Cementing the Future of Concrete

Transcription

1 THE INDUSTRIAL-ACADEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE Cementing the Future of Concrete Professor Karen Scrivener EPFL, Laboratoire Materiaux de Construction

2 Concrete is by far and away the most used material in the world Price ($/t) Titanium Aluminium Polyamide Polythelyne Steel Wood Metals Ceramics Polymers Bricks / Masonry Concrete Annual production (t/yr) Source: INTRODUCTION à LA SCIENCE DES MATÉRIAUX, Kurz,Mercier, Zambelli,. PPUR, 3rd ed

3 Why? Availability - The raw materials are available everywhere 3

4 It is made from the most common elements in the Earth s crust Na Mg K rest =1.6% Mg S Na K rest Ca Fe Al O Limestone: CaCO 3 O Ca Si Si Fe Al earth s crust Clay: 4

5 Why? Availability - Transportable - The raw materials are available everywhere Grey powder in bulk or bags 5

6 Why? Availability - Transportable - Easy to use - The raw materials are available everywhere Grey powder in bulk or bags Add water and stir 6

7 Why? Availability - Transportable - Easy to use - Flexible - The raw materials are available everywhere Grey powder in bulk or bags Add water and stir Can fill any form with negligible shrinkage 7

8 Photo Alain Herzog 8

9 Why? Availability - Transportable - Easy to use - Flexible - Durable - The raw materials are available everywhere Grey powder in bulk or bags Add water and stir Can fill any form with negligible shrinkage Lasts for centuries 9

10 Pantheon in Rome, built in 120 AD 10

11 Why? Availability - Transportable - Easy to use - Flexible - Durable - The raw materials are available everywhere Grey powder in bulk or bags Add water and stir Can fill any form with negligible shrinkage Lasts for centuries And all this at a bargain prices with low environmental impact! 11

12 Comparative energy and CO 2 costs Material MJ/kg kgco 2 /kg Cement Concrete Masonry Wood Wood: multilayer Steel: Virgin Steel: Recycled Aluminium: virgin Aluminium recycled Glass fibre composites Glass Relative energy, CO 2 ICE version 1.6a Hammond G.P. and Jones C.I 2008 Proc Instn Civil Engineers 12

13 Comparative energies in use Energy of producing 1m of column to support 1000 tonnes Energy of producing 1m of pipe Fuel (litres) Energy (kwh) concrete brick steel 0 concrete PVC polyethylene 13

14 And yet, the enormous volumes used mean that concrete production accounts for some 5-8% of the man-made CO 2 worldwide Price ($/t) Titanium Polyamide Aluminium Polythelyne Steel Wood Metals Ceramics Polymers Bricks / Masonry Concrete a 1% reduction In CO 2 emissions associate with cement and concrete would have the same overall impact as a 100% reduction for steel production Annual production (t/yr) Source: INTRODUCTION à LA SCIENCE DES MATÉRIAUX, Kurz,Mercier, Zambelli,. PPUR, 3rd ed

15 And demand is forecast to rise: to meet the demands of a growing world population 15

16 Sustainable development Fair development e.g. for developing countries : - cost - technology - resources Average living space per person ~ 7 m 2 China - ~ 30 m 2 Europe 16

17 There is no magic bullet solution 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% CO 2 on every m 3 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. 17

18 We need to master an increasingly diverse range of solutions: optimised according to LOCAL raw materials and applications CO 2 emissions

19 1 tonne of cement leads to the emission of kg CO 2 Origins of CO 2 emissions in cement production 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 CaCO3 CO 2 will mean decomposition changes in the chemistry (CHEMICAL) of the cement: Fuel therefore its reactions and potential performance 19

20 Reducing Chemical CO 2 will change the composition of cement therefore all its reactions and properties! Na Mg K rest Mg S Na K rest Al Ca Fe O Reduce Ca Ca O Si Si earth s crust But the composition of the Earth s Crust limits the possible chemistries Therefore it is possible to build a systematic framework to understand all possible solutions Fe Al 20

21 The current approach reducing the clinker factor CO 2 Process optimisation clinker factor Clinker Gypsum Cement SCMs Supplementary Cementing Mateirals Limestone Fly ash Slag Silica fume Natural pozzolan Often by-products or wastes from other industries 21

22 The current approach reducing the clinker factor Clinker Factor [%] Target 2008 Forecast Source: HOLCIM 22

23 But increasing substitution of these material is reaching a limit due to: - technical performance - availability Metakaolin Rice husk ash Silica fume Burnt shale Natural pozzolana Used in cement Reserve Blast furnace slag Fly ash Cement Limestone Mill. tons/year 2003 figures 23

24 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 experiments to give necessary improvement. 24

25 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

26 PROCESS The study of microstructure is central to moving from empirical relationships towards an understanding of the links between the fabrication of a material and its properties PROPERTIES 26

27 The iron carbon phase diagram, circa 1900 δ Temperature C γ L L + γ C γ + Fe 3 C Temperature K α Steels 1 α + Fe 3 C 723 C Cast Irons 2 3 % weight carbon More than 90% of steels are simple alloys (mixtures) of iron and carbon With just two components the phases expected can be plotted as a function of temperature on a piece of paper 27

28 Microstructures of steel with increasing carbon content 0.1% 0.25% 0.35% 0.45% 0.6% Increasing hardness 28

29 Even with 3 components: CaO SiO 2 Al 2 O 3 A three dimensional model is needed. However computers allow any number of components (dimensions) to be dealt with and relevant information shown 29

30 The cement limestone phase diagram, circa 2000 Matschei, T; Lothenbach, B; Glasser, FP CEM CONC RES This diagram explains why cement with 5% addition of fine limestone 5% less CO2 have better properties 30

31 Why can be done now TEM We now have the experimental characterisation techniques and the computational tools to tackle this complexity from a fundamental scientific standpoint rather than relying on empirical relations. NMR AFM - force 31

32 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 32

33 Resulting mirostructure pores sand (aggregate) outer or undifferentiated C-S-H inner C-S-H partially reacted cement grain calcium hydroxide (CH) 33

34 C-S-H Layers of Ca-O Silicate chains Water I.G. Richardson Cem Conc Res, 38, 2008,

35 In the first minutes, Fresh alite the reaction is controlled by the formation of tiny pits of the surface of the cement grains Freshly fractured surface of cement grain P Juilland, et al Cem Conc Res, 40, 2010, Surface after 2 minutes in water 35

36 We can now predict the phases that form from the chemistry of the system cement reaction hydrates CH Alite C 3 S Ca 2+ 2 H2SiO - 4 C-S-H Belite C 2 S Aluminate C 3 A Ferrite C 2 (A,F) gypsum C$.H x Limestone Cc - Al(OH) 4 OH - 2- SO 4 2 CO - 3 AFm Ettringite AFt 2- SO 4 - OH 2- CO 3 36

37 We can even understand how the phases change as we add different materials SiO 2 gel Silica Fume Natural pozzolan C/S 1.7 C/S 0.83 C-S-H Portland Cement C-A-S-H Fly Ash C Slag C 3 ASH 4 F strätlingite Metakaolin Limestone Ca(OH) 2 Al(OH) 3 C 3 AH 6 C 3 A.xx Aft AFm 37

38 A reference concrete and one containing slag 100% PC 1year 60% PC + 40% slag 1year These changes in structure have an important effect on properties 38

39 Even down to the nanometre level OPC, high Ca/Si, fibrillar OPC/slag, lower Ca/Si, foil like R. Taylor, I.G. Richardson, R.M.D. Brydson Cem Conc Res, 40, 2010,

40 Some implications for durability Important to understand mechanisms: we cannot directly measure performance over 100+ years in the laboratory 40

41 Reducing calcium content; reduces buffer to carbonation Mg S Na K rest +H 2 O CaO Ca(OH) 2 O Reduce Ca Ca CO 2 +CO 2 Si CaCO 3 Fe Al 41

42 This is what occurs if carbonation is not controlled 42

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

44 Other implications: CHEMICAL Changes in alkali binding (ASR) Changes in chloride binding (corrosion) Changes in sulfate resistance PHYSICAL Changes in transport 44

45 Importance of modelling approaches Models enable experiments to be linked to theory Computer based models can deal with the complexity of systems such as cement. 45

46 EPFL model µic: Many possibilities Anisotropic growth Hollow shells Alternate cements Additives Branched growth 46

47 Many million grains reacting in a 100 µm 3 box, computed in a few minutes Kumar 2010 Dissolution ions in solution phases precipitating 47

48 Monophase Polyphase Same composition, Different assemblages : Same parameters 48

49 Properties from microstructure: hydration 100 µm 49

50 Properties from microstructure Water molecule 2.8 Å Absorption of individual layers of water molecules 50

51 Fit free adsorption curves 51

52 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 tools needed to assess the functional and environmental performance of current and new materials. 52

53 Need for co-ordinated interconnected approach THE INDUSTRIAL-ACACEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE 12 Industrial Partners 53

54 Need for co-ordinated interconnected approach THE INDUSTRIAL-ACACEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE 23 Academic Partners 54

55 Concrete part of the solution optimised cements and concretes required to better exploit alternative energy sources Low-heat concrete for hydro dams UHPC for offshore foundations Special well cement for deep drillings 55

56 Concrete for sustainable development: a prime concern of major companies Almost CO 2 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 56

57 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 mechanisms to predict long term properties Coordinated effort between industry and academia 57

58 THE INDUSTRIAL-ACADEMIC RESEARCH NETWORK ON CEMENT AND CONCRETE Thank you 58