Properties enhancement of recycled aggregate concrete through pretreatment of coarse aggregates – Comparative assessment of assorted techniques

In this study, the intrinsic properties of recycled coarse aggregates (RC), associated with bonded mortar, were modified with two different pretreatment techniques viz-a-viz HCl pretreatment and Na₂SO₄ pretreatment, while maintaining a fixed aggregate-to-solution ratio of 1:4.5. The residual bonded mortar was quantified to evaluate the potential of both techniques. HCl pretreatment yielded greater removal of bonded mortar content (BMC), almost twice as high as achieved by Na₂SO₄ pretreatment. Subsequently, the concretes were developed (termed as recycled aggregate concrete; RAC) by incorporating HCl treated coarse aggregates (HTC) and Na₂SO₄ treated coarse aggregates (STC). Both natural and recycled (untreated) fine aggregates (NF and RF, respectively) were used. Control specimens with natural coarse aggregates (NC) were prepared for comparative assessment. The resulting properties showed significantly influenced by bonded mortar content (BMC). About 14% higher compressive strength was achieved by using HTC in comparison with untreated RC, while a mere corresponding decline of 5% was seen when compared with NC. Likewise, the carbonation resistance and the resistance to chloride ion penetration showed better performance for HTC and STC incorporated concretes. Such superior performance is attributed to the denser interface (between the aggregate and paste matrix) with reduced pores/voids, as assessed from the optical and scanning electron microscopy. Further, the determined properties were used to develop regression models for the prediction of RAC properties. The prediction equations thus obtained showed remarked precision with the experimentally determined results, and as such these can be used for strength and durability prediction.