Mechanical And Material Properties of Air Entrained High Strength Concrete At Elevated Temperatures

Abstract

The performance of high strength concrete (HSC) under fire conditions is an established concern in concrete industry. The kinetics and mechanisms involved in processes that affect the fire behavior of HSC are mostly controlled by its mechanical and material properties, thermo-mechanical interactions, and type of structural component exposed to fire. The weaknesses of HSC in infrastructure under fire conditions preclude its applications in fire resistance applications unless significant modifications are done either to concrete mix or the structural design. For many years, polypropylene fibers have been used to attain a certain amount of essential porosity in HSC under fire resistance applications. Air entrained HSC however, can provide a suitable alternative to conventional HSC under fire conditions, especially due to its permeability properties in hardened state. An experimental program was designed to obtain high strength air entrained concrete and study its performance at elevated temperatures in 23 to 800°C temperature range. In this study, material properties of air entrained HSC at varying air volume of 4% and 8% were investigated and compared with conventional HSC at elevated temperatures for residual and unstressed test conditions. Mechanical tests namely compressive strength, splitting tensile strength, stress-strain response, elastic modulus, and spalling behavior under a relatively higher heating rate of 10°C/min were studied. Additionally, changes in physical properties consisting of mass loss, scattered electron microscopy analysis and cracking behavior were also carried out. Results show that air entrained concrete performed better at elevated temperature with improved mechanical properties and spalling mitigation. Conversely, an increased air content in concrete did not depict a performance improvement at elevated temperatures.