Investigation of using recycled powder from the preparation of recycled aggregate as a supplementary cementitious material

摘要

Considerable amounts of hybrid powder are produced when recycled aggregate is being prepared. An economic and environmental-friendly method of treatment is to take this recycled hybrid powder (RHP) as a sort of supplementary cementitious material for concrete and mortar. However, the application of RHP requires a deep understanding of its capacity and limitations, which relies on the clarity of properties possessed by the single powder contained in it. Therefore, in this study, the properties of recycled concrete powder (RCP) and recycled brick powder (RBP) as well as the impact of their incorporation on the mortar properties were investigated. The results showed that RBP had a lower negative impact on the workability of mortar than RCP due to its lower specific surface area and porosity. The water requirement ratios of RBPs and RCPs with different levels of fineness varied from 103 to 105% and from 110 to 114%, respectively. The activity indexes of RBPs reached the range between 82 and 87% at 90 days as a result of the pozzolanic effect, while those of RCPs varied from 72 to 78%. Moreover, RBP exhibited an excellent contribution to the flexural strength, which was ascribed to its favourable interfacial bonding with cement paste. Mercury intrusion porosimetry analysis also indicated that the addition of RBP led to a refined pore structure by reducing the average pore diameter. Notably, an improved shrinkage resistance was achieved by the incorporation of high-fineness RBP. A detrimental RCP particle-cement paste interfacial zone was observed in RCP-containing mortars, which was speculated to be an important reason for the appreciable decline in mechanical and durability-related properties. (C) 2020 Elsevier Ltd. All rights reserved.