Investigation on the physical stability of calcium-silicate-hydrate with varying CaO/SiO2 ratios under cryogenic attack

Abstract The cryogenic attack (−170 °C) degradation mechanisms to cement-based materials have not reached an overwhelming consensus. This work aimed to reveal the degradation role of cryogenic attack to the physical properties of calcium-silicate-hydrate (C-S-H) with varying CaO/SiO2 (C/S) ratios. The topographic features, nanomechanical property, and volumetric stability of C-S-H grains and the basic building blocks were progressively investigated by atomic force microscopy (AFM), AFM-based indentation, nitrogen adsorption, and short-term helium inflow. The results revealed that the cryogenic attack could lead to degradation to C-S-H itself even without the presence of water. Firstly, the elastic moduli of individual C-S-H phases such as Low-Density (LD) C-S-H and High-Density C-S-H decreased, this nanoscale mechanical degradation was consistent with the macroscopic mechanical degradation of cement-based materials. Secondly, microcracks formed in C-S-H phases under the cryogenic attack. These destructive microcracks were likely to form inside or between C-S-H grains, which was dependent on C/S ratios. Thirdly, the cryogenic attack resulted in collapse of the intraglobular pores, leading to volume shrinkage of C-S-H basic building blocks, which initiates the formation of local defects and microcracks.