Evaluation of mechanical properties and post-fire cured strength recovery of recycled aggregate concrete

Purpose The purpose of the study is to evaluate the suitability of post-fire curing for normal and Recycled Aggregate Concretes (RAC) with and without fibres. Design/methodology/approach The study includes the testing of RAC specimens, i.e. 150 mm cubes and cylinders with 300 mm length and 150 mm diameter with hybrid fibres (0.15% polypropylene fibres + 0.35% steel fibres) along with fly ash. The specimens were exposed to elevated temperatures between 400 to 700 degrees C with 100 degrees C intervals for 2 h of duration and the post-fire exposed samples were further subjected to water curing for a period of 7 days. The compressive strength, split tensile strength and Rebound Hammer Number (RHN) were measured at room temperature, after exposure to elevated temperatures and post-fire curing. Findings The result shows that the compressive strength reduces by a maximum of 61.25% for 700 degrees C and maximum retain in strength, i.e. 71.2% (in comparison to specimens kept at room temperature) is observed for 600 degrees C post-fire cured specimens. The split tensile strength reduces by more than half for 500 degrees C and above temperatures, whereas 400 degrees C specimens exhibits a significant regain in strength after post-fire curing. To validate the results of compressive strength, the Rebound Hammer test has been conducted. The RHN value decreases by 41.3% for 700 degrees C specimens and the effectiveness of post-fire curing is observed to be considerable up to 500 degrees C. Practical implications The conclusions from the study can be used in assessing the extent of damage and to check the suitability of post-fire curing in further continuing the utilisation of a fire damaged structure. Social implications Utilisation of secondary materials like recycled aggregates and fly ash can be made in the production of concrete. Originality/value Specimens with fibres performed better when compared to specimens without fibres and post-fire curing is found to be effective up to 500 degrees C.