Temperature effect on density, strength, and microstructure of sustainable coal char-cement grout

Abstract

Coal char, a coal pyrolysis product, is a lightweight carbon-rich material, which exhibits significant potential as an innovative and sustainable construction material. Recent research has indicated that the coal char addition enhances the engineering performance of conventional cement grout at ambient temperature. This experimental study evaluates the performance of coal char-cement grouts under varying curing temperatures (−25, 5, 25, and 35 °C) and conditions (sealed and water-soaked), focusing on the impacts of char contents (≤30 %) and temperatures on the bulk density, unconfined compressive strength, mineralogical, and microstructural properties of grouts. Findings reveal that grouts cured at 5, 25, and 35 °C possess 7.0–7.9 %, 5.3–5.4 %, and 5.1–6.4 % higher bulk density than those cured at −25 °C, primarily attributable to water absorption in water-soaked curing conditions. Furthermore, at −25 °C, the increasing compressive strength is obtained in low w/c ratio (0.8) grouts as char content increases. Compared to curing temperatures of 5 and 35 °C, char-cement grout at an ambient temperature of 25 °C demonstrates better strength performance because of more hydration products formed, higher calcite content, the predominance of amorphous calcium silicate hydrate, and the reduction in the crystalline phase of portlandite.