Modeling the influence of limestone filler on cement hydration using CEMHYD3D

The ASTM C150 standard specification for Portland cement now permits the cement to contain up to 5% of ground limestone. While these and much higher levels of limestone filler substitution have been employed in Europe and elsewhere for many years, changing the ASTM standard has been a slow process. Having computational tools to assist in better understanding the influence of limestone additions on cement hydration and microstructure development should facilitate the acceptance of these more economical and ecological materials. With this in mind, the CEMHYD3D computer model for cement hydration has been extended and preliminarily validated for the incorporation of limestone at substitution levels up to 20% by mass fraction. The hydration model has been modified to incorporate both the influence of limestone as a fine filler, providing additional surfaces for the nucleation and growth of hydration products, and its relatively slow reaction with the hydrating cement to form a monocarboaluminate (AFmc) phase, similar to the AFm phase formed in ordinary Portland cement. Because a 20% limestone substitution substantially modifies the effective water-to-cement ratio of the blended mixtures, the influence of limestone substitutions on hydration rates is observed to be a strong function of water-to-solids ratio (w/s), with significant acceleration observed for lower (e.g., 0.35) w/s, while no discernible acceleration is observed for pastes with w/s = 0.435. Published by Elsevier Ltd.