Towards engineering the epoxy and cementitious materials at the nanoscale

Abstract

The building block of our contemporary society is built upon civil infrastructures. The materials used to construct such infrastructure are adopted based on not only their properties but also their cost regarding finance and environmental impacts. To be able to set up a more efficient design of a structure, characterizing the behavior of existing materials and innovating new materials along with more sophisticated synthesis procedure are required. However, this process is extremely demanding concerning resources and knowledge, and accordingly, the use of computational approaches at the fundamental length scales is a rational way to acquire a more comprehensive insight into the material's behavior and properties. The use of epoxy and cementitious materials in the construction of new and repair of existing infrastructures has been growing dramatically over the past decades. The epoxies are amorphous materials, whereas Calcium-Silicate-Hydrate (C-S-H) as the binding phase of cementitious materials has a more complicated structural configuration and characterizing the mechanical behavior of each one requires the knowledge of molecular structure and dynamics that should be contemplated independently. For Epoxy, a methodology is developed to imitate cross-linking process between a resin and curing agent at the nano level, and then the effect of such curing is studied. The improvement of bulk properties of epoxy due to the formation of interconnected networks is noted. Furthermore, the effect of moisture on the degradation of the epoxy network is explored. In the second part, C-S-H as a main binding phase in cementitious materials is studied using free energy perturbation (FEP) method. The atomic structures of C-S-H with various constituent ratios are built, and the source of cohesion between the layers of crystalline and glassy C-S-H at the molecular level in the presence of entropic effects is studied. Since C-S-H layers can be treated as granular objects, a novel global free energy landscape is developed which buries in itself the effect of surface roughness during sliding. It is expected that introducing a new generation of the potential of mean force which involves the sliding component will light the path toward a more comprehensive modeling approach for granular materials.