Investigation of the effect of powdered rubber reinforced by different materials on the performance of concrete

Around all over the world, scrap tires are one of the materials that cause serious environmental problems due to the rapid development of technology and modern evolutions. The expansion of the automotive industry has caused the exuberance of used rubber as one of the environmental pollutants has attracted focus of many researches, in recent decades. It is not possible to dispose of used rubber in the environment because the tire decomposes at a very low speed. Therefore, the optimal use of these rubbers in various industries has become a necessity to reduce environmental pollution. For this purpose, in this research, the powdered rubber is used with different percentages in concrete replacement to sand and cement. Since adding rubber to concrete reduces the compressive strength, the flexural strength, and other properties of concrete, hence in this study rubber was reinforced by two physical methods (silica fume and cement coating), and three chemical methods (sodium hydroxide, sulfuric acid and potassium permanganate). The samples are made in 60 different designs, including 30 cement replacement designs (5, 7.5, 10, 12.5, 15%) and 30 sand replacement designs (5, 10, 15, 20, 25%). The results showed that powdered rubber replacement to sand has better results in terms of compressive strength than replacement to cement. Generally, compressive strength of concrete and the amount of rubber are almost inversely proportional. As the amount of rubber increases, the compressive strength of concrete decreases in all reinforcement methods, except reinforced by silica fume and cement coating. Hydrophobicity, accounts for this indirect relationship as this feature of rubber makes it unable to mix well with other components of concrete. Also, the results of flexural strength showed an inverse relationship with the amount of rubber in concrete. The results of the water contact angle test showed that the reinforcement methods are effective and made the rubber surface hydrophilic. The results of the thermal insulation test of concrete, using the device designed in this study, showed that the higher amount of rubber in the concrete means the less heat conduction so it can be effective in energy saving. Also, SEM (the Scanning Electron Microscopy) test showed that the reinforcement methods are effective, make a better combination of rubber particles with other concrete ingredients.