Effect of high temperatures on concrete produced with steel fibers subjected to surface treatment with nanosilica: pullout behavior, mechanical properties, and numerical simulation

Abstract

The use of steel fiber reinforced concrete (SFRC) as total or partial replacement for conventionally reinforced concrete has become popular in recent decades, especially to produce precast elements. In general, SFRC structures are susceptible to fire during their lifetime, which results in the deterioration of the mechanical properties and loss of bearing capacity. Nevertheless, current standards and guidelines do not provide sufficient parameters for the fire design of such structures. Furthermore, the understanding of the mechanisms that govern the post-cracking behavior of SFRC exposed to high temperatures is not sufficiently investigated in the literature, especially regarding mineralogical changes in the fiber-matrix interface and its correlation with the mesoscale behavior. In this sense, the surface treatment of steel fibers can bring benefits in terms of material performance when exposed to fire. To ensure the safety of SFRC structures, this study aims to evaluate the influence of surface treatment with nanosilica on the pullout behavior of steel fibers exposed to elevated temperatures. Pullout tests with multiple fibers and double block configuration will be performed at temperatures of 150, 300, 450 and 600 °C. The fiber-matrix interface will be evaluated using the SEM/EDS technique aiming to characterize the microstructural changes as a function of temperature. Additionally, the effect of surface treatment and temperature on the compressive and tensile properties of the composite is going be evaluated. Finally, the results will serve as the basis for a numerical model with explicit and discrete representation of the fibers in the matrix to simulate the behavior of SFRC structures exposed to fire. Above all, the results obtained can be applied to ensure safety, efficiency, and economy in SFRC structures. (AU)