Recent advances in understanding the hydration of limestone calcined clay cements (LC3)
Open access
Date
2023Type
- Conference Paper
ETH Bibliography
yes
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Abstract
Limestone and calcined kaolinitic clays are unique among supplementary cementitious materials due to their high and widespread availability. Furthermore, their combined reactivity enables substitutions of clinker of 50% (or more), while reaching comparable strength to PC (or pozzolanic cements) and enhanced durability properties. During the last 4 years, our understanding on the hydration mechanisms governing the behavior of these cementitious systems has evolved substantially, opening new possibilities for optimization and further development of the technology. The sulfate requirement of LC3 , which is commonly observed to be higher as conventional PC, has been proven to be controlled by sulfate adsorption mechanisms rather than the total reactive alumina content of the system. The precipitation of hemi and monocarboaluminate in LC3 was directly associated with the third hydration peak observed in isothermal calorimetry. Formation of carboaluminates is enhanced by the reaction of carbonates from limestone and alumina from metakaolin and has a significant contribution to strength gain and porosity reduction at early ages. Carboaluminates precipitate in pores remaining after clinker dissolution and remain stable in the long-term. At later ages, it has been observed that the reaction of metakaolin slowdowns due to the lack of large saturated pores where hydrates can precipitate. However, further reduction of the critical pore entry radius and total porosity was still observed, suggesting that precipitation might also take place in the pore solution film that lines the internal surface of partially saturated pores. In addition, precipitation of strätlingite was observed combined with a substantial reduction in Ca/Si ratio of C-A-S-H, in agreement with trends observed from thermodynamic modeling at equilibrium. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000636037Publication status
publishedBook title
Further Reduction of CO2-Emissions and Circularity in the Cement and Concrete Industry, 16th International Congress on the Chemistry of Cement 2023 - ICCC2023Volume
Pages / Article No.
Publisher
Thailand Concrete AssociationEvent
Subject
Sustainability; Hydration; Carboaluminates; Sulfate requirement; PorosityOrganisational unit
03891 - Flatt, Robert J. / Flatt, Robert J.
Funding
208719 - Ultra-green concrete (UGC): the pathway to save 800 Mt of CO2 per year (SNF)
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