Experimental study on mechanical properties, microstructural of lightweight concrete incorporating polypropylene fibers and metakaolin at high temperatures

The main purpose of this experimental research is to investigate the effect of high temperature between 200 and 600 °C on microstructural and mechanical properties of lightweight concrete containing Polypropylene fibers (PP) and Metakaolin. This study includes 12 mixing samples. The percentage replacement of cement by Metakaolin considered in this experimental study are 0, 10, and 20% by weight of cement and percentage of PP fiber content between 0.1% and 0.8% by volume of concrete. The mechanical properties encompass the compressive and tensile strengths, ultrasonic pulse velocity (UPV) test, impact test, and SEM analysis. An impact test was performed to evaluate the ductility index. The results show that the compressive strength of 28-day specimens decreases with increasing temperature. Also, water absorption decreased by 6.8% in samples without PP fibers and 10% Metakaolin (P0M10) at temperatures from 200 °C to 400 °C. PP fibers with 0.4% and 0.8% in the mixing design reduces cracking of concrete and makes the concrete durable at high temperatures. The sample with 0.8% PP fibers and 10% Metakaolin (P0.8M10) showed 233.34% increase in absorption energy compared to the sample of P0M0 at 20 °C in impact test.