Overview of calcined clay and calcined clay cements_M.Magistri_Mapei Italy.pptx

It take about

1. Overview of Calcined Clay and Calcined Clay Cements Chemistry, mineralogy, hydration and performances Day in day out , construction sites all around the world can count on Mapei Matteo Magistri, October 2022

2. 2 The future of cement Calcined clay cements – Overview Portland cement-based concrete on the long term will be the most common building material worldwide. Cement production is forecast for 2050 between 4.7 and 5.1 billion tons/y. Data source: IEA/CSI Technology Roadmap – Low-Carbon transition in the cement industry

3. 3 The future of cement Environmental impact of cement/concrete production, with respect to greenhouses gases emission, is (and will be) the main concern: Direct CO 2 emissions associated to clinker production 0.842 t CO 2 /t clinker Data from 19% cement plants worldwide Average clinker factor in cements 0.65 Strong local differences ( average Europe: 0.74 - Ireland , Denmark : 0.9 – Germany: 0.71 - Netherland : 0.46) Direct CO 2 emissions associated to cement production 0.54 t CO 2 /t cement Considering average clinker factor Total specific electric energy consumption for cement production 100-110 kWh/t cement Corresponding to 50-55 kg CO 2 /t cement ( considering energy mix with 0.5 kg CO 2 /kWh) Concrete emissions Non reinforced : 250 kg CO 2eq /m 3 Reinforced : 312 kg CO 2eq /m 3 Considering typical C30/C37 ready mix concrete Data source: M.Schneider , “The cement industry on the way to a low-carbon future”, ICCC2019, Prague. Calcined clay cements – Overview

4. 4 Considering Emission Trading Scheme already implemented in some regions and present quotation of CO 2 , reduction in the release of GHG (Greenhouse Gases) will have a huge potential for cost saving. The future of cement Calcined clay cements – Overview

5. 5 The future of cement Several strategies are available for reduction of CO 2 emissions from cement production: Strategy Comments Improvement in thermal energy efficiency Limited potential: already reached the state of the art. Use of alternative fuels Average substitution range in Europe: 41% (100% reported in some plants). Good potential, limited to availability of suitable waste. Reduction of clinker factor Good potential for CO 2 reduction . Related to local and global availability of Secondary Cementitious Materials. Need to improve blended cements performances. Alternative cements: CSA, geopolymers, belite Potentially high reduction of CO 2 , but high raw materials/investment cost and limited applicability. Improve electrical energy efficiency Limited potential. CCS/U – Carbon Capture and Storage/Use Theoretically extremely high or complete reduction of CO 2 . Presently at pilot plant stage (although long term experience exists in oil sector). First operative industrial CCS forecast for 2024-2030 in Norway. Calcined clay cements – Overview

6. 6 Secondary cementitious materials: generalities The definition “ Secondary Cementitious Material ” includes all materials that may behave like cement in some conditions : SCMs have little or no cementitious properties, but when finely divided and in presence of water they chemically react with calcium hydroxide to form compounds with cementing properties ( pozzolanic reaction ). Calcium hydroxide is usually supplied by hydration of Portland clinker. The use of SCMs is described in several international/local standard and in many best practices of the cement industry. Calcined clay cements – Overview

7. 7 Secondary cementitious materials: EN 197-1 In the latest decades, the European Standard EN 197-1 has described the composition of common cements in terms of main and secondary constituents . There were limitations in the use of limestone together with other SCMs. Calcined clay cements – Overview

8. 8 Secondary cementitious materials: EN 197-1 If SCMs + limestone were used, there were limits on clinker reduction (at least 65% clinker must be present in the recipe). The SCM that allows higher substitution is blast furnace slag. Natural clays calcined were already considered in the list of SCMs. Calcined clay cements – Overview

9. 9 Secondary cementitious materials: EN 197-5 New EN 197-5 has been recently released : there are more possibilities for blended cements composition. The interaction between limestone and calcined natural pozzolan is fundamental for high clinker reduction in calcined clay cements. Calcined clay cements – Overview

10. 10 Data source: K.Scrivener et al., Calcined clay limestone cements (LC3), Cement&Concrete Research 114 (2018), 49-56. Original data by R.Snellings . Calcined clay cements – Overview Secondary Cementitious Materials: global availability Unfortunately, the availability of blast furnace slag, fly ash, natural pozzolan is not enough for a relevant clinker substitution beyond the present average level. On the other hand, a large volume of clays (silico-aluminate) and limestone exists on earth surface.

11. 11 Availability of SCMs may be very different depending on geographical area, this is the reason why the use of SCMs (type, level of cement substitution, addition in concrete or cement) is not uniform worldwide... Europe : Slag (Eastern EU, steel industry ), limestone (Southern EU), pozzolan , fly ash . Far East : limestone , natural pozzolans . Africa : Limestone (North Africa), limestone / pozzolans (Central), limestone / fly ash (South). North America : Several types of SCMs used in concrete. India : fly ash ( coal power plants ). South America : Limestone, pozzolans Calcined clay cements – Overview Secondary Cementitious Materials: global availability

12. 12 Data source: A.Ito , R.Wagai , Global distribution of clay-size minerals on land surface for biogeochemical and climatological studies, Sci Data 4, 170103 (2017). Calcined clay cements – Overview … but clays with potential for calcination seem to be widely available more or less everywhere in the world, including economies/countries under development where high cement demand is forecast in the near future. Kaolinitic clays are those with highest potential for pozzolanic behavior once calcined. SCMs: global availability

13. 13 Secondary cementitious materials: chemistry Considering chemical composition, Secondary Cementitious Materials with pozzolanic properties are mainly based on silicon and aluminum , with highly variable calcium content , (although lower than Portland clinker). Reduced calcium content means lower CO 2 emissions, although the whole production process should be considered. For example, fly ash and blast furnace slag come from high temperature processes and global CO 2 emission level may be high. On the other hand, these materials are available as by products and their use is highly appreciated. Calcined clay cements – Overview

14. 14 Secondary cementitious materials: chemistry Due to lack of calcium in comparison to Portland clinker, SCMs need to be activated by supplying the missing CaO . Moreover, silicon and aluminum need to dissolve , and dissolution usually proceeds in alkaline conditions. These are the key points of pozzolanic behaviour and alkaline activation , when SCMs are mixed with cement: Dissolution of silicon/aluminum in alkaline conditions; Reaction with calcium to give hydration products. Calcined clay cements – Overview

15. 15 Secondary cementitious materials: mineralogy/morphology Amorphous fraction is fundamental for SCMs reactivity: quartz (crystalline silica) is completely inert when added to cement, while “glassy” silica gives pozzolanic reaction. Crystalline silica ( quartz ). Higher energy is needed to break down the crystals : strong conditions (strong acids/ alkalis , high temperature) are required for dissolution . Amorphous silica ( glass ). Lower energy is needed to break down the solid : moderate alkalinity , room temperature are enough for dissolution “ Amorphous ” means that there is no long-range order in the arrangement of atoms in the structure of solid material: this reduces the energy needed to bring atoms in a solvent (water). Calcined clay cements – Overview

16. 16 Secondary cementitious materials: mineralogy/morphology In addition to chemical composition, other parameters related to mineralogy and morphology play a key role. Secondary Cementitious Material Mineralogy Requirement for good reactivity Slag Amorphous calcium silicates and silico-aluminates Mainly amorphous ( glass > 95%), fineness , suitable chemical composition Fly ash Mainly mullite and hematite ( crystalline ) + amorphous silico-aluminates High amorphous content , fine spherical particles , low unburnt carbon Pozzolan Several types of alumino-silicate minerals , volcanic origin Amorphous fraction , morphology , fineness , low clay content . Calcined Clay Metakaolin and other clay-related minerals High metakaolin content , high amorphous fraction , fineness , Fe 2 O 3 . Calcined clay cements – Overview

17. 17 Calcined clays: structure and activation Clay minerals are mainly composed of silicon and aluminum oxides. Tetrahedral silicates and octahedral aluminates are arranged in a layered structure . From different packing of these layers, we obtain a wide number of different clays. Calcined clay cements – Overview Images source: M.Antoni , Investigation of cement substitution by blends of calcined clays and limestone, Thesis EPFL (2014).

18. 18 Calcined clays: structure and activation Several types of clay minerals are known and normally found in nature, depending on structural pattern obtained from a different stacking of layers . Calcined clay cements – Overview Images source: M.Antoni , Investigation of cement substitution by blends of calcined clays and limestone, Thesis EPFL (2014).

19. 19 Calcined clays: structure and activation In addition to silicon/aluminum, other elements are present (Na, Ca, Mg, Fe, …) for charge balance. Water (in form of hydroxyl groups) is usually hosted between layers. This is very important for activation … Calcined clay cements – Overview Images source: M.Antoni , Investigation of cement substitution by blends of calcined clays and limestone, Thesis EPFL (2014).

20. 20 Calcined clays: structure and activation …and the reason is that the release of water at high temperature promotes an increase in the structural disorder and a higher “amorphous” character. After thermal treatment, the reactivity of Si and Al increases , allowing pozzolanic properties. Temperature range for calcination is usually between 400-900°C, much lower (in some cases less than a half) of the temperature needed for clinkerisation (1450°C). Considering that clays have little or no carbonate content (we are below the decarbonation temperature anyway), the advantages in terms of CO 2 emissions are evident. Calcined clay cements – Overview Images source: M.Antoni , Investigation of cement substitution by blends of calcined clays and limestone, Thesis EPFL (2014).

21. 21 Calcined clays: structure and activation Activation of clay refers to the modifications of chemical/mineralogical/morphological structure that promotes the pozzolanic behavior, and this is usually obtained through a thermal process (calcination). The key point for activation is that during calcination, some clay minerals are “de-hydroxylated” : hydroxyl groups (-OH) are removed and released in form of water. This makes the aluminum and silicon reactive. Actually, the situation is more complicated: upon heating, three major phenomena take place: de-hydration : release of water molecules not bound in the silico-aluminate structure. De-hydroxylation : removal of hydroxyl groups and activation of silico-aluminate. Recrystallisation : conversion of disordered structure obtained after de-hydroxylation to more stable phases, without pozzolanic activity. Calcined clay cements – Overview

22. 22 Calcined clays: structure and activation Activation of clay refers to Calcined clay cements – Overview Images source: Vv.Aa ., Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL, Materials and Structures (2022) 55:3.

23. 23 Calcined clays: structure and activation The problem is that natural clays are usually a mixture of different types of clay minerals , with different de-hydroxylation and recrystallisation temperature range: Kaolinite clay: 400-600°C Illite clay: 450-700°C Montmorillonite clay: 600-800°C Pyrophyllite: 500-900°C During calcination of natural clays, it is difficult to find the optimum calcination temperature . Moreover, fineness and presence of quartz/feldspar (that do not interfere with calcination but absorb heat reducing the efficiency of the process) play a role in finding optimum temperature. Once defined (e.g. in lab) the required optimal calcination temperature, a uniform and complete industrial calcination requires higher temperature, depending on the efficiency of the process. Kaolinitic clay is the best for pozzolanic activity after calcination. Calcined clay cements – Overview

24. 24 Calcined clays: structure and activation Calcination technologies: Rotary kiln : similar to clinker kiln, efficient for large operations and volumes. Flash calcination : clay is finely ground and transported with a gas flow in the firing area, where it is heated at required temperature for a very short time (flash). Calcined clay cements – Overview Images source: Vv.Aa ., Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL, Materials and Structures (2022) 55:3.

25. 25 Calcined clays: use in cement After calcination, natural clays can be used in cement as other traditional Secondary Cementitious Materials. They are added through inter-grinding, or separate grinding and blending. Particularly interesting is the ternary blend OPC + calcined clay + limestone , thanks to synergic reactivity. Calcined clay cements – Overview Source: Mapei internal data. CEM I MK Metakaolin Limestone Blast Furnace Slag Reference: OPC 100% - - - 15% clinker reduction 85% 15% - - 45% clinker reduction , CC+LS 55% 15% 30% - 45% clinker reduction , slag 55% - - 45%

26. 26 Calcined clays: use in cement Typical results after clinker reduction with CC: reduction in early strength Increase in late strength Reduction in workability Calcined clay cements – Overview Source: Mapei internal data.

27. 27 Calcined clays: use in cement Typical results after clinker reduction with CC: reduction in early strength Increase in late strength Reduction in workability Calcined clay cements – Overview Source: Mapei internal data.

28. 28 Calcined clays: use in cement Typical results after clinker reduction with CC: reduction in early strength Increase in late strength Reduction in workability Calcined clay cements – Overview Source: Mapei internal data.

29. 29 Calcined clays: use in cement Similar data are found in literature (but decrease of workability sometimes is not widely described, although it is a very important technological parameter). Calcined clay cements – Overview Source: M.Antoni et al, Cement substitution by a combination of metakaolin and limestone, Cement&Concrete Research 42 (2012).

30. 30 Calcined clays: use in cement To summarize: Calcined clays have very good pozzolanic properties and can be obtained with technologies normally available (e.g. rotary kiln). High late strength, decrease in early strength (similar or better than slag). There is a positive interaction with limestone : blend CC + LS allows high substitution with lower cost/reduced CO 2 emissions. The optimum blend is reported to be CC:LS = 2:1 (commercially known as LCCC or LC 3 or Limestone Calcined Clay Cement). Side effect: decrease in workability /high water demand. Calcined clay cements – Overview Source: M.Antoni et al, Cement substitution by a combination of metakaolin and limestone, Cement&Concrete Research 42 (2012).

31. 31 Calcined clays: hydration An insight in the hydration mechanism of calcined clay and calcined clay limestone cements could help us in finding suitable strategies for performances optimization. Calcined clay cements – Overview Portland cement clinker hydration Silicates dissolution: Ca 3 SiO 5 + 3H 2 O = 3 Ca 2+ + H 2 SiO 4 2- + 4 OH - Formation of C-S-H + Ca(OH) 2 : 3Ca 2+ + H 2 SiO 4 2- + 4OH - = C-S-H + Ca(OH) 2 Dissolution of SCM in pore water + formation of secondary hydration products Release of H 2 SiO 4 2- , Al(OH) 4 - in pore water. Formation of secondary hydration products: consumption of available Ca(OH) 2 , formation of secondary C-S-H and other hydration products depending on chemistry of pore water (Aft or Afm phases such as ettringite, monosulphate , hemi- and monocarbonate in presence of SO 4 2- or CO 3 2- ). H 2 SiO 4 2- + Al(OH) 4 - + Ca(OH) 2 = C-S-H, Aft, Afm Secondary (=formed in a later stage, once calcium hydroxide becomes available) hydration products contributes to the development of mechanical strength and to the reduction of porosity.

32. 32 Calcined clays: hydration In addition to “typical” mechanism of SCMs hydration, calcined clay and calcined clay/limestone blended cements have some particular features: High Al content Al content in calcined clay is usually quite high. This promotes the formation of Al-based hydration products such as ettringite (Aft) and monosulphate / monocarbonate ( Afm ). Moreover, the C-S-H products have a high Al-substitution . Presence of carbonate CO 3 2- Limestone (CaCO 3 ) content promotes the stability of Hemi- and Mono-carbonate phases , rather than monosulphate . Calcined clay cements – Overview Typical composition of hydrated CC-LS cement paste and late curing ages: amorphous C-S-A-H (Calcium Silicate Hydrates with high Al content), Ettringite, Mono-carbonate, calcium hydroxide. Ettringite and mono-carbonate formation during the whole period to 28 days contribute to filling the porosity, with a more compact and stronger microstructure (better strength).

33. 33 Calcined clays: hydration Phase evolution of CC-LS cement during first 24h. Calcined clay cements – Overview Source: M.Antoni et al, Cement substitution by a combination of metakaolin and limestone, Cement&Concrete Research 42 (2012).

34. 34 Calcined clays: hydration Why calcined clay cements have poor workability? The reason is that calcined clay… is clay! Clay minerals have a very porous structure , and in particular the morphology based on “ lamellae ” (plates) that have a high potential for water absorption and high friction when particles of clay must flow e.g. in a slurry cement + water. This structure is partially maintained after calcination . Calcined clay cements – Overview Images of volcanic pozzolan and kaolinitc clay (source: clay mineralogy and soil structure).

35. 35 Calcined clay cements: optimization Considering what has been described before, and considering the general requirements for good blended cements, the following parameters should be taken into account when calcined clay and calcined clay-limestone cements must be optimized: Optimum gypsum content: the correct sulphate level during hydration of cement allows a better and more complete reaction of clinker, with consequent higher release of calcium hydroxide. This is the concept of “optimum gypsum”. In the case of CC-LS cements this is even more important because: the presence of high Al and CO 3 2- promotes the formation of high ettringite content: SO 3 level should be increased in order to avoid lack of sulphate; High fineness of CC and LS promotes the “filler effect” (increase in hydration due to high specific surface available for the hydrates formation): another reason for increased risk of insufficient sulphate. A good tool to investigate the optimum sulphate is the isothermal calorimetry. Calcined clay cements – Overview

36. 36 Calcined clay cements: optimization Fineness and particle size distribution : hydration of cement is basically a reaction between solid and water and the increase in the specific surface of solid (interface solid-water) accelerates the kinetics of the process. For blended cements and for CC+LS cements this is really important: a higher exposure of calcined clay surface to the contact with alkaline water accelerates the dissolution rate and the reactivity; High fineness of limestone promotes the “filler effect” with benefit in hydration kinetics; Separate grinding may be interesting for separate optimization of clinker/CC particle size distribution. Higher clinker fineness promotes higher early strength, higher CC fineness promotes strength development, but the effect on workability should be evaluated. Suitable grinding aids may help in fineness and PSD optimization. Considering what has been described before, and considering the general requirements for good blended cements, the following parameters should be taken into account when calcined clay and calcined clay-limestone cements must be optimized: Calcined clay cements – Overview

37. 37 Calcined clay cements: optimization Alkalis content: Na 2 O and K 2 O accelerate early strength development. This is related to pH of pore solution (that is the water saturated of salts and contained in the pores of hardened mortar and concrete). Alkalinity of pore solution is controlled by calcium hydroxide solubility product (that promotes a pH higher than 12.5) and by presence of soluble alkalis , that shifts the pH toward 13.0-13.5. Higher pH promotes the dissolution of amorphous silico-aluminates and accelerates cement hydration + reaction of CC. Alkalis on the other hand have a negative effect on late strength, but late strength can be balanced by reactivity of CC. Considering what has been described before, and considering the general requirements for good blended cements, the following parameters should be taken into account when calcined clay and calcined clay-limestone cements must be optimized: Calcined clay cements – Overview

38. 38 Calcined clay cements: optimization Use of chemical activators : the drop of early strength that follows clinker reduction may be partially balanced by the addition of suitable chemical activator. These chemicals can positively influence the: availability of calcium hydroxide from clinker hydration, thanks to acceleration of clinker reactivity; release of silicon and aluminum from SCMs. Improvement of workability : this important technological parameter can be remarkably improved by a suitable cement additive with properties of plasticizer . Considering what has been described before, and considering the general requirements for good blended cements, the following parameters should be taken into account when calcined clay and calcined clay-limestone cements must be optimized: Calcined clay cements – Overview

39. 39 Effect of chemical additive on strength development: improvement of early strength (addition in mixing water). Calcined clay cements – Overview Source: Mapei internal data. Calcined clay cements: optimization

40. 40 To conclude, calcined clay and calcined clay/limestone cements allow high levels of clinker reduction, with strength performances similar (or superior) to high quality blended cements (e.g. blast furnace slag cements) and workability that can be controlled by the use of suitable additives. Calcined clay cements – Overview Source: K.Scrivener et al., Calcined clay limestone cements (LC3), Cement&Concrete Research 114 (2018), 49-56. Original data by R.Gettu et al. Calcined clay cements: conclusion Other parameters such as durability, resistance to carbonation, resistance to chloride, protection of steel reinforcement, are comparable to “traditional” cements. The potential for CO 2 saving has been calculated in several publications and it is similar or higher than blended cements with similar substitution level.

41. 41 Bibliography K.Scrivener , F.Martirena , S.Bishnoi , S.Maity : Calcined clay limestone cements (LC3). Cem&Concr . Res. 114 (2018) 49-56. M.Antoni : Investigation of cement substitution by blends of calcined clays and limestone, Thesis EPFL (2014). A.a. V.v.: Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL, Materials and Structures (2022) 55:3. M.Antoni et al: Cement substitution by a combination of metakaolin and limestone, Cem&Concr . Res. 42 (2012) 1579-1589. Calcined clay cements – Overview

42. 42 Thank you for your attention www.mapei.com