Performance of Polypropylene Fiber Reinforced GGBFS-based Alkali Activated Composite under Elevated Temperatures

This study evaluates the impact of incorporating polypropylene fibers on the endurance of 100% ground granulated blast furnace slag (GGBFS) based alkali-activated composite (AAC) exposed to elevated temperatures. In addition, the impact of critical variants, like polypropylene fiber volume fractions, fiber length, alkaline solution monomer ratio, and curing regime, on the overall performance of the fibrous composites under high temperatures was evaluated. While the polypropylene fiber content was varied at 0, 0.15, and 0.3%, two polypropylene fiber lengths, 12 and 20 mm, were examined to assess their influence on the composite thermal stability. The alkaline activating solution monomer ratios (Na2SiO3/NaOH, denoted as SS/SH ratio) was varied at 2.5 and 3.0, and two different curing regimes were adopted; the ambient curing regime, with temperature 24±2°C and 65% RH, and the heat curing regime, with 24 h heat curing in the oven at 65°C, for all mixes. The specimens were subjected to high-temperature effects at 150, 300, 600, and 800°C, and the results of residual compressive strength, residual density, and ultrasonic pulse velocity (UPV) were examined, before and after the exposure, to assess the impact of high thermal conditions. In addition to the visual inspection, SEM analyses were carried out to evaluate the effect of different parametric variances on the microstructure properties of the fibrous AACs under high-temperature exposure. The fibrous composite variants with short (12 mm) polypropylene fibers length and most of the variants with 0.15% long (20 mm) polypropylene fibers exhibited high thermal stability and better residual compressive strength than the equivalent control non-fibrous mixes when exposed to temperatures of 150 and 300°C. Further, the increase in alkali solution monomer ratio (SS/SH) from 2.5 to 3.0 has negatively influenced the overall thermal resistance of composites across all variants.