In this study, the usability of raw rice husk (RRH) instead of polypropylene fibers (PP) in high-strength concrete was investigated to prevent spalling, improve mechanical, physical, and thermophysical properties of concrete after high temperature treatment. Carbon dioxide (CO2) and carbon monoxide (CO) emissions of concrete mixes were also measured at different temperatures. The test results show that when RRH is used at 3% of cement by weight it can prevent explosive spalling and can be a suitable alternative to PP. Due to the lower thermal conductivity of RRH, the RRH mixes had lower thermal conductivity values at all temperatures compared with the PP mixes. The addition of RRH slightly decreased the mechanical properties of the concrete and modified its thermophysical properties by decreasing thermal conductivity and the vapor diffusion resistance factor. Up to 300 degrees C, the CO and CO2 emissions of the RRH mixes were similar or in some cases lower than those of the PP mixes. At 600 degrees C, the CO2 and CO emissions of the RRH mixes were higher than those of the PP mixes. (C) 2015 American Society of Civil Engineers.