very interesting results. Compared with solutions generated
by commercial and common cement (high-pH), the low-pH cement generated a very small
content in potassium and therefore a negligible illitisation of Friedland Ton (Push et al
2003). Analysis using XRD and a cationic-exchange-capacity (CEC) were performed in
order to study the chemical behaviour between the Callovo-Oxfordian clay from the
Meuse/Haute Marne area and an alkaline solution. A closed-system experiment with a
representative solution of CEM I containing NaOH, KOH and Ca(OH)2 was performed at
different temperatures (from 60 to 120 °C) and different timescales (from 6 to 168 h).
Results show precipitation of zeolite, tobermorite and katoite while mica and chlorite
showed no change contrasting with smectite and illite - smectite interstratifications which
were strongly reactive. This study allowed the authors to suggest three different alterations
in phyllosilicate in relation to pH and chemical composition of the solution: (1) pH of 10 or
12, precipitation of solution components; (2) pH of 14 for NaOH and KOH, precipitation of
19
amorphous phases + alkali silicates, and (3) pH 14 for a solution in equilibrium with
portlandite, precipitation of amorphous phases + silicates (Ramirez et al 2005).
20
Table 1: Compilation of the state of the art regarding the interaction between Clay-bearing rocks and cement. Ref. (Dauzeres et al ,
2010)
Materials Solutions T (°C) Times Results Reference
Opalinus Clay NaOH150–175–
20050 days Analcime, vermiculite, Na-rectorite Chermak, 1992
Opalinus Clay KOH150–175–
20050 days Philipsite, K-feldspar, K-rectorite Chermak, 1993
Opalinus ClaypH 13.2 with NaOH, KOH,
Ca(OH)230 540 days
Zeolites formation, C–A–S–H, dolomite
dissolution, calcite, Fe-hydroxydes,
syngenite
Adler et al , 1999
Clashach Sandstone Ca(OH)2 equilibrium 25 280 daysQuartz and feldspar dissolution,
C–S–H precipitationBraney et al , 1993
Friedland ClaypH 9.4 and 8.1 (equilibrium
with a low-pH cement)5 months No evolution. Low Illitization Push et al , 2003
Tournemire Argillite pH 13 25–70 1 to 3 monthsDolomite and pyrite dissolution.
Calcite precipitationDevol - Brown et al , 2007
Sandstone+Clays+
FeldsparsCa(OH)2 solution 20–40 250 to 730 days
C–S–H and alkaline silica gels
precipitationVan Aardt et al , 1977
Maqarin Biomicritic ClaysNatural water hyperalkaline
Ca–OH–SO4 (pHN12.5)100000 to 1 million years
C–S–H gels, ettringite and thaumasite
precipitationMilodowski et al , 2001
Searles Lake Clayey RockNatural waters-low
alcalinity (9bpHb10)3 millions years
Smectite replacement (70%) by Fe-illite,
analcime and K-feldspar precipitationSavage et al , 2010
Callovian–Oxfordian
Argillite
pH 13.2 (NaOH, KOH,
Ca(OH)2)60 1 year
Smectite partial dissolution and illite.
Microcrystalline quartz dissolution.
Solubilization of organic matter.
Tobermorite type C–S–H formation.
Claret et al , 2002
Callovian–Oxfordian
ClaysNaOH, KOH, Ca(OH)2 60–90–120 6, 24, 168 h
Analcime, chabazite, phillipsite, katoite
and tobermorite formation. Smectite
dissolution in illite/smectite mixed layer.
Ramirez et al , 2005
Callovian–Oxfordian
Argillite
pH 12.7; Portland
cement type solution20 4 days
Alkaline solution impact on the organic
matter compounds.Elie et al , 2004
Clayey rocks
21
Chapter 3: Materials
Introduction
The origin, composition and description of the clay rocks used in this research are presented
in this chapter. A summary of the four clay rock samples is presented in Table 2. The
composition of different types of cement used in the preparation of grouts is also explained, as
well of additives such as silica fume. For the Nirex Reference Vault Backfill (NRVB), the
description of the components of this designed grout based in Ordinary Portland Cement is
also provided (limestone flour and lime). Finally, the elaboration of the samples examined is
described, as well as the nomenclature used.
3.1 Mudstones
3.1.1 The Whitby Mudstone
The Whitby Mudstone Formation consists in a 70 – 90 m of exposed black and grey
mudstones and shales exposed at the coast of northeast England. Its mineralogy is well
described in a previous research (Pye, 1985). Three facies were identified by Morris (1979) in
the Whitby Mudstone: bituminous shale, weakly laminated restricted facies shales and normal
facies shales and the Whitby Mudstone Formation was divided into five sub-units by Powell,
(1984). Those units were denominated the Grey Shale Member, Jet Rock Member, Alum
Shale Member, Peak Mudstone Member and Fox Cliff Siltstone Member. Compared to many
mudstones (Clarke, 1924), the Whitby Mudstones contain less Si, Mg, Ca and Na but more Al,
Ti, Fe and K.
Regarding to the formation conditions of each of the sub-units, The Grey Shale Member, Jet
Rock Member and much of the Alum Shale Member were deposited during a period of marine
transgression. Sediments become thinner up from the base of the sequence, having the finest
sediments in the middle of the Alum Shale Member and having a rapid increase in quartz silt
content above this level. The Peak Mudstone Member and the Fox Cliff Siltstone Member are
mostly silty.
Four type of shale facies were also recognized in Morris, 1979:
22
a) Normal shale facies.
Consisting of grey silty mudstones with dispersed siderite concretions, trace fossils and
diverse fauna are abundant in these facies. These facies have a large content of quartz, micas,
chlorite and kaolinite. Less than a 10% of siderite and calcite are found and there are also
traces of plagioclase, K- feldspar and carbonate-apatite. Calcite and dolomite are almost
absent. Normal facies have a grey and weakly laminated appearance. Images from BSEM
show little preserved grain–size lamination. Compared with the bituminous facies shales,
normal facies show high degree of isotropy however micas show a preferred orientation. The
sizes of quartz grain are around 60 µm with an angular or sub–angular shape. Biotite and
muscovite micas with dimensions up to 100 µm can be found. The majority of quartz, chlorite
and mica are detrital but some mica have suffered post–depositional alteration. Some of those
micas have split parallel to the cleavage plane in such a way that allows crystals like
authigenic pyrite, kaolinite, carbonate and anatase to grow between the parted sheets. Stacks
composed completely of authigenic kaolinite can also be found in the normal shale facies.
Authigenic pyrite can occur in both as framboids and larger euhedral crystals. Carbonate is
also present in the form of randomly dispersed rhombs, patches of intergranular cement in the
more silty sediments and irregularly shaped grains. Pyrite is usually found enclosed by siderite.
b) Restricted shale facies.
This consists of poorly laminated dark grey shales with dispersed calcareous concretions.
These facies differ little from the normal facies in mineralogy. On average the siderite content
is lower. Pyrite is abundant but carbonate is rare. Restricted shale facies from the lower Alum
Shale Member contain more kaolinite but less detrital particles and chlorite than the ones in
the Grey Shales. Bioturbation has not completely destroyed the grain size lamination of the
restricted facies shales of the upper Grey Shale Member and a preferred orientation is by the
micas in the burrowed areas. Grain size was found to have a maximum of 60 µm but the
majority of grains are finer than 15 µm. Kaolinite appears to be partly diagenetic in origin, it is
present in the form of packets between the quartz and micas grains. Pyrite framboids and
rhombs are present but less than in the bituminous facies shales. In the lower Alum Shale the
restricted shale facies are poorly laminated. The absence of micro grain–size laminations is
confirmed by the BSEM examination which also reveals a moderate degree of bedding–
23
parallelism of the micas. Sediments contain quartz and silt grains that consist mostly of fine–
grained biotite and muscovite micas, chlorite, illite and kaolinite. The size of those grains is
normally larger than 10 µm.
c) Bituminous shale facies.
This consists of finely laminated black shales with numerous large calcite concretions with
some pyrite skins. The main minerals contained within the bituminous shale facies are quartz,
kaolinite, fine-grained micas, illite – smectite, chlorite, pyrite and calcite. Feldspar, carbonate
– apatite and subsidiary dolomite are also present. Figure 1 provides details of bituminous
facies in the Whitby Mudstone. Siderite is not present in these facies. Dolomite is the most
abundant mineral in bituminous shale facies in the Whitby formation (Clarke, 1924). There is
a higher content of Ca, Fe and P than the restricted shale facies and also a higher content of S
and organic C according to Gad et al (1968). Bituminous facies are thinly laminated.
Regarding to the size of the grains, most of them are smaller than 15 µm and the maximum
size is 50 µm. Quartz grains are angular shaped. The size of micas is up to 80 µm in the coarse
laminae and in the fine laminae just a few exceed 15 µm. Quartz grains and micas are partially
supported by a matrix of kaolinite and illite–smectite. Much of the clay is detrital but some
kaolinite appears to be authigenic. Pyrite and carbonate minerals are a major constituent of the
rock. Pyrite is about 5 – 10 µm with a framboid shape. Carbonates appear as imperfectly
formed rhombic crystals of calcite and dolomite. The large size of those rhombs is up to 25
µm together with the relation with surrounding clay-rich sediments is a clear evidence of the
authigenic origin. The surrounding clay matrix has been deformed in many cases around the
rhombs which indicates an early pre-compactional origin. Bituminous shales are not notably
fissile despite the high degree of parallelism and their well-developed lamination found in
micas and clay minerals.
24
The sample analysed in this research comes from the bituminous shale facies of the Whitby
formation. ESEM analysis was undertaken to determine the characteristics of this sample (see
Figure 1).
3.1.2 Kimmeridge Clay Formation
According with Morgans-Bell et al. (2001), the Kimmeridge Clay Formation consists
essentially of mudrocks that are usually characterized as medium–dark – grey, dark–grey–
black laminated, greyish–brownish–black. Other mudstones are inserted in between layers
with the above characteristics and are characterized from medium–grey to creamy–white
coccolith limestone, and minor grey and pale–yellow limestones and dolostones. The top of
the formation comprises siltstones and silty mudstones. Other variations of these mudrocks
occur within the formation on a small and large scale (0.5 to 1.5m and tens of meters).
According with (MacQuaker & Gawthorpe, 1993), five lithofacies have been identified in the
formation: clay rich mudstones, silt–rich mudstones, nanoplankton–rich mudstones, laminated
mudstones, and concretionary carbonates. Components of these facies are allochthonously
derived from the surrounding landmasses consisting of silt–grade quartz of biogenic carbonate,
Pyrite
Quartz
Organic matter
Mica Clay matrix
Figure 1: Whitby Mudstone ESEM. ESEM detail of a bituminous shale facies
from the Whitby Mudstone Formation
25
phosphate, as well as organic matter and diagenetic sources consisting of pyrite, ferroan and
nonferroan concretionary carbonates, authigenic clay minerals and organic matter.
a) Clay–Rich Mudstones: Hand specimens look grey and tend to break up into small lath –
shaped fragments <5mm. They don’t usually show sedimentary structures but shell
pavements and bioturbation can be observed. Clay–rich mudstones are composed mostly
of detrital clay comprising predominantly muscovite, illite/smectite, and kaolinite. They
also contain some disseminated organic matter, silt–grade quartz and crushed molluscan
shell debris. Pyrite is present in the form of framboids and shell fragments. Calcareous
nanoplankton is only a minor component.
b) Silt-Rich Mudstones. Hand specimens appear typically pale grey and can contain an
abundant shelly fauna in the presumed source area. In regions away from the possible
source area they are typically dark brown to black and are commonly very light weight
with low fauna diversity. Silt–rich mudstones contain abundant silt–grade quartz in a
clay and amorphous organic matter matrix. They are more organic–rich than clay–rich
mudstones and typically contain just a minor nanoplankton component. Significant
quantities of macro–shell debris are sometimes present. Most of these mudstones are
non-laminated but some show residual lamination.
c) Nannoplankton–Rich Mudstones. These mudstones have a range of compositions.
Coccoliths form thin, well–cemented ledges that are easily differentiated from the
surrounding mudstones and are usually referred to as “coccolith limestones”. When they
are relatively carbonate-poor they appear pale–grey and covered with small white
“blebs”. They usually show only bioturbation and shell pavements but no other
sedimentary structures. Nanoplankton–rich mudstones contain a low diversity of benthic
fauna. In thin sections samples show little evidence of microlamination, however the
weathered unit may present some fissility due to flattened organic matter. Pristine
coccolliths and other calcareous nannoplankton compose a significant proportion of the
carbonate material. Fine–grained clays (such as muscovite, illite/smectite, and minor
kaolinite), amorphous organic matter, and framboidal pyrite compose the rest of the
matrix. Compared with the silt–rich mudstones, detrital quartz silt is relatively
26
uncommon. Early carbonate and diagenetic kaolinite can be found within microfossil
tests. In thin section samples show little evidence of microlamination, however the
weathered unit may present some fissility due to flattened organic matter. Pristine
coccolliths and other calcareous nanoplankton compose a significant proportion of the
carbonate material. Fine–grained clays (such as muscovite, illite/smectite, and minor
kaolinite), amorphous organic matter, and framboidal pyrite comprise the rest of the
matrix. Compared with the silt –rich mudstones, detrital quartz silt is relatively
uncommon. Early carbonate and diagenetic kaolinite can be found within microfossil
tests.
d) Laminated Mudstones. In hand specimen they are commonly brown and usually
extremely ‘lightweight’ and they look laminated in cut surfaces. Mineralogical
variations make the laminae visible, like pyrite/carbonate layers within organic matter or
the presence of flattened organic matter. Pyrite concretions and intraformational, angular
rip–up clast can also be present. In thin section laminated mudstones can be identified as
either composed of flattened organic matter or can intercalate layers of carbonate and
organic matter. Organic carbon concentrations in the laminated mudstones may be as
high as 42.4% and is dominated by organic matter of algal origin. Organic-rich samples
(>30%) also contain some silt–sized quartz and clay. Laminated mudstones with less
than 30% of TOC also contain some carbonate in the form of scarce coccoliths and an
authigenic assemblage consisting of ankerite and ferroan and nonferroan dolomite. In
carbonate – rich samples calcareous macrofossil debris can be common.
e) Concretionary Carbonates. Concretionary carbonates form major erosion – resistant
ledges. Carbonates show a poorly laminated structure and contain diverse trace – fossils
assemblage. In thin section can be observed than concretionary carbonates are composed
of equigranular, inclusion–rich authigenic iron–rich carbonates (90%), ferroan dolomite,
ferroan calcite, and ankerine. Total organic carbon concentration is up to 12%. Other
minor components of the concretionary carbonates are dispersed coccolith plates, pyrite,
clay minerals and amorphous organic matter.
27
The sample used in this research correspond to a laminated mudstone based on the images
obtained by ESEM, see Figure 2, Pyrite, organic matter and quartz silt are easy to identify.
Laminae are clearly observed in the images obtained from this sample.
3.1.3 Holywell shale
The Holywell Shale formed in an early Carboniferous organic – rich basin. This formation
has received many different names (e.g. Holywell Shales, Hodder Mudstone, Worston Shales,
Sabden Shale, Caton Shale, etc.) (Andrews, 2013) and Waters et al. (2009) confirm that the
Holywell Shale Formation is the former name for what is now called collectively called the
Bowland Shale Formation. The shale consists of dark marine mudstones with intercalated
feldspathic sandstone and impure limestone and the Holywell Shale Formation formally
referred to the dark grey euxinic shales in North Wales.
Fewtrell and Smith (1980) explain that the Bowland Shale Formation comprises sandstones,
shales, and disturbed thin limestones. Shales from this formation are thinly bedded, black and
pyritiferous and are quite different from shales of lower Carboniferous formations.
Figure 2: Kimmeridge Clay ESEM. ESEM detail of a laminated mudstone from
the Kimmeridge Formation
Pyrite
Clay
Quartz silts
28
Sandstones are laterally impersistent and interbedded with shales. There are only a few thin
limestones which are coarse and turbiditic.
3.1.4 Pyritiferous Shale
Pyritiferous shale is a member of the Redcar Mudstone Formation which constitutes the
“Lower Lias” in the Cleveland Basin. The greater part of the formation is exposed at Robin
Hood’s Bay. This formation is about 225 to 250 m thick at the coast and up to 280 m or more
inland. It thins to the west to only 194 m near Thirsk and to the south in the margin of the
Cleveland Basin with only 30 or 40 m thick.
The Redcar Mudstone Formation has been divided into four parts. The lower part is called
the Calcareous Shale Member which comprises numerous thin beds of medium shelly
argillaceous limestone; this member tends to become sandier upwards. XRD analysis indicates
47% content quartz, 37% mica, 17% kaolinite, 3% dolomite, 2% illite/smectite, 1% calcite, 1%
pyrite and 1% albite. Above the Calcareous Shale Member appears the Siliceous Shale
Member which is about 30 m thick and comprises silty mudstones with calcareous siltstone
and sandstone intercalated. XRD analysis shows 38% quartz, 32% mica, 15% kaolinite, 4%
illite/smectite, 1% dolomite and 1% albite. The top of the Redcar Formation is divided into the
Pyritiferous Shale and the Ironstone shale. The Pyritiferous Shale comprises siltstones and
grey fissile mudstones with thin beds of shelly limestones occurring in the middle of the
formation. Pyritiferous shales are usually grey to dark grey shales, clearly micaceous, soft and
a with large replacement of fossils by pyrite and also small nodules of pyrite. XRD analysis
shows a 37% content of mica, 29% of quartz, 21% of kaolinite, 8% calcite, 3% pyrite and 2%
illite/smectite. Ironstone shale comprises mudstones with sideritic ironstone nodules. XRD
analysis show a 42% content of mica, 24% quartz, 21% kaolinite, 6% calcite, 3%
illite/smectite, 2% pyrite, 1% chlorite and 1% gypsum.
29
Table 2: Summary of clay rocks used in this research.
Clay rock Description
Whitby
Mudstone
This consists of finely laminated black shales with numerous
large calcite concretions with some pyrite skins. The main
minerals contained within the bituminous shale facies are
quartz, kaolinite, fine-grained micas, illite – smectite,
chlorite, pyrite and calcite. Feldspar, carbonate – apatite and
subsidiary dolomite are also present
Kimmeridge
Clay
Consists essentially of mudrocks that are usually
characterized as medium – dark – grey, dark – grey – black
laminated, greyish – brownish – black. Organic-rich samples
(>30%) also contain some silt – sized quartz and clay.
Holywell Shale The shale consists of dark marine mudstones with
intercalated feldspathic sandstone and impure limestone
Pyritiferous
Shale
Comprises siltstones and grey fissile mudstones with thin
beds of shelly limestones occurring in the middle of the
formation. Pyritiferous shales are usually grey to dark grey
shales, clearly micaceous, soft and a with large replacement
of fossils by pyrite and also small nodules of pyrite
30
3.2 Cement
Hewlett & Massazza, 2003 and Blezard, 2003 defined cement as adhesive substance with
the property of uniting fragments of solid matter to a compact whole. According to CEMEX,
cement is the adhesive that binds particles of fine aggregate together. The mixture of cement
with water to form a paste is called the fine matrix. Cements depend upon a reaction with
water rather than air for strength development, hence are called hydraulic materials. The
chemical reaction that takes place when water is added to cement is called hydration. It begins
immediately and continues while water is still present.
There are two mains types of cementitious commercial materials, lime mortars and Portland
cements.
Lime mortars generally harden and gain strength by the evaporation of the water and by
absorbing carbon dioxide from the atmosphere. This transforms, gradually, lime into calcium
carbonate.
Lime mortar: It is made by burning chalk or limestone (CaCO3) to produce quicklime (CaO)
which is later mixed with water to form hydrated lime. This mixture hardens and reacts with
carbon dioxide (CO2) from the air to form again chalk (CaCO3)
Chalk/limestone is burn to produce quicklime
CaCO3 + HEAT = CaO + CO2
Hydration of quicklime to produce hydrated lime
CaO + H2O = Ca(OH)2
Reaction of hydrated lime to produce chalk
Ca(OH)2 + CO2 = CaCO3
31
Portland cement: It is made by burning limestone or clay (at very high temperatures (1400
to 1600 °C).
In manufacturing process of Portland cement, calcium carbonate (CaCO3) is decomposed
into Calcium oxide (CaO) and Carbon dioxide (CO2) at around 900 °C. With an increase of
temperature above 900 °C CaO starts reacting with silica to form dicalcium silicate (Ca2SiO5)
which is one of the main compounds in Portland cement. Alite (Tricalcium silicate) is formed
by 1300 – 1550°C. Other phases melted such as Calcium aluminate and calcium ferrite react to
form Tricalcium aluminate and Tetracalcium aluminoferrate.
There are four main compounds in the Portland cement. Given the complexity of its
chemical composition, a shorthand notation of the chemical compounds is found in literature
as shown in Table 3. Gypsum is added to the cement clinker to retard the reaction with
Tricalcium aluminate and provide resistance to sulphates.
Table 3: Shorthand form of chemical compounds found in Portland cement
Compound Formula Shorthand form
Calcium oxide CaO C
Silicon dioxide SiO2 S
Aluminium oxide Al2O3 A
Iron oxide Fe2O3 F
Water H2O H
Sulphate SO3 S
Tricalcium silicate Ca3SiO4 (C3S) – Large amounts of heat are produced from the reaction
between tricalcium silicate and water, and calcium silicate hydrate is formed. It is the main
contributor to the early strength of cement hydrate.
Tricalcium silicate + water calcium silicate hydrate + lime + heat
2C3S + 6H C3S2H3 + 3CH, H = 120 cal/g
Dicalcium silicate Ca2SiO5 (C2S) – It reacts slowly with water and forms calcium silicate
hydrate, as well as C3S. The heat generated by this reaction is dissipated because of the slow
32
reaction and significant temperature rises do not occur. It contributes to strength to at later
ages.
Dicalcium silicates + water → calcium silicate hydrate + lime
C2S + 4H C3S2H3 + CH, H = 62 cal/g
Tricalcium aluminate Ca3Al2O6 (C3A) – It releases a relatively large amount of heat since it
reacts very rapidly with water. The addition of gypsum can retard this reaction if it is added
during the grinding stage.
Tricalcium aluminate + gypsum + water → ettringite + heat
C3A + 3CSH2 + 26H C6AS3H32, H = 207 cal/g
Ettringite then reacts with the remaining tricalcium aluminate to form monosulfate aluminate
hydrate crystals.
Tricalcium aluminate + ettringite + water → monosulfate aluminate hydrate
2C3A + 3 C6AS3H32 + 22H → 3C4ASH18
Tetracalcium aluminoferrite Ca4Al2Fe2O10 (C4AF) – reacts rapidly with water but does not
produce much heat or strength. It reacts in two progressive steps, first by reacting with water
and gypsum to form ettringite and then reacting with the formed ettringite to produce garnets.
Ferrite + gypsum + water → ettringite + ferric aluminium hydroxide + lime
C4AF + 3CSH2 + 3H → C6(A,F)S3H32 + (A,F)H3 + CH
3.2.1 Microcement
MICROCEM 650 is a controlled fine cement produced by the company TARMAC. It is made
by finely grinding Portland cement clinker with small quantities of additives. Microcements
are usually used as injection grouts since they have an excellent performance in tight fissures
33
and low - porosity soils. MICROCEM 650 is particularly suitable for injection into cracks,
joints to produce a water - tight mass of grouted rock (Lafarge Tarmac, 2014).
3.2.2 CEM II/A-LL 42,5N
This is a cement denominated as Portland-limestone cement (PLC) produced by the
company TARMAC that contains between 80 to 94% of Portland cement clinker, 6 to 20%
limestone and 0 – 5% of minor additional constituents. It is very similar to the conventional
Portland cement (CEM I) and in most cases can be interchangeable however some differences
can be recognised:
Concrete containing PLC will demand slightly less water than conventional Portland cement
and once hardened it will be lighter in colour and will have a smoother surface than CEM I
concrete.
3.3 Silica fume
Microsilica or silica fume is a by–product of the production of alloys containing silicon or
elemental silicon. High–purity quartz is heated usually to 2000 °C in an electric arc furnace
producing very fine non–crystalline silica. More than 95% of the particles are less than 1 µm
and most of the particles are in spherical shape. The specific surface area of microsilica varies
from 15000 and 30000 m2/kg. The specific gravity of silica fume (2.2) is lower than Portland
cement, then the addition of silica fume does not increase the concrete density. Typical
chemical composition of microsilica is shown in Table 4. Content of silica fume is usually
higher than 80wt% Si. Microsilica can also contains small amounts of CaO, Al2O3, Fe2O3 and
other alkali contents. Carbon content is usually less than 2%. Mineralogical composition of
silica fume consists mainly of an amorphous silica structure with little crystalline particles.
34
Table 4: Chemical composition of the most common types of microsilica
Content of fume (wt%)
Si FeSi
75%
FeSi 75%
(heat
recovery)
FeSi
50%
FeCrSi CaSi SiMn
SiO2 94 89 90 83 83 53.7 25
Fe2O3 0.03 0.6 2.9 2.5 1.0 0.7 1.8
Al2O3 0.06 0.4 1.0 2.5 2.5 0.9 2.5
CaO 0.5 0.2 0.1 0.8 0.8 23.2 4.0
MgO 1.1 1.7 0.2 3.0 7.0 3.3 2.7
Na2O 0.04 0.2 0.9 0.3 1.0 0.6 2.0
K2O 0.05 1.2 1.3 2.0 1.8 2.4 8.5
C 1.0 1.4 0.6 1.8 1.6 3.4 2.5
S 0.02 0.1 2.5
MnO 0.06 0.2 0.2 36.0
LOI 2.5 2.7 3.6 2.2 7.9 10.0
Silica fume was first tested in Norway in the early 1950s proving to increase the strength of
concrete and to provide a better performance in sulphate environments. The cohesiveness of
concrete mixture increases when very fine particles of microsilica are added. The
incorporation of silica fume to concrete affects its microstructure. Microsilica has the effect of
reducing the large pores of cement paste into smaller pores consequently changing the
structure of the cement paste (Yogendran and Langan, 1987). Permeability is also affected by
the addition of microsilica. Water penetration showed to be up to 6 times lower than for a
normal concrete mixture (Fidjester and Frearson, 1994).
Silica fume has also proved to enhance concrete durability and improve the physical and
chemical properties of concrete. Microsilica can have a paradoxical effect regarding to
carbonation of mortars and concretes. In one side, microsilica consumes calcium hydroxide of
the cement paste which can increase the risk of carbonation; however microsilica reduces the
permeability of concrete which may result in lower carbonation (Vennesland and Gjorv, 1983).
35
Incorporation of silica fume has showed to provide a better resistance to mortars and concretes
against sulphate solutions. A replacement of at least 15% of silica fume for normal Portland
cement proved to give a satisfactory resistant even after 4 years of immersion in sulphate
solution. (Fiskaa & Betong, 1983)
3.4 Nirex Reference Vault Backfill
The Nirex Reference Vault Backfill (NRVB) is a high-pH backfill developed by former UK
body (NIREX) to analyse safety and environmental matters regarding deep geological disposal
of nuclear waste. NRVB is composed of Portland cement, hydrated lime and limestone flour.
It was designed to provide a reduction in radionuclide migration from the near field to a
Geological Disposal Facility. NRVB was designed to have a relatively low strength, to be
highly porous in order to promote homogeneous chemical conditions within the GDF,
allowing waste retrievability and to allow gas migration.
The composition of NRVB is shown in Francis et al., 1997:
Portland Cement (‘Ordinary Portland cement’) = 450 kg/m3
Limestone flour = 495 kg/m3
Lime (‘Limbux hydrated lime’, from Tarmac) 170 kg/m3
Water (mains tap water) = 615 kg/m3
The same proportions were used in order to create a homogenous paste to make the samples.
3.4.1 Limestone flour
Calcium carbonate or limestone is a hard, compact, considerably impervious, fine to very
fine grained calcareous sedimentary rock. Calcareous rocks have a high compressive strength
(60 – 170 MPa) and very low porosity. Limestone powder can be produced by grinding of
high purity limestone. The addition of large amounts limestone to concrete reduces the
strength; however the addition of up to 10% of limestone does not reduce it significantly.
Limestone slightly increases the shrinkage of cement mixture, according with a study of
Adams & Race, 1990 where they investigated the effects of limestone addition to Portland
cement types I and II, however Alunno-Rosetti & Curcio, 1997 concluded that limestone had
36
no effect of shrinkage of cements from two different plants comparing samples with no
limestone addition against a 20% limestone addition.
Permeability of concrete is decreased with the new refined pore structure caused by the
nucleation effect of the fine particles of calcium carbonate which causes a reduction in the
pore connectivity. Other studies have confirmed that limestone addition to Portland cement
decreases its permeability regardless of the amount of limestone added.
3.4.2 Hydrated lime
Hydrates lime is made by crushing, grinding, washing and screening typically hard - rock
Carboniferous limestone and then burning it at approximately 950 °C. The resulting product is
called quicklime (CaO) which is then mixed with water to obtain hydrated lime (Ca(OH)2).
The requirements for construction hydrated lime are contained in the British Standard BS EN
459-1 . The composition of Hydrated Lime used to form NRVB cement in this research is
shown in Table 5.
Table 5: Composition of Hydrated Lime
Calcium Hydroxide - Ca(OH)2 97.0% (min 95.0)
Magnesium Hydroxide - Mg(OH)2 0.50% (max. 1.4)
Carbon Dioxide - CO2 0.70% (max. 1.00)
Silica - SiO2 0.70% (max. 1.00)
Alumina - Al2O3 0.10% (max. 0.20)
Iron Oxide - Fe2O3 0.06% (max. 0.10)
Sulphur - S 0.01% (max. 0.025
Moisture - H2O 0.25% (max. 0.75)
Arsenic - As 0.3 ppm (max. 1.0)
Fluorine - F 65 ppm (max. 110)
Lead - Pb 1.3 ppm (max. 5.0)
Manganese - Mn 175 ppm (max. 250)
Loss on ignition 24.80%
37
3.5 Sample formulation and nomenclature
A total of 7 cement mixes, usually referred as mortars, were used in this research. Two
different types of Portland Cement were used (MICROCEM 650 and CEM II/A-LL 42,5N).
Formulation of the 7 cement mortars and nomenclatures is described in Table 6. OPC and
PMS mortars are the only two mixes containing aggregates such as sand, since they are regular
constructions grouts. MPC3 is a standard high-pH grout with a high water-to-binder-ratio (w/b)
and addition of superplasticizer described in Table 6, MPC5 is also a standard high-pH grout
with no addition of superplasticiser. PMS3 is a low-pH grout mixture which has been
proposed by POSIVA Oy, which is a research company for nuclear waste disposal, (Holt,
2008), with an addition of silica fume ≈40%. PMS5 has the same composition of PMS3 but
with no addition of superplasticiser. The aim of testing different mortars is to provide a wide
range of cement - based mixtures that might be likely to be used as a backfill or sealing in the
GDF context and can be found in the literature (Kim et al., 2011,Kronlöf, 2005; Swift et al.,
2010). All mixtures were elaborated according with the British Standard BS EN 998-2:2010.
NRVB and mortars MPC5, PMS5, MPC3, MPS3 were elaborated according with the literature
procedures since they are neither standard nor commercial grouts/mortar and their elaboration
methods have not been yet established. The interaction in the cement/clay interface was
undertaken by combining these grouts with pieces of clay rocks described in Table 2. Table 7
shows the combinations of cement mixture/lithology interfaces examined. Further details in
the elaboration of specimens are provided in Chapter 4.
38
Table 6: Composition (wt%) of the 7 mixtures utilized in this research.
CODE OPC MPC Sand MS Ca(OH)2 CaCO3 SP W w/b w/c
OPC 28.58 57.14 14.28 0.50 0.50
PMS 27.7 55.41 2.77 0.27 13.85 0.45 0.50
MPC5 55.19 44.81 0.81 0.81
PMS5 24.42 16.8 58.75 1.42 2.41
MPC3 54.95 0.44 44.61 0.81 0.81
MPS3 24.27 16.7 0.67 58.36 1.42 2.41
NRVB 26.01 9.83 28.61 35.55 1.37 1.37
OPC= Ordinary Portland Cement, MPC= Micro Portland Cement, Sand= Regular
construction sand, MS= Microsilica, Ca(OH)2= Hydrated lime, CaCO3= Limestone flour,
SP= Superplasticiser, W= Water, w/b= water-binder ratio, w/c= water-cement ratio.
Table 7: The cement mixtures and clay-bearing lithologies used in the experiments
SAMPLE
NUMBER
MIXTURE LITHOLOGY
OPC1 Mortar of Ordinary Portland cement (OPC mixture) Kimmeridge clay
OPC2 Mortar of Ordinary Portland cement (OPC mixture) Holywell clay
OPC3 Mortar of Ordinary Portland cement (OPC mixture) Yorkshire clay
OPC4 Mortar of Ordinary Portland cement (OPC mixture) Whitby Mudstone
PMS1 Mortar of Ordinary Portland cement with 10% silica
fume (PMS mixture)
Kimmeridge clay
PMS2 Mortar of Ordinary Portland cement with 10% silica
fume (PMS mixture)
Holywell clay
PMS3 Mortar of Ordinary Portland cement with 10% silica
fume (PMS mixture)
Yorkshire clay
PMS4 Mortar of Ordinary Portland cement with 10% silica
fume (PMS mixture)
Whitby Mudstone
NRV5 Nirex Reference Vault Backfill ( NRVB mixture) Whitby Mudstone
NRV6 Nirex Reference Vault Backfill ( NRVB mixture) Holywell clay
39
3.6 Sample preparation
All samples were cured for 28 days under saturated conditions before any testing. Curing is
the required process of concrete and other cement-mixtures where strength is gained.
In order to perform permeability tests, it was necessary to manufacture small moulds with
cylindrical shape of 2.5 cm diameter and 10 cm length. Once the samples were ready they
were unmould and then cut into smaller plugs to perform permeability test described in
Chapter 4.
With samples MPS3 and MPC5 described in Table 6, it was not possible to elaborate
cylinders due to shrinkage so it was necessary to elaborate small grout blocks that were then
drilled after curing in order to obtain the 2.5cm plugs needed to perform porosity and
permeability tests. The samples for the analysis of the permeability at the cement/mudstone
interface were elaborated by placing a 1.5cm diameter mudstone core at the centre of a
cylindrical mould of 2.5cm diameter and 10 cm height where cement mixture was poured
when fresh. This was done with a small holding ring as shown in Figure 3, designed to keep
NRV7 Nirex Reference Vault Backfill (NRVB mixture) Yorkshire clay
NRV8 Nirex Reference Vault Backfill (NRVB mixture) Kimmeridge clay
OPC5 Ordinary Portland Cement grout w/c 1.4 (OPC mixture
with water-cement ratio of 1.4)
Whitby Mudstone
OPC6 Ordinary Portland Cement grout w/c 1.4 (OPC mixture
with water-cement ratio of 1.4)
Holywell clay
OPC7 Ordinary Portland Cement grout w/c 1.4(OPC mixture
with water-cement ratio of 1.4)
Yorkshire clay
OPC8 Ordinary Portland Cement grout w/c 1.4 (OPC mixture
with water-cement ratio of 1.4)
Kimmeridge clay
PMS5 Ordinary Portland Cement grout with 40% silica fume Whitby Mudstone
PMS6 Ordinary Portland Cement grout with 40% silica fume Holywell clay
PMS7 Ordinary Portland Cement grout with 40% silica fume Yorkshire clay
PMS8 Ordinary Portland Cement grout with 40% silica fume Kimmeridge clay
40
the mudstone core from moving during the curing and which was easily removed by cutting
the outer extreme where the holding ring was placed. All samples were cured for 28 days
under saturated conditions before any test.
A standard food mixer was utilized for cement mixing in a stainless bowl. Dry components
were mixed first and then water was added. If superplasticiser was needed, it was added at last.
All components of mixtures were weighted in a laboratory scale according to the required
1.5cm
2.8cm
2.5cm
10
cm
1.5 cm
2
.5
cm
1.5 cm
2
.5
cm
Figure 3: Special mould specifications and details. (Top left) Photograph of the
acrylic glass pipe used as mould. (Left below) Schematic of the rings used to keep
mudstone cores in place. The ring on the left is placed on the top of the mould to
prevent the mudstone core from moving and at the same time allowing cement
paste to flow through the spaces at the sides. The right one is placed at the bottom
of the mould. It is not totally pierced so mudstone cores can be fixed by the space
in the middle and at the same time it functions as a cap preventing cement paste
from escaping the mould. (Right) Diagram of the acrylic mould specially
fabricated. The thickness of the wall is 3mm with 25mm internal diameter. When
15mm mudstone core is used it is placed in the middle by the cap in the bottom and
the ring on the top.
.
41
formulation. Once the mixture was ready it was poured into the acrylic moulds as shown in
Figure 4.
For mineralogical and element mapping in the cement-mudstone interface, small quantities
of mixtures were poured into small containers with around 2 - 3cm diameter and then
fragments of mudstones were immediately added to the mixture (see Figure 5). The resultant
disks were then removed from the moulds and cured. Samples were then sliced in order to
identify the areas where the cement was making contact with the mudstone. Once identified,
polished sections of these areas were made for ESEM and electron probe microanalysis
Figure 4: Cement mixing procedures. (Above left) Food mixer with stainless
bow utilized for cement mixing in the laboratory. (Below left). Portland cement
being weighted. (Above right) Cement paste ready after mixing. (Below centre)
Cement paste being poured into acrylic mould with mudstone core being held by
cap and ring. (Below right) Cement sample after 24 hours.
42
(EPMA). Five out of seven mixtures were used to perform element mapping using the ESEM
and EPMA.
.
Figure 5: Thinsection making. (Above left) Cement paste being poured into
moulds (2.5cm diameter 2cm height). Small pieces of mudstone were placed
inside. (Up right) Disk of cement paste with a visible mudstone piece within it
ready to be sent to the sectioning laboratory to obtain polished thin sections.
(Down left) Polished thin sections ready.
43
4 Methodology
Introduction
Thinsections of the samples were subject to a series of analysis using Optical Microscope,
Electron microscope and Electron microprobe. Cement plugs were subject to permeability and
porosity measurements. Descriptions of methods and equipment are presented in this chapter.
4.1 Light microscopy
All of the thinsections were examined with transmitted light microscope in order to identify
optical changes in the interface of cement/clay rocks. The equipment was a Zeiss Axioskop 50
as shown in Figure 6. Images were acquired with an AxioCam MRc5 installed in the
microscope.
Figure 6: Zeiss Axioskop 50
44
4.2 ESEM and analysis
The ESEM equipment utilized in this research was a Philips FEI XL30 shown in Figure 7.
The ESEM is a non-destructive electron optical technique capable of producing images from
hydrated samples in their near natural state (Donald et al., 2000). It can operate from high
vacuum to a pressure level such that wet specimens can be analysed (Danilatos, 1994).
Therefore an ESEM has all the advantages of a conventional SEM but removes the high
vacuum restrictions given the characteristic of analysing wet, oil, dirty or non – conductive
samples in their natural state without preparation or modification.
Figure 7: ESEM. FEI XL30 Environmental Scanning Electron Microscope-Field Emission
Gun in the Williamson Research Centre
A scanning electron microscope consists of an electron column, a sample chamber, detectors
and a viewing system. In the top of the column an electron gun generates the electron beam.
This electron beam is accelerated down the column to the sample. The electron beam can be
generated with different electron guns (tungsten, lanthanum hexaboride and field emission),
all of them sharing the same purpose of generating a directed electron beam with sufficient
current and with the smallest possible size. The electron beam is then re-converged and
focused into a de-magnified image with a series of magnetic lenses and apertures in the
column. The final lenses focus the beam in to the smallest spot possible on the surface. The
beam then exits the column into the sample chamber. The sample chamber contains a stage
45
where the sample can be manipulated and an airlock to insert and remove the sample and to
access detectors and other accessories.
Images obtained by the SEM are generated by constructing a virtual image from the signals
emitted by the sample. It is achieved by scanning its electron beam line by line. The beam
illuminates only a single point at a time to create the overall image in the pattern, the signals it
generates vary in strength, reflecting differences in the sample. Other modern instruments can
convert the analogue output signal into a series of numeric values than can be then
manipulated as desired.
There are two main signal types produced by the electron beam: secondary electrons (SE)
and backscattered electrons (BSE). Secondary electrons are atoms with very low energy that
have been ejected by the interactions with the primary electrons of the beam. They can escape
only regions near the sample surface which means that they represent the topography of the
sample. Backscattered electrons are high energy electrons that have been scattered by elastic
collisions with the nuclei of sample atoms, and their intensity is controlled by atomic number.
Backscattered images therefore provide important information about the sample composition
(Johnson, 1996).
Thin sections analysed in the ESEM were carbon-coated before placed in the sample holder. A
conductive tap was also put from top of the thin section to the holder as shown in Figure 8.
The test was conducted with a pressure of 1.24 x 10-4
mBar with beam energy of 15 Kv.
46
Figure 8: Thin section detail. Polished thin section placed in the sample holder of the ESEM
4.3 EMPA analysis
The Electron Microprobe Cameca SX-100, shown in Figure 9, is the equipment used to
analyse samples in this research. Electron probe - microanalysis is a qualitative and
quantitative elemental microanalysis that involves bombardment of a solid with a focused
electron beam of electrons, focussed down to 1 micron (Macphee & Lachowski,
2003)(“EPMA: Electron Probe Micro-Analysis,” n.d.). X-ray photons emitted by the various
elemental species have characteristic energies and wavelengths and their intensity is collected
by wavelength sensitive spectrometers (Wavelength Dispersive Spectroscopy (WDS)). The
identification of elements by WDS is based in Bragg's law which states the angles for coherent
and incoherent scattering from a crystal lattice (Bragg, 1913) and EMPA uses various
moveable, shaped monocrystals as monochromators.
47
Figure 9: EPROBE. Cameca SX-100 Electron Microprobe in the Williamson Research
Centre
EMPA allows a non-destructive elemental analysis of up to micron - sized volumes, with
sensitivity at the level of 100sppm. EMPA is equipped with a built - in microscope tools that
allow SEM, BSE imaging, simultaneous X-ray and sophisticated visible light optics with
magnification ranging from 40 to 400 000x.
The high resolution and wavelength spectrometry produces higher resolution chemical
mapping and quantitative analyses to complement the qualitative spectra of SEM/EDS. EMPA
is the primary solid phase analyser for microscale compositions mostly used in geochemistry,
mineralogy, geochronology, physical metallurgy, nuclear metallurgy, material science,
48
cements, etc. The elements analysed were Ca, Al, Si, Fe, K, Na and Mn. It was done by setting
the spectrometers at the wavelength of the highest counts of an element as defined by the
standards CaSiO3, Al2O3, SiO2, FeO, KAlSi3O8, NaAlSi3O8, MnO2.
4.4 Cement permeability
Besides strength, permeability is one of the parameters that directly affect the durability of
cement based mixtures (Abbas & Carcasses andJ-P Ollivier, 1999). Permeability is a very
important property, especially in applications such as the isolation of waste materials. Within
the Nuclear Waste management context, cement based mixtures are likely to be used as
backfill material or immobilisation material for the matrix of waste where radionuclide
containment is the main function of those mixtures. Many disposal concepts include the use of
cement in different phases of the project. Those mixtures should meet low voidage, adequate
strength and low permeability requirements(Ian G Crossland & Vines, 2001).
Permeability plays an important role in producing an effective seal to a depository to avoid
water or gas borne radionuclides escaping (I G Crossland & Vines, 2001) and also in the
containment of radionuclides inside the wasteform matrix (waste immobilisation). The latter is
achieved by controlling pH and therefore chemical conditions are expected inside the waste
matrix. In contrast to forming an impermeable seal it is sometimes advantageous to have large
porosities and relatively high permeability conditions to encourage reactions and homogeneity
within the matrix.
Most of the repository concepts consider one material for immobilisation of the waste
matrices and another for backfilling the repository. Potential mixtures to be used in the
wasteform matrix are usually Ordinary Portland Cement based mixtures with some additives
such as fly ash, blast-furnace slag, or polymers.
4.4.1 Oscillating Pore Pressure Method
Given the low permeability value for cement mixtures found in the literature, with values
ranging from 𝑘 =10-15
to 𝑘 =10-19
m2 (Atkinson, 1985)
for regular concrete, an Oscillating
Pore Pressure Method was chosen to determine the permeability of the samples used in this
research. Argon gas was used as pore fluid.
49
Methods with oscillating boundary conditions have been used to measure thermal diffusivity
(Cerceo & Childers, 1963). The method developed by Kranz 1990 and is well explained in
Bernabé, 2006. The method consists in a way to use pore pressure oscillation to determine k.
A jacketed sample is placed within a vessel where a confining pressure is applied; the sample
is then loaded with the desired pore pressure by an upstream and downstream reservoir.
Through a computer-controlled pump, an oscillation of the upstream fluid 𝑃𝑈 = 𝐴𝑈𝑒𝑖(𝜔𝑡+𝜃𝑈)
is applied to the sample and the resulting downstream variations in the reservoir, 𝑃𝐷 , are
logged. The terms in the equations are as follows:
PU = Upstream pressure
PD = Downstream pressure
AU = Upstream amplitude
AD = Downstream amplitude
θU = Upstream phase
θD = Downstream phase
ω = angular velocity
PTr = Transient pressure
The response in the downstream reservoir, 𝑃𝐷, generally consists of three terms, a transient
term 𝑃𝑇𝑟 which approach to zero over a long-time limit, a noise term with a small amplitude
and a broad spectrum, and finally the major response, 𝐴𝐷𝑒𝑖(𝜔𝑡+𝜃𝐷).
Several tens of cycles are run in order to have enough data to overcome the short-time
transient term. A series of cycles at the beginning may be simple discarded because of this
effect. An example of upstream and downstream signals from one of the samples tested in the
experiments is shown in Figure 10. Transient phase is found in 3 cycles before it reaches the
steady – state oscillation.
50
Figure 10 Oscillating pore pressure readings.
Fourier analysis is then applied to the remaining cycles and 𝐴𝐷𝑒𝑖(𝜔𝑡+𝜃𝐷) is obtained
corresponding to a sharp peak.
The downstream to upstream amplitude ratio is denoted as 𝐴 = 𝐴𝐷 𝐴𝑈 < 1⁄ , and the phase-
shift as 𝜃 = 𝜃𝐷 − 𝜃𝑈 > 0.
The square-root of the 𝜔 components of the downstream and upstream power spectra give
the amplitude ratio 𝐴. 𝜃 is the phase of the 𝜔 components of the cross-spectrum. By plotting
𝐴 and 𝜃 against time 𝑡 it is possible to verify that early time transient effect has vanished away.
For homogeneous materials, 𝐴 and 𝜃 can be written in the long-time limit as
𝐴𝑒−𝑖𝜃 = (1 + 𝑖
√𝜉𝜂sinh [(1 + 𝑖)√
𝜉
𝜂] + cosh [(1 + 𝑖)√
𝜉
𝜂])
−1
Where ξ and η are dimensionless parameter defined by
𝜉 =𝑆𝐿𝛽
𝛽𝐷, 𝜂 =
𝑆𝑇𝑘
𝜋𝐿𝜇𝛽𝐷
Where
S= sample cross-section area
L= sample length
9.4
9.6
9.8
10
10.2
10.4
10.6
200 400 600 800 1000 1200 1400 1600 1800 2000
Pu
/Au
an
d P
d/A
d
Time
Downstream pressure Upstream pressure
Transient behaviour
51
β= sample storativity
𝛽𝐷= downstream reservoir storage
k= sample permeability
µ= fluid viscosity
The relationship between 𝜉, 𝜂, 𝐴 and 𝜃 can be represented in a nomogram, like shown in
Figure 11, where the limits for physical meaning of 𝜉 and 𝜂 can be clearly identified.
The nomogram shows lines of constant 𝜂 and 𝜉 plotted in a log10(𝐴, 𝜃) space. The values of
log10( 𝜂) are indicated by horizontal numbers and the values of ξ by vertical numbers. The
space enclosed between 𝜉 = 0 and 𝜉 = ∞ lines contain the physically meaningful region.
Points in the left of 𝜉 = 0 and to the right of 𝜉 = ∞ are in principle not possible. A negative
value in 𝜉 would indicate a negative storativity.
52
Eq. (1) is no linear and it must be solved numerically for 𝜉 and 𝜂. 𝑘 and 𝛽 can be obtained
once 𝜉 and 𝜂 are calculated using Eq. (2). An iterative method is common to solve those
equations. First a starting point is chosen (𝜉0, 𝜂0) and then (𝐴0, 𝜃0) is calculated and compared
with the logged data (𝐴, 𝜃)
4.4.2 Permeability procedures
Once the 2.5cm cylinders of cement mixture were cured they were cut into smaller plugs of
up to 5 cm length based on the equipment capabilities and the permeability expected for each
of the different mixtures. Permeability was measured as a function of effective pressure.
Figure 11: Space solution for equation 1. Nomogram where 𝐥𝐨𝐠𝟏𝟎(𝑨,𝜽) are plotted
and 𝜼 and 𝝃 can be obtained. Ref. (Bernabé et al., 2006)
Log10( )
53
Figure 12: Permeameter scheme. Diagram of the sample placed inside the pressure vessel.
The computer displays the downstream signal and controls the upstream pore pressure
oscillation by moving a piston that uses a servo – controlled motor on the volumometer.
In some cases it was necessary to adjust the downstream reservoir volume since the
permeability was relatively high to be measured with the pore pressure method and too low to
be measured with the constant flow permeameter and it was not convenient to make the plug
any shorter.
All samples were dried in the oven at 50 °C and once they were dried they were kept in it if
they were not being tested. Samples with high water-cement ratio and high calcium carbonate
content showed fractures when they were being drying even after a few minutes of water loss.
Those fractures made it worthless to measure the permeability in that condition since the gas
would pass through the fractures and would in no way represent the permeability of the
cement structure. Thus it was not possible to test those samples in a dry condition. In order to
overcome this issue and to obtain meaningful measurements, mixtures were made again and
poured into sealed bags where they were left to cure with pore water for 28 days and then
plugs were drilled from them. Those samples were labelled and kept in sealed bags in order to
avoid any additional water loss and the subsequent cracking. Those plugs were later trimmed
to the desire length for testing.
54
Once the plugs were trimmed they were jacked in order to be tested at different effective
pressures by varying the confining pressure and keeping constant the pore pressure (See
Figure 13). Samples were tested with effective pressures ranging from 5 to 30 MPa while
maintaining a constant pore pressure of 10 MPa in order to analyse the effects of effective
pressure in permeability.
Besides the delay caused by the cracking of some of the samples, for some samples, it was
necessary to adjust the period of the wave in order to get a response in the downstream
pressure. Most of the samples were tested with periods ranged between 100 and 200 seconds,
Figure 13 Cement cores for permeability tests. (Above left) Cement sample OPC after
being unmoulded. (Above right) Cement sample after being unmoulded. In the left part the
cap used is visible the cap to prevent cement escaping from the mould. Lower left) Cement
mixture (water – cement ratio = 1.4) after being cut and ready to be tested.
55
whereas some other samples, like MPC3, were tested with 10000 seconds periods in order to
obtain a response in the downstream pressure. This caused a more serious delay in the
progress of the experiments, since for every effective pressure it was necessary to get at least
10 cycles in order to overcome the transient effect, sometimes more. It was achieved only after
27 hours test for one sample for one effective pressure. All this impeded to repeat the test
several times like it was done with other samples.
MPS3 sample did not even produce a response in the downstream pressure with a 10000
seconds period, so it was just considered as impermeable since it was being tested partially
saturated due to cracking presented when sample was subject to water loss. With such a long
period other problems raised with the equipment such as leakage in the pipes inside the
permeameter which leaded to a revision of the equipment and more delay in the progress of
the research. The equipment was left overnight with a known pressure and the pressure was
logged every second to find out if pressure was decaying. The effect of leaking was not a
problem for periods under 12 hours, but for longer tests it was a problem that caused resulting
data not to be as precise as desired.
56
4.5 Cement Porosity
5 samples were tested in the Digital Helium Porosimeter DHP -100, shown in Figure 14,
which relays in Boyle’s law method to determine porosity based in gas volume difference and
pressure (Draper, 1861). The determination of effective porosity is achieved by placing the
sample into a core holder with a known volume. Then helium is allowed to expand at a
constant temperature inside the holder until the pressure reaches equilibrium. Grain volume is
calculated by the new gas pressure measurement. Bulk volume is calculated by determining
the volume of the sample. Effective porosity is then calculated by the difference between grain
volume and bulk volume (Aplin, 1999). The same samples tested in the permeameter were
tested in the porosimeter.
∅ℎ𝑐 =(𝑉𝑏 − 𝑉𝑔)
𝑉𝑏
Where:
∅ℎ𝑐= Effective porosity
𝑉𝑏=Bulk volume
𝑉𝑔=Grain volume
Figure 14: DHP -100. Digital Helium Porosimeter from ResLab manufacturer.
57
Chapter 5: Results
5.1 Transmitted and reflected light microscopy
Prior to ESEM analysis, the polished thinsections sample were examined using transmitted
and reflected light microscopy in order to identify areas where possible chemical alteration
may have occurred. All samples were analysed but it was only possible to identify 2 samples
where a very clear optical alteration was present. Samples PMS4 and OPC4 (mortar of
Ordinary Portland Cement and mortar of Ordinary Portland Cement with 10% of microsilica,
both with Whitby Mudstone) both showed a visible alteration all around the interface between
the cement matrix and the mudstone. The cement matrix in PMS4 and OPC4 seemed to be
altered in such a way that it had the appearance to be slightly more transparent near the
interface, however no visible change was observed in the adjacent mudstone (see Figure 15
and Figure 16). All other samples didn´t show any clear visible alteration under the optical
microscope as shown in Figure 17 and Figure 18 (samples OPC2 and PMS3 respectively), but
analysis under ESEM was, nonetheless, performed in attempt to identify minor changes.
58
Cement matrix
Whitby Mudstone
Figure 15: OPC4 optical analysis. (Left) OPC4 polished thin section under transmitted cross polarized light. The darker
area at the top corresponds to the Whitby Mudstone meanwhile the bottom area with some white sand grains corresponds to
the cement paste. It is possible to identify the lighter colour of the cement paste near the interface. (Red dotted line). The
fracturing of the quartz will have happened during cement formation. (Right) Same sample under plane transmitted light.
The interface line between the cement paste and the Whitby Mudstone is clearer. An intermittent gap along the interface and
also identify the change in colour within the cement paste. There is no observable evidence of alteration within the
mudstone.
Cement matrix
Whitby Mudstone
59
Figure 16: PMS4 optical analysis. (Left) PMS4 polished thin section under transmitted cross polarized light. The
darker area at the right corresponds to the Whitby Mudstone meanwhile the area to the left shows fractured sand grains
correspond to the cement paste. It is possible to identify the lighter colour of the cement paste near the interface, as in
the OPC4 sample. (Right) Same sample under the transmitted plane polarised light. The interface line between the
cement paste and the Whitby Mudstone is clear. It is also possible to appreciate some sort of gap along the interface and
also identify the change in colour within the cement paste. There is no observable evidence of alteration within the
mudstone.
Whitby Mudstone
Cement matrix
Whitby Mudstone
Cement matrix
60
Figure 17: OPC2 optical analysis. (Left) OPC2 in transmitted cross polarised light. The interface line is barely
distinguishable since cement paste and claystone show the same interference colours, however claystone (Holywell clay)
is slightly darker. (Right) Same sample under the transmitted plane polarised light. Colour in cement paste appears to be
uniform in the entire matrix as well as the claystone where there is no optical evidence of any disturbance or alteration.
Interface line was drawn in red.
Holywell shale
Cement matrix
Holywell shale
Cement matrix
61
Figure 17: PMS3 optical analysis. (Left) PMS3 sample in transmitted crossed polarised light. Cement paste and mudstone
show different colours. Cement paste matrix does not show any optical variation. It is possible to observe a fracture that
passes through the mudstone in the left of the image and through the interface line to the right. Sand grains are easily
identifiable as well as a small bubble trapped by the resin during the manufacturing of the section. (Right) Same sample
under the transmitted plane polarised light. Two different facies (cement paste and mudstone) are easily distinguishable. The
fracture is clearly seen. There is no optical evidence of disturbance or alteration in the cement paste or the mudstone.
Cement matrix
Yorkshire shale Yorkshire shale
Cement matrix
62
5.2 ESEM analysis
Once the possible zones were identified, the same thin section samples were analysed under
the ESEM. BSE light images were obtained and element mapping was performed. Element
mapping for Al, C, Ca, K, Mg, Mn, S and Si was undertaken for all the samples (Figure 19,
Figure 20, Figure 22, Figure 25, Figure 26 and Figure 27). Even with the elements maps from
ESEM it was still unclear what interactions were taking place in the zones with lighter colour
found in samples OPC4 and PMS4 since there was no evidence of change in the elements like
an exchange of Ca or Al
Element mapping did reveal the different facies/minerals within the mudstones and
claystones and also identified the formation of calcite crystals within the cement paste, and the
binding with grains of sand in the case of OPC4 and PMS4. From the element mapping it was
also clear that in the interface different facies were exposed to the cement paste (micas,
organic matter, pyrite concentration), but this did not correspond to colour changes.
OPC4 BSE image is shown in Figure 18 and Ca, Al and Si maps are shown in Figure 19 and
Figure 20. Ca appears abundant in the cement matrix while is almost absent in the mudstone
matrix. Al is present in both cement and mudstone matrix, abundant in the mudstone and
concentrated in some facies within the cement. The interface line is very clear from the BSE
image and from the Al maps. There is no evidence to support the idea that the Ca migration is
linked to any particular facies/mineralogy within the Whitby Mudstone Si map shows the
presence of this element in both matrixes. Bright Si concentration within the cement matrix
corresponds to sand grains used in OPC mortar. Despite the alteration zone spotted with
optical microscopy in OPC4 sample, it was not possible to spot a particular change in this area
with element maps from ESEM.
A BSE detail of OPC4 with higher magnification is given in Figure 21. Al map of OPC4
(Figure 22) with higher magnification showed a small exchange of Al from the mudstone into
the cement matrix and Ca from the cement paste to the mudstone. Si map did not reveal any
interaction in the interface (Figure 23). Another more detailed of OPC4 is showed in Figure 24.
Again Ca and Al maps suggest a migration of Al from the mudstone into the cement matrix,
and a migration of Ca from the cement matrix into the mudstone (Figure 25), however the
63
images are not clear enough to prove it. This was also present in PMS3 Al, and Ca maps
(Figure 26). Both Al and Ca appear to cross the interface, however it was not yet very clear if
the exchange was taking place and since ESEM element mapping does not provide
concentration element mapping, it was not possible to determine the cause of the clearer
colour along the interface in OPC4.
BSE image of OPC5 is shown in Figure 27. The interface is well defined and there are no
signs of alteration of migration of Ca or Al.
64
Figure 18: OPC4 SEM analysis. Cement-mudstone interface of the OPC4 sample
(Portland cement and Whitby Mudstone) taken with the ESEM using BSE. A small gap
between the cement and the mudstone matrix is clearly seen. In the mudstone is also
possible to identify some micaceous and organic facies. Big grains on the left of the
image correspond to sand grains (very high Si content) as part of the cement paste.
Cement matrix
Whitby Mudstone
65
Figure 19: OPC4 element mapping. (Top) Calcium map from OPC4 taken with the ESEM.
Blue colour shows areas where there is a Ca concentration. It is clear that cement paste (left of
the image) is Ca rich meanwhile Whitby Mudstone has little or none calcium. The interface line
is very clear and does not show an exchange of calcium from the cement paste to the mudstone.
Black spots in the cement paste indicate the presence of sand grains. Brighter areas of Ca in the
cement paste show indicate the presence of calcite crystals. (Down) Aluminium map of the
same sample taken with the ESEM. Higher Al concentrations are mostly in the right side of the
image which corresponds to the Whitby Mudstone. Small Al spots can be identified in the
cement paste which is common for Ordinary Portland Cement. Interface line is also very easy to
identify. From Al map is possible to see the small gap formed in between the cement paste and
the mudstone. Black spots in the Whitby Mudstone correspond mainly to S concentration
(pyrite).
66
.
Figure 20: OPC4 Si map from SEM Silica map from OPC4 taken with the ESEM. Si is
found mainly in the irregularly shaped sand grains within the cement matrix. It is also
present in the cement phases and in the mudstone.
67
Figure 21: OPC4 SEM analysis. OPC4 cement (left) - mudstone (right) interface. Interface
line is marked in red. The larger clastic grains in the mudstone are fine grained clay-matrix
(right) and the different components of the mudstone are adjacent to the cement.
68
Figure 22: OPC4 element mapping. (Top) Al concentration is highest in the Whitby
Mudstone (right). The interface line is clear and it does not show a real Al migration
from the mudstone into the cement paste. The Al concentrations found within the cement
paste represent the Ca-Al phases. Maps appear to be a little blurry and it could be caused
by the magnification of the image. (Below) Ca map of OPC4 ESEM map. It shows
abundant Ca concentration in the cement paste (left) and little Ca concentration in the
mudstone (right). At the interface higher Ca is seen the mudstone areas (indicated by the
two arrows)
69
Figure 23: OPC4 Si map from SEM Silica is found in the Whitby Mudstone as
well as in the cement matrix. Two different tones of colour can be identified
from Si map. One corresponds to the right of interface (red line) which is a
brighter colour than the one in the left of the interface. Si in the cement paste
indicates the presence of Ca - Si phases.
70
Figure 24: OPC4 SEM analysis. Cement (left) -mudstone (right) interface of
OPC4. The interface is shown by the red line. The bright aggregate of grains in the
top right are pyrite and the elongate grains (centre) are micaceous/clay phases.
71
Figure 25: OPC4 element mapping. (Top) Calcium map of area displayed in Figure 24.
Cement paste area is well defined by the Ca concentration and does not seem to pass over
the interface line which indicates that Ca is not migrating into the mudstone. (Down) Al
map obtained with the ESEM with a magnification of 6400x. Meanwhile Ca
concentrations is well defined, Al concentration is not at all clear and appears blurry near
the interface line and does not really seem to pass over the interface. Black spots within
the Al concentrations refer to pyrite concentrations (S rich).
72
Element mapping was also performed in samples PMS3 (Figure 26), OPC2, OPC5 (Figure 27)
that did not show any alteration under the optical microscope. Those samples did not show any
alteration or element migration under the analysis with the ESEM; however Ca, Al and Si
maps were useful to identify facies within the mudstone. Analysis with EMPA focused on
OPC4, PMS4 and NRV5. OPC4 and PMS4 were the only two samples that showed a visible
alteration found by optical and element mapping form ESEM. NRV5 sample did not show any
alteration at the interface but it was chosen to be studied with EMPA element maps in order to
analyse the facies within the cement paste.
73
Figure 26 PMS3 element mapping. (Top left) BSE ESEM image of cement -
mudstone interface of PMS3 sample (Ordinary Portland Cement with microsilica
addition with Yorkshire Clay). The bright (charging) grains are quartz. (Top right) Al
map obtained with the ESEM. The clay matrix of the Yorkshire Clay. From Al maps
there is no evidence of Al migration to the cement paste. (Down left) Ca map obtained
with the ESEM. Cement matrix is clear and coincides with the interface line which
indicates lack of Ca migrating into the mudstone. (Down right) Si map obtained with
the. Quartz grain is visible within the clay matrix of the Yorkshire clay. The presence of
high Si content in the cement matrix corresponds to microsilica used in the mixture.
74
Figure 27 OPC5 element mapping.
(Top left) ESEM BSE image of the OPC5 sample. The interface is shown by the red
line. Acicular salt crystals, likely to be from pore fluids in the cement, can be seen in
the centre. (Top right) Ca map obtained with the ESEM. Cement matrix is well defined
and matches with the interface line. There is no evidence that suggest any Ca
migration from the cement paste into the Yorkshire Clay. (Bottom left) Al map
obtained with the ESEM. Clay matrix is well defined and the borders match with the
interface line. (Bottom right) Si map obtained with the ESEM. Irregularly shaped
grains appear with a bright colour within the Yorkshire Clay. It is worth noting that
there is no Si grains in the cement paste since sand was not used in the formulation of
this mixture.
75
5.3 EMPA analysis
Samples OPC4, PMS4 and NRV5 were analysed under the EPMA in order to identify and
quantify alterations in the cement matrix. With the EPMA it was possible to map element
concentration. From Ca maps in samples OPC4 and PMS4 it was clear that Ca was being
depleted from the interface towards the cement matrix. This area was up to 250 µm across the
surface into the cement matrix. At the beginning it was supposed that Ca was being swapping
but it was not possible to identify any other element that changed either in the cement matrix
or the mudstone.
Al maps did not show any particular alteration close to the interface. Fe, K, Mg, Mn, Si and
S maps did not show either alterations or interactions with the cement paste.
From ESEM images there was an indication that some Ca migrated into the mudstone
matrix, however EPMA images revealed that what appeared to be Ca migrating into the clay
matrix was in fact a portion of the cement matrix that remained attached to the mudstone core
before the interface cracked.
Ca depletion was not present in other samples and other element maps did not show either
any alteration. It is still not clear the process that causes Ca to deplete near the interface but it
is clear that it was present in only one mudstone (Whitby Mudstone) and it was also only
present with the commercial mixtures and not with the specially designed low pH mixtures.
Because of the lack of alteration in the mudstone and claystones it was attempted to analyse
Ca absorption by placing small pieces of mudstone (around 1mm diameter) into a 0.5 M
solution of Calcium Chloride CaCl2 for 72 hours and then polished blocks were made where
the pieces of mudstones was held by resin and then cut in order to be able to analyse the edge
under the EPMA, however again there was no evidence of alteration or Ca absorption in any
of the samples.
It was possible to identify the most common mineralogical phases within the cement matrix
(Oss, 2005). Tricalcium silicate, Dicalcium silicate and Tricalcium aluminate were spotted by
comparing Ca, Al and Si element maps (see Figure 31 and Figure 35). Maps were analysed at
different concentration index in order to identify minor changes but besides Ca depletion,
76
there is no evidence that suggest Ca migration from the cement matrix into the mudstone or Al
migration from the mudstone into the cement or any other alteration. Maps from other samples
different than OPC5 and PMS5 do not show evidence of alteration; however mineralogical
facies were also identified from Al, Ca and Si. Some high content Ca zones were identified as
unhydrated cement particles.
Special attention is given to the NRVB sample since it was not found element mapping
images in the literature. In the NRVB cement, there was no evidence of alteration in the
cement or claystone. Element maps from EPMA was useful to identify some Calcium
Hydroxide facies were high Ca content was found but Si and Al were low within the cement
matrix.
Figure 28 shows a BSE image of OPC4 sample on the right and Ca map on the left, both
obtained with EPMA. Ca map showed that Ca concentration is decreasing towards the
interface, however there no indications that Ca is migrating into the mudstone. Fractures
within the cement paste appeared to have created 3 different Ca concentration zones. The first
zone, Zone 1, goes from the interface with the mudstone up to 250 μm towards the cement
matrix. Zone 2 goes up to 200 μm from limit with Zone 1 towards the cement matrix. Zone 3
coincides with other fractures and sand grains edges and it shows a more homogeneous Ca
concentration. Fractures in this zone do not appear to create new Ca concentration zones.
By comparison with Al and Si maps, also from EMPA, some mineral were identified within
the cement paste. Unhydrated cement particles appear as red spots in Ca map. This high Ca
concentration spots do not match with Si or Al concentration. They are indicated with a white
arrow.
Al map of OPC4 is shown in Figure 29, as well as BSE image. Aluminium appears
abundant in the mudstone matrix. It is also present in the cement matrix but only a few spots
with high Al concentration can be identified.
Si appears also abundant in the mudstone matrix as shown in Figure 30. High Si
concentrations is also found in sand grains form the cement matrix. However there are a few
other high-Si spots within the cement matrix. A particular zone from the OPC4 EMPA
77
element mapping was chosen to compare Ca, Al, and Si concentration. This are is contained
within the black square in top left corner in Figure 30 and it is presented in Figure 31.
Figure 31 shows Ca, Al and Si maps from the same zone contained in the black square in
Figure 30. Left image shows Ca concentration, Central image shows Al concentration and
right image shows Si. White arrows in Ca and Si element maps indicate zones matching high
Ca and Si concentration, which presumably indicates the presence of alite. Black arrows show
matching high Ca and Al concentration. This presumably indicates the presence of Tricalcium
aluminate.
Point analysis was attempted to undertake in EMPA, however thin sections appeared to be
not enough uniform to properly perform a point analysis.
PMS4 is shown in Figure 32. On the right a BSE image is presented. On the left a Ca map is
presented. In this sample it was possible to identify 2 different zones based on Ca
concentration. Zone 1 goes from the interface up to 200 – 250 µm towards the cement matrix.
The limit is defined mostly by the edges of sand grains. A crack seems to divide cement
matrix from the mudstone. Some Ca concentration is spotted within the mudstone, which
might suggest the migration of this element into the rock. However from optical analysis
showed in Figure 16 the presence of that particular Ca concentration in the edge of the
mudstone correspond actually to cement matrix, since the fracture occurred within the cement
matrix and not between the contact surfaces. Si map from Figure 33 shows abundance of this
element in the mudstone matrix. It is also present in sand grains in the cement matrix. Other
spots with high Si are indicated with arrows, this does not correspond to sand grains. Al map
from Figure 34 shows abundance of Al in the mudstone. From this element map it can be also
observed that part of the cement matrix is attached to the mudstone and a crack was formed
within the cement paste as observed in Figure 16. Some high-Al spots are marked with arrows.
The black square in Al map contains a zone that is analysed in Figure 35. In this last figure, Si
map is shown in left, Al map at centre and Ca map on the right. Black arrow in Si map (left)
shows a high-Si spot that also contains high-Ca concentration. This presumably indicated the
presence of alite. In Al map (centre), white arrow indicates a high-Al concentration that has
also high-Ca concentration, which can presumably be linked to Tricalcium aluminate.
78
NRV5 is shown in Figure 36 containing BSE, Ca, Al, and Si maps. Ca appears to be
abundant in the NRVB matrix. Al is abundant in the Yorkshire rock. Very high Ca
concentration spots in NRVB are indicated with black arrows. These spots does not match
with high Al or Si content, actually Al and Si appear to be particularly low where these high-
Ca concentration spots are presented. This is presumably related to unhydrated phases within
the NRVB matrix.
79
Figure 28: OPC4 EPMA analysis. (Left) Ca map of sample OPC4 polished thin section using EPMA. The Ca
concentration decreases away from the interface. Red spots within the cement matrix correspond to calcite crystals. Black
spots correspond to irregularly shaped sand grains. The fractures within the cement matrix coincide with the 2 different limits
between Zone 1 and Zone 2 and between Zone 2 and Zone 3. Zone 1 goes up to 250 µm from the interface towards the
cement matrix and the limit coincides with the fractures and the sand grains edges. Zone 2 goes up to 200 µm from limit with
Zone 1, the limit with Zone 3 coincides with other fractures and sand grains edges. Zone 3 has a more homogeneous Ca
concentration and fractures within Zone 3 do not appear to create new sections where Ca concentration decreases. There is
no evidence for Ca migration into the mudstone. High Ca spots correspond to unhydrated cement particles. (Right) BSE
image of sample OPC4 from a polished thin section. Three optically distinct zones (1, 2 and 3) in the cementitious materials.
Z
one
1
Unhydrated
cement particles Zone 1
Zone 2
Zone 3
Zone 1
Zone 2
Zone 3
Unhydrated
cement particles
80
Figure 29: OPC4 EPMA analysis. (Left) Al map of sample OPC4 polished thin section using EPMA. There is high Al
concentration in the clay matrix within the Whitby Mudstone. There is also Al concentration within the cement matrix which
forms Tricalcium aluminates facies. Black spots correspond to sand grains in the cement matrix. There is no indication of Al
variation in the 3 different zones where Ca appears to change. (Right) BSE image of sample OPC4 from a polished thin
section.
Zone 1
Zone 2
Zone 3
Zone 1
Zone 2
Zone 3
81
Figure 30: OPC4 EPMA analysis. (Left) Si map of sample OPC4 polished thin section using EPMA. There is high Si
concentration in the sand grains within the cement matrix. Si is also found in the mudstone with high concentrations spots
appearing in yellow and orange. Within the cement paste, some high Si concentrations appear in clear blue but there is no
evidence to suggest Si variation within the cement matrix or the mudstone. Places where Si is high within the cement paste
indicate the presence of Tricalcium silicate. The square in the top left of the image is the detailed area described in Figure 31.
(Right) BSE image of sample OPC4 from a polished thin section.
Zone 1
Zone 2
Zone 3
Zone 1
Zone 2
Zone 3
82
Figure 31: OPC4 EPMA analysis. (Left) Detailed Ca map of sample OPC4 polished thin section using EPMA. White
arrow indicate high-Ca zones matching high-Si zones in cement matrix which may indicate which indicates the presence of
Tricalcium silicate (Alite (CaO)3SiO2). (Centre) Detailed Al map where high-Al spot within the cement matrix is indicated
with black arrow. The same spot presents high-Ca concentrations which may indicate the presence of Tricalcium aluminate
((CaO)3Al2O). (Left) Detailed Si map .White arrow indicates high-Si content within cement matrix matching high-Ca
content.
83
Zone 1
Zone 2
Zone 1
Zone 2
Figure 32 PMS4 Ca map by EPMA analysis (Left) Ca map obtained with the EPMA of a polished thin section of PMS4.
There are two well delimited areas named Zone 1 and Zone 2. Ca has a lower concentration near the interface (Zone 1); this
zone goes towards the cement matrix for up to 200 µm. There are no visible fractures within the cement matrix. Black spots
correspond to irregularly shaped sand grains. Red spots correspond to calcite crystals. The limit between Zone 1 and Zone 2
mostly matches the edges of the sand grains. In the mudstone (lower part of the image) it is possible to find Ca
concentration, however from other optical analysis it was found that the fracture between cement matrix and mudstone
actually occurred within the cement matrix so a thin layer of cement remained attached to the mudstone. Ca depletion is also
present in this thin layer of cement. Even one calcite crystal appears to be fractured and a small portion of it remained
attached to the mudstone (left of the image). (Right) BSE image of the same area obtained with the EPROBE. There two
well differentiated areas within the cement matrix.
84
Zone 1
Zone 2
Zone 1
Zone 2
Figure 33: PMS4 Si map by EPMA analysis (Left) Red spots in the top of the image are mostly irregularly shaped sand
grains. Whitby Mudstone shows to have a high Si content within its clay matrix. Some of the red spots in the cement
matrix do not correspond to sand grains since they present a high Al content (See Figure 34). High Si spots that do not
correspond to sand grains are indicated with arrows. (Right) BSE image of the same area obtained with the EPROBE.
High Si spots are indicated wit arrows.
85
Zone 1
Zone 2
Zone 1
Zone 2
Figure 34: PMS4 Al map by EPMA analysis. (Left) Most of the high Al content is found in the clay matrix of the
Whitby Mudstone; however some high Al spots are easily identified within the cement matrix. Black frame in the
centre of the image correspond to the detailed area described in Figure 35 (Right) BSE image of the same area
obtained with the EPROBE. High Al spots are indicated with arrows.
86
Figure 35: PMS4 element map detail by EPMA analysis (Left) Detail of Si map from PMS4. Si facies are spotted in
green while sand grains appear red. Si matrix matches with Ca matrix from the image in the right which indicates the
presence of Tricalcium silicate (Alite (CaO)3SiO2). Special spot where high Si concentration and high Ca
concentration match is indicated with a black arrow. (Centre) Detail of Al map from PMS4. Al facies are spotted
green and red within the cement matrix. Black spots correspond to sand grains. A particular spot where Tricalcium
aluminate ((CaO)3Al2O) can be appreciated is indicated with a white arrow. (Right) Detail of Ca map from PMS4. Ca
facies appear green, yellow and red. Black spot correspond to sand grains. Black arrow indicated Tricalcium silicate
since it matches with Si concentrations found from Si maps. White arrow indicates Tricalcium aluminate.
87
Figure 36: NRV5 element maps by EPMA. (Top left) BSE image obtained by EPMA of
NRVB cement with Yorkshire clay. The cement matrix correspond to the top left of the
image. There is no evidence of alteration either in the NRVB or the claystone. (Top right)
Ca map from NRV5. Calcium facies are clearly present in the cement matrix with high Ca
concentration spots. Some high Ca spots are indicated with arrows. (Bottom left) Si map
from NRV5. High Si content is found in the claystone but also in some areas in the cement
matrix. There is no evidence of alteration in Si distribution however a few darker areas can
be observed where Ca content is high (marked with arrows). (Bottom right) Al map from
NRV5. Clay matrix from Yorkshire Claystone shows high Al content. Some Al content is
also found in the cement matrix. Al content is found to be low where cement matrix has a
high Ca content (marked with arrows).
88
Table 8: Resume of all samples analysis.
SAMPLE
NUMBER
Cement mixture – lithology Results after 28 days
interaction with pore water
OPC1 Mortar of Ordinary Portland cement -
Kimmeridge clay
None
OPC2 Mortar of Ordinary Portland cement -
Holywell clay
None
OPC3 Mortar of Ordinary Portland cement -
Yorkshire clay
None
OPC4 Mortar of Ordinary Portland cement – Whitby
Mudstone
Ca depletion in the interface up
to 250µm
PMS1 Mortar of Ordinary Portland cement with 10%
silica fume - Kimmeridge clay
None
PMS2 Mortar of Ordinary Portland cement with 10%
silica fume - Holywell clay
None
PMS3 Mortar of Ordinary Portland cement with 10%
silica fume - Yorkshire clay
None
PMS4 Mortar of Ordinary Portland cement with 10%
silica fume - Whitby Mudstone
Ca depletion in the cement
matrix near the interface up to
250µm
NRV5 Nirex Reference Vault Backfill - Whitby
Mudstone
None
NRV6 Nirex Reference Vault Backfill - Holywell
clay
None
NRV7 Nirex Reference Vault Backfill - Yorkshire
clay
None
NRV8 Nirex Reference Vault Backfill - Kimmeridge
clay
None
OPC5 Ordinary Portland Cement grout w/c 1.4 - None
89
Whitby Mudstone
OPC6 Ordinary Portland Cement grout w/c 1.4 -
Holywell clay
None
OPC7 Ordinary Portland Cement grout w/c 1.4 -
Yorkshire clay
None
OPC8 Ordinary Portland Cement grout w/c 1.4 -
Kimmeridge clay
None
PMS5 Ordinary Portland Cement grout with 40%
silica fume - Whitby Mudstone
None
PMS6 Ordinary Portland Cement grout with 40%
silica fume - Holywell clay
None
PMS7 Ordinary Portland Cement grout with 40%
silica fume - Yorkshire clay
None
PMS8 Ordinary Portland Cement grout with 40%
silica fume - Kimmeridge clay
None
90
5.4 Permeability
The original objective of manufacturing cylindrical cement samples with a rock core was to
measure permeability in the altered interface; however these samples were not appropriate to
perform the test since they cracked when water loss was present (i.e. drying to allow gas from
permeameter to flow). This cracking was not present when the cement samples did not contain
a rock core; therefore the measurement of six unweathered cement samples was undertaken
with the oscillating pore pressure test in order to measure the permeability of cement mixes.
Samples tested are described in Table 9. NRVB sample was tested using a constant flow
method. The only sample that was not tested was the result of cracking due to water loss.
Despite of trying to test the sample partially saturated with pore water from curing, it was not
possible to obtain any measurement of permeability neither with the oscillating pore pressure
method or constant flow method.
In most of the samples the test was repeated in order to study the effect of effective pressure
in the cement permeability, however most of the samples showed not to be affected by
changes in effective pressure since the results show negligible variation in permeability.
MPS3 sample was very difficult to measure due to shrinkage and cracking. It was necessary
to test the sample with partially saturated cores (form pore water) but results were inconsistent
and it was necessary to use very long periods in order to obtain a downstream pore pressure
signature which made very difficult test repletion. One test was 27 hours long.
All results are summarised in Figure 43.
91
Table 9: Test conditions for every sample
CODE Period
(seconds)
Amplitude
(MPa)
Pore
pressure
(MPa)
Number of test
performed
Test
OPC 100 0.5 10 3 Oscillating pore pressure
PMS 200 0.5 10 3 Oscillating pore pressure
MPC5 100 0.5 10 2 Oscillating pore pressure
PMS5 50 0.5 10 3 Oscillating pore pressure
MPC3 10000 0.5 10 1 Oscillating pore pressure
MPS3 10000 0.5 10 1 Oscillating pore pressure
NRVB 2 Constant flow method
MPC5 sample was tested twice and did not show to be affected significantly by effective
pressure. Values range from 5 x 10-17
m2
for 5MPa effective pressure in the first cycle to 4.43
x 10-17
m2 for 30 MPa effective pressure in the second cycle, which is practically negligible
compared with the variation of permeability of other materials like mudstone which variates in
orders of magnitude with effective pressure (McKernan, Rutter, Mecklenburgh, Taylor, &
Covey-Crump, 2014). Results are shown in Figure 37.
92
Figure 37: MPC5 permeability results
OPC was tested twice and did not show to be affected by effective pressure since the values
of permeability were almost the same in both tests. Results are presented in Figure 38.
Permeability values range from 2.69 x 10-17
for 10 MPa effective pressure in the first cycle to
2.49 x 10-17
m2
for 30 MPa effective pressure in the second cycle, which is a small change.
This value is within the same order of magnitude than MPC5. Results are shown in Figure 38.
93
Figure 38: OPC permeability results
PMS5 was tested 3 times. This sample showed to be slightly affected by effective pressure
since it decayed with every test. For the same effective pressure (5 MPa) permeability changed
from 2.73 x10-17
m2 for the first test to 1.59 x10
-17 m
2 for the third test. All test matched at 30
MPa effective pressure with a value of 1.39 x10-17
m2 . The second point (10 MPa) in the first
test does not match with the trend line from all the other points. It is still unclear why this
happened since the sample was not moved during the test and all the parameters, except for
effective pressure were kept constant. A leakage can be discarded since the rest of the points
show more consistency one to another.
94
Figure 39: PMS5 permeability results
NRV sample was tested with constant flow method in the same equipment that the
oscillating pore pressure method by making the rotor in the upstream to move until a constant
differential pressure was obtained between upstream pore pressure and downstream pore
pressure. It was done manually by turning on and off the rotor every test since the equipment
is designed to operate automatically only the oscillating pore pressure test. Results are
presented in Figure 40. It appears like effective pressure has a slight effect in permeability
since it decreases in the second cycle of test. NRVB was tested 4 times with constant flow
method. The first test shows a decrease in permeability as effective pressure was increased,
permeability decreased from 1.84 x 10-17
m2 to 9.29 x 10
-17 m
2. The second, third and fourth
test resulted in the same values for every effective pressure and it only decreases from 1.06 x
10-17
m2 to 9.29 x 10
-18 m
2. It makes clear that effective pressure did not affected significantly
permeability after the first test, however the decrease in permeability in the first test is
negligible compared with other materials within the repository such as mudstones and shales.
95
Figure 40: NRVB permeability results
PMS was tested three times at only two effective pressures (10 and 30 MPa) and 3 effective
pressures in last cycle (10, 20 and 30 MPa). This was due a time limitations since it was the
last sample to be tested. Permeability values range from 1.88 x 10-18
m2 to 3.78 x 10
-19 m
2 for
10 MPa effective pressure and it decreased up to 4.95 x 10-19
m2 for 30 MPa effective pressure.
Results are shown in Figure 41.
96
Figure 41: PMS permeability results
MPC3 was tested only once due to the very long period needed to obtain a downstream pore
pressure signature. Data was processed several times since the permeability somehow changed
from one processing to another. Data was processed with the same MATLAB process than all
the other samples and yet permeability values for 30 MPa effective pressure was scattered.
This sample was tested partially saturated with pore water which could be the reason for the
very low permeability found (10-21
m2). MPC5 appear to be more affected by effective
pressure than all the other samples tested since permeability decreases a whole order of
magnitude from 5 MPa effective pressure to 30 MPa effective pressure. Results are shown in
Figure 42.
97
Figure 42: MPC3 permeability results
98
When compared k results all together, the effect of Effective pressure in permeability does
not seem to be significant. Results show k values ranging from 10-21
to 10-16
m2. Effective
pressure ranged from 5 to 30 MPa. Almost all the samples showed to have a constant k value
regardless of the Effective pressure. Only MPC3 showed to be affected more by effective
pressure
Figure 43: Summarised permeability results.
Typically a downstream to upstream amplitude ratio 𝐴𝐷 𝐴𝑈 ≈ 0.5⁄ is enough to reach a
reliable data processing. To achieve this it was necessary to adjust parameters such as T and
sometimes the downstream volume. The NRVB sample has the higher permeability (k=10-16
)
and it was not possible to obtain k with the oscillating pore pressure test since all the solutions
were out of the solution space in the nomogram. To overcome this issue a constant flow test
99
was performed with the same equipment. In the constant flow test gas was made to pass
through the sample at a constant flow rate and then the pressure differential was recorded in
order to obtain the permeability. From literature the common permeability values for gas in
concrete or grout range from 10-18
to 10-16
m2 (Abbas, Carcasses, & Ollivier, 1999).
The lower permeability value of 10-21
corresponds to the sample MPC3 which was measured
partially saturated with pore water. It was not possible to measure this sample in a dry state
since it started to crack with water loss.
5.4 Porosity
4 samples were tested in the Digital Helium Porosimeter. The addition of Microsilica and
the usage of Microcement seemed to reduce the porosity in the samples. The regular cement
mixture (OPC) which contains sand and Ordinary Portland Cement has a porosity of 19.25%
and the addition of 10% Microsilica (PMS) reduces its porosity to 13.95%. The usage of
microcement instead of ordinary Portland cement reduces porosity in the same order than
microsilica.
One interesting result is that the special cement NRVB has a very large porosity found by
testing two samples of NRVB where porosities of 42.68 and 44.99% were obtained. This
mixture loses almost half of its weight when drying but at the same time keeps permeability
with in an average range.
MPC5 resulted with a porosity of 13.39 %. Results are summarised in Table 10. 3 samples
were attempted to measure porosity while partially saturated (PMS5, MPC3 and MPS3), but
cracking and shrinkage and were present during the test due to water loss, so it was not
possible to make any porosity measurement.
100
Table 10: Porosity results. Porosities obtained with the Digital Helium Porosimeter
The porosity values obtained are porosity of undisturbed samples. The change in porosity in
cement matrix was not able to measure with helium porosimeter due to lack of reaction
between the cement matrix and the mudstone and to the cracks that appeared in the samples
with mudstone core embedded. Therefore the porosity of unaltered cement plugs was
measured in samples that were not affected by shrinkage due to water loss.
Sample P1 P2 Weight 1.0" disc in Disc volume GV GD BD porosity
(ID) (Bar) (Bar) (Grams) matrix cup (ml) (ml) g/cm3
g/cm3
%
NRV 7.606 4.184 15.997 532100 39.75 7.2012 2.2214 1.27 42.68
NRV 7.604 4.059 18.003 532000 37.93 8.0960 2.2237 1.22 44.99
OPC 7.598 4.295 57.006 432000 24.63 23.1414 2.4634 1.99 19.25
OPC 7.587 4.478 32.318 531000 35.80 13.2227 2.4441 1.99 18.63
PMS 7.595 4.597 32.687 531000 35.80 13.9282 2.3468 2.02 13.95
MPC5 6.851 4.413 20.823 540000 39.82 11.5762 1.7988 1.56 13.19
101
Chapter 6 Discussion
The Ca depletion alteration in the cement matrix was already found in other research with
regular concrete mixture and Opalinus Clay (Jenni, Mäder, Lerouge, Gaboreau, & Schwyn,
2014). Decrease in Ca concentrations has been related to dissolution of Ca phases such as
portlandite. However, this alteration was found to take place after a considerable amount of
time (2.2 years) and interaction with groundwater. It also showed Mg enrichment in the
cement paste near interface which was not found in this research.
Temperature used in this research was room temperature (20-25 °C). Literature has covered
a wide range of temperatures in the cement-clay interaction, from 25 °C (Dauzeres et al., 2010)
up to 150 °C (Mohammed, Pusch, Warr, Kasbohm, & Knutsson, 2015). Alterations in the
cement matrix and clay minerals within the rock occur at faster rates and are more extensive
when temperature is enhanced. Cement is found to be degraded by decalcification, sulphate-
attack and carbonation. When carbonation occurs, a high-Ca zone is found in the surface
expose to CO2 or H2O leading to a calcite precipitation which competes with portlandite
dissolution (caused by low-Ph due to carbonation) generating a decalcification in the cement
matrix.
Sulphur migration from clay rocks into cement matrix are generated by the low-pH in the
cement matrix caused by carbonation. The dissolution of portlandite creates an increase in
cavities where ettringite is able to precipitate. This precipitation does not occur near the
carbonated zone (low-pH) but when S reaches a pH high enough for precipitation.
Carbonation is plausible to be the cause of the decalcification found in samples OPC4 and
PMS4. These could be caused by the exposure to water from curing process and CO2/HCO3
migrating from the clay into cement. Literature also shows that the addition microsilica
decreases portlandite content which lead to low carbonation (Taylor, 1990). This would
explain why samples with up to 40% of microsilica addition showed no alteration under
ESEM and EMPA.
In the other hand, the results of the special cements such as the NRVB indicates that
alterations between the cement matrix and the surrounding host rock might not be an issue in
102
an early stage of interaction. Silica fume appears to play an important role in decreasing
porosity and avoiding the alteration of the cement matrix by reducing the voids as found by
Blandine et al., 2008.
The mechanism of alteration of cement matrix might be dissolution of calcium hydroxide
phases by carbonic acid create by the dissolution of carbon dioxide into the aqueous phase.
CO2 + H2O → H2CO3 (aq)
And then
Ca(OH)2(s) → Ca2+(aq) + 2OH−
(aq)
When carbonation occurs, Portlandite dissolution leads to an increase in porosity in the
weathered zone. These cavities created by Portlandite dissolution are commonly zones where
calcite and ettringite precipitate, thus refilling voids within the cement matrix. When cement
reacts with a clay rock, porosity conditions changes over time leading finally to a clogging
where porosity in the interface is strongly reduced. This clogging leads to a reduction of fluids
across the interface, which basically would stop geochemical alteration process and slow
down mass transport across the interface (Kosakowski & Berner, 2013). However, the
precipitation of crystal minerals such as calcite leads to a significant increase in cracks within
the cement matrix, which increase permeability, allowing fluids to reach the unweathered
cement matrix (Ruiz-Agudo, Kudłacz, Putnis, Putnis, & Rodriguez-Navarro, 2013).
Permeability and porosity of cement mixtures are found consisting with literature. Despite
the failure to obtain samples to analyse the permeability of cement-clay interface, the
permeability of cement matrix was measured and compared with the permeability of the
Whitby Mudstone (one of the potential host rocks) which ranges from 10-21
to 10-18
m2
(McKernan et al., 2014) when measured with oscillating pore fluid pressure. The lowest value
corresponds to permeability measured perpendicular to layering. MPC5 sample showed a
particular low permeability value. This can be caused by having measured the sample when
partially saturated since it would crack when exposed to drying. For the rest of the samples,
103
permeability ranges between 10-18
to 1016
m2. PMS sample show the lowest permeability from
the samples measured in dry condition. This is not surprising since the addition of microsilica
reduces the porosity and permeability of cement. Cements samples show little or none
pressure sensitivity. This is due to fluid flowing through equant pores rather than crack-like
pores like the case of the Whitby Mudstone, for instance.
Cracking of cement samples due to water loss is a major concern. Besides not allowing to
manufacture samples to measure permeability in dry conditions, cracks are likely to appear in
GDF since saturated conditions are not necessarily predominant at all times. Groundwater is
expected to eventually saturate the GDF, but during the operation and filling of the repository,
cement is likely to be exposed to air, which would lead to a temporary water loss. Further
investigation is needed in order to assess the performance of cement mortars during water loss
conditions.
Further investigation is recommended regarding the chemical interaction of cement-clay
interfaces with possible UK host rocks (Whitby Mudstone, Yorkshire Clay, Kimmeridge, Clay,
and Holywell Shale). It would be recommended to undertake experiments in a longer period of
time and with different temperatures (suggested 70 °C) and hyperalkaline fluids. This would
allow investigating the interaction in the long term rather than the short term where clearly
there is not much of interaction taking place. Regarding permeability measurements, a
different arrange of the cement-clay interface is needed since the proposed arrange of rock
core in cylindrical cement samples is strongly affect by cracks appearance. Porosity of
potential altered cement can be measured with Mercury intrusion rather than helium
porosimeter.
Further analysis with small cuts of the interface zone are recommended to be undertaken
since equipment such as ESEM does not require samples to be in the form of a thin section for
SEM analysis.
In the special case of NRVB, permeability found with the constant flow method was slightly
lower by one order of magnitude than the one reported in the literature (Ian G Crossland,
2007). Values in this research found permeability to be 10e-17 whereas literature report 10e-
16 m2. It is worth nothing the difficulties found in measuring permeability in NRVB since it
104
was not achieved with the oscillating pore pressure and the test had to be adapted to perform
the constant flow method; however it was possible to replicate the results by repeating the test.
Porosity in NRVB appears to be the characteristic that makes the difference with the other
cement mixtures proposed. NRVB shows a porosity of 44 %, more than double that other
cement mixtures, which create voids where CaOH2 can be dissolved and buffer the
groundwater pH to limit migration of radionuclides.
The usage of conventional mortars such as OPC4 and PMS4 might be not advised as a
buffer or backfill in the repository. Ca depletion showed in an initial stage of reaction indicates
that these two samples can be strongly degraded with time and conditions within the
repository. NRVB does not show these problems.
Chapter 7 Conclusions
Little reactivity between proposed cement mixtures and possible host rocks for GDF in the
UK has been found in an initial setting stage of 28 days. SEM and EMPA analysis do not
show any evidence to suggest that the cement or the clay matrix within the rock is being
subject to alterations. Only two samples (OPC4 and PMS4) showed a clear decalcification
zone near the interface with the Whitby Mudstone. The addition of high quantities of
microsilica to cement mortars appears to decrease the reactivity of cement by decreasing the
content of soluble Ca-phases like Portlandite. This Ca-depletion zone is likely to be originated
by carbonation however further investigation is advised to undertake to corroborate this
observation.
Permeability of the cement-clay composite was not possible to measure due to cracking of
the cement hence permeability and porosity was measure in unweathered cement samples
when cracks did not appear due to water loss. They show low permeability as expected from
the literature and when compared with permeability of one of the possible host rocks in the
UK (Whitby Mudstone) cements are not likely to be more permeable than permeability
parallel to layering, however cracking due to water loss is an issue that need to be addressed
and further research in this matter is encouraged.
105
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