Abstract
In this paper, recycled bricks and recycled concrete were applied to prepare eco-friendly recycled mixed powder (RMP) cementitious material, as a supplementary to replace conventional cement for improve the recycling of construction and demolition waste. Based on the effect of cementitious materials on the hydration of silicate cement, the effects of RMP on the workability, mechanical properties and microstructure of recycled mixed powder concrete (RMPC) with the different replacement ratios and the 8:4 and 6:4 mixing ratio of recycled brick powder (RBP) and recycled concrete powder (RCP) were investigated. The results showed that the fluidity of the mix decreased with increasing of the replacement ratio and the mixing ratio of RBP and RCP, but the influence of the fluidity was smaller within 15% replacement ratio. As the replacement ratio increases, the internal pore structure of RMPC tends to be loose and porous, which exhibits a significant pore volume distribution characteristic. The number of large capillaries was considerably increased at replacement ratio of 45%. The 7 d compressive strength of RMPC was slightly lower than that of ordinary concrete. The compressive and splitting tensile strengths of RMPC at 28 d increased by 4.2% and 10.1%, respectively, with increasing curing age at 15% replacement ratio and 6:4 mixing ratio. The RMPC mechanical strengths with RBP and RCP at the mixing ratio of 6:4 was higher than those of 8:2. Finally, a basis for the recycling of RBP and RCP in the construction industry can be provided by the results of this study.
Highlights
With the rapid development of urbanization, a large amount of construction and demolition waste (C&DW), dominated by waste concrete and clay bricks, has been increased continuously [1–3]
The effect of recycled brick powder (RBP) fineness on concrete strength was studied by Zheng et al [12], and the results showed that the 28d compressive strength decreased by 4.25% when the RBP fineness was increased from 0.04 mm to 0.06 mm, and by 4.53% when the fineness was increased from 0.04 mm to 0.1 mm, under the condition that the RBP replacement ratio was 20%
The water demand ratio of RBP and recycled concrete powder (RCP) was tested by the standard GB/T 1596-2017 “Fly ash used in cement and concrete”
Summary
With the rapid development of urbanization, a large amount of construction and demolition waste (C&DW), dominated by waste concrete and clay bricks, has been increased continuously [1–3]. Recycled brick powder (RBP) ground from waste clay bricks was found to have favorable volcanic ash activity [8,9]. With the increase of hydration time the volcanic ash activity of RBP gradually increased and a large number of gels were produced to improve the pore structure, enhancing the late mechanical strength. The results of the literature [16,17] showed that the 28d compressive strength of mortar mixed with 15% RCP was increased by 30% and the bond strength by 6%, and the pore structure was refined and the compactness was improved compared to that of ordinary mortar. The volcanic ash activity of RCP is lower compared to that of the RBP, and the concrete mechanical strength decreases faster after the incorporation of RCP [8]. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were utilized to investigate the hydration properties and the microstructure evolution of RMPC, and the mechanism of the change of RMPC mechanical properties was revealed
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