Influence of Coal Char Addition on the Heat of Hydration and Rheological Behavior of Cement Grout

Abstract

Cement grout is widely used in underground excavations and constructions. Recent research reveals that coal char, a sustainable coal-derived material, can enhance the engineering properties of traditional cement grouts, such as higher compressive strength and lower bleeding at room temperature. However, the effect of coal char addition on the heat of hydration and rheological behaviors of char-cement grouts at lower or higher temperatures remains unclear. In this study, considering different w/c ratios (0.8–1.2) and char contents (10%–30%), the heat of hydration of char-cement is investigated to understand the hydration mechanism of cement with adding char. The rheological behaviors of new char-cement grouts at two different temperatures of 5 and 35°C are studied. It is found that the addition of char at the same w/c ratio leads to a higher first heat flow peak in the initial reaction period and facilitates hydration reaction in cement grouts based on cumulative heat evolution over a longer period (typically >14 h). The effect of 5 and 35°C on rheological behaviors of char-cement grouts is consistent with the respective pure cement grouts. A simple model based on cumulative flow resistance is proposed for describing the rheological behavior and can well fit all pure cement and char-cement grouts with a relatively high average R2 value of 99.7%.