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

近年来，建筑业的重点已经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4 Gt水泥，生产过程中产生的碳排放量为1.5 Gt。因此，寻找替代粘合剂至关重要，这些粘合剂最好独立于其他工业部门。一种这样的粘合剂是煅烧粘土，其在世界范围内可获得，但其化学和矿物组成变化很大。此外，目前不存在用于无钙地质聚合物体系的合适的掺合物。本研究项目的目的是确定合适的高效减水剂的无钙地质聚合物，并确定使用地质聚合物模型系统的作用机制。作为模型系统，偏高岭土和类金属基材料通过溶胶-凝胶过程合成，并与水玻璃溶液混合。这允许使用无钙系统。市售的缩聚物超增塑剂（三聚氰胺磺酸和β-萘磺酸甲醛缩聚物）和具有不同骨架的PCE超增塑剂（MPEG、APEG、HPEG和IPEG）用于分散地质聚合物模型体系。最初，由于结构研究，确定了在高碱性环境中的流动效应和化学稳定性。此外，合成了在无钙地质聚合物的高碱性环境中表现出高稳定性的淀粉超增塑剂。通过改变电荷类型、电荷量和分子量（100 kDa）的分子参数来合成淀粉超增塑剂<100 kDa and >，并且确定了诱导在无钙模型地质聚合物中的高分散性能的关键参数。通过流变实验研究了添加高效减水剂后的地质聚合物模型体系的流变行为。记录粘度和屈服点的变化以及流变特性的时间依赖性，并与参考地质聚合物胶进行比较。由于添加有效的高效减水剂的zeta电位的变化的调查提供洞察流动效应是否是由表面相互作用引起的。此外，在早期地质聚合物反应过程中的吸附程度被确定。研究结果与高效减水剂的结构参数有关。微观结构的调查可以提供信息，如果有效的超增塑剂改变硬化地质聚合物胶中的空气，毛细管和凝胶孔的内容。然后，可以评估地质聚合物模型系统中高效减水剂的有效性，并将结果转换为普遍有效的作用机制（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).