Recycled aggregate concrete incorporating fly ash: Comparative study on particle packing and conventional method

In the present study, particle packing method (PPM) of mix proportioning is applied in a novel way for recycled aggregate concrete (RAC) incorporating fly ash as a partial replacement of cement. Lesser fresh mortar content was achieved by PPM which resolves the major concern of excess adhered mortar in RAC. Theoretical packing density (PD) obtained using compaction-interaction packing model was compared with experimental PD. 18% and 28% reduction in cement content was observed for RAC with 20% and 30% fly ash replacement respectively due to PPM mix proportions as compared to conventional method at water-binder ratio of 0.45. Compressive strength, flexural strength and modulus of elasticity of RAC with fly ash showed comparable results with natural aggregate concrete in PPM. The rate of long term compressive strength gain was about 11%-20% and 30% in RAC and natural aggregate concrete (NAC) respectively. Split tensile strength and modulus of elasticity in RAC was comparable in both the conventional as well as PPM methods. Flexural strength was improved in RAC incorporating fly ash mix due to PPM. Statistical analysis showed better tensile strength for RAC as compared to NAC up to the characteristic compressive strength of 25 MPa. Poor tensile behaviour was reported for high strength recycled aggregate concrete. The results suggest that, the particle packing method can be used in RAC with fully replaced recycled aggregates incorporating fly ash (up to 30% replacement) for sustainable construction practices.