Sustainable normal and high strength recycled aggregate concretes using crushed tested cylinders as coarse aggregates

- The research program was designed to investigate the fresh and hardened properties of normal and high strength recycled aggregate concretes.
- The recycled coarse aggregates (RCA) were sourced from tested and crushed concrete cylinders.
- Attaining a recycled aggregate concrete mix while reusing tested cylinders would have positive economic and environmental implications.
- Results indicated that the replacement of NCA with different percentages of RCA did not have negative effect on the consistency of fresh concrete.
- Average reductions of around 10% were recorded for all tested hardened properties relative to the control mix for both NSC & HSC mixes.

The paper reports on a research program that was designed at the American University of Beirut (AUB) to investigate the fresh and hardened mechanical properties of a high performance concrete mix produced with partial or full substitution of crushed natural lime-stone aggregates with recycled aggregates from crushed tested cylinders in batching plants. Choosing crushed cylinders as source of recycling would result in reusing portion of the waste products of the concrete production industry. An extensive concrete batching and testing program was conducted to achieve two optimum normal and high strength concrete mixes. The variables were the nominal concrete strength (28 or 60 MPa) and the percentage replacement of natural coarse aggregates with recycled aggregates from crushed tested cylinders (0, 20, 40, 60, 80, or 100%). Normal strength tested cylinders were used as source of the recycled aggregates for the normal strength concrete (NSC) mix and high strength tested cylinders were used for the high strength concrete (HSC) mix. Tests on the trial batches included plastic state slump and hardened state mechanical properties including cylinder compressive strength, cylinder splitting tensile strength, modulus of elasticity, and standard beams flexural strength. The results indicated no significant effect on the slump and around 10% average reduction in the hardened mechanical properties for both investigated levels of concrete compressive strength.