Hydration kinetics, strength, autogenous shrinkage, and sustainability of cement pastes incorporating ultrafine limestone powder

Abstract

This study investigated the effects of ordinary limestone powder (OLP) and two ultrafine limestone powders (ULPs) on the early and late age hydration characteristics of cement pastes with low water-to-binder (w/b) ratios of 0.21. The compressive strengths and autogenous shrinkage rates were also examined. Calorimetry and setting data showed that finer limestone powder (LP) significantly shortened the induction period and setting time of the paste and accelerated the early hydration reaction. The kinetic model showed that the rates of nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D) increased, and the duration of process I decreased with increasing LP fineness. This indicated that the increased rate from the early hydration reaction was closely related to accelerated nucleation of smaller LP particles. Thermogravimetric-differential thermal analyses (TG-DTA) revealed that the finer LPs generated more hydration products and improved hydration degree in the later stages. Moreover, under favorable conditions for nucleation and increased effective w/b ratios, the hydration products of the LP pastes were formed rapidly, exceeding those of the pure paste at late stages. A finer LP increased the compressive strength and autogenous shrinkage, but due to the reduction in clinker, the compressive strength and autogenous shrinkage were lower than those of the pure paste. Mercury intrusion porosimetry (MIP) showed that the cumulative volume of the pores greater than 50 nm decreased when the LP was finer, thus increasing the compressive strength and autogenous shrinkage. The incorporation of 25 vol% ULP (dv,50 = 2.653 μm) decreased the CO2 emissions per unit 28-day compressive strength by 17.34% compared to those of the pure paste. This study improves our understanding of the hydration behavior and properties of ULPs in cement-based materials with low w/b ratios and improves the use of LPs in HPC and UHPC.