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要的技术进步之一。每年生产近40亿吨水泥，造成严重的环境影响，如二氧化碳排放量高（约占全球人为二氧化碳的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。其中一个最有前途的策略是部分替代传统的波特兰水泥替代低碳粘合剂。在这方面，镁硅酸盐水合物结合剂(（MgO) x-SiO2 - (H2O)y, M-S-H）引起了人们的强烈关注。MgO基水泥是在二氧化硅存在下由MgO水化生成M-S-H。反应性氧化镁可以通过燃烧镁硅酸盐或镁碳酸盐来生产，也可以采用更环保的策略，如从盐水或海水中生产。与波特兰水泥生产相比，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，研究表明M-S-H水泥浆体与波特兰水泥相比有明显的缺点（如需水量大、凝结时间长、抗压强度低）。为了开发出具有竞争力的装订材料，需要解决这些不利因素。聚合物添加剂被广泛应用于水泥工业，以提高其性能。其中，聚羧酸酯醚（pce）能够减少养护所需的水，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进行调谐的优点。采用合适的pce，可以解决M-S-H粘结剂需水量大等问题。这个项目的总体目标是获得一个基本的理解结晶的M-S-H在没有和存在的聚合物添加剂。了解M-S-H的成核和生长将为开发一种新型粘合剂铺平道路，这种粘合剂可以在机械性能上模仿波特兰水泥，同时对环境的侵蚀较小。首先，分析纯M-S-H的形成，以阐明结晶过程。接下来，我们将研究不同有机添加剂对M-S-H结晶过程的影响，以识别改善M-S-H性能的潜在候选物。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具有挑战性。因此，单体和均聚物的影响将提前评估。随着新获得的这些影响的知识，pce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粘合剂的性能。

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.