Investigation of the effect of fiber type and amount on the performance of cement-based composites under repetitive loading

Reinforced-concrete structures are exposed to various cyclic loads such as traffic loads, temperature changes, winds, sea waves, earthquakes. A continuous decrease in the stiffness of the structure exposed to these loads occurs at the end of it, resulting in fatigue collapses. Conventional concrete is known to have poor performance under cyclic loads and is not recommended for use under dynamic loads unless it contains some kind of reinforcement. The addition of various fibers to concrete also improves many properties of concrete, including cracking resistance, resistance to fatigue loads, ductility and impact resistance. Based on this, Engineered Cementitious Composite (ECC) have been developed in recent years, created using various polymer fibers. These composites produced using poly-ethylene (PE), poly-vinyl alcohol (PVA), high-tensile poly-propylene (HTPP) fibers as polymer fibers; high ductility and toughness are provided with multiple crack behavior under tensile, flexural and shearing loads. This behavior also increases the ductility performance of polymeric fiber composites under cyclic loads. Within the scope of this thesis, the fatigue performance of HTPP, PVA and HYBRID composites which HYBRID is produced by using both HTPP and PVA fiber in equal proportions, at the rates of 1.5% and 2% are examined. Firstly, these composites with tensile strengths were subjected to load-controlled cyclic loading with 75%, 85 and 95% of average tensile strengths. As a result of the experiments, "the stress-unit strain" and "stress-number of cyclic" curves of the samples were drawn. In order to determine the stiffness change under repeated load, the secant modulus values of each cycle were calculated and the number of cracks on the samples were recorded with the help of an optical hand microscope. In terms of fatigue performance, considering the conditions that a structures come across in the field, it has been observed that composites with 2% PVA fiber have reached the highest tensile strength and the highest number of cycles it can perform at this strength.