Effect of moisture condition and brick content in recycled coarse aggregate on rheological properties of fresh concrete

The effect of moisture condition and recycled brick aggregate (RBA) content in recycled coarse aggregate (RCA) on the rheological properties of recycled aggregate concrete (RAC) was examined in this study. Empirical workability parameters like slump and slump flow, as well as the rheological parameters including dynamic yield stress, plastic viscosity and static yield stress, were detailed investigated in 45 min after mixing. Besides, the relationship between rheological parameters and empirical workability parameters was also analyzed. The results showed that RAC performed greater effect on the time variable characteristics of rheological properties when compared with normal concrete. The change rate of rheological properties of RAC made with RCA in air-dry condition was lower than that of RAC made with RCA in either oven-dry or saturated surface-dry conditions. The empirical test results on both slump and slump flow of fresh RAC fitted well with the corresponding dynamic yield stress calculated by the rheological test results. The rheological results of RAC without RBA all had a greater change in the first 45 min than that of RAC with 10%-30% RBA. RBA had limited effect on the time variable characteristics of rheological properties of fresh concrete due to the ultra-high water absorption rate in the 1st min after contacting with water.