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

水泥是世界上最常用的建筑材料，也是人类历史上最重大的技术进步之一。每年生产近40亿吨水泥，造成重大环境影响，如高二氧化碳排放量(约占全球人为二氧化碳排放量的7%)。因此，在过去的几十年里，开发生态可持续水泥一直是科学界的首要任务。最有希望的战略之一是用替代的低碳粘结剂部分取代传统的波特兰水泥。在这方面，镁-硅酸盐-水化粘结剂((MgO)x-SiO_2-(H_2O)_y，M-S-H)引起了人们的强烈关注。氧化镁水泥是在二氧化硅存在下通过氧化镁水合生成M-S-H而生产的。活性氧化镁可以通过燃烧硅酸镁或碳酸镁或采用更环保的策略(如从盐水或海水中生产)来生产。与波特兰水泥制造相比，使用这些替代来源获得氧化镁大大减少了二氧化碳排放。然而，M-S-H水泥净浆的研究表明，与波特兰水泥相比，M-S-H水泥存在显著的缺点(如用水量高、凝结时间长、抗压强度低)。需要解决这些不利因素，才能开发出具有竞争力的绑定材料。聚合物外加剂在水泥工业中被广泛使用，以提高其性能。其中，聚羧酸醚(PCE)能够减少养护所需的水量，提高水泥浆体的可浮性。此外，PCE还具有可通过改变其化学结构来调节的优点。采用合适的PCE可以解决M-S-H粘结剂用水量大等问题。本项目的总体目标是对M-S-H在没有和存在聚合物添加剂的情况下的结晶过程有一个基本的了解。了解M-S-H的成核和生长将为开发一种新型粘结剂铺平道路，这种粘结剂可以在机械性能方面与波特兰水泥相媲美，同时对环境的侵蚀性较小。首先，将分析纯M-S-H的形成，以阐明结晶过程。随后，考察了不同有机添加剂在M-S-H结晶过程中的影响，以期找出改善M-S-H性能的潜在候选者。由于PCE具有复杂的结构，与成核前和成核后物种的特定相互作用可能很难阐明。因此，单体单元和均聚物的影响将被提前评估。有了这些影响的最新知识，PCES结构的设计将以目标导向的方式改变结晶过程，从而改善M-S-H粘结剂的性能。

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.