Effect of recycled aggregates with different parent strength and fly ash on flexural strength of recycled aggregate concrete prisms

Fast consumption of conventional ingredients of concrete and waste generated due to demolishing old buildings is a multi-fold problem in the concrete industry. Hence the sustainable alternative of it is the need of the day. In this research work effect of binary blending of demolished waste and fly ash on the flexural strength of plain concrete prism is presented. The properties of aggregates and cement are evaluated. The physical and chemical properties of fly ash were determined. Recycled aggregates from demolished waste with different mix ratios (1:2:4 and 1:1.5:3) were used. Optimization of recycled aggregates; by evaluating concrete cylinders in 12 batches; showed 35% as optimum. At the optimum dosage of recycled aggregates fly ash was used from 2.5% to 15% with an increment of 2.5% to optimize its dosage. Compressive strength test of the standard-size cylinders and their comparison with control concrete showed a 10% dosage of a fly as the optimum percentage to replace the cement in the concrete matrix. Using both optimized dosages of recycled aggregates and fly ash prism specimens of900mmx150mmx300mm were cast in four batches. The beam specimens were cured for 28 days followed by an evaluation of flexural strength and deflection under centric load in the universal testing machine. Test results of flexural strength (only 15% loss) showed good potential for both waste materials in the concrete matrix. Recycled aggregate with higher parent strength showed better performance than its other counterparts. With higher-strength recycled aggregates residual flexural strength was recorded as equal to 93%. For all specimens recorded deflection was within the allowable limits of ACI-318.