Aggregate presaturation and concrete mixing technique for upscaling the use of fine recycled concrete aggregate

Abstract

The porous structure of fine recycled concrete aggregate (FRCA) affects the properties of concrete and limits its use beyond 30 %. This study aims to improve the quality of concrete prepared with 100 % FRCA. Past work confirmed that the aggregate saturation level and concrete mixing methods influence the performance of FRCA concrete. To upscale the use of FRCA, a new modified presoaking method for mixing FRCA concrete is proposed, along with assessing the effect of three saturation levels (50 %, 75 %, and 100 %) and four mixing methods: conventional, presoaking, two-third presoaking, and modified presoaking. The compressive strength, flexural strength, static and dynamic modulus of elasticity, and the density of the interfacial transition zone (ITZ) were examined. Results showed that concrete with partially saturated FRCA exhibited better mechanical properties. The modified mixing method provided consistent results and an ITZ with lesser void content, indicating higher reliability than the conventional, presoaking, and two-third presoaking methods. At a 50 % saturation level of FRCA, the results for the modified presoaking method showed higher compressive strength, flexural strength, static, and dynamic modulus by 10 %, 9 %, 12 %, and 20 %, respectively, in comparison to concrete mixed by a conventional method consisting of 100 % saturated FRCA. This work provides clarity on appropriate processes and practices for the utilization of FRCA in concrete and facilitates a circular economy in the construction industry.