Investigation on the replacement of lithium carbonate as accelerator for calcium aluminate cements and its underlying working mechanism

替代碳酸锂作为铝酸钙水泥促进剂及其作用机理研究

• 批准号: 429917653
• 负责人: Professor Dr. Johann Plank
• 金额: --
• 依托单位: Lehrstuhl für Bauchemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/429917653?language=en
• 关键词: Investigation; replacement; lithium; carbonate; accelerator

For the acceleration of alumina cements and ternary binder systems, more than a thousand tons of lithium salts are taken each year from the supply chain and are irretrievably cemented e.g. into floorings. However, this precious element is needed in large quantities for the production of electric cars, resulting in a higher price and poor availability for the construction industry. Against this background, it is highly desirable to find an alternative for lithium in construction applications. Surprisingly, it was found in earlier research at the chair of construction chemistry relating to the intercalation behavior of microbially produced and natural biopolymers into Zn-Al-LDHs that alginates accelerate the hydration of alumina cement. This was completely unexpected as it is known that such biopolymers generally retard Portland cement. The accelerating effect is also very interesting because alginates represent a renewable resource with practically unlimited availability. Furthermore they are completely non-toxic as alginates are commonly used in the food industry (e.g. as thickener). As for the algae, different kinds can be differentiated, e.g. green algae, red algae and brown algae, which in turn are divided into different subclasses and species. Commercial alginates are obtained exclusively by extraction from brown algae (Phaeophyceae). Preliminary investigations conducted so far showed that addition of 0.1 M.% of a randomly selected commercial sodium alginate to an alumina cement containing 50 m.% Al2O3 reduced the setting time by half. It therefore seems to be promising to examine systematically selected alginate samples for their accelerating effect, to determine an optimal structural composition and to investigate the underlying mechanism of this effect. For this purpose, the accelerating effect is to be verified by various methods including heat flow calorimetry (detects the amount of heat released by the cement during hydration), ultrasound measurements (shows the development and densification of the microstructure based on the passage time of the sound wave through the medium) and mechanical strength measurements on mortars. To fully understand the mechanism of action of the alginate, also specific alginate derivations, an investigation of the effect on individual clinker phases such as CA and C12A7, an analysis of the influence of the alginate on the ion content in the cement pore solution and the nucleation and crystallization of the C-A-H phases will be studied. Finally, the effect of alginates on the ternary binder system OPC/CAC/AH will be investigated. This system produces fundamentally different hydrates compared to pure aluminate cement. In contrast to pure CAC, there no C-A-H phases are formed, but instead ettringite presents the main hydration product.

为了加快氧化铝水泥和三元粘结剂体系的生产，每年从供应链中提取超过1000吨锂盐，并将其不可回收地粘结到地板中。然而，电动汽车的生产需要大量的这种珍贵元素，导致建筑行业的价格更高，可用性差。在此背景下，非常希望找到锂在建筑应用中的替代品。令人惊讶的是，在建筑化学主席关于微生物产生的和天然生物聚合物嵌入Zn-Al-LDH中的行为的早期研究中发现，藻酸盐加速了氧化铝水泥的水化。这是完全出乎意料的，因为已知这样的生物聚合物通常延迟波特兰水泥。加速效应也是非常有趣的，因为藻酸盐代表了具有几乎无限可用性的可再生资源。此外，它们是完全无毒的，因为藻酸盐通常用于食品工业（例如作为增稠剂）。至于藻类，可以区分不同的种类，例如绿色藻类、红藻和褐藻，它们又被分为不同的亚类和种类。商业藻酸盐仅通过从褐藻（褐藻纲）中提取获得。到目前为止进行的初步调查显示，添加0.1M.%将随机选择的市售藻酸钠加入到含有50 m.% Al 2 O3使凝固时间缩短一半。因此，它似乎是有希望的，以检查系统选择的藻酸盐样品的加速效果，以确定最佳的结构组成，并调查这种效果的潜在机制。为此，将通过各种方法验证加速效应，包括热流量热法（检测水泥在水化过程中释放的热量）、超声波测量（基于声波通过介质的时间显示微观结构的发展和致密化）和砂浆的机械强度测量。为了充分理解海藻酸盐的作用机制，以及特定的海藻酸盐衍生物，将研究对单个熟料相（例如CA和C12 A7）的影响的调查，海藻酸盐对水泥孔溶液中的离子含量以及C-A-H相的成核和结晶的影响的分析。最后，将研究海藻酸盐对三元粘合剂体系OPC/CAC/AH的影响。与纯铝酸盐水泥相比，该系统产生根本不同的水合物。与纯CAC相比，没有形成C-A-H相，而是钙矾石呈现主要水化产物。