Experimental Study on Impact Resistance of Fiber Reinforced Concrete Made with Stone Cutting Industry Waste Mohammadreza rezaei Mohammadreza.rezaei96@cv.iut.ac.ir Date of Submission: October 21,2020 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc Language: Farsi Supervisor: Dr. Mohammadreza Eftekhar, eft@cc.iut.ac.ir Many structures are subjected to various impact loads during their service life such as the effects of the blast, the traffic loads, and the projectile collision loads. It is necessary that research about the behavior of the construction materials due to the destructive effects of these loads. Concrete is one of the most widely used materials in construction. Therefore, the performance and the reinforcement ways of this material should be investigate. In recent years, environmental concerns have been raised due to the increase in industrial waste. Finding a way of reducing and recycling these wastes is required in the waste management field. Using these wastes in the production of concrete has been created a new concept named green concrete. In addition to solving the environmental problems caused by the waste, green concrete also reduces the use of natural resources. The building stones industry is one of the industries that are faced with the problem of waste materials. In stone cutting industrial units, many unusable stone fragments and sludge due to the stone cutting and shaping operations are produced. In this research, these pieces of stone and sludge have been performed in the production of concrete. In the present study, to achieve the research objectives, the wastes of 3 types of marble, travertine, and granite stones and the sludge of each of these stones have been used as coarse aggregate and partial replacement of cement, respectively. Hybrid fibers (steel-polypropylene) with volume fractions of 0.5% (0.25% steel and 0.25% polypropylene) and 1% (0.5% steel and 0.5% polypropylene) have been used to investigate the behavior of concrete subjected to impact loads as the primary purpose of this research. Nine mix designs have been considered for each type of coarse aggregate (27 mix designs Collectively). The type of sludge used in each design is proportional to the type of consumption coarse aggregate in that design. A control design was considered for each category of mix designs, and the effects of using fibers, sludge, and microsilica was investigated. In some designs, 10% cement was replaced by Sludge of stones, and in others, 20% cement was replaced by 10% sludge and 10% microsilica. Based on the results of experiments, travertine sludge has a positive effect on impact, compressive, and flexural strength of concrete specime But marble and granite sludge decreased the values of the mentioned mechanical properties; So that these sludges decreased the impact resistance of concrete by 33% and 16%, respectively. Simultaneous use of microsilica and sludge has significantly affected the mechanical properties of concrete, which is a kind of positive synergism of these materials to improve concrete performance. Using 0.5% hybrid fibers increases the energy absorption capacity of specimens to 3.3 and 4 times for initial cracking and ultimate failure, respectively, due to the impact. In addition, load-bearing capacity subjected to impact loads would be occurred by the fibers after the initial crack, but the nonfibrous concrete specimens subjected to the impact loads are ruptured after the first crack. Due to using 0.5% fibers, compressive strength and modulus of rupture in contrast to the impact resistance are reduced up to 28.8% and 25.1%, respectively. All the mentioned mechanical properties have been improved by increasing the fiber volume fraction from 0.5% to 1%. However, the effect of increasing fiber volume fraction is very significant on the impact resistance. Compared to the control specimens, the number of required blows increased to 9.7 and 11 times for initial cracking and ultimate failure, respectively. Regarding the effect of coarse aggregate type, it can be said that marble coarse aggregate compared to granite and both of them compared to travertine coarse aggregate provide more compressive strength and modulus of rupture for concrete. In the case of impact resistance, the effect of marble and granite coarse aggregate is almost the same, and the number of required blows of those compared to travertine coarse aggregate increases to 31% for cracking and ultimate failure. Key Words: Impact resistance, Green concrete, Stone cutting sludge, Microsilica, Fibers.