Control of the M-S-H Crystallization for Building a Green Future

点击翻译按钮获取中文摘要

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 cement 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). These detriments need to be solved in order to develop a competitive binding material. Polymeric additives are widely used in cement industry in order to enhance its properties. Among those, polycarboxylate ethers (PCEs) are capable of reducing water needed for curing and enhancing the floatability of cement paste. 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. First, the formation of pure M-S-H will be analysed in order to elucidate the crystallization process. Following, the influence of different organic additives during the crystallization of M-S-H will be investigated with the purpose of recognize potential candidates for the improvement of M-S-H properties. Since PCEs have complex architectures, specific interactions with pre- and post-nucleation species could be challenging to elucidate. Therefore, the influence of monomeric units and homopolymers will be assessed in advance. With the newly obtained knowledge of the effects caused by those, PCEs structures will be designed with the aim of modifying the crystallization process in a target-oriented manner and hence, improving M-S-H binders properties.