Rheological and early hydration of cementitious material containing recycled concrete powders collected from recycled aggregates

Abstract

Recycled aggregate (RA) is the primary approach to treatment and utilization of construction and demolition waste in China. During RA preparation, many finer powders with sizes smaller than 0.15 mm are produced compared with those of the natural aggregate preparation, which further reduces the RA quality. Direct separation and individual use are expected to improve the performance of RAs and develop their potential applications in fine powders. Recycled concrete powders with sizes smaller than 0.15 mm (recycled coarse powder, RCP), 0.075 mm (recycled medium powder, RMP) and 0.045 mm (recycled fine powder, RFP) were collected. The rheological and early hydration of cementitious materials containing different volumes of RCP, RMP, and RFP were investigated. The incorporation of RCP decreased the yield stress and plastic viscosity of the cement paste and improved the workability of the slurry, whereas the incorporation of RMP and RFP increased the yield stress and reduced the fluidity of the cement paste compared to that of the pure cement sample. The time-dependent properties of the rheological parameters indicated that the cement paste containing RCP exhibited shear-thinning properties, whereas those incorporating RMP and RFP displayed shear-thickening characteristics. The addition of RMP and RFP increased the initial heat of dissolution of the cement paste and caused the cumulative heat release in 24 h to exceed that of pure cement paste. The effect of RFP on the hydration products and microstructure of the cement paste resulted in mechanical properties comparable to those of mortar without recycled concrete powder.