cementing the future of concrete

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

Why?

Availability - The raw materials are available everywhere

3

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?


Transportable - Grey powder in bulk or bags

5

Why?



Easy to use - Add water and stir

6

Why?




Flexible - Can fill any form with negligible shrinkage

7

Photo Alain Herzog

8

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Why?





Durable - Lasts for centuries

9

Pantheon in Rome, built in 120 AD

10

Why?





Durable - Lasts for centuries

And all this at a bargain prices

with low environmental impact!

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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

14

And demand is forecast to rise:to meet the demands of a growing world population

15

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

17

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

18

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

23

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

27

0.1% 0.25% 0.35% 0.45% 0.6%

Microstructures of steel with increasing carbon content

Increasing hardness

28

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

29

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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C-S-H

• Layers of Ca-O• Silicate chains• Water

I.G. RichardsonCem Conc Res, 38, 2008, 37-158

34

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

37

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

40

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

41

This is what occurs if carbonation is not controlled

42

Lower buffering can be compensated by better curingFrom BRE via MDA Thomas, UNB 43

Other implications:

CHEMICAL• Changes in alkali binding (ASR)• Changes in chloride binding (corrosion)• Changes in sulfate resistance

PHYSICAL• Changes in transport

44

Importance of modelling approaches

Models enable experiments to be linked to theoryComputer based models can deal with

the complexity of systems such as cement.

45

EPFL model µic: Many possibilities

Anisotropic growth Hollow shells

AdditivesAlternate cements Branched growth

46

Kumar 2010

Many million grains reacting in a 100 µm3 box, computed in a few minutes

Dissolution Þ ions in solution Þ phases precipitating47

Monophase Polyphase

Same composition, Different assemblages : Same parameters

48

Properties from microstructure:

hydr

atio

n

100 µm49

Properties from microstructure

Water molecule

2.8 Å

Absorption of individual layersof water molecules

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Fit free adsorption curves

51

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

53

Need for co-ordinated interconnected approach

23 Academic Partners

THE INDUSTRIAL-ACACEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE

54

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

55

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

THE INDUSTRIAL-ACADEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE

Thank you

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cementing the future of concrete

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