THE INDUSTRIAL-ACADEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE
Cementing the Future of Concrete
Professor Karen Scrivener
EPFL, Laboratoire Materiaux de Construction
Source: INTRODUCTION à LA SCIENCE DES MATÉRIAUX, Kurz,Mercier, Zambelli,. PPUR , 3rd ed 2002
MetalsCeramicsPolymers
Concrete
Bricks / Masonry
Aluminium
Titanium
SteelPolyamide
WoodPolythelyne
Annual production (t/yr)
Pric
e ($
/t)
10
102
103
104
105
103 105 107 109 1011
Concrete is by far and away the most used material in the world
2
earth’s crust
MgK
rest
Na
CaFe
Al
Si
O
It is made from the most common elements in the Earth’s crust
Limestone: CaCO3
Mg
S
AlFe
KNa
rest
Ca
Si
O
Clay:
4
=1.6%
Why?
Availability - The raw materials are available everywhere
Transportable - Grey powder in bulk or bags
5
Why?
Availability - The raw materials are available everywhere
Transportable - Grey powder in bulk or bags
Easy to use - Add water and stir
6
Why?
Availability - The raw materials are available everywhere
Transportable - Grey powder in bulk or bags
Easy to use - Add water and stir
Flexible - Can fill any form with negligible shrinkage
7
Photo Alain Herzog
8
Why?
Availability - The raw materials are available everywhere
Transportable - Grey powder in bulk or bags
Easy to use - Add water and stir
Flexible - Can fill any form with negligible shrinkage
Durable - Lasts for centuries
9
Why?
Availability - The raw materials are available everywhere
Transportable - Grey powder in bulk or bags
Easy to use - Add water and stir
Flexible - Can fill any form with negligible shrinkage
Durable - Lasts for centuries
And all this at a bargain prices
with low environmental impact!
11
Comparative energy and CO2 costsMaterial MJ/kg kgCO2/kg
Cement 4.6 0.83
Concrete 0.95 0.13Masonry 3.0 0.22
Wood 8.5 0.46
Wood: multilayer 15 0.81
Steel: Virgin 35 2.8
Steel: Recycled 9.5 0.43
Aluminium: virgin 218 11.46
Aluminium recycled
28.8 1.69
Glass fibre composites
100 8.1
Glass 15.7 0.85
ICE version 1.6aHammond G.P. and Jones C.I 2008 Proc Instn Civil Engineerswww.bath.ac.uk/mech-eng/sert/embodied/
Rel
ativ
e en
ergy
, CO
2
12
60
230
350
0
50
100
150
200
250
300
350
concrete brick steel
40
190
350
0
50
100
150
200
250
300
350
concrete PVC polyethylene
Ene
rgy
(kW
h)
Fuel
(litr
es)
Energy of producing 1m of column to support
1000 tonnes
Energy of producing 1m of pipe
Comparative energies in use
13
Source: INTRODUCTION à LA SCIENCE DES MATÉRIAUX, Kurz,Mercier, Zambelli,. PPUR , 3rd ed 2002
MetalsCeramicsPolymers
Concrete
Bricks / Masonry
Aluminium
Titanium
SteelPolyamide
WoodPolythelyne
Annual production (t/yr)
Pric
e ($
/t)
10
102
103
104
105
103 105 107 109 1011
And yet, the enormous volumes used mean that concrete production accounts for some 5-8% of the man-made CO2 worldwide
a 1% reductionIn CO2 emissions associate withcement and concrete would have the same overall impact as a 100% reduction for steel production
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Sustainable development
Fair development e.g. for developing countries : - cost- technology- resources…
Average living space per person – ~ 7 m2 China - ~ 30 m2 Europe16
http://southamericanexperts.files.wordpress.comhttp://www.bbc.co.uk/suffolk/content/images
• Despite the frequent press articles
• There is no magic bullet solution
• A radically different material will be a niche product with less than 1% of the market(e.g. calcium aluminate cements)
• The ability to save 5-10% CO2 on every m3
of concrete is orders of magnitude more important
• But under the current approach, each small increment of change takes years to reach the field due to large empirical data base which needs to be built up.
There is no magic bullet solution
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1990 2000 2010 2000 2030 2040 2050
CO
2em
issi
ons
We need to master an increasingly diverse range of solutions:optimised according to LOCAL raw materials and applications
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1 tonne of cement leads to the emission of 650 – 900 kg CO2
60
40
CaCO3 decomposition (CHEMICAL)Fuel
The production process is highly optimised it is
estimated that < 2%further savings can be
made here
Use of waste fuels, which can be > 80% reduces the demand
for fossil fuels
Decreasing “chemical” CO2 will mean changes in the chemistry of the cement: therefore its reactions and potential performance
Origins of CO2 emissions in cement production
19
Reducing “Chemical” CO2 will change the composition of cementtherefore all its reactions and properties!
Mg
S
AlFe
KNa
rest
Ca
Si
O
earth’s crust
Reduce Ca
MgK
rest
Na
CaFe
Al
Si
O
But the composition of the Earth’s Crust limits the possible chemistriesTherefore it is possible to build a systematic framework to understand
all possible solutions20
↓ CO2
Clinker
Natural pozzolanSilica fumeFly ash
Process optimisation ↓ clinker factor
Gypsum Cement
SCMs – Supplementary Cementing Mateirals
Slag
The current approach – reducing the clinker factor
Limestone
Often by-products or wastes from other industries21
60
65
70
75
80
85
90
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Targe
t
2008
Forec
ast
Clin
ke
r F
ac
tor
[%]
Source: HOLCIM
The current approach – reducing the clinker factor
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0 500 1000 1500 2000 2500
Cement
Fly ash
Blast furnace slag
Natural pozzolana
Burnt shale
Silica fume
Rice husk ash
Metakaolin
Mill. tons/year
Used in cement
Reserve
2003 figures
Limestone
But increasing substitution of these material is reaching a limit due to:- technical performance- availability
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Why has progress been so slow
Cement contains:> 5 reacting phases releasing > 10 species into solution, + minor elements from raw materials
We could not tackle this complexity – until recently,
Service >100 years – difficult to predict from lab scale
\ Incremental trial and error
We don’t have time to do all the experimentsto give necessary improvement.
24
Concrete is complex because it is made from natural
raw materials which have impurities and variability
However it obeys well established physical
and chemical laws – e.g. thermodynamics
25
PROCESS
PROPERTIES
The study of microstructure is central to moving from empirical relationships
towards an understandingof the links between
the fabrication of a material and
its properties
26
The iron carbon phase diagram, circa 1900
% weight carbon
4.30
543210
723°C0.80Steels Cast Irons
0.02
2.061147°C
2000
1800
1600
1400
1200
1000
800500
700
900
1100
1300
1500
1700
Tem
pera
ture
°C
Tem
pera
ture
K
γ
α
δ
L + γ
L
γ + Fe3C
α + Fe3C
More than 90% of steels are simple alloys (mixtures) of iron and carbonWith just two components the phases expected can be plotted as a function of temperature on a piece of paper
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0.1% 0.25% 0.35% 0.45% 0.6%
Microstructures of steel with increasing carbon content
Increasing hardness
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Even with 3 components:CaO – SiO2 – Al2O3
A three dimensional model is needed.
However computers allowany number of components (dimensions) to be dealt with and relevant information shown
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The cement limestone phase diagram, circa 2000
This diagram explains why cement with 5% addition of fine limestone– 5% less CO2 – have better properties
Matschei, T; Lothenbach, B; Glasser, FP
CEM CONC RES 2007 37 551-558
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Why can be done now We now have the experimental
characterisation techniquesand the computational toolsto tackle this complexity from a fundamental scientific standpoint rather than relying on empirical relations.
TEM
AFM - force
NMR
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What is the structure of concrete at the microscopic level?
At the start: unconnected grains and water:The reaction of cement with water results in a doubling of solid volume, hydrates bridge gaps between reacting grains and leads to setting and hardening
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partially reactedcement grain
“inner” C-S-H
“outer” or“undifferentiated”
C-S-H
sand (aggregate)
calcium hydroxide(CH)
poresResulting mirostructure
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35
Fresh alite
P Juilland, et al Cem Conc Res, 40, 2010, 831-844
In the first minutes, the reaction is controlled by the formation of tiny pits of the surface of the cement grains
Freshly fractured surface of cement grain Surface after 2 minutes in water
AliteC3S
reactioncement hydrates
BeliteC2S
AluminateC3A
FerriteC2(A,F)
“gypsum”C$.Hx
LimestoneCc
CH
C-S-H
EttringiteAFt
-24SO-OH
-23CO
AFm
H SiO2 42-
OH-
-4)OH(Al
-24SO
Ca2+
23CO -
We can now predict the phases that form from the chemistry of the system
36
We can even understand how the phases changeas we add different materials
C3A.xxAftAFm
Portland Cement
Slag
Fly Ash
C
Natural pozzolan
SilicaFume
Limestone
Metakaolin
F
C3ASH4
Ca(OH)2 Al(OH)3
SiO2 gel
C3AH6
strätlingite
C/S 1.7
C-S-H
C/S 0.83
C-A-S-H
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100% PC 1year 60% PC + 40% slag 1year
A reference concrete and one containing slag
These changes in structure have an important effect on properties
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Even down to the nanometre level
R. Taylor, I.G. Richardson, R.M.D. BrydsonCem Conc Res, 40, 2010, 971-983
OPC, high Ca/Si, fibrillar OPC/slag, lower Ca/Si, foil like
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Some implications for durability
Important to understand mechanisms:we cannot directly measure
performance over 100+ yearsin the laboratory
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Reducing calcium content; reduces buffer to carbonation
Mg
S
AlFe
KNa
rest
Ca
Si
O
Reduce Ca
CaCO3
CaO Ca(OH)2
+H2O
CO2Ý +CO2
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Other implications:
CHEMICAL• Changes in alkali binding (ASR)• Changes in chloride binding (corrosion)• Changes in sulfate resistance
PHYSICAL• Changes in transport
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Importance of modelling approaches
Models enable experiments to be linked to theoryComputer based models can deal with
the complexity of systems such as cement.
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EPFL model µic: Many possibilities
Anisotropic growth Hollow shells
AdditivesAlternate cements Branched growth
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Kumar 2010
Many million grains reacting in a 100 µm3 box, computed in a few minutes
Dissolution Þ ions in solution Þ phases precipitating47
Properties from microstructure
Water molecule
2.8 Å
Absorption of individual layersof water molecules
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Sustainable use of concrete can be achieved through:
• A systematic, science-based understanding of cementitious processes and materials at the nanoscale:
• Extended across all the scales involved in cement and concrete production to:
• Provide the multidisciplinary assessment and prediction toolsneeded to assess the functional and environmental performance of current and new materials.
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Need for co-ordinated interconnected approach
12 Industrial Partners
THE INDUSTRIAL-ACACEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE
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Need for co-ordinated interconnected approach
23 Academic Partners
THE INDUSTRIAL-ACACEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE
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optimised cements and concretes required to better exploit alternative energy sources
Concrete part of the solution
Low-heat concrete for hydro dams
UHPC for offshore foundations
Special well cementfor deep drillings
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Concrete for sustainable development:a prime concern of major companies
Almost CO2 free binders from slag and sulfate (Holcim)
Concretes with active TiO2, self cleaning breaks down pollutants in air (Heidelberg)
High range water reducers facilitate the use of recycled aggregates (Sika)
Grinding aids lower energy for grinding (Sika)
Ultra high strength concrete (Ductal) (Lafarge), reduce amount of material needed
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To conclude...
• Like it or loath it, there is no alternative to concrete to meet the world’s need for buildings and infrastructure
• To improve the sustainability of cementitious materials we must start to use a wider range of materials
• Optimise according to local materials and application
• Need to understand performance based on mechanisms – we have the science to do this
• Need models based on mechanismsto predict long term properties
• Coordinated effort between industry and academia57