Cement is one of the most consumed materials in the world. The cement industry is responsible for a large portion of global carbon dioxide emissions. Cement production and therefore carbon dioxide emissions can be decreased by increasing the durability and enhancing the mechanical properties of cement-based materials. On the other hand, an important weakness of concrete is its weak tensile properties, which are the main reasons for its failure and low durability. Therefore, over the past 30 years, many studies have focused on improving tensile properties using a variety of physical and chemical methods. One of the most successful attempts is to use polymer fibers in the structure of concrete to obtain a composite with high tensile strength and ductility. However, a thorough understanding of the mechanical behavior of fiber-reinforced concrete requires knowledge of fiber cement interfaces at the nano scale. In this study, a combination of experimental and molecular dynamics (MD) techniques is used to study the nanostructure of fiber cement interfaces. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis are used to obtain a better understanding of the C-S-H fiber (in cement chemistry notation, C = CaO, S=SiO2, and H=H2O) interfaces. The results show that the C/S ratio changes in the interface of cement and polymeric fibers and is largely affected by the functional group of the polymers. The results are then used to propose a more realistic molecular dynamics model for C-S-H in the vicinity of the three most used polymeric fibers: polypropylene, polyvinyl alcohol, and nylon-6. The full atomistic simulations show that the molecular structure of C-S-H at the interface depends on the properties of the polymer functional group. The adhesion energy between the polymeric fibers and the relevant C-S-H structure is then computed using atomistic simulations. The adhesion energy between C-S-H and polymers increases with the polarity of the fiber. The mechanical response of cement paste with added polymeric fibers is then experimentally studied using the split-cylinder test. The experimental results further show that the adhesion energies between the fibers and cement increase as a function of the polarity of the fibers
