Influences of elevated temperature and re-curing on the compressive performance of lightweight concrete containing metakaolin: Experiments and prediction models

The influence of elevated temperatures on the compressive behavior of lightweight concrete (LWC) has become a topic of interest due to the importance of safety assessment, fire-resistant design, and repair of structures affected by fire. However, there has been a lack of research about the water re-curing of thermally compromised concrete. Therefore, the current study aims to investigate the impact of elevated temperatures and water re-curing on the compressive performance of LWC with different proportions of metakaolin (0, 5, 10, 15, and 20 %). The LWCs were heated at temperatures of 300 and 600 °C, followed by the application of water re-curing process. Then, further degradation and recovery of the LWCs were examined. The LWC performance was explored through calculating the axial stress-strain response and mechanical parameters such as toughness, modulus of elasticity and compressive strength. Fracture mode and visual observations were also studied. The results indicate that there is a remarkable decline in the mechanical features of the LWCs by increasing temperature. At 600 °C, the most significant deterioration is observed with average reductions of 24 %, 65 % and 39 % in toughness, modulus of elasticity and compressive strength, respectively. The LWC with metakaolin exhibits superior behavior at high temperatures compared to the LWC without metakaolin. The water re-curing improves the mechanical performance of the LWCs. The recovery of strength, toughness and modulus of elasticity for the LWCs at the investigated temperatures are 11–26 %, 8–28 %, and 4–50 %, respectively. Besides, models are presented to forecast the mechanical features of the LWCs with metakaolin under elevated temperatures. The predicted outcomes display appropriate accuracy compared to the present experimental results and those of other researchers. Ultimately, response surface method is employed to identify the optimum design parameters.