Role of Limestone Powder in Early-Age Cement Paste Considering Fineness Effects

Abstract

This paper investigates the influence of limestone powder (LS) fineness on the early-age properties of portland cement paste. Blended pastes with LS were prepared based on volumetric ratio and their fresh properties, chemical shrinkage, and hydration were measured. Fresh properties were evaluated by water demand for normal consistency, yield stress, plastic viscosity, and bleeding ratio. Chemical shrinkage was measured using the helium pycnometry method. Hydration products and the hydration process were analyzed by X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), and calorimetry tests. Results show that LS significantly affects the properties of portland cement and this effect greatly depends on its fineness. Specifically, LS coarser than cement decreases water demand, plastic viscosity, and yield stress, while finer ones have the opposite effects. Plastic viscosity is related to the particle density (particle number per 100 μm3 solids) and specific surface area of total powders. Bleeding resistance is improved for blended paste with finer LS. Chemical shrinkage results demonstrate that LS indeed increases chemical shrinkage per gram of cement because of promotion on cement hydration. But this influence on the volume change of total paste is mitigated because of the dilution effect. XRD patterns show that LS does not react with cement hydrates at 24 h and preliminarily indicates the promotion of LS on cement hydration. Calorimetry results further confirm that LS accelerates and amplifies cement hydration despite its fineness and this promotion is more significant when LS is finer. This promotion is also confirmed by hydration degrees calculated from both heat of hydration and nonevaporable water content.