Behaviour of Slag-Fly Ash Based Geopolymer Concrete with Graphene Nanoplatelets

The carbon dioxide emission from the production of ordinary Portland cement (OPC) industry is a major concern for the construction industry. The use of alternative materials to OPC is a feasible approach to meet the demand for concrete infrastructure development without compromising its strength and serviceability performances. In previous research studies, binders formed by the alkaline activation of aluminosilicate materials are usually termed as ‘Geopolymer binders’. The by-products such as ground granulated blast furnace slag (GGBFS) from iron industries and fly ash (FA) from coal combustion power plants as aluminosilicate sources are commonly used to form geopolymer binders. The additional environmental benefit, by using these aluminosilicate materials to from geopolymer concrete, is the reduction of chemical hazard which could happen by dumping these by-products to the ground. The geopolymer concrete manufactured from these materials can provide adequate strength and serviceability for the concrete structures. The addition of nanoparticles in concrete enhances the strength and serviceability characteristics of concrete. In this study, the graphene nanoplatelets are used to improve the fresh and hardened state properties of slag-fly ash-based geopolymer composites. The ambient curing condition is adopted throughout this study. The commercial grade graphene nanoplatelets are added to the geopolymer composites. The poly carboxylate ether-based high range water reducer admixture is used for the dispersion of graphene nanoplatelets and to improve the workability of geopolymer composites. In this study, firstly, the effect of adding different percentages of graphene on the workability and strength of geopolymer paste and mortar are examined. The addition of graphene improved the compressive strength of geopolymer paste and mortar without any detrimental effect on the workability of geopolymer composites. Secondly, graphene is added to the geopolymer concrete to investigate the mechanical properties such as compressive, flexural, splitting tensile and direct tensile strengths of geopolymer concrete with graphene. The mechanical properties of geopolymer concrete with graphene are compared with the mechanical properties of geopolymer concrete without graphene. The addition of graphene enhanced the mechanical properties of geopolymer concrete. The direct shear strength of geopolymer concrete without and with graphene is investigated using a simple method developed in this study. The available methods in the literature to determine the direct shear strength of concrete had some limitations and inconsistencies. Therefore, a new method is developed to determine the direct shear strength of concrete. The direct shear strength of geopolymer concrete without and with graphene are determined by using the developed method. It is found that the addition of graphene enhanced the direct shear strength of geopolymer concrete and provided higher shear strength than the shear strengths of OPC concrete without and with graphene. The design life of reinforced concrete structures is influenced by the bond strength of steel reinforcement in concrete. The pull-out tests are performed to determine the effect of graphene nanoplatelets on the bond strength of steel bars in geopolymer concrete without and with graphene. The steel bars of different diameters are used to examine the effect of graphene on the bond strength. The addition of graphene improved the bond strength of geopolymer concrete. The durability characteristics of geopolymer concrete are also examined without and with the addition of graphene. The tests are conducted to observe the resistance of geopolymer concrete against severe chemical attacks including sulphuric acid, resistance against chloride penetration and water absorption. The addition of graphene enhanced the durability characteristics of geopolymer concrete. The addition of graphene in slag-fly ash-based geopolymer concrete significantly improved the properties of geopolymer concrete and is recommended for practical applications in the construction industry. The benefits would be reductions in carbon dioxide emissions, environmental sustainability and improved strength and serviceability of the concrete structures.