Assessment of Thermal Damage in Hybrid Fiber-Reinforced Concrete

Abstract

Three-point bending tests on high-strength concrete specimens after exposure to high temperatures are presented, with a detailed evaluation of process zone size. The variables considered for the high-strength concrete were the types of fiber reinforcement: steel microfibers, polypropylene microfibers, and a hybrid combination of steel and polypropylene microfibers. Both virgin (no heat related damage) and heat treated specimens were tested by conducting experiments at ambient conditions approximately one month after exposure to the high temperature. For both undamaged and heat treated specimens, acoustic emission monitoring and high-resolution interferometric measurements were used to characterize the evolution of the finite size of the process zone as a function of the applied load. The size and shape of the localized damage zone due to prepeak microcracking are two of the significant factors influencing the strength of quasibrittle materials, i.e., the structural scaling. This paper reveals that the material ductility increases with the thermal damage, which is explained by the increase in the fracture process zone size. As a consequence, a correct interpretation of the experimental data requires an identification of fracture parameters through indirect methods.