Scaling of strength in hardened cement pastes - Unveiling the role of microstructural defects and the susceptibility of C-S-H gel to physical/chemical degradation by multiscale modeling

Abstract

The scaling of strength across hierarchically structured composite materials is accented by the presence of defects with distinct morphology and origin appearing within the microstructure. In hardened Portland cement pastes, these defects manifest as capillary pores, microcracks, and air voids. The transition of material strength from the nano-to-microscale is bridged in the present paper by a validated computational model based on a hierarchical representation of the paste microstructure, resting solely on realistic microstructural features. The model unravels and quantifies the strength scaling mechanisms arising from the various types of defects and critically assesses the susceptibility of C-S-H gel to physical and/or chemical deterioration, quantifying their impact on the gel's structural integrity which subsequently projects as a decrease of the material's load-bearing capacity. The fully-developed model is subsequently used as a quantitative tool to assess the strength degradation of cement paste exposed to a magnesium sulfate attack occurring at low temperature.