Mechanical and microstructural properties of pavement quality concrete using both Class-F fly-ash and copper slag

This research deals with the improvement in the mechanical properties of pavement quality concrete (PQC) when mixed with Class-F Fly-Ash (FA) and Copper Slag (CS) as replacements for ordinary Portland cement (OPC) and river sand (RS), respectively. Forty-eight different PQC mixes of M40 and M50 grades were prepared, in which RS is replaced by CS to the extent of 100%, and OPC is replaced by FA to the extent of 30%, with each replacement done at a certain increment. The combined effects of CS and FA on fresh and hardened concrete properties such as workability, density, water absorption, volume of voids, cube compressive strength, split tensile strength, flexural strength, cylinder compressive strength and ultrasonic pulse velocity (UPV) are experimentally investigated. All mixes containing up to 20% FA and up to 100% CS replacements showed increased strength compared with that of the control mix. The PQC mix containing 20% FA and 60% CS resulted in superior strength properties at a 90-day curing period. However, PQC mixes with 30% FA showed a decrease in strength properties with respect to the control mix. X-ray diffraction (XRD) and scanning electron microscope (SEM) studies were employed for the characterisation of selected PQC samples. Furthermore, multiple linear regression equations were established to predict all the strength parameters. The PQC mixes made with FA and CS provide superior strength, reduce waste disposal problems and preserve natural resources for future generations, making such developed mixes sustainable.