Fundamental physical properties of graphene reinforced concrete.

Abstract

The global warming has increased with unprecedented levels during the last couple of decades and the trend is uprising. The construction industry is responsible for nearly 10% of all carbon emissions, mainly due to the increasing global population and the large demand for housing and civil infrastructure. Concrete, which is the most used construction material worldwide, is found in every type of building as it provides long term structural stability, support and its main constituent cement, is very cheap. Consequently, due to the raising concerns of high average temperatures, the research community started investigating new, innovative methods for substituting cement with 'greener' materials whilst at the same time improving the intrinsic properties of concrete. However, the manufacturing complications and logistics of these materials make them unfavourable for industrial applications. A novel and truly revolutionary method of enhancing the performance of concrete, thus allowing for decreased consumption of raw materials, lies in nanoengineering the cement crystals responsible for the development of all mechanical properties of concrete. Graphene, a two-dimensional sheet of carbon atoms arranged in a hexagonal lattice, is the most promising nanomaterial for composites' reinforcement to this date, due to it's exceptional strength, ability to retain original shape after strain, water impermeability properties and non-hazardous large scale manufacturing techniques. I chose to investigate the addition of liquid-phase exfoliated graphene suspensions for concrete reinforcement, aiming to improve the fundamental mechanical properties of the construction material and therefore allowing the industry to design buildings using less volume of base materials. First, the method of liquid exfoliation of graphene was developed and the resulting water suspensions were fully characterised by Raman spectroscopy. Then, concrete samples were prepared according to British standards for construction and tested for various properties such as compressive and flexural strength, cyclic loading, water impermeability and heat transport. A separate, in-depth, study was carried out to understand the formation and propagation of micro-structural cracks between the concrete's internal matrix planes, and graphene's impact on total fracture capacity and resistance of concrete. Lastly, multiple experiments were performed to investigate the microcrystallinity of cement hydration products using X-Ray diffraction. In general, all experimental results show a consistent improvement in concrete's performance when enhanced with graphene on the nanoscale level. The nanomaterial improves the mechanical interlocking of cement crystal, thus strengthening the internal bonds of the composite matrix. This cheap and highly scalable method for producing and mixing graphene with concrete turns it into the first truly applicable method for industrial applications, with a real potential to have positive impact on the global warming by decreasing the production of concrete.