Effect of graphene oxide on the hydration and microstructure of fly ash-cement system

Though graphene oxide (GO) can strengthen and toughen cement-based material and GO and fly ash (FA) can play a synergetic effect and offset the drawbacks of each other, the mechanism of GO on the hydration of FA-cement system is not clear and should be further investigated. In this paper, the effect of GO on the hydration heat evolution and hydration degree of FA-cement composite materials was characterized by isothermal calorimetry, non-evaporative water content, XRD, TGA and FA reaction degree test. The morphology and pore structure of hardened cement paste were characterized by SEM and MIP. The results show that GO at dosage of 0.01 wt% and 0.03 wt%, respectively, has a limited accelerating effect on the cement hydration at the early stage. However, it can affect the overall hydration of FA-cement system by accelerating the secondary hydration of FA at the later stage. The addition of GO also has a noticeable influence on the pore structure of hardened composite cement paste, decreasing the total pore volume and especially the volume of harmful pores. Meanwhile, the dosage of GO and FA can refine the CH crystal of composites, which is helpful to mutual binding between CH and CSH gel. These three factors including acceleration of the secondary hydration of FA, the modification of pore structure and refinement of CH crystal may contribute to the mechanical strength of composite GO-FA-cement system.