Hydration Mechanisms in Low-Clinker Composite Cement Systems

Cement, pp. 100194

Abstract

The hydration mechanism of the low-clinker binders (cement ≤ 45%) incorporating either calcined clay or natural pozzolana together with limestone were investigated in this study. The reactivity of calcined clay and natural pozzolana were evaluated using synthetic portlandite (CH) pastes, to calirfy the influence on microstructural development kinetics and corresponding early and later age strength performance. Calcined clay in low clinker mixtures exhibited rapid early reaction, promoting the formation of hydration products such as AFm and C-(A)-S-H within the first 7 days. This accelerated reaction enhanced microstructural densification and early compressive strength. While mixtures incorporating natural pozzolana demonstrated slower hydration kinetics, with more pronounced hydrate formation occuring after 7 days. By 90 days, significant increases in AFm and C-(A)-S-H phases were observed, aligning with continued strength development. In this paper it was found that natural pozzolana mixtures formed higher total hydrate volumes at later ages than calcined clay mixtures. Sodium sulfate addition enhanced early age strength by accelerating hydration, while later strength was unchanged or slightly reduced, likely due to limited availability of saturated pore space for continued hydration. Nevertheless, the presence of reactive SCMs largely compensated for this effect.

Authors 5

1. Aysha Anagreh corresponding Aachen Institute of Building Materials Research

   RWTH Aachen University

   Affiliation as printed

   Heidelberg Materials, Global Research & Development, Oberklamweg 2-4, Leimen 69181, Germany

   Institute of Building Materials Research at RWTH Aachen University, Aachen 52062, Germany

2. Maciej Zając
   Affiliation as printed

   Heidelberg Materials, Global Research & Development, Oberklamweg 2-4, Leimen 69181, Germany

3. Mohsen Ben Haha
   Affiliation as printed

   Heidelberg Materials, Global Research & Development, Oberklamweg 2-4, Leimen 69181, Germany

4. Arnaud Muller
   Affiliation as printed

   Heidelberg Materials, Global Research & Development, Oberklamweg 2-4, Leimen 69181, Germany

5. Thomas Matschei Aachen Institute of Building Materials Research

   RWTH Aachen University

   Affiliation as printed

   Institute of Building Materials Research at RWTH Aachen University, Aachen 52062, Germany