High temperature properties of fiber reinforced high strength concrete

Concrete structures fabricated with high strength concrete (HSC) experience degradation of strength and spalling when exposed to extreme fire conditions. To mitigate fire induced spalling in HSC; different types of fibers are often added to concrete. Presence of fibers influence the properties of HSC and knowledge of high temperature properties is essential for evaluating the fire response of structures made of fiber reinforced HSC. In this paper, thermal and mechanical properties of four types of HSC are evaluated. The four types of concrete comprise of plain HSC, and HSC with 3 types of fibers namely steel, polypropylene and hybrid (steel + polypropylene) fibers. For thermal properties specific heat, thermal conductivity, and thermal expansion are measured, whereas for mechanical properties compressive and tensile strength are measured in the temperature range of 20-800°C (68-1472°F). Results from mechanical property tests show that addition of steel fibers enhances tensile strength of HSC which is beneficial against fire induced spalling. Results from thermal property tests show that presence of fibers increase the specific heat and thermal expansion of fiber reinforced concrete that will affect the development of fire induced thermal gradients and thermal stresses in HSC cross-section. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of fiber reinforced HSC (FRHSC) as a function of temperature. The proposed thermal and mechanical property relationships can be used as input data in computer models for evaluating fire response of structures made of FRHSC.