Concrete is the most widely used construction material all over the world. Constant efforts are going on to enhance the physio mechanical and chemical properties of concrete material. This is done by nanoengineering the properties of 'cement' which is one of the most important component of concrete.
Functionalization of cement using nanomaterials are performed for mechanical reinforcement, fabrication of self cleaning materials and for reducing the environmental pollution. A work published by Dimov et al. in Advanced functional materials clearly explains about the mechanical reinforcement of cement by graphene. They developed graphene suspension in water from graphite flakes using high shear blending. The produced graphene suspension was then mixed with cement, dry sand and coarse aggregate. The mixing ratio of cement, dry sand and coarse aggregate was 1:2:3 respectively. After proper mixing the so formed concrete paste was fixed in molds for making concrete cubes. They were then removed from the mold after 24 hours and then immersed in water for curing.
The role of graphene in reinforcing concrete
The mechanical properties of concrete materials are commonly evaluated by measuring their uniaxial compressive strength and flexural strength. In order to evaluate the reinforcing nature of graphene, the mechanical properties of graphene-concrete composite were compared with standard concrete. For that, cubes and beams of graphene-concrete composite and standard concrete were developed. The compressive strength evaluation was performed using cubes of dimension 10×10×10 cm. The stress vs strain curve plotted during uniaxial compression testing demonstrated that graphene-concrete composites exhibited a steeper elastic region in the curve compared to that of standard concrete. This indicates the higher stiffness of graphene-concrete composite compared to standard concrete. The flexural strength is measured using a three point bending test performed on concrete beams of dimension 10×10×400 cm. The stress vs strain graph obtained for flexural evaluation has also shown an increment in mechanical property for the graphene-concrete composite.
Cement is a mixture of calcium, aluminium, silicon, iron etc. Upon reaction with water cement forms calcium silicate hydrate (C-S-H) gel which is one of the major reasons behind the mechanical property of concrete. Graphene can interact with various elements forming this gel structure. This interaction causes alteration in morphology of the hydration crystals. The high surface energy of graphene causes binding with the C-S-H gel particles and thus acts as the nucleation sites. The growth of the C-S-H gels along the graphene flakes results in the enhancement of bond strength of cement.
The role of graphene in altering the water permeability of concrete
The extent of fluid penetration is one of the important parameters determining the durability of concrete material. The water permeability of graphene-concrete composite was evaluated by immersing in water and then compared with that of standard concrete. It was found that the graphene-concrete composite acts as a barrier against water infiltration. This strengthens the water resistance and there by durability of concrete material.
Reference : https://doi.org/10.1002/adfm.201705183