Influence of graphene oxide as dispersed phase in cement mortar matrix in defining the crystal patterns of cement hydrates and its effect on mechanical, microstructural and crystallization properties

In the present investigation, graphene oxide (GO) was prepared using oxidative treatment of graphite by Hummer's method. The synthesized graphene oxide (GO(a)) was characterized by FTIR, SEM/EDS, TEM, XRD, TGA and AFM. Size-reduction of GO(a) (which had a 14 nm sheet thickness and 900 nm average sheet size) was done using planetary ball milling, which produced GO(b) with a sheet thickness of 3 nm and an average sheet size of 100 nm. The effectiveness of GO(a) and GO(b) nanosheets at different dosages (by wt% of cement) in the improvement of mechanical strength of cement mortar matrices has been evaluated, and explained on the basis of microstructural analysis using FE-SEM observations, as well as from crystallization patterns using XRD patterns of GO-cement nanocomposites (GO-CNCs). Well-defined crystal growths of cement hydrates were observed, as revealed by FE-SEM micrographs, and crystallization patterns were found to be dependent upon factors such as the type of GO nanosheets, the concentration of GO and the curing time. The as-synthesized GO(a) (1% by weight of cement) enhanced the compressive strength of composites by a maximum of 63%, whereas the size-reduced GO(b) (1% by weight of cement) promoted better crystalline structures with a maximum strength enhancement of 86%. The present research work aimed to enhance GO reactivity by increasing its exfoliation and its count by mechanical milling, and to exploit it as a low-cost dispersed phase which has different sheet thicknesses and sheet sizes, for the strength enhancement of cementitious matrices by regulating crystal patterns and microstructural features.