Graphite-enabled Cementitious Composites: A Smart and Resilient Solution for Future Infrastructure
Concrete, as the most widely used construction material on Earth, is one of Earth’s most versatile, strong, and affordable materials. However, concrete infrastructure tends to degrade with extended service life due to environmental and mechanical impacts. Carbon-based materials have been incorporated into a cement matrix as conductive fillers to develop an intrinsic self-sensing concrete to monitor structures without the need for embedded, attached, or remote sensors while maintaining or improving its mechanical properties and durability. Graphite is a particularly attractive filler to use in practical engineering due to its good conductivity and low cost. The aim of this study is consequently to develop, through material characterisation techniques, experimental testing and numerical modelling, self-sensing cementitious composites for resilient smart infrastructure by embedding graphite into cementitious materials. Material characterisation experiments were firstly systematically conducted to determine the optimal material proportion and investigate the dispersion, rheology, micro-structural, chemical, mechanical, electro-conductivity and piezoresistivity properties of the graphite-cement composites. Results showed an effective mixing with a uniform dispersion of the graphite with good hydration, adequate workability and enhanced strength of the composites with graphite concentrations up to 10%. A novel measurement technique has been successfully developed to accurately measure the composites with the time, loading, displacement, electrical properties and Digital Image Correlation data synchronised to one file controlled by Python codes. Through numerical simulation, an equation for the relationship between the measured electrical resistance and the sample geometry variables has been proposed for the first time to provide design guidance for the measurement techniques. Electro-mechanical tests were conducted to investigate the piezoresistivity and damage-sensing performance of the developed cementitious composites with low graphite content. Test results indicated a stable and reliable piezoresistive performance with high stress and strain sensitivities in its elastic range. Moreover, the electrical signals showed noticeable changes with accumulative cracks developed in all directions, which can be used to indicate the plastic deformation and damage of the cementitious material and thus provide a pre-failure warning. Cementitious composites with all tested graphite concentrations (≤ 10%) have presented stable sensing performance. Experiment and numerical simulations were further conducted on old plain concrete samples to explore and validate the possibility of achieving self-sensing on as-built concrete structures. It was found that provided with simple and cost-effective measurement techniques, plain concrete itself is already self-sensing without the addition of expensive conductive fillers. This is extremely promising to be applied to practical engineering for structural health monitoring. The outcomes of this study have significantly advanced the state of the art in smart cementitious construction materials and will help to deliver a safer and more resilient future infrastructure and built environment.
Cementitious composites, Finite Element Modelling, Graphite, Self-sensing, Smart infrastructure, Structural health monitoring
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