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Recycled concrete aggregates (RCAs) have inferior qualities compared with natural aggregates, mainly attributed to the porous nature of the attached cement mortar. To improve the quality of the RCAs, an environmentally friendly and cost-effective method is proposed to treat RCAs in this study. In this method, RCAs are first soaked in acetic acid solution, in which the acetic acid reacts with cement hydration products attached to the surface of the RCAs. This reaction weakens the attached mortar, making it possible to remove it from the RCAs by mechanical rubbing later. The treated RCAs have lower water absorption and less cement mortar attached. Once used as aggregates in new concrete, these RCAs can enhance the compressive strength of the concrete at 28 days up to 25%. It is safe and clean to apply this new method since no dangerous chemical is used and no detrimental chemicals are introduced into the treated RCAs. More importantly, zero hazardous waste solution is generated since the waste solution of the treatment can be used to produce high value-added products, permanently store CO 2 , and regenerate acetic acid. As an example, the waste solution of the treatment was used as admixture for new concrete, which improved the strength of the concrete by 14%. [ABSTRACT FROM AUTHOR]

The sol–gel method was applied to synthesise xerogels of C2AS and C2S at ambient temperature. Then they were thermally treated at 600, 900, 1100 and 1250°C and the crystallisation of C2S and C2AS was characterised using X-ray diffraction (XRD). The evolution of the heat of hydration of these samples was investigated at 70°C using a conduction calorimeter. The microstructure of the samples, separately cured under hydrothermal conditions (7 days at 70°C), has been examined by means of SEM. Calorimetric measurements of hydration heat evolution showed that C2AS and C2S, synthesised via sol–gel method are much more active during hydration than their related clinker minerals synthesised by the conventional method. Furthermore, hydration activity of samples depends chiefly on calcination temperature. While C2S calcined at 900°C has the most intense hydration rate, C2AS has the same aspect when calcined at 1100°C. The hydration products of C2S, heat treated at 600°C, are well crystallised as characterised by XRD analysis. Large gehlenite hydrate crystals were observed to form during the hydration C2AS prepared via sol–gel processing. [ABSTRACT FROM AUTHOR]