Structural Deterioration and Mechanical Degradation of Limestone Calcined Clay Cement (LC3) Under Elevated Temperature

The cement industry is facing demanding challenges to reduce carbon emissions. The use of limestone calcined clay cement (LC3) has been identified as one of the sustainable ways to reduce the industry's carbon footprint by up to 40% at relatively low costs. Meanwhile, LC3 has shown great potential as a 3D-printing material. However, recent studies revealed higher strength loss in LC3 composites than in ordinary Portland cement composites at elevated temperatures. Such degradation is mainly induced by water evaporation, which expands micro pores and undermines the microstructures of cement hydrate such as calcium alumina silicate hydrate (C-A-S-H). Therefore, investigating the intrinsic structural deterioration of LC3 under elevated temperature is urgently required to understand the mechanisms underlying their poor mechanical performances. In this work, a series of molecular models are constructed to elucidate the fire performance of newly developed LC3 composites. Specifically, molecular simulations are employed to reproduce the physical-mechanical behaviours of LC3 at elevated temperatures, in which the water evaporation under the high temperature is illustrated. The evaporation process of pore water, interlayer water and intralayer water is thoroughly described. Further, the mechanism underlying the poor high-temperature resistance of LC3 is uncovered. The evaporation of water leads to the twist of the silicate chain in C-A-S-H, which initiates the structural deterioration of LC3. Besides, the inner pore pressure is also extremely increased, resulting in the spalling of LC3 in micro and mesoscale. This work portrays the fire performance of LC3 and provides original insights to understand the mechanisms of their structural and mechanical degradation at elevated temperatures.