The effects of polyproylene fiber and air entraining admixture addition on high performance concrete exposed to elevated temperatures

Abstract

As the use of HPC increases in structures, the risk of being exposed to fires also increases. Unlike NSC, strength and durability of HPC are more influenced by fire conditions and also HPC is more prone to spalling at elevated temperatures due to its dense microstructure which limits the ability of water vapor to escape from concrete. Recent studies showed that addition of PP fibers into HPC is an efficient way to avoid spalling of concrete because PP fibers melt in concrete above 170 o C and form microchannels which permit the evacuation of gases in pores. On the other hand, using various additives such as mineral and chemical admixtures in HPC was found to be efficient to limit the reduction in strength and durability of HPC. Therefore in this study, PP fiber and AEA with various ratios were used in HPC incorporating blast furnace slag so as to create interconnected reservoirs and to improve fire resistance of HPC. Nine mixes of HPC with 0.24 water-to-binder ratio and various PP and AEA contents were produced and 18 series were obtained. These series subjected to 300 o C, 600 o C and 900 o C with a heating rate of 10 o C/min and after air cooling, residual compressive strength tests were conducted. 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, TGAs 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 o C, PP fibers reduced the residual strength. 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.