Adsorption of superplasticizers in alkali-activated materials - Fluorescence microscopic in-situ investigations

碱激发材料(AAM)与普通硅酸盐水泥(OPC)相比，在二氧化碳平衡方面以及在许多情况下在耐久性方面具有优势。这种耐久性的提高是由于形成了不同于由OPC制成的混凝土中的C-S-H相的强度形成相。所使用的原材料是富含硅和铝的矿物材料，它们理想地以细小颗粒和活性形式存在。主要使用的前驱体是磨细的高炉矿渣、飞灰或煅烧粘土。由于这些材料属于潜在的水力或火山灰材料，因此必须刺激化学反应。碱性活化剂可用于此目的；主要使用碱性氢氧化物或水玻璃，但也可使用碱性硫酸盐或碳酸盐溶液。尽管前驱体和碱激活剂的可能组合有多种，但如果想要将其效果与OPC进行比较，仍没有已知的有效高效减水剂用于这些体系。大多数可用的高效减水剂都会失效，特别是在碱激活剂浓度较高的情况下。可能相互作用的复杂矩阵是由前体、碱激活剂的类型和浓度以及高效减水剂的类型组合而成的，这需要在新拌和硬化混凝土的研究中进行高度的经验努力。在最近完成的DFG资助项目389127734中，利用荧光显微镜原位研究了高效减水剂在矿物颗粒上的吸附行为。这种分析方法是在项目中建立的，关于高效减水剂吸附行为的结果已经可以直接与流变性和胶凝体系中的凝结行为相关联。阳离子浓度对吸附行为的影响，从而对高效减水剂效果的影响是可以证明的。因此，该方法适用于高效减水剂在不同前驱体和不同碱性活化剂溶液中的吸附行为的时间分辨研究。本项目的目的是系统地研究AAM在前驱体、激发剂溶液和所用高效减水剂的变化情况下的变化。微观研究将与对新鲜和硬化混凝土的研究相关联，在这些研究中，相同的参数是不同的。除了进一步发展原位荧光显微镜来研究高效减水剂的吸附行为外，各种研究结果的相互关联将为了解高效减水剂在AAM中的作用机理提供一般性的见解。这将促进碱激发粘结剂的使用，并提高这些系统的性能。特别是考虑到使用不含OPC或不含OPC的系统日益重要，这一目标具有跨学科的重要性。

Alkali-Activated Materials (AAM) have advantages compared to Ordinary Portland Cement (OPC) in terms of CO2 balance and in many cases in terms of durability. This increase in durability is due to the formation of strength-forming phases, which differ from the C-S-H phases in concrete made of OPC. The raw materials used are mineral materials rich in silicon and aluminium, which are ideally present as fine particles and in reactive form. Mainly used precursors are ground granulated blast furnace slag, fly ash or calcined clays. Since these materials belong to the group of latent hydraulic or pozzolanic materials, a stimulation of the chemical reaction is necessary. Alkali activators can be used for this purpose; alkali hydroxide or water glasses are mostly used, but, alkali sulfate or carbonate solutions can also be used. Despite the variety of possible combinations of the precursors and alkali activators, there are still no effective superplasticizers known for these systems, if one wants to compare the effectiveness with that of OPC. Most available superplasticizers lose their effectiveness, especially at higher concentrations of the alkali activators. A complex matrix of possible interactions results from the combination of precursors, types and concentrations of alkali activators as well as the types of superplasticizers, which require a high empirical effort in fresh and hardened concrete investigations. In the recently finalised DFG-funded project 389127734 the adsorption behaviour of superplasticizers on mineral particles was investigated in-situ by fluorescence microscopy. This method of analysis was established within the project and results on the adsorption behaviour of superplasticizers could already be directly correlated with rheological properties and the setting behaviour in cementitious systems. The influence of cation concentrations on the adsorption behaviour and thus on the effectiveness of superplasticizers could be proven. Thus, this method is suitable for time-resolved investigations of the adsorption behaviour of superplasticizers on various precursors and in different alkaline activator solutions. The aim of this project is the systematic investigation of AAM under variation of the precursors, the activator solutions and the used superplasticizers. Microscopic investigations will be correlated with investigations on fresh and hardened concrete in which the same parameters are varied. In addition to the further development of in-situ fluorescence microscopy for the investigation of the adsorption behaviour of superplasticizers, the correlation of the results of the various investigations will provide general insights into the mechanisms of action of superplasticizers in AAM. This will facilitate the use of alkali-activated binders and improve the performance of these systems. Especially with regard to the increasing importance of the use of OPC-free or -reduced systems, this objective is of interdisciplinary importance.