Partschefeld Stephan, Tutal Adrian, Halmanseder Thomas, Schneider Jens, Osburg Andrea
Chair of Construction Chemistry and Polymer Materials, F.A. Finger Institute of Building Materials Science, Bauhaus-Universität Weimar, 99423 Weimar, Germany.
Materials (Basel). 2023 Jul 31;16(15):5369. doi: 10.3390/ma16155369.
Calcined clays are interesting starting materials to be used as SCMs (supplementary cementitious materials) in cements or to be converted to geopolymers by activation with a high alkaline activator. The adjustment of the properties in the fresh state, especially regarding the consistency of these binders, is almost exclusively achieved by the addition of water, since commercially available superplasticizers seem to be ineffective in low-calcium geopolymer systems. The aim of this study was a systematic investigation of various PCE (polycarboxylate ester/ether) superplasticizers (methacrylate ester PCE: MPEG, isoprenol ether PCE: IPEG, methallyl ether PCE: HPEG) with respect to their stability in different alkaline activators (NaOH, KOH, sodium and potassium silicate solutions). The effectiveness of superplasticizers (SPs) in low-calcium geopolymer binders was verified by rheological tests. Size exclusion chromatography was used to investigate if structural degradation of the superplasticizers occurs. The investigated PCE superplasticizers showed a thickening effect in the low-calcium geopolymer system. Depending on the alkalinity of the activator solution, a degradation process was detected for all the PCEs investigated. The side chains of the PCEs are cleaved off the backbone by basic ester and ether hydrolysis. The highest degree of degradation was found in sodium and potassium silicate solutions. In alkaline hydroxide solutions, the degradation process increases with increasing alkalinity.
煅烧粘土是一种有趣的起始材料，可作为水泥中的SCMs（辅助胶凝材料），或通过用高碱性活化剂活化转化为地质聚合物。在新拌状态下调整性能，特别是这些粘结剂的稠度，几乎完全通过加水来实现，因为市售的高效减水剂在低钙地质聚合物体系中似乎无效。本研究的目的是系统研究各种PCE（聚羧酸酯/醚）高效减水剂（甲基丙烯酸酯PCE：MPEG、异戊烯醇醚PCE：IPEG、甲基烯丙基醚PCE：HPEG）在不同碱性活化剂（NaOH、KOH、硅酸钠和硅酸钾溶液）中的稳定性。通过流变学试验验证了高效减水剂（SPs）在低钙地质聚合物粘结剂中的有效性。采用尺寸排阻色谱法研究高效减水剂是否发生结构降解。所研究的PCE高效减水剂在低钙地质聚合物体系中表现出增稠效果。根据活化剂溶液的碱度，检测到所有所研究的PCE都有降解过程。PCE的侧链通过碱性酯和醚水解从主链上断裂下来。在硅酸钠和硅酸钾溶液中发现降解程度最高。在碱性氢氧化物溶液中，降解过程随碱度的增加而增加。
