Effect of polysaccharides on setting and rheological behavior of gypsum-based materials

In this study, the effect of two polysaccharides including hydroxypropyl starch (HPS) and hydroxypropyl methyl cellulose (HPMC) on setting and rheological behavior of gypsum-based materials (GM) pastes were investigated through a series of setting and rheological property tests and microstructure characterization. The results show that HPS is mainly adsorbed on hemihydrate gypsum particles and can promote flocculation or deflocculation structures in different dosages range, as a consequence behaving as a thickener and setting accelerator below the critical dosage of 0.02 wt%, while acting as a retarder beyond this dosage. Besides, the excess HPS would be also selectively adsorbed on dihydrate gypsum crystals and result in the oriented growth. By comparison, HPMC tends to disperse in interstitial solutions and can wrap plenty of free water inside their structures, viscosifying interstitial solutions and strengthening flocculation structures simultaneously. Therefore HPMC has thickening and setting accelerating effects in all dosages range.