Effects of surface modified recycled coarse aggregates on concrete’s mechanical characteristics

Abstract

Sustainable concrete using recycled coarse aggregates from construction and demolition waste is gaining popularity in the construction industry, but has poor mechanical characteristics due to old cement mortar adhering to aggregate surfaces. This study uses two processes (abrasion treatment and cement slurry treatment) to modify the surface of recycled coarse aggregates (RCA) to minimize the strength loss of RCA and enhance the bonding properties of the concrete matrix and RCA. Surface-modified RCA replaced coarse aggregates in varying percentages, ranging from 0 to 100% in 25% increments. To comprehend the effects of surface-modified RCA, the workability, compressive strength, flexural strength, split tensile strength, microstructural characteristics (XRD, SEM, and EDAX), and modulus of elasticity of concrete are evaluated. Surface-modified RCA improves concrete’s mechanical characteristics, but abrasion-treated RCA has significantly greater strength than reference concrete up to 50% replacement level, while cement slurry treatment has slightly lower strength. Test findings reveal that among all the two processes of surface modifications of RCA, abrasion treatment is more effective and efficient. At 100% replacement level, surface-modified RCA by abrasion treatment reduces compressive, flexural, and split tensile strength by 10.89%, 10.42%, and 09.92% compared to reference concrete, while surface-modified RCA by cement slurry treatment reduces these values by 14.80%, 13.27%, and 12.76%. Surface modifications improve bonding properties of RCA and cement matrix, reducing porosity and resulting in dense and strong ITZs compared to unmodified RCA.

Keywords

• mechanical characteristics
• recycled coarse aggregates
• scanning electron microscopy
• surface modification
• x-ray diffraction