Quick Hardening Properties of the Cement Paste Partially Replaced by the Calcined-Milled Wood Fly Ash

Abstract

The rapid growth of the construction industry has led to issues such as increased consumption of natural resources, energy usage, and carbon emissions. Integrating waste materials into the construction industry can help alleviate environmental problems. This study explored wood fly ash (WFA) generated from wood pellet combustion as a cement substitute material. To enhance the reactivity efficiency of WFA as a cement substitute, we conducted physical pretreatment, including calcination at 800°C, followed by ball milling and sieving. The focus was on evaluating the chemical and mechanical properties induced by the pretreatment of WFA when incorporated into cement matrix during the early age stages. Specimens were manufactured by weight substitution of 10%, 20%, and 30% of before pretreatment (BT) and after pretreatment (AT) WFA for cement, and consistency of the workability was maintained by adding a water reducer. The physical pretreatment altered the chemical composition and particle characteristics of WFA. In AT_WFA, the presence of CaO and MgO induced a rapid reaction with water compared with BT_WFA, resulting in high heat release during hydration, shortening the setting time, and improving compressive strength. The deficiencies in gypsum and sulfate in BT and AT_WFA integrated into the cement matrix, promoting the formation of hydrogarnet, and more actively increasing the early heat of hydration in AT_WFA compared with BT_WFA. The presence of CaO and its relatively high alkalinity in AT_WFA led to faster consumption of C2S and C3S compared with ordinary portland cement (OPC), contributing to an increase in early compressive strength. The results of this study illustrate how the physical pretreatment influenced the material characteristics of WFA and its impact on the early-stage phase development in cement. This understanding can contribute to the assessment of the durability and long-term performance, including mechanical properties, of cement composites containing WFA with pretreatment.