Fire behavior of high‐contents recycled aggregate concrete composite slabs with small openings

Recycled aggregate concrete (RAC) is increasingly being used in the construction of structural elements. However, the performance of RAC elements under fire is usually considered to be inferior to that of normal concrete (NC) elements. This study investigates the fire behavior of RAC composite steel slabs with and without openings. Ten slabs of size of 1.0 m × 2.2 m were cast either with no opening, one or two circular openings, and one or two square openings. Five of the slabs were manufactured with 100% RAC, while the other five slabs were made with NC. The concrete slabs were loaded and subjected to fire tests at a temperature of about 900°C for 120 min. Test results show that RAC composite slabs have lower stiffness (thus larger mid‐span deflections) under fire exposure compared to their counterpart NC slabs. In terms of the recorded temperature–time curves, RAC slabs showed similar performance to that of NC slabs. The ratio of soffit temperature to the temperature at the top of slab was considerably smaller for RAC slabs compared to NC slabs. RAC slabs also showed more spalling than NC slabs. Experimental test results were numerically verified using PyroSim® software with the two showing good agreement. A series of new design charts for composite RAC slabs with desired fire endurance are proposed. This study is expected to promote the wider use of RAC in construction of structural elements, particularly of composite slabs exposed to extreme temperatures.