A group of scientists from China, the USA and the UK has reportedly proposed a novel approach to create smart cement in the Construction and Building Materials journal. For centuries now, cementitious composites have been used in the civil engineering industry. Although the central requirement of such materials mainly demands mechanical and physical properties such as durability, lately there has been increasing research in filling them with functional properties as well, thereby leading to the field of smart cementitious composites. Know more on the subject at SURFACES REPORTER (SR).
Understanding smart cementitious
Other than the various functionalities which are generally required by civil engineers, electrically conductive properties possess several benefits. It includes building health monitoring, electromagnetic shielding and de-icing capabilities. Smart cementitious composites can not only improve the resilience, safety and lifetime performance and carbon footprint of structures but also decrease maintenance costs. To understand their electrically-conductive additives for smart cementitious composites, several materials such as carbon black, carbon nanotubes, carbon fibers and graphene have been investigated. That being said, direct incorporation into the cementitious matrix has been the most commonly used approach in these studies.
The effect of incorporating these materials directly into the cementitious matrixes causes a decrease in electrical resistivity. There is a critical problem with this approach despite research and studies that have shown improvements by several orders of magnitude. The processes are costly, energy-intensive and time-consuming and the improvements come at the cost of the composite’s mechanical strength.
To achieve satisfactory electrical conductivity a large proportion of these materials is also required. Direct admixing will only cause increased viscosity and reduce the workability of the final mixture. This will affect the properties of durability and strength of the final hardened composites. To overcome this, a new method is required to thoroughly understand the potential of smart cementitious composites.
A new study has been proposed that can potentially overcome the issues with conventional admixing processes. In the field of materials science, achieving a low-cost method that would maintain the mechanical and physical properties of cementitious materials and also improve their electrical conductivity is a key concern. The study showcases fine aggregates that are coated with conductive graphene-based materials. In the first step, a uniform coating of graphene oxide had been applied to the sand and then annealed at 300 oC. To further reduce the coating to grapheme, microwave treatments had been employed.
The researchers evaluated the wettability and conductivity of graphene, graphene oxide, and reduced graphene oxide to learn the optimization of the process. Additionally, coating efficiency and the nano-materials’ effects on the aggregate particles’ physical properties had also been assessed. The researchers further analysed and assessed the mechanical strength, flowability, micro-structure and water sorption of the prepared cementitious mortars.
The outcome of the study demonstrated that the novel approach could produce cementitious composite mortars with necessary electrical properties without having a negative effect on the mechanical and physical properties of the final product. Instead of directly incorporating nano-materials into the mortar, coating the sand particles allows significant uses and benefits for producing smart cementitious composites. It also brings out enhanced self-sensing abilities and reduced electrical resistivity of the cementitious mortar.
An improved flowability had also been observed that addresses the issue with mortar viscosity faced by the conventional process. Also, no notable reduction in water absorption or mechanical strength had been observed. Nearly 62 per cent coverage of sand particle surfaces by graphene had been revealed through the SEM analysis where the average thickness of the coating was around 8.8 per cent. Further compressive testing also showed that the coating developed in the study gives the mortar dependable piezoelectric responses to compressive loading. Since the nano-coating method does not rely on binder chemistry, it can be implemented universally across different cementitious composites with conventional or non-conventional binder materials.
Image credits: Top The Constructor; Above General Electric (images for representational purpose)