Microstructure and early-age properties of Portland cement paste - Effects of connectivity of solid phases

Reliable information about the early-age properties of cementitious materials is vital in order to assure high quality and avoid problems in performance throughout the life of a concrete structure. This article describes the effect of the connectivity of the solid phase in the microstructure on the mechanical behavior of cement pastes. The authors report on an experimental study of the development of the compressive strength and elastic moduli of the Portland cement pastes with three different water-cement ratios (0.35, 0.5, and 0.6) cured under an isothermal condition (25 deg C.). In addition, the cement hydration model HYMOSTRUC3D was used to simulate the formation of the microstructure. The authors conclude that the percolation threshold of the solid phase in the microstructure of a cement paste is closely related to the w/c (water to cement ratio) that is used. The solid phase percolated earlier, and at a lower degree of hydration, in a cement paste with a lower w/c than in a paste with a higher w/c. The specific effective contact area is a microstructure parameter that describes the degree of interparticle bonding among the hydrating particles. The specific effective contact area appears to be directly related to both the measured compressive strength and the elastic moduli.