矿物掺合料对聚羧酸减水剂与水泥相容性的影响

高性能减水剂与水泥适应性差会导致混凝土流动性和坍落度损失过快,矿物掺合料将影响高性能减水剂与水泥的相容性。对比研究矿物掺合料种类和掺量对水泥净浆、砂浆和混凝土流动性的影响;采用TOC法测试了矿物掺合料对聚羧酸减水剂吸附量的影响;分析了矿物掺合料影响聚羧酸减水剂与水泥相容性的机理。结果表明,粉煤灰和矿渣对提高水泥净浆流动性具有一定的叠加效应,可用胶砂减水率的加权平均值进行量化;硅灰对水泥浆体流动性的不利影响远大于粉煤灰和矿渣的辅助减水分散作用,不利于改善聚羧酸减水剂与水泥的相容性;粉煤灰和矿渣增加聚羧酸减水剂在水泥体系中的吸附量;粉煤灰和矿渣对聚羧酸减水剂在混凝土中的减水分散效果有改善作用但不显著。

Effect of Mineral Admixtures on the Compatibility of Polycarboxylate Superplasticizer and Cement

Quick loss of fluidity and slump is commonly happened in concrete due to poor compatibility between superplasticizer and cement, which can be affected by the use of mineral admixtures. The effects of fly ash, slag and silica fume on fluidity of cement pastes, mortars and concretes were studied, and their effects on the content of polycarboxylate superplasticizer adsorbed on cement were tested by TOC method. Then, the compatibility between polycarboxylate superplasticizer and cement affected by fly ash, slag and silica fume was analysed. The results show that the beneficial impact of fly ash combined with slag on the fluidity of cement paste could be regarded as a superposition effect and quantified by the weighted average of the water-reducing rate. Silica fume has an adverse effect which is greater than the additional water-reducing effect of fly ash and slag on the fluidity of cement paste, which is unfavourable to the compatibility between polycarboxylate superplasticizer and cement. Fly ash and slag increase the effective adsorption content, resulting in good dispersion or high water reducing by polycarboxylate superplasticizer. There exists additional water-reducing effect induced by fly ash and slag in concrete but not obviously.