High performance concrete under elevated temperatures

• Performance of HPCs under elevated temperatures.
• Use of PP fibers with air entraining admixture to decrease damage.
• Decreased spalling and increased residual strength.
• Complete disintegration of dense matrix under very high temperatures.
• Microstructural examination of cement paste–aggregate interface.

In this study, PP fibers and air entraining admixture (AEA) were used together in an high performance concrete (HPC) mix so as to create interconnected reservoirs in concrete and to improve fire performance of HPC. For this reason, nine mixes of HPC incorporating blast furnace slag with 0.24 water-to-binder ratio and various PP and AEA contents were produced. Specimens were cast in two different sizes in order to see the effect of size and 18 series of specimens were obtained. These series subjected to elevated temperatures (300 °C, 600 °C and 900 °C) with a heating rate of 10 °C/min and after air cooling, residual mass and compressive strength of specimens were determined. The heated specimens were observed both at macro and micro scales to investigate the color changes, cracking and spalling of HPC at various temperatures. Also, thermogravimetric analyses were performed on powder samples from each nine mixes. Results showed that addition of AEA diminished the decrease in residual strength but this result was found to be irregular after 300 °C for thick specimens. The collaboration of AEA and PP fibers decreased the risk of spalling of HPC. Also, size of specimen was found to be important in deterioration of HPC.