Partschefeld Stephan, Aschoff Jasmine, Osburg Andrea
Finger Institute of Building Materials Science, Bauhaus-Universität Weimar, 99423 Weimar, Germany.
Materials (Basel). 2025 Sep 4;18(17):4154. doi: 10.3390/ma18174154.
Water-reducing admixtures are of enormous importance to adjust the workability of alkali-activated materials. Especially in geopolymers activated by highly concentrated alkaline solutions, the polycarboxylate ether (PCE) superplasticizers are less effective than in conventional cementitious systems. The aim of this study was to clarify the reasons for the lower dispersing performance of PCE and the synthesis of alternative dispersing agents based on the biopolymer starch to improve the workability of highly alkaline geopolymers. Furthermore, the focus of investigations was on the role of activator type and concentration as key parameters for geopolymer reaction and interaction of water-reducing agents. Therefore, in this study the conformation of three different types of PCE (MPEG: methacrylate ester, IPEG: isoprenol ether, and HPEG: methallyl ether) and synthesized starch admixtures in sodium and potassium hydroxide solutions (1 mol/L up to 8 mol/L) were studied. Furthermore, the dispersing performance, adsorption behavior, and influence on reaction kinetics in metakaolin-based geopolymer pastes were investigated in dependence on activator type and concentration. While the PCE superplasticizers show coiling and formation of insoluble aggregates at activator concentrations of 3 mol/L and 4 mol/L, the synthesized starch admixtures show no significant change in conformation. The cationic starch admixtures showed a higher dispersing performance in geopolymer pastes at all activator concentrations and types. The obtained adsorption isotherms depend strongly on the activator type and the charge density of the starch admixtures. The reaction kinetics of geopolymer pastes were not significantly influenced using the synthesized starch admixtures. Especially the cationic starch admixtures allow the reduction of liquid/solid ratios, which leads to higher flexural and compressive strengths.
减水剂对于调节碱激活材料的工作性至关重要。特别是在由高浓度碱性溶液激活的地质聚合物中，聚羧酸醚（PCE）高效减水剂的效果不如在传统胶凝材料体系中。本研究的目的是阐明PCE分散性能较低的原因，并合成基于生物聚合物淀粉的替代分散剂，以改善高碱性地质聚合物的工作性。此外，研究重点是活化剂类型和浓度作为地质聚合物反应及减水剂相互作用的关键参数所起的作用。因此，本研究考察了三种不同类型的PCE（MPEG：甲基丙烯酸酯、IPEG：异戊烯醇醚和HPEG：甲基烯丙基醚）以及合成淀粉外加剂在氢氧化钠和氢氧化钾溶液（1 mol/L至8 mol/L）中的构象。此外，还研究了基于偏高岭土的地质聚合物浆体中，分散性能、吸附行为以及对反应动力学的影响，这些均取决于活化剂类型和浓度。当PCE高效减水剂在活化剂浓度为3 mol/L和4 mol/L时呈现卷曲并形成不溶性聚集体时，合成淀粉外加剂的构象没有显著变化。阳离子淀粉外加剂在所有活化剂浓度和类型下，在地质聚合物浆体中均表现出更高的分散性能。所得到的吸附等温线在很大程度上取决于活化剂类型和淀粉外加剂的电荷密度。使用合成淀粉外加剂时，地质聚合物浆体的反应动力学没有受到显著影响。特别是阳离子淀粉外加剂能够降低液固比，从而提高抗折强度和抗压强度。
