Multiscale micromechanical damage model for compressive strength based on cement paste microstructure

Compressive strength is one of the most important and tested mechanical properties of cement paste. This paper presents a new four-level micromechanical model for compressive strength applicable on both pure and blended cement pastes. The model assumes that intrinsic tensile strength of C-S-H globules governs the compressive strength of cement paste. Crack propagation on all hierarchical levels starts once tensile stresses on a randomly inclined ellipsoidal inclusions within C-S-H exceed cohesive stress. The inclusion of unhydrated clinker, supplementary cementitious materials, other hydration products, or entrapped (or entrained) air further decreases the compressive strength of cement paste. The multiscale model uses volume fractions of principal chemical phases as input parameters as well as introduces a spatial gradient of C-S-H between individual grains which has a pronounced impact on predicted compressive strength. Calibration of the model on 95 experimental compressive strength values shows that the intrinsic tensile strength of C-S-H globule amounts to 320 MPa. Principal factors influencing compressive strength evolution are "C-S-H/space" ratio, volume of entrapped (entrained) air, and the spatial gradient of C-S-H.