EVALUATION OF THE MECHANICAL AND RHEOLOGICAL PROPERTIES OF RECYCLED SELF-COMPACTING CONCRETE AND REINFORCEMENT WITH MICROCILICA

Self-compacting concrete (SCC) is highly flowable concrete that can fill formwork without any mechanical vibrationis and able to flow under its own weight. In recent years, use of SCC has increased for placement in congested reinforced concrete structures with difficult casting conditions. On the other hand, environmental protection and waste recycling have become hot issues of common concern in the international community. The generated construction waste due to the global building (structure) removal and demolition, war, earthquakes etc. is becoming huge. In addition, the concrete with recycled aggregate is economically justifiable. In this study, the effect of replacing different percentages of fine and coarse recycled aggregates on the mechanical and rheological properties of SCC is evaluated. For this purpose a self-compacting concrete control mixture with natural aggregates is prepared in the first step. Then in the second step, recycled fine and recycled coarse aggregates with levels of 25, 50, 75 and 100 percent, replacing natural fine and natural coarse aggregates, in two distinct phases, and fresh and hardened concrete tests are done. Fresh concrete tests include: diameter of the slump, slump T50, funnel V, Box U, L-box tests and hardened concrete tests include: compressive, tensile and flexural strength tests. In each phase, a mixture that has the least negative changes in terms of mechanical and rheological properties compared with the control mixture, is selected for the next step of the research. Results showed that the mixture with 25\% replacement of fine recycled aggregates and the mixture with 25\% replacement of coarse recycled aggregates have the least negative changes compared with the control mixture. In the next step, to improve the weakened properties of the mixtures with 25\% replacement of coarse or fine recycled aggregates, cement is replaced by microsilica with levels of 5, 7.5 and 10 percent. Results show the mixtures with 25\% recycled aggregates and 5\% microsilica have closer properties to the control mixture and can be a proper alternative to the control mixture.