Study on the essential properties of recycled powders from construction and demolition waste

Recycled fine aggregates and waste powders can be ground into ultrafine powders, defined as recycled powders (RPs), for effective utilization of construction and demolition (C&D) waste. However, the performance of RPs relies on their original sources, the complex components of which hinder their applications. In this study, six common types of RPs were prepared from different sources of C&D waste with their properties comparatively examined in detail, including the chemical composition, micro morphology, fineness and hydration heat. Subsequently, the water requirements of standard consistence and setting time of pastes incorporating different RPs, together with the flowability and mechanical properties of the corresponding mortars were investigated. The results showed that the irregular and rough shapes of RPs required higher water consumption to achieve a standard consistency of paste. The higher alkali-content and lower content of SO₃ of RPs contributed to the higher heat evolution rates of pastes with RPs in the first 30 min, but the pastes with RPs exhibited lower cumulative hydration heats than cement after 1d. The additional use of RPs decreased the flowability, density and strength of mortar. The mixed brick powder and clay brick powder had the relative positive impact on the mechanical properties of mortar at later ages, illustrating their great potential for use in cement matrix. The maximum reduction of strength was about 20% when the replacement ratio was limited to 30%.