Properties evaluation of concrete made with recycled coarse aggregate modified by graphene oxide

Previous application of graphene oxide (GO) in recycled aggregate concrete (RAC) is the direct replacement of cement or binder to achieve performance improvement. To develop a more efficient recycled aggregate (RA) modification technique and improve the properties of the corresponding RAC, this paper performed GO solution pre-spraying and pre-soaking treatment on RA. The modification efficiency of GO was evaluated by compressive strength, interfacial transition zone (ITZ) properties, and chloride ion permeability of RAC. The results show that the pre-spraying and pre-soaking methods improved the compressive strength of RAC at different ages by 20%–28.6 % and 8.3%–30.8 %, respectively. The GO-modified RAC also exhibited lower electric flux in the chloride ion permeability tests. However, no significant effect was observed on the elastic modulus of RAC. The modified RAC showed lower total porosity and harmful pore content. Meanwhile, the GO-modified ITZ between old and new mortar had denser hydration products. As a result, the elastic modulus and hardness of the ITZ increased by 27.8%–65.8 % and 9.8%–107 %, respectively, while the width of the ITZ decreased by 15.4%–30.8 %. The good filling and nucleation effect of GO were credited with the enhancement mechanism of RA by pre-spraying and pre-soaking methods.