Evaluation of mechanical characteristics of high strength concretes reinforced with steel and polypropylene fibers exposed to wet and dry cycles in magnesium sulfate environment

Concrete Damaging and reduction of durability characteristics under sulfate attack is one of the important matters. Compared to the situation where concrete is always immersed in sulfate environments, the damages caused in dry and wet conditions are more complex. The dry and wet cycle is a significant factor that affects on the sulfate attack of concrete. Some concrete structures such as piers, are subject to wet and dry cycles due to sea tides, which causes a continuous process of destructive ions entering to the concrete matrix during wetting, and increasing cracks during the drying process. Considering the wide using of high-strength concrete and the weaknesses of this concrete in the mentioned conditions, the present study has investigated the compressive strength, tensile strength, separation and shrinkage test of HS, FRHSC concrete reinforced with polypropylene (PP), steel (ST) and hybrid fibers under the conditions of dry and wet cycles in the environment containing magnesium sulfate for 6 months. The results of this study show that although dry and wet cycles reduce the strength of concrete containing steel fibers, the effect of these fibers in increasing the compressive and tensile strength of HS concrete is much greater compared to PP fibers. The use of steel fibers, polypropylene and a combination of steel fibers and polypropylene has reduced the shrinkage of high-strength concrete samples by 13, 24 and 33%, respectively (compared to HS concrete without fibers).