Enhancing the elastic modulus of concrete prepared with recycled coarse aggregates of different quality by chemical modifications

Abstract

Due to the presence of attached old mortar in recycled concrete aggregate (RCA), the elastic modulus of the prepared recycled aggregate concrete (RAC) is generally lower than that of normal concrete, which limits the application of RAC as structural concrete. To improve the elastic modulus of RAC, three different chemical modification methods, including fly ash-silica fume (FS) slurry, nano-SiO2 (NS) solution and carbonation modifications, were carried out in this study. RCAs of different quality were used to verify the applicability of the three methods. The SEM and XRD tests were used to reveal the modification mechanism. The results show that the elastic modulus of RAC can be improved by any of the proposed chemical modification methods, among which the effect of the FS slurry is the most significant with the growth rate of 7.56%–10.56% in terms of different RAC. The modification effect of different methods on the elastic modulus of RAC, which is similar with the corresponding peak stress, is consistent with that on the quality of recycled aggregate. The SEM and XRD results show that the modified RAC has less micro-pores, denser interfacial transition zone and hydration products, which are also the main reasons for the improvement of the elastic modulus.