Cement Chemistry for Engineers, Cape Town 31st January 2013

Lecture 5: Effect of SCMs on durability

Different forms of degradation

Generic effects of SCMs

Causes of concrete degradation

1%

4% 5%

90%

Others

Freeze / Thaw

Alkali Silica Reaction Corrosion

I am sorry I do not know the source or veracity of these figures,

but they are probably pretty close to the truth

Impact of SCMs

degradation 1st mech 2nd mech General

Impact

SCMs

Carbonation binding transport Negative

Chloride Transport Binding Positive

ASR Pore solution

pH

Alumina Positive

Freeze thaw saturation ?? Negative

Sulfate Conversion

of Afm

embedded in

CSH to

ettringite

transport Claimed

positive

CARBONATION

Reducing calcium content; reduces buffer to carbonation

Mg

S

AlFe

KNa

rest

Ca

Si

O

Reduce Ca

CaCO3

CaO Ca(OH)2

+H2O

CO2 +CO

2

C-S-H + CO2 various intermediates CaCO3 + SiO2nH2O + H2O CH + CO2 CaCO3 + H2O

Aluminate hydrates + CO2 CaCO3 + hydrated alumina

Ferrite hydrates + CO2 CaCO3 + hydrated alumina + iron oxides

All CaO content can react with CO2,

not just portlandite

Effects more pronounced with poor curing From BRE via MDA Thomas, UNB

Effect of SCMs on carbonation

Capacity to bind CO2 is most important.

Cement with less chemical CO2 inevitably has less capacity to bind CO2

Transport (through carbonated layer) is secondary.

Good curing can partially offset effects of lower binding capacity

The balance between these effects needs to be further explored

These considerations are important for reinforced concrete, but there is

no obstacle to using low CaO binders in non reinforced applications:

blocks, bricks, pavers roof tiles

CHLORIDE INGRESS

Effect of SCMs on chloride transport

• Now transport is dominant

• Binding is secondary, but important

• C-S-H (a lot which binds a little) and Freidel’s salt (a little which binds a

lot), overall play roughly equal roles in binding.

• SCMs with high alumina content will give significant increase in binding

capacity

1 10 100 1000 10000

Age (days)

Lab. Concretes

W/CM = 0.60 - 0.63

Field Concretes

W/CM = 0.57 - 0.59

OPC

Fly Ash

10-17

10-18

10-19

10-20

10-21

Per

mea

bil

ity

(m

2)

Effect of fly ash on permeability – long term effect

Source Mike Thomas

100

1000

10000

100000

1 10 100 1000

Age (days)

RC

P (

Co

ulo

mb

s)

W/CM = 0.50

Control (no slag)

25% Slag

50% Slag

Effect of slag on RCPT

Source Mike Thomas

Example of influence of fly ash on binding

CORROSION OF STEEL IN OPC & 30FA CONCRETE 35 N/mm2, 11 years FAMCET Exposure

OPC OPC/30FA

Source: CSIR Contract nr:BB078 5600 5671 Slide from

ASR, PhD Theodore Chappex, EPFL

Effect of blended pastes on ASR expansion

SCMs are effective in reducing deleterious ASR (empirical additions):

Field & Lab experience:

Silicon and Aluminium addition are involved in the reduction of expansion

Aluminium rich SCMs are more effective against ASR

The exact mechanism by which it happens is unclear!

5%

15%SFQ

15%MK

10%SFQ

10%MK

OPC

Samples in alkaline solution

Systems Studied

Experimental systems:

MK

OPC

Q - Filler

SF

OPC

Si

Al

95, 90, 85%w

5, 10, 15%w

7.65, …%w

7.35, …%w

Paste sample

Pore solution

Piston

EDS Pore solution extraction

TGA

C-S-H EDS analysis

The Si/Ca increase with increasing substitution for both systems (MK and SF-Q)

The Al/Ca is constant for SFQ at all substitutions levels and increase with MK substitution

Pastes can be compared in term of pore solution concentration

300 days:

100

150

200

250

300

350

400

450

K[mmol/l]

OPC

5SFQ

5MK

10SFQ

10MK

15SFQ

15MK

0

50

100

150

0 100 200 300 400 500

Na[m

mol/l]

me[day]

5MK

5SFQ

10MK

10SSFQ

15SFQ 15MK

Pore solution analysis

- The silanol binding capacity is confirmed - No improve of fixation is observed up to 2 years in Al rich systems

Al doesn’t increase the alkali fixation capacity of C-S-H in blended pastes! Another phenomena is involved to control ASR in presence of Al!

Comparatively, the fixation capacity of SFQ and MK are similar. Aluminium has no influence on the fixation capacity of alkalis

C-S-H fixation capacity estimation

New approach: focus on the aggregates

90 days: 300 days:

Pore solution composition of MK pastes

MK systems provide aluminium ions in the pore solution – A peak of aluminium appears during the first 90 days

0

0.5

1

1.5

2

2.5

3

3.5

0 100 200 300 400 500 600

Al[mmol/l]

me[day]

OPC

15MK

10MK

5MK

21

22

23

There is a clear influence of

aluminium ions on aggregates gel

formation!

• First effect is lowering of pH of pore solution

• Lower C/S C-S-H absorbs more alkalis

• SCM high in alumina also inhibit directly dissolution of amorphous

silica

Effect of SCMs on ASR

SULFATE ATTACK, PhD Cheng Yu, South East University, China and EPFL

Crystallization pressure theory Scherer, 2002 2004

IAP > Ksp

IAP = (Ca2+)6 × (Al(OH)4

-)2 × (SO4

2-)3 × (OH -)4

s c = (R ×T / vcrys. ) × ln(IAP /Ksp)

1. Supersaturated solution,

2. Confined crystal growth of solid product

s c =gCL (dA / dV) =gCL (2 / r)

6Ca2+ +2Al(OH)4

- +3SO4

2- + 4OH - +26H2O®C3A ×3CS ×H32

For pressure > 2MPa, r < 100nm Scherer, 1999

Expansion theories

This is only plausible theory

1. Large crystals of

AFm/AFt in “pocket”

3. Pore solution?

2. Fine AFm crystals

in C-S-H

OPC paste before Sufate Attack

Mapping (SO3 profiles)

BUT, mainly reflects the sulfate uptake by solid phases,

not the sulfate content in pore solution.

Amount of sulfate in solid phase (Ettr. & Gypsum) ≠ Expansion

How to measure the sulfate content in pore solution

Relationship between sulfate bound to C-S-H (S/Si) and [SO42-] in pore

solution

Barbarulo et al, 2008

Water cement ratio Sample size Sulfate concentration

M1 0.55 1×1×16 cm 3g/L

M2 0.55 2×2×16 cm 3g/L

M3 0.55 4×4×16 cm 3g/L

M4 0.55 2×2×16 cm 10g/L

M5 0.55 2×2×16 cm 30g/L

Experiment and results: OPC

V solution / V sample = 28

Renew every 2 weeks

(every week at first 4 weeks)

3 month curing

Surface removed

T = 20°C

Expansion

w/c=0.55 2×2×16cm

Effect of concentration

Very similar penetration profiles

120d

What cause the different expansion at 120d?

5mm

120d

4mm

120d

3mm

120d

2mm

120d

4mm 2mm 3mm

120d

The reaction between SO42- and solid phase buffer the [SO4

2-] in pore solution,

depth by depth.

Sample in 30g/L has more sulfate bound in C-S-H than low concentration ones,

probably can explain the difference of expansion

EDS of C-S-H

As sulfate ions penetrate in the cement paste,

they react with unconstrained aluminate phases,

mainly AFm in the pockets,

this buffers the increase of [SO42-] in pore solution.

When all freely transformable Al2O3 has reacted,

the [SO42-] in solution will increase,

constrained AFm within C-S-H can then react to ettringite

and exert expansion force.

Once cracking occurs, SO42- can entry freely and,

react even with Ca2+ to form gypsum in cracks.

Explanation of expansion

Slag blends

SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O TiO2

Slag 31.53 15.85 0.32 36.87 9.69 2.76 0.44 0.332 1.76

w/c=0.55 55S5 2×2×16cm

Expansion

3g/L

10g/L

30g/L

Surface

spalling

• Complicated

• Interaction of:

• buffering effects,

• amount of constrained AFm and

• perhaps transport effects

• Cannot say that blended cements have “chemical” resistance to

sulfate attack if they contain alumina.

• Need for test methods more representative of reality where surface

loss is more important than macroscopic expansion

Effect of SCMs on sulfate resistance

Impact of SCMs

degradation 1st mech 2nd mech General

Impact

SCMs

Carbonation binding transport Negative

Chloride Transport Binding Positive

ASR Pore solution

pH

Alumina Positive

Freeze thaw saturation ?? Negative

Sulfate Conversion

of Afm

embedded in

CSH to

ettringite

transport Claimed

positive

• Durability is not a materials property – depends on environment

• SCMs may improve or worsen durability depending on exposure

condition

• It appears that “1.5 C/S” CSH may slow down transport of water and

chloride

• Carbonation can be a potential problem, for reinforced concrete due to

lack of buffering capacity.

• ASR undoubtedly improved by SCMs

• Sulfate attack (and probably Freeze Thaw) are complex and need to

be better understood.

Summary

Cement Chemistry for Engineers, Cape Town 31st January 2013

End Lecture 5

Further reading

Sustainability:

Sustainable development and climate change initiatives: J.S. Damtoft, J. Lukasik, D. Herfort, D.

Sorrentino, E.M. Gartner. Cement and Concrete Research 38, (2008), 115-127

Straight talk with Karen Scrivener on cements, CO2 and sustainable development: American

Ceramic society Bulletin vol 91 no. 5

http://www.nanocem.org/fileadmin/nanocem_files/documents/misc/Ceram_Bull_article_May_20

12.pdf

Hydration:

The Microstructure of Concrete, Scrivener, K.L., in Materials Science of Concrete I, Skalny, J.P.

ed (American Ceramic Society, Columbus, Ohio) 1989, 127-161

Mechanisms:

Dissolution theory applied to the induction period in alite hydration, Juilland, P. Gallucci, E.,

Flatt, R. Scrivener, K. , Cement and Concrete Research 40 (6), 831-844, 2010

Studying nucleation and growth kinetics of alite hydration using μic, Bishnoi S., Scrivener, K.L.

Cement and Concrete Research, 39, (10) 849-860, 2009

Densification of C−S−H Measured by 1H NMR Relaxometry Arnaud C. A. Muller, Karen L.

Scrivener, Agata M. Gajewicz, and Peter J. McDonald J. Phys. Chem. C 2013, 117, 403−412,

dx.doi.org/10.1021/jp3102964

Further reading

SCMs Hydration:

Supplementary cementitious materials: Review Barbara Lothenbach, Karen Scrivener, R.D.

Hooton, Cem Conc Res, 41(12) 1244-1256, 2011

Methods for determination of degree of reaction of slag in blended cement pastes, Vanessa

Kocaba, Emmanuel Gallucci, Karen L. Scrivener, Cem Conc Res 42, (3) 2012, 511–525

Cement substitution by a combination of metakaolin and limestone, M. Antoni, J. Rossen, F.

Martirena K. Scrivener, Cem Concr Res 42 (2012) 1579–1589

Durability:

Alkali fixation of C–S–H in blended cement pastes and its relation to alkali silica reaction,

Théodore Chappex, Karen Scrivener Cem Conc Res, 42(8) 2012, 1049-1054 DOI:

10.1016/j.cemconres.2012.03.010

Mechanism of expansion of mortars immersed in sodium sulfate solutions, Cheng Yu, Sun Wei,

Karen Scrivener, Cem Conc Res, 43, 2013, 105-111

All EPFL publications available though: http://infoscience.epfl.ch/

Further reading

EPFL Theses: http://library.epfl.ch/en/theses/

T. Chappex, The role of aluminium from supplementary cementitious materials in controlling

alkali-silica reaction. 2012

W. Kunther, Investigation of Sulfate Attack by Experimental and Thermodynamic Means. 2012

A. Quennoz, Hydration of C3A with Calcium Sulfate Alone and in the Presence of Calcium

Silicate. 2011

A. Chabrelie, Mechanisms of degradation of concrete by external sulfate ions under laboratory

and field conditions. 2010

P. Juilland, Early hydration of cementitious systems. 2009.

V. Kocaba, Development and evaluation of methods to follow microstructural development of

cementitious systems including slags. 2009.

R. Fernandez Lopez, Calcined clayey soils as a potential replacement for cement in

developing countries. 2009.

M. M. Costoya Fernández, Effect of particle size on the hydration kinetics and microstructural

development of tricalcium silicate. 2008.

S. Bishnoi, Vector modelling of hydrating cement microstructure and kinetics. 2008.