How Air Voids Affect the Performance of Concrete Subjected to Fire

Abstract

Spalling is a hazardous phenomenon that structures will experience during a fire. It has been extensively studied recent years. Inclusion of polypropylene fibers in concrete mix are commonly treated as a feasible method against spalling as they can increase the permeability of concrete in high temperature environments to release the interior pressure. Recently, air entrained concrete is thought to be a suitable alternative to polypropylene fiber reinforced concrete under fire conditions. The fundamental point of this study is to identify how the percentage of air voids, and the combination of polypropylene fibers and air entraining admixture can affect the permeability of concrete and therefore the occurrence of spalling phenomenon. For this reason, twelve mixes of concrete with different water to cement ratios, and various polypropylene fibers and air void content were produced. Fire experiment were carried on the specimens using a standard ASTM E-119 fire curve for the duration of 90 minutes, reaching 1850 °F in a furnace. In this study compressive strength, mass loss and photographic documentation of specimens were investigated and compared. Results show that addition of air entraining admixture helps reduce compressive strength loss, but the trend was found to be irregular.