A number of different complex reactions occur during the hydration of cement that yields a porous, complex multi-phase, heterogeneous and amorphouscement paste matrix. The most important hydration product of the cement-based materials, Calcium Silicate Hydrates (C-S-H), is believed to be responsible for its cementitious properties such as hardness, cohesion, strength etc.,and hence is being considered as the genomic code of the cement-based materials. A comprehensive understanding of their chemistry (atomic structure) could lead to an improved control of their material properties at the nano scale. But the continuous changes that occur in the atomic structure of C-S-H with respect to time and environment make experimental investigation of its structure extremely difficult. However, certain characteristics of C-S-H are already unveiled, that it is a layered structure comprising Calcium and water molecules sandwiched between the tetrahedral silicate chains. Hence, a computational approach is sought in this work to investigate the atomic structure of C-S-H which in turn will help in understanding the related experimental studies. In this research work, as a start, the atomic structure of C-S-H is modeled with the help of atomic configurations of some naturally existing perfect crystals like Tobermorite, Jennite,etc., that have closer structural similarities with C-S-H. The mechanicalproperties (Poisson's ratio, Young's, Bulk, and Shear moduli) of C-S-H predicted with the help of Energy Optimization studies are in close agreement with the experimental data. It is evident from the computations that thelength of the silicate chains has a significant effect on the bulk properties of C-S-H. Possible atomic structures for C-S-H are also suggested. Further, this study provides avenues to investigate the configurations of low-density and high-density C-S-H structures.
Abstract