An experimental into effect of temperature rise on mechanical and visual characteristics of concrete containing recycled metal spring

Recycled fibers can enhance the compressive, tensile, and flexural strength of the concrete exposed to high temperatures. The main effect of these fibers on concrete is to reduce the generation of wide cracks developed by heat and pressure. Their behavioral mechanism is such that by bridging between cement paste and aggregates, the concrete structure is strengthened and as a result, cracks with great widths will not be developed. In this paper, the effect of elevated temperatures on the mechanical properties of concretes containing steel and polypropylene fibers as well as recycled metal springs with bore diameters of 8, 12, 16, and 20 mm, is experimentally studied. The results approve that using metal springs increases the concrete's strength for up to 80%. Among different types of fibers added to the concrete, the springs with a bore diameter of 12 mm and steel fibers could most effectively improve the compressive and tensile strengths, respectively. Furthermore, the threshold temperature at which the strengths will severely decline is measured at 500 degrees C.