Effect of Six Hour Fire on Flexural Strength of RC Beams made with 50\% Coarse Aggregates from old concrete: Part 1: Normal mix

Abstract

Shifting of people from villages/small cities to big cities poses a serious issue of accommodation and other associated infrastructure. For the solution of said issue, demolition of old structures to construct new high-rise buildings is opted. The demolishing waste is an additional problem for the project, particularly due to unavailability of the dumping space in many areas. A method of addressing the issue is by using it in new concrete. This research study presents an experimental investigation to check the effect of a 6-hour fire at 1000◦C on the bending resistance of reinforced concrete beams prepared by replacing 50% conventional coarse aggregate with coarse aggregate from demolished concrete. 24 RC beams of 0.9m × 0.15m × 0.15m size are cast using 1:2:4 mix and 0.54 water cement ratio. To reinforce the beams 2#4 bars in each tension and compression zones are used. Out of 24 beams, 12 are cast with all-natural coarse aggregates to compare the results. After 28-days standard curing, all beams are exposed to fire for 6 hours in purpose made oven. The beams are then left at room temperature for 24-hours followed by testing of all the beams in universal load testing machine with central point loading. Load and deflection are monitored at regular intervals. Comparison of the results with control specimen shows that the proposed beams observed 13.43% reduction in flexural strength which is quite smaller. The beams failed in shear which complies with the failure mode of normal concrete beams. Thus, the proposed material has good fire resistance when used in reinforced concrete beams.