Atomistic modeling of C-S-H: bulk and surface

By replacing part of Portland cement with so-called supplementary cementitious materials (SCMs) it is possible to reduce the CO2 footprint of the cement industry. These SCMs are commonly limestone, calcined clay, slag and fly ash. While doing so the early age hydration and strength are affected, which presents a limitation in SCM usage. Recent studies on minor elements, particularly zinc, indicate that it is possible to achieve an accelerating effect in this early hydration period. Observations indicate that this accelerating effect comes from zinc's role in modifying the calcium silicate hydrate (C-S-H) structure, the main hydration product. In the effort to be able to engineer the reactivity of cement hydration with use of zinc we need to know the nature and location of zinc which is incorporated in C-S-H, as current evidence suggests. A clear understanding of the underlying atomistic structure can be obtained from combining atomistic modeling techniques with advanced experimental techniques, such as NMR. While previous research was hindered by poor C-S-H models, we are following on the work of Kunhi Mohamed, who introduced a systematic approach for construction of realistic atomistic C-S-H models. Based on experimental evidence we will introduce zinc, and possible other minor elements, in-to the structure and calculate the energetics, which will give a better understanding of preferable zinc sites. The main challenges are extending the cementitious force field with realistic zinc interactions and the construction of representative C-S-H surfaces.