Performance enhancement of recycled aggregate concrete using treated construction and demolition waste and cashew nutshell ash

Abstract

This study examines the enhancement of mechanical and durability properties of Recycled Aggregate Concrete (RAC) produced from construction and demolition concrete waste (C&DW) to promote sustainable construction practices. A Control Mix (CM) of M30 grade concrete was compared with recycled aggregate concrete containing 25, 50, 75, and 100% Recycled Coarse Aggregate (RCA), along with a treated variant incorporating 100% RCA pre-soaked in fly ash slurry. Additional mixes incorporated Recycled Fine Aggregate (RFA) at 10, 20, 30, 40, and 50 % and Cashew Nutshell Ash (CNA) at 25, 20, 15, 10, and 5% as partial replacements for manufactured sand (M-Sand) and cement, respectively. The CM achieved the highest compressive strength of 50.97 MPa at 56 days, while the Treated Recycled Aggregate Concrete (TRAC) reached 50.71 MPa, about 27% higher than the untreated mix due to improved interfacial bonding and reduced porosity. The mix containing both RFA and CNA attained 47.03 MPa, equivalent to 92% of the control, indicating the synergistic effects of pozzolanic reactivity and internal curing. The TRAC also exhibited superior tensile and flexural strengths with the highest stiffness. Moderate replacement levels of CNA and RFA achieved the lowest chloride permeability and sorptivity. This confirms the combined use of treated recycled coarse and fine aggregates and CNA produced durable, high-performance concrete with enhanced sustainability.