Hydration of Concrete Containing Hybrid Recycled Demolition Powders

Abstract

If not properly managed, the hybrid powders produced during recycling mixed construction and demolition (C&D) materials will present a serious hazard to the environment and human health. Recent studies have found that a potential green way to reuse these powders is to add them as a cement replacement in concrete. In this study, the mechanisms of the concrete–clay brick hybrid recycled powder (CB-HRP) in cement hydration have been comprehensively investigated by utilizing isothermal calorimetric test, Raman spectroscopy measurement, and nanocharacterization including atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging analysis. Based on its behavior in heat generation, it is found that the CB-HRP serves as a filler material in concrete that exhibits a higher heat of wetting than normal portland cement. In the Raman identification, the spectrum of concrete containing the CB-HRP is compared with that of the benchmark samples. It is noticed that the calcium–silicate–hydrate (C─ S─ H) peak in the spectrum, which is absent in over two-thirds of the samples made of normal concrete, appears in all the samples containing the CB-HRP. In the SEM scan, the backscattered electron (BSE) technique was used to probe the distribution of different phases in concrete microstructure. Based on the contrast image, it is found that C─ S─ H phase and calcium hydroxide (CH) phase are precipitated along the boundary of the CB-HRP. This is further confirmed by the modulus profile and phase distribution obtained by the AFM characterization. The present investigation shows that the CB-HRP will promote the cement hydration by serving as a precipitation host.