Fabrication and characterisation of graphene oxide cement composites

Although ordinary Portland cement (OPC) is one of the most widely used construction materials in the world, its relatively weak tensile strength and proneness to cracks limit wider structural applications. Graphene oxide (GO) offers an interesting prospect of two-dimensional nanosheets in reinforcing OPC. Investigation of GO-reinforced cement composites is at a relatively early stage and very limited research into the effectiveness of GO in enhancing the tensile or flexural strengths of OPC is available. Thus there is a significant need for further studies in this area to understand the reinforcing behaviour of GO in cement matrix, including the dispersion of GO and the effect of GO on OPC paste in terms of mechanical properties, workability and microstructure. This study develops a fabrication protocol for the production of GO-paste and subsequently characterises the mechanical properties of the composite. Specifically, the objectives of this study are (1) to understand the procedure of preparing GO nanomaterial, (2) to study the dispersion behaviour of GO and (3) to investigate the role of GO in reinforcing cement matrix via mechanical properties and microstructural observations. As an emerging field of study, the procedure of incorporating GO nanomaterial into cement composites is yet to be established. During the production of GO, a two-step oxidation is applied to attach oxygen functional groups into the GO nanosheets. To ensure that GO is well dispersed in water as single-layered nanosheets, mild ultrasonication is supplied. The size distribution and dispersion quality of the GO produced is studied using zeta potential. This step is necessary to determine the optimal ultrasonication input, which is established as 15 J/mL. To develop high-performance GO-reinforced OPC paste, the dispersion of GO in water, alkali and aqueous solutions is studied. UV-vis confirms that only a mild sonication input is required for GO to be well dispersed in water. However, GO undergoes agglomeration when exposed to very alkaline solutions exceeding pH 13, highly concentrated ionic solutions, or in the presence of calcium ions. Therefore, the use of surfactants in the form of cement admixtures is crucial to protect GO against agglomeration. The incorporation of GO (of 0.02 wt.% of cement) substantially enhances the mechanical properties of plain cement. For example, the tensile strength is improved by 68.3% and flexural strength by 53.5%. These enhancements in the tensile and bending strengths may be attributed to the filling of GO in nano-sized colloidal pores and bridging over cracks. Moreover, a pore solution rich in calcium ions converts GO nanosheets into GO paper, producing stronger reinforcement. This project lays the foundation for other researchers and practitioners to better understand and apply the novel GO-cement composite with improved mechanical properties in the design of structures.