High-Strength Concrete Containing Recycled Aggregate Treated by Using Carbonation Technique.

This research aims to investigate the compressive strength, modulus of elasticity and drying shrinkage of high-strength concrete using cement and fly ash as a binder at a ratio of 75:25 by weigh. Natural coarse aggregate (NCA) was replaced by recycled coarse aggregate (RCA) which was improved its physical properties by carbonation process. There were 3 methods to enhance RCA quality as follows: 1.) recycled coarse aggregate was directly cured by (RC), 2.) recycled coarse aggregate was soaked in calcium carbide solution and then cured with (RCC), and 3.) recycled coarse aggregate was soaked in calcium carbide mixed with fly ash solution and cured with (RCCF). Treated aggregates from all methods were cured with at the ages of 1, 3 and 7 days. RCA having the best physical properties from each method was used as a coarse aggregate in the concrete. The results showed that all methods had potential for improving RCA from curing period of 1 day whereas the curing period of 7 days exhibited the best physical properties. It is noted that RCCF method was the best process to enhance properties of RCA. The compressive strengths of concretes containing treated RCA (RC, RCC and RCCF) at 28 days were higher than that of concrete containing untreated RCA by 6, 12 and 14% and the elastic modulus was increased by 2, 5, and 9%, respectively. Additionally, drying shrinkage of the concrete was reduced with the use of carbonation-enhanced RCA aggregates.