Enhancing the Resistance to Elevated Temperature of Alkali-Activated Slag Concrete: A Comparative Study of the Role of Polypropylene Fibers

Alkali-activated concrete (AAC) gained considerable attention from the beginning of its discovery as a substitute for conventional concrete (CC) due to its superior properties and powerful environmental impact. This paper investigated physical and mechanical characteristics, considering the presence of polypropylene fibers (PPFs), of ambient cured alkali-activated slag concrete (AASC) at ambient temperature, 25°C, and after exposing to elevated temperatures, 300°C, 600°C, and 900°C. For a comparison purpose, a similar CC was also investigated by observing changes in the physical and mechanical characteristics. Visual inspection, weight changes, compressive strength, flexural strength, bond strength, and ultrasonic pulse velocity tests were carried out. Also, scanning electron microscope (SEM) and thermogravimetric analysis (TGA) tests were used for microstructure analysis. Test results demonstrated that the AASC achieved higher mechanical properties than similar CC at ambient temperature. Results also showed that the AASC has a higher resistance to elevated temperatures than the CC due to its higher resistance to spalling and cracking, its higher recorded residual mechanical properties after exposure to elevated temperatures, and its higher thermal stability and resistance to degradation recorded by the microstructure analysis. The inclusion of polypropylene fibers decreased most of the studied properties for both AASC and CC. However, the reduction in mechanical properties for AASC was higher than that for CC at equivalent PPF content.