Graphene-engineered cementitious materials: a systematic experimental study = Materiali cementizi ingegnerizzati con grafene: uno studio sperimentale sistematico

Cement-based composite materials (CBCMs), including mortar and concrete, are the most common and widely used materials in construction. Ordinary Portland cement (OPC) is known as a principal constituent of CBCMs acting as a binder for the other aggregates presented in the CBCMs. The quasi-brittle behavior, low toughness, and poor tensile strength of these materials are of major concerns since they are responsible for poor durability and high maintenance costs. In the last decade, on the way of the rapidly growing interest toward nanotechnology, several researchers proposed an approach based on the interaction at the nanoscale level between the cement matrix and selected nanostructures that might result in macroscopical advantageous effects. For this purpose, graphene-based materials, including graphene nanoplatelets (GNPs), nano graphite platelets (NGPs), and graphene oxide (GO), have been proposed to offset the brittleness of the CBCMs. The main objective of this PhD research work is to develop graphene-based cementitious composites (GBCCs) using low cost and commercially available graphene nanoplatelets (GNPs), nano graphite platelets (NGPs), and graphene oxide (GO). The project further investigated the effect of these nanomaterials on the rheology, microstructure, mechanical, and physical properties of a commercial premixed mortar at both early (7 and 14 days) and later ages (28 days). A full set of graphene engineered cementitious composites has been prepared using EN-998-2 premixed mortar as matrices, two GNPs water pastes, one NGPs powder, and two GO (one water suspension and one powder). The actual impact of the different GBMs and their dosage (i.e.0.01, 0.1, or 0.2% by weight of cement) was assessed in terms of rheology of fresh admixtures along with density, microstructural features, permeability (i.e .initial surface absorption, water contact angle, volume of permeable voids and chloride ion diffusion), physical properties (i.e. thermal and electrical conductivity, damping ratio) and mechanical properties (i.e. flexural and compressive strength) of the hardened nanocomposites. It is concluded through various characterization and experimental campaigns that all GBMs regulated the microstructure of the cementitious composites along with the densification and influenced the permeability, physical, and mechanical properties of GBCCs uniquely. A significant improvement in the permeability, physical, and mechanical properties of newly developed GBCCs has been achieved, and that could be due to the generation of distinctive microstructure generated by the pozzolanic behavior of these nanofillers. Based on the observations of test results and comprehensive characterization, the possible mechanisms of permeability barriers, conductive pathways, and microstructure developments of GBCCs have been established.