Performance of Recycled Concrete Aggregates (RCA) in Concrete Mix Design

Abstract

This thesis explores the possibility of using recycled concrete aggregate (RCA), derived from demolished structures, as a sustainable alternative to natural aggregates in concrete mix design. The objective is to evaluate whether RCA serves as an alternative to develop sustainable concrete which can sustain satisfactory performance of conventional concrete. Four new concrete mixture designs in which RCA can be used as a replacement of natural aggregates at 0%, 25%, 50% and 75% by volume are examined in the research. The concrete samples went through compressive strength test, and their durability was evaluated by freeze-thaw and salt-water exposure. RCA mixes resulted in an increase in porosity and surface cracking under repeated freezing cycles, making the test particularly important. The study also includes the process of making concrete mixtures and molds, highlighting the properties of RCA during the mixing and compaction stage. The results show a notable decrease in compressive strength as the proportion of RCA increases. Moreover, the study found that due to delayed hydration, higher RCA ratios required longer time to achieve their full strength. Freeze-thaw testing showed greater initial scaling in RCA mixes, but not over longer cycles. This indicates that, while RCA is more vulnerable early, its long-term performance under freeze-thaw may not be inferior due to high porosity. Additionally, the weight and density of concrete were reduced by approximately 15% at a 50% replacement level, indicating potential benefits for lightweight concrete applications. These findings provide valuable insights into the viability of RCA in sustainable concrete production, particularly for non-structural or low-load application.