Evaluation of mechanical properties of concrete by replacing natural aggregates with fine and coarse recycled aggregates

Recycled concrete aggregates are one of the types of recycled aggregates that have the most abundance compared to other recycled aggregates. In this research, by using the replacement of recycled concrete aggregates instead of natural aggregates, the mechanical properties of this type of concrete have been investigated. The replacement of natural aggregates with recycled aggregates was done in four percentages of 0, 15, 30 and 45, and this replacement was done both independently (i.e. sand or gravel separately) and simultaneously (both sand and gravel together). According to the use of 50% sand and 50% sand in the reference mixing plan and by replacing the percentages with coarse and fine recycled concrete aggregates, 21 mixing plans were used. The ratio of water to cement was kept constant in all mixing plans and was considered equal to 0.42. To compensate for the decrease in strength due to the replacement of recycled aggregates, micro silica in different percentages of 7.5 and 15 and super plasticizers were used in the mixing designs. By performing various tests, the mechanical properties of concrete samples were investigated. The results showed that the best mixing design in terms of compressive strength is the design containing 7.5% micro silica and 15% recycled sand, in terms of tensile strength, the design containing 7.5% micro silica and 45% recycled sand, in terms of flexural strength, the design containing 7.5% micro silica and 30% recycled sand, the plan containing 15% micro silica and 15% recycled sand was determined. By examining the mechanical properties of concrete samples, it was determined that the recycled mixing plans contain 15%, 30% recycled gravel and 45% recycled sand with 7.5% microsilica, as well as the mixing plan of 15% recycled sand with 15% microsilica. , among the recycled mixing plans, they had the highest amount of overall utility.