Strength properties of ordinary Portland cement concrete containing high volume recycled coarse aggregate and volcanic ash

Abstract

Due to the increasing demand and declining reserve of natural coarse aggregate, waste recycling is one of the most viable options for sustainable development in concrete production. The paper assessed the compressive and tensile strength of ordinary Portland cement concrete containing high-volume recycled coarse aggregate (RCA) and volcanic ash (VA). Concrete of grade 60 was designed using the Department of Environment (DoE) method of mix design to produce concrete cubes of 100 × 100 × 100 mm and cylinders of 200 × 100 mm using a water/binder ratio of 0.35. The recycled coarse aggregate concrete (RCAC) was produced using ordinary Portland cement, 15% VA, 100% recycled coarse aggregate (RCA), natural fine aggregate and water while the conventional concrete was produced using ordinary Portland cement, natural fine and coarse aggregate, and water. The hardened concrete cubes and cylinders were subjected to compressive and tensile strength at 7, 14, 28, 56, and 90 days. The microstructure of the concrete samples was also evaluated. Results obtained from the study showed that the conventional concrete had higher compressive strength than the RCAC by 12.8% and 7.12% at 28 and 56 days respectively. However, at 90 days, RCAC attained higher compressive strength than conventional concrete by 1.5%. Similarly, the conventional concrete had higher tensile strength than RCAC by 12.87% and 6.45% at 28 and 56 days respectively. At 90 days, RCAC attained higher tensile strength than that of conventional concrete by 4.55%. Higher compressive and tensile strength improvement at 90 days exhibited by RCAC was due to the pozzolanic reactivity of VA which yielded additional calcium silicate hydrate (C-S-H) at a later age. It is recommended that up to 100% of normal coarse aggregate could be replaced with recycled coarse aggregate especially when pozzolanic material (VA) is to be added.