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Cement & concrete solutions for underground structure
MOUSSA BAALBAKI
Head of Products & Solutions Portfolio
Siam City Cement (Lanka) Ltd
AGENDA
• Degradation mechanism
• Key durability indicators
Key challenges to cope with increasing society’s need for construction materials
• From prescriptive to performance based specification
Sustainable performing concrete
• What really matters to us
Durability of underground concrete
Conclusion
In theory – What really matters to usGlobal population growth over the last 2,000 years, with the doubling times marked
Source: Michael F. Ashby, Materials and the Environment
World population development [bn inhabitants]
In practice – What really matters to usWorld population grow & Ongoing trend towards urbanization, particularly in emerging countries
47% urban
60% urban
3.2 3.32.9
5.0
1970 2000 2030
36% urban
1.32.4
urbanrural
70% urban
2.8
6.4
2050
Both trends will significantly increase society’s need for construction materials
Source: United Nations, World Urbanization Prospects: The 2007 Revision (www.un.org)
Next to water concrete (~ 7 billion m3) is by far the most widely used material in the world (economic, availability, versatility, durability and adaptability)
Construction sector has an important ecological footprint…Unfortunately we use these natural resources at a rate that cannot be sustained indefinitely
Source: World Green Building Council, The ecological footprint
30 – 40% 40 – 50%17% 25% 33%
Wood harvest CO2 emissions Energy use Raw material use
Fresh water consumption
Important to highlight that Portland cement and concrete
• Use large volume of raw materials quarried from the earth
• Their production requires a large amount of energy
• And manufacture of OPC emits a large amount of CO2
The real matter – in practiceGlobal climate change from the so-called greenhouse gas emissions (mainly CO2, methane & nitrous oxide)
Therefore the construction sector must promote sustainable and performing solutions which:
• Emit less CO2 (Green House Gas)
• Offer extended service life of concrete structures with reduced maintenance cost
• Is economically viable
• Support the overall commitment to sustainable development
CO2 - emissions in clinker production (electricity neglected)
• Three main levers to reduce CO2
• Modern plants
• Reduction of clinker content
• Usage of alternative fuels
Blended cements for high sustainable performing concrete…emitting very low CO2 emission during production
Is ordinary portland cement (OPC) still needed in modern construction?Can we meet customer demands?
European domestic deliveries by cement type (2000 -2010) - Data : Cembureau
75% are blended cements
(CEM II / CEM III, CEM IV and CEM V)
25% is CEM I = OPC : mainly used for high end prefabricated reinforced elements (pre-stressed/post-tensioned and winter concreting (< 10°C)
What do all these strategic infrastructures have in common?
Confederation bridge
Canada - 1997
V. de Gama bridge
Portugal - 1998
Öresund tunnel
Sweden - 2000
Medway bridge
UK - 2001
Monaco floating dyke
France - 2002
Rion Antirion bridge
Greece - 2005
Millau bridge
France - 2004
100 – 120 years specified service life design
Performance based specifications including durability indicators
Designed with blended cements (Slag, FA, SF)
Today the tallest, deepest, heaviest structures and also the longest sea
infrastructures in the world are concrete structures produced with SPC
Burj Khalifa - + 800m Nord sea offshore platform-350 m / ~1 Mio t
Jiaozhou bay bridge - 40 km
AGENDA
• Degradation mechanism
• Key durability indicators
Key challenges to cope with increasing society’s need for construction materials
• From prescriptive to performance based specification
Sustainable performing concrete
• What really matters to us
Durability of underground concrete
Conclusion
• Today most concrete standards follow a prescriptive approach for durability, establishing minimum cement contents, maximum w/c ratios etc., leading to commoditization
• This prescriptive approach has shown to be insufficient to reach the durability performance goals
• There is a noticeable trend towards Performance Based Specifications (PBS), where a minimum performance has to be achieved, based on standard tests
• Some countries have already put in place performance tests and specifications for certain exposure classes
• Performance based specification of concrete are already an essential selection criterion in large construction projects
Concrete standards - Current situation
• The classical prescriptive approach specifies a durability Indicator based on w/c ratio that:
• is increasingly questionable (syndrome of concrete cube strength!)
• is very difficult to control in practice
• does not encourage innovation and is an obstacle for sustainable concrete mix designs
• does not guarantee durability, as reality has confirmed
• By checking the end product, a performance-oriented mindset is created in all players:
• contractors: deliver the end product to be tested
• producers: develop most efficient design, produce and deliver the concrete with the required performance
• raw material suppliers (cement, additions, admixtures): produce and deliver their products to achieve the target performance in concrete application
Pitfalls of Prescriptive Design
• Degradation mechanisms different between mechanical instability and chemical instability
• Application of concrete technology knowledge limited – it is more important what are the mix proportions than what are the obtained properties
• Most of the limiting values cannot be checked during construction
• Ensured service life of 50 years
Pitfalls of Prescriptive Design
Maslenica Bridge, 1997Gubasevo Bridge, 1990
Source: Bjegović, D.; Stipanović Oslaković, I.; Serdar, M. From Prescriptive Towards Performance-based
Durability Design of Concrete // Workshop - Cement and Concrete for Africa. Berlin : BAM Federal Institute
for Materials Research and Testing, 2011. 50-58
Mix design, type of materials
Cover depth
Construction procedures
(Eventual protective measures)
PRESCRIPTIVE DESIGN
STANDARD (e.g. EN 206-1)
IDENTIFY the exposure environment
CONSTRUCTION and QUALITY
CONTROL TESTS on moulded
specimens (cured under standard
conditions)
COMPLIANCE?
PREQUALIFICATION TEST
(usually base only on
compressive strength)
NO
YES
ACCEPTANCE
Repair and
maintenance
measures
(protection)
YES
NO
?
Mix design, type of materials
Cover depth
Construction procedures
PERFORMANCE BASED DESIGN
DETERIORATION MODE
(e.g. transport mechanism)
IDENTIFY the exposure
ENVIRONMENT
(quantify environmental load)
CONSTRUCTION
QUALITY CONTROL ON SITE
Moulded specimens + concrete
cover depth + In situ concrete
assessment
COMPLIANCE?
SLM check
PREQUALIFICATION
TEST
+
Determination of durability indicator
in lab test simulating
deterioration mode
NO
YES
ACCEPTANCEBirth Certifcate
PROTECTION
REPAIR &
MAINTENANCE
MEASURES
MONITORING
YES
NO
DURABILITY INDICATORS Testing methods (simulation of
environment and deterioration mode)
Service life model
Criteria for the evaluation
PR
ES
CR
IPT
IVE
SERVICE LIFE MODEL
(input parameters: environment,
durability indicators)
YES
NO
Service Life Prediction Models
FIB Model
Code
Duracrete
Life-365
Stadium
Duracon
Fédération internationale du béton
Jacques Marchand, SIMCO
AGENDA
• Degradation mechanism
• Key durability indicators
Key challenges to cope with increasing society’s need for construction materials
• From prescriptive to performance based specification
Sustainable performing concrete
• What really matters to us
Durability of underground concrete
Conclusion
Porosity and permeability – key drivers for concrete durability
Muller, A.C.A. et al., J . Phys. Chem. C 117 (1), 2013
• Permeability of concrete is paramount to assure water-tightness and durability of underground
structures
• Capillary pores start to be connected when w/c > 0.40
• When w/c > 0.65 most capillary pores are connected
1 mm
C-S-H
Why blended cements promote refinement of pore structure of matured concrete (chemical and microstructural effects)
+FA
+Ca(OH)2 or ` Portlandite
+OPC/silicates
Water
OPC
Hydration
reaction
C-S-H Slag
Pozzolanic
reaction
Blended Cement
Blended cements promote refinement of pore structure of matured concrete (chemical and microstructural effects)
C-S-H gel pores
Capillaries pores
Ca(OH)2
Deterioration processes that may affect the service life of concrete constructions
• Electrochemical (steel corrosion induced by CO2 or Cl-)
• Chemical attack (sulphate, acid, pure water, DEF, AAR)
• Physical attack (frost, frost + salt, abrasion, cracks)
Most physical-chemical deterioration processes are strongly influenced by the degree of saturation of
the concrete pores
• Carbonation occurs only at intermediate degrees of saturation
• Frost damage happens only when concrete is near saturation
• Alkali-silica gel can expand only in the presence of moisture
• Chemical attack can only happen through aqueous solutions of the aggressive components
• Corrosion reactions need a conductive electrolyte to progress (moist concrete)
Classification of Concrete Deterioration Processes
Performance Testing of Concrete
indirect
performance tests
direct
performance testsExposure classes (EN 206)
XD – Corrosion induced by chlorides other than from sea water
XS – Corrosion induced by chlorides from sea water
XC – Corrosion induced by carbonation
XF – Freeze-thaw attack
XA – Chemical attack
cause of
deterioration
chloride pitting
corrosion
carbonation/
corrosion
freeze thaw
sulfate attack
chemical attack
(pH, NH+,Mg2+,..)
chloride diffusion ASTM C 1556
chloride permeability ASTM C 1202
chloride migration SIA 262/1-B,
NT Build 492
electrical resistivity RILEM TC 154
AASHTO TP 95
Penetrability Tests
water penetration EN 12390-8
capillary water absorption / porosity
SIA 262-1/A
O2-permeability RILEM 116-PCD
on-site permeability SIA 262-1/E(Torrent)
O2-Diffusion EMPA
critical chloride content
RILEM TC
CTC
acc. carbonation
SIA 262-1/I,
CEN/TS
12390-12
nat. carbonation
RILEM CPC 18
General Tests
compressive strength EN 12390-3
sulfate resistance
SIA 262-1/DASTM C1012
freeze-thawresistance
SIA 262-1/C
Chloride resistance – Degradation mechanism
Na Cl+Ca (OH)2
Hydrated calcium aluminates
From C3A, C4AF, slag, FA
+
Calcium Chloroaluminates
« Friedels salt »
= Soluble CaCl2
Specific Resistivity [Wm] (RILEM TC 154, AASHTO TP 95)
Chloride Ion
Penetrability
Surface Resistivity Test
100-mm X 200-mm
(4 in. X 8 in.)
Cylinder
(KOhm-cm)
a=1.5
150-mm X 300-mm
(6 in. X 12 in.)
Cylinder
(KOhm-cm)
a=1.5
High < 12 < 9.5
Moderate 12 - 21 9.5 - 16.5
Low 21 - 37 16.5 – 29
Very Low 37 - 254 29 – 199
Negligible > 254 > 199
Chloride Migration or Resistivity (SIA 262/1-B, NT Build 492)
Sketch of test
Xd
measurementTest in progress
Correlation between W/C and maximum chloride migration coefficient DRCM*10-12
m2/s @ 28 days
0
5
10
15
20
25
0.35 0.4 0.45 0.5
Ch
lori
de
mig
rati
on
co
effi
cien
t D
RC
M*1
0-1
2m
2/s
W/C
CEM I
CEM III>50% slag
CEM I + 18-30% FA
2.5
8
11
Maximum chloride migration coefficient DRCM for various cover depths as function of binder type and exposure class for a design service life 100 years
Mean concrete cover depth over steel [mm]
Maximum value DRCM*[10-12 m2/s]
CEM I / OPCCEM III-A
36 - 65% slagCEM III-B
66 - 80% slagCEM II-B/V
20 – 30% FA
Reinforcing steel Pre-stressing steel XS2 / XS3 XS2 / XS3 XS2 / XS3 XS2 / XS3
35 45 1.5 1.0 1.0 5.5
40 50 2.0 1.5 1.5 10
45 55 3.5 2.5 2.5 15
50 60 5.0 3.5 3.5 22
55 65 7.0 5.0 5.0 30
60 70 9.0 6.5 6.5 39
Boldface values are practically achievable by present day concrete technology with currently used w/b Italic values are not achievable (lower values) or not recommended (higher values)
Slag / FA
OPC
The major features of the immersed tunnel solution includes
• 120 years Service life
• Over 18 km long with four tunnel tubes comprising
• Two double-lane motorway tubes
• Two rail tubes
• 79 standard elements every 217 m and 10 special elements for technical installations
• Construction time: 6.5 years
• Construction budget (2008 prices): 6 Billion US$
• Owner: the Danish state
The Fehmarnbelt Fixed Link will connect Scandinavia and continental Europe with a combined rail and road connection between Denmark and Germany.
Quantities• Concrete for elements 2.5 million m3• Reinforcement 0.3 million tons• Ballast concrete 0.4 million m3• Structural concrete 0.2 million m3• Cement 0.8 million tons
Solution for the precast elements - 24,10m length
SCC 50/60 –self compacting concrete for rank 2 elements
• Cement III A 42,5 N-LH with 50% GBFS
• w/c = 0,39
• Fly ash – 40 kg
• Ground limestone – 40 kg
• Fine sand (0-0,5mm) – 430 kg
• Sand (0,5-4mm) – 422 kg
• Crushed stones (4-8mm) – 337kg
• Crushed stones (8-16mm) – 454 kg
• SPL – 1,9%
• Air entertainer – 3%
Requirements – elements for 120 years Service life
• High resistance to Chloride attack
• Rc 6h – min. 10 MPa
• Rc 28d – min. 60 Mpa
• Very low permeability
Carbonation- Degradation mechanism
CSH
Poorly soluble Salts
CaCO3
DENSIFICATION, PROTECTION
CSH
Water
CO2
CALCITE
Ca(OH)2
Ca(OH)2 + CO2 + H2O CaCO3 + 2H2O
Drop in pH
13.0-12.5 < 9
Carbonation – effects
pH CH
External effect
EFFLORESCENCESE Steel corrosion (depasivation)
Internal effect
CO2
Spalling of concrete
Accelerated Carbonation (SIA 262-1/I,CEN/TS 12390-12)
Splitting of a slice Cleaning and spraying of indicator solution
Freezing color change Measuring carbonation depth
Photographic
documentation
Testing procedure according to SIA 262-1/Appendix
Design Live
Resistance to Carbonation
KN (mm/a)
50 years
XC3 & XC4 < 5.0
100 years
XC3 < 4.0
XC4 < 4.5
Sulphate resistance – Degradation mechanism
CaSO4 2H2O
Secondary gypsum
(causing internal
pressures)=
Hydrated
calcium
aluminates
+
C3A 3CaSO4 32H2O
Na2 SO4Ca (OH)2
+
Originating from ground water,
industrial environments, air
pollution, …and set regulator
0.1
1
10
100
(I) CEM I 52.5N
(II) CEM III/B42,5 L-
LH/HS/NA
(III) CEM III/A42.5N
(IV) CEMII/A-D
(V) CEM II/A-S 42-5R
(VI) CEM I52,5 R
(VII) CEMII/B-LL 32.5R
(VIII) CEMIV/A 32,5 R
(IX) CEM IV/B32,5 R
(Xa) BOS-Rheolith
(Xb) Durolith
rel.
len
gth
ch
ange
[‰
]
Sulphate Resistance
SIA 262-1/D, wz=0.40 SIA 262-1/D, wz=0.65 SIA 262-1 Limit
Sulphate Resistance of Concrete (SIA 262-1/A)
measured sulphate expansion of Dls [‰]
Sulfate Resistance
> 1.2 low
< 1.2 high
AGENDA
• Degradation mechanism
• Key durability indicators
Key challenges to cope with increasing society’s need for construction materials
• From prescriptive to performance based specification
Sustainable performing concrete
• What really matters to us
Durability of underground concrete
Conclusion
• Performance based specified sustainable concrete will be specified more often for its increased durability than for its strength
• Extended service life
• Better use of natural ressourses
• Lowest CO2 footprint / concrete m3
• There is a noticeable trend towards Performance Based Specifications (PBS)
• Specifiers and suppliers face a challenge in translating the long-term durability requirements into specifications for laboratory testing
• The efficiency of concrete as a sustainable construction material should be considered in a wider perspective than simply its unit price
• Concrete produced with blended cements have higher resistance to aggressive conditions (low permeability and chemical resistance)
Conclusion