Particle packing optimization and pore structure assessment of ternary cementitious system based on X-ray computed tomography and mercury intrusion porosimetry

Abstract

The introduction of high-volume steel slag into ordinary Portland cement (OPC) has a negative effect on the pore structure due to its poor hydraulic reactivity. Synergistic effects between steel slag and ground granulated blast furnace slag (GGBFS) in cementitious system have drawn increasing attention. In this study, the modified Andreasen and Andersen (MAA) model was adopted for the mixture design of ternary cementitious system incorporating high-volume ultrafine steel slag (USS) and GGBFS without a compromise in strength. X-ray computed tomography (X-CT) and mercury intrusion porosimetry (MIP) were applied to characterize the pore structure of various cementitious mortars in terms of porosity, pore size, pore number, pore morphology and homogeneity. Results manifested that the adverse impact of USS addition on the pore structure of binary cement was effectively mitigated in the ternary cement USS-GGBFS-OPC after mixture optimization, whereby the pore size was shifted toward a finer distribution and simultaneously with a higher uniformity and consequently promoting the compressive strength development. An increase of cumulative pore volume as captured by X-CT was associated with an exponential decrease of the number of pores while together with larger pore sizes. The increase in the number of small pores led to an increase in the pore tortuosity and degree of sphericity. The fractal dimension of pores was negatively correlated with pore inhomogeneity and compressive strength. These findings provide new insights into homogeneity-oriented mixture design of composite cementitious binders based on gap-graded particle packing, together with their synergistic effects on hydration progress.