The structure of cement derivatives (cement-based materials) is complex and not fully understood. They are formed by self-assembly of different chemical species in a specific way to form basic building blocks (or units); the size of these units is on the order of a few nanometers. After they are formed, these basic units arrange themselves into larger units, still nanometric in size, which constitute the cementitious matrix. The distinctive macroscopic properties of cementitious materials arise from their unique structural arrangement. This paper is an introduction to the results obtained by the Centre for Nanomaterials Applications in Construction over the past 5 years. The approach used in this study is a combination of experimental and numerical (multiscale simulation) techniques. On the one hand, the study shows how the addition of nanosilica particles can modify the mechanical properties of the cement matrix as well as its resistance to the calcium leaching process. On the other hand, the study illustrates how computational modeling is a valuable tool for gaining insight into the complex calcium silicate hydrate nanostructure and for designing improved cementitious materials.