Authors: Sura Dinakar Sagar, Gangam Saileela
Abstract: The excessive depletion of natural river sand and granite stone has raised profound ecological and sustainability concerns, compelling the global construction sector to evaluate solid agro-industrial wastes as circular aggregate alternatives. This experimental research conducts an exhaustive physical, mechanical, durability, and microstructural investigation on sustainable High-Performance Concrete (HPC) produced by substituting virgin fine aggregate with granulated industrial copper slag (CS) at 0%, 20%, 40%, 60%, 80%, and 100% replacement levels, and conventional crushed granite coarse aggregate with alkali-treated coconut shell aggregates (TCSA) at 0%, 10%, 15%, and 20% by volume. Discarded agricultural coconut shells were pretreated with a 5% sodium hydroxide (NaOH) chemical solution to remove non-cellulosic waxy cuticles, pectin, and free sugars, reducing water absorption from 23.4% down to 8.65% and strengthening interfacial transition zone (ITZ) mechanical adhesion. A comprehensive laboratory testing suite encompassing compressive strength (3, 7, 28, and 90 days), split tensile strength, flexural modulus, ultrasonic pulse velocity (UPV), water absorption, sulfate attack resistance (5% Na2SO4), and rapid chloride permeability testing (RCPT) was carried out across 8 detailed mix formulations. Experimental data indicates that the optimum dual-waste mix incorporating 40% copper slag and 15% treated coconut shells achieves a 28-day compressive strength of 66.8 MPa, a 90-day strength of 71.4 MPa, a flexural strength of 6.78 MPa, an ultrasonic pulse velocity of 4.58 km/s, and a charge passage of only 1,120 Coulombs. SEM and EDS micrographs validate the formation of a dense, compact matrix where secondary C-S-H gels interlock with chemically etched bio-aggregate cellular pores, proving the viability of multi-waste sustainable HPC for structural engineering applications.
