An Investigation on Interfacial Adhesion Energy Between Polymeric and Cellulose-Based Additives Embedded in C-S-H Gel

Shalchy, Faezeh

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An Investigation on Interfacial Adhesion Energy Between Polymeric and Cellulose-Based Additives Embedded in C-S-H Gel

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Concrete is one of the most widely used materials in the world. It is also one of the most versatile while complex materials which human have used for construction. However, an important weakness of concrete (cement-based composites) is its weak tensile properties. Therefore, over the past thirty years many studies were focused to improve its 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 the knowledge of fiber/matrix interfaces at the nanoscale. In this study, a combination of atomistic simulations and experimental techniques has been used to study the nanostructure of fiber/matrix interfaces. A new model for calcium-silicate-hydrate (C-S-H)/fiber interfaces is also proposed based on Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Finally, the adhesion energies between the C-S-H gel and three different polymeric fibers (polyvinyl alcohol, nylon-6 and polypropylene) were numerically studied at the atomistic level, since adhesion plays a key role in the design of ductile fiber reinforced composites. The mechanisms of adhesion as a function of the nanostructure of fiber/matrix interfaces are further studied and discussed. It is observed that the functional group in the structure of polymer macromolecule affects the adhesion energy primarily by changing the C/S ratio of the C-S-H at the interface and further by absorbing additional positive ions in the C-S-H structure. Then the mechanical response of cement paste with added polymeric fibers were studied. A correlation between adhesion energies and the load-displacement curve in split-cylinder test was found. Moreover, as there is a great interest in cellulose-based cement composites, bamboo fibers is added to the cement paste and the fiber/matrix interface and its effect on structure of C-S-H were investigated.

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