On residual strength of high-performance concrete with and without polypropylene fibres at elevated temperatures

Cubes of 100×100×100 mm3 and cylinders of 100×100×515 mm3 were designed and fabricated with C50, C80 and C100 high-performance concrete (HPC) mixed with and without polypropylene (PP) fibres, respectively. These specimens were heated in an electric furnace, approximately following the curve of ISO-834, with a series of target temperatures ranging from 20 to 900 °C. No explosive spalling was observed during the fire test on HPC specimens with PP fibres, whereas some spalling occurred for HPC specimens without PP fibres. The relationship between the mass loss and the exposure temperature was investigated. In addition, the heated and cooled cubes and prisms were tested under monotonic compressive loading and four-point bending loading, respectively. The degradation of both the residual compressive strength and the residual flexural strength was analyzed. Furthermore, the effects of PP fibres on the residual mechanical strength of HPC specimens at elevated temperatures were also investigated. Finally, a fire-resistance design curve relating the residual compressive strength to temperature, as well as a design curve relating the residual flexural strength to temperature, were proposed based on the statistical analysis of the test data.