Albeit concrete’s ubiquitous presence in our built environment, our knowledge of elementary processes affecting its macroscopic properties is rather limited. To achieve deeper levels of understanding, it is imperative to uncover the true molecular structure of calcium-silicate-hydrates (C-S-H), the binding phase of cement paste responsible for its strength and durability properties. In this work, we discuss the co-existence of C-S-Hs of different molecular structures at a given stoichiometry from the viewpoints of the atomistic simulations. To this end, we propose a statistical physics-based approach to construct realistic models for C-S-H. Subsequently, we employ high-throughput combinatorial simulation framework to construct a database of realistic C-S-H models with calcium-to-silicon ratio (C/S) between 1.1 and 2.1. This finding has broad implications on the correlation between chemistry and physical properties of cementitious materials.