Identification of mechanisms of action of conventional superplasticizers and novel bio-based flow agents in calcium-free geopolymer model systems

近年来，建筑业的重点已转向创新技术和材料。众所周知，水泥生产对环境有重大影响；每年生产约4GT水泥，生产过程中产生的碳排放占1.5GT。因此，寻找替代粘结剂是至关重要的，这些粘结剂最好独立于其他工业部门。一种这样的粘结剂是煅烧粘土，这种粘土在世界各地都可以买到，但其化学和矿物组成差别很大。此外，目前还不存在适用于无钙地聚合物体系的外加剂。本研究项目的目的是确定适用于无钙地聚合物的高效减水剂，并利用地聚合物模型系统确定其作用机理。以偏高岭土和偏高岭土为模型体系，采用溶胶凝胶法合成了偏高岭土和偏高岭土基材，并与水玻璃溶液混合。这就允许使用无钙系统。使用市售的聚合油高效减水剂(三聚氰胺磺酸和β-萘磺酸甲醛缩合物)和主链不同的聚氯乙烯高效减水剂(mpeg、apegg、hpeg和ipeg)分散地聚合物模型体系。首先，通过结构研究确定了在高碱性环境中的流动效应和化学稳定性。此外，还合成了在无钙土聚合物的高碱性环境中表现出高稳定性的淀粉高效减水剂。通过改变电荷类型、电荷数量和分子质量(&lt；100 kDa和&gt；100 kDa)的分子参数，合成了淀粉高效减水剂，并确定了在无钙模型土聚合物中导致高分散性能的关键参数。通过流变学实验研究了添加高效减水剂的模型地聚合物体系的流动行为。记录了粘度和屈服点的变化以及流变性随时间的变化，并与参考的地聚物胶进行了比较。通过研究有效减水剂的加入对Zeta电位的影响，可以了解流动效应是否是由表面相互作用引起的。此外，还确定了早期地聚合物反应过程中的吸附程度。这一结果与高效高效减水剂的结构参数有关。微观结构研究可以提供信息，如果有效的高效减水剂改变了硬化的地质聚合物胶中空气、毛细管和凝胶孔的含量。然后，可以评估关于高效减水剂在地聚合物模型体系中的有效性的结果，并将结果转换为一般有效的作用机理(经验模型)。

In recent years, the focus in construction industry has transitioned towards innovative technologies and materials. It is well known that the production of cement has a significant impact on the environment; by manufacturing around 4 Gt of cement annually, the carbon emissions created during the production process are accounted to 1.5 Gt. Hence, the search for alternative binders, that are preferably independent from other industrial sectors, is essential. One such binder is calcined clays, which are available worldwide but vary widely in their chemical and mineralogical composition. Furthermore, no suitable admixtures currently exist for calcium-free geopolymer systems. The objective of this research project is to identify suitable superplasticizers for calcium-free geopolymers and to determine the mechanism of action using geopolymer model systems. As model systems, metakaolin- and metaton-like base materials are synthesized via a sol-gel process and mixed with water glass solutions. This allows the use of calcium-free systems. Commercially available polycondensate superplasticizers (melamine sulfonic acid and β-naphthalenesulfonic acid formaldehyde polycondensates) and PCE superplasticizers with variation of the backbone (MPEG, APEG, HPEG and IPEG) are utilized to disperse the geopolymer model systems. Initially, the flow effect and chemical stability in the highly alkaline environment is determined due to structural investigations. In addition, starch superplasticizers that exhibit high stability in the highly alkaline environment of calcium-free geopolymers are synthesized. Starch superplasticizers are synthesized by varying the molecular parameters of charge type, charge amount, and molecular mass (<100 kDa and >100 kDa), and key parameters, that induce high dispersion performance in the calcium-free model geopolymers, are identified. Rheological experiments are conducted to characterize the flow behavior of the model geopolymer systems with addition of the effective superplasticizers. The change in viscosity and yield point as well as the time dependence of the rheological properties are recorded and compared to a reference geopolymer glue. Investigations on the change of the zeta potential due to the addition of effective superplasticizers provide insight whether the flow effect is caused by surface interactions. Moreover, degrees of adsorption during the early geopolymer reaction are determined. The results can be associated with the structural parameters of the effective superplasticizers. Microstructural investigations can provide information if the effective superplasticizers change the contents of air, capillary, and gel pores in hardened geopolymer glues. Then, the findings on the effectiveness of superplasticizers in the geopolymer model systems can be evaluated and the results can be converted into a generally valid mechanism of action (empirical model).