Effects of elevated temperature on mechanical properties and microstructures of alkali-activated mortar made from low calcium fly ash-calcium carbide residue mixture

Abstract

This research investigated the high-temperature resistance of alkali-activated mortar (AAM) using Class F fly ash (FA) blended with calcium carbide residue (CR) as a binder. The FA was blended with CR at 15 %, 30 %, and 45 % by weight. Sodium hydroxide (NaOH) and sodium silicate solution (Na2SiO3) was used as activator in the ratio of 2:1 by weight. The sodium hydroxide solution concentrations were 6, 8, and 10 M, the liquid-to-binder ratio was 0.85, and the binder-to-fine aggregate ratio was 1:2.75 by weight. The study assessed physical characteristics, compressive strength, weight loss, and microstructural analysis, subsequent to being subjected to 2-hour heating at 400, 600, and 800 °C. According to the findings, the highest compressive strength (prior heating) was recorded as 41.3 MPa after 28 days and this was observed in samples where 30 % of CR was combined with 70 % of FA. Meanwhile, when exposed to elevated temperatures, the compressive strength of all samples was decreased. The decomposition of Ca(OH)2, C-S-H, and C-A-S-H gel in the matrix as indicated by the microstructure result was conformed to the result of compressive strength loss. Nonetheless, when the samples were sintered at 800 °C, a new crystalline phase was formed, resulting in a slightly increase in compressive strength compared to samples sintered at 600 °C.

Keywords

• Calcium carbide residue
• Fly ash
• Alkali-activated mortar
• Elevated temperature
• Fire resistance