Cristina Ruiz Agudo

Cement is the most commonly used building material in the world and one of the most significant technological advances in the history of humanity. Nearly four billion tons of cement are manufactured every year causing major environment impacts such as high CO2-emissions (~7 % of global anthropogenic CO2). Therefore, the development of eco-sustainable cements has been top-priority during the last decades for the scientific community. One of the most promising strategies is the partial replacement of conventional Portland cements by alternative low carbon binders. In that respect, magnesium-silicate-hydrate binders ((MgO)x-SiO2-(H2O)y, M-S-H) have caught strong attention. MgO-based cements are produced by hydration of MgO in the presence of silica to generate M-S-H. Reactive MgO can be manufactured by burning Mg-silicates or Mg-carbonates or by using more environmentally friendly strategies like production from brines or seawater. The use of these alternative sources for obtaining MgO reduces substantially CO2-emissions in contrast to Portland cement manufacturing. Nevertheless, investigations of M-S-H cement paste evidence significant disadvantages comparing with Portland cement (e.g. high water demand, long setting times and low compressive strengths) and these drawbacks need to be solved in order to develop a competitive binding material. The use of polymeric additives (polycarboxylate ethers (PCEs)) to reduce water needed for curing and enhance the floatability of cement paste is common practice in the cement industry. In addition, PCEs bear the advantage of being tuneable by modification of their chemical structure. By using the suitable PCEs, problems such as high water demand of M-S-H binders could be tackled. The overall aim of this project is to gain a fundamental understanding of the crystallization of M-S-H in absence and in presence of polymeric additives. Understanding nucleation and growth of M-S-H will pave the way towards the development of a novel binder that could emulate Portland cements regarding mechanical performance and, at the same time, being less aggressive to the environment.