A mix design method for self-compacting recycled aggregate concrete targeting slump-flow and compressive strength

Abstract

If waste concrete and excavated engineering soil can be recycled into self-compacting concrete, it could not only alleviate the shortage of natural resources but also realize the sustainable development of self-compacting concrete technology. Therefore, a novel method is proposed for designing self-compacting recycled aggregate concrete (SCRAC) mix. The method is developed by target slump-flow and target compressive strength, avoiding tedious adjustments and laboratory re-testing at the concrete level. The proposed method first determines the contents of natural and recycled coarse aggregate based on the target slump-flow and those of natural and recycled sand are then obtained. Then, the required effective water-cement ratio is calculated based on the target compressive strength. The required admixture content is determined based on the paste rheology. Eleven mixtures designed in this manner were cast and tested. The tested variables included the target slump-flow, target compressive strength, replacement ratio of recycled coarse aggregate (RCA) and recycled sand (RS) from the excavated engineering soil, and coarse aggregate size. The results showed that the proposed method was applicable to SCRAC with a 600–800 mm target slump-flow, 40–60 MPa target compressive strength, 0–100% RCA, 0 and 100% RS, and 5–10, 5–16, and 5–20 mm coarse aggregate sizes. Finally, SCRAC using the RCA and punching residues was successfully fabricated to further verify the feasibility of the proposed method. The proposed method provides design guidance for self-compacting concrete containing RCA and RS obtained from excavated engineering soil.