Effects of superplasticizer type on packing density, water film thickness and flowability of cementitious paste

• Different types of superplasticizer have different dispersion effects.
• They all have beneficial effects on packing density and water film thickness.
• Even at same water film thickness, they have different effects on flowability.
• This may be caused by different effectiveness in cohesiveness reduction.

Superplasticizer (SP) is nowadays an indispensable ingredient for the production of concrete. With SP added, the cementitious materials would be dispersed to reduce agglomeration, and thus the packing density, water film thickness (WFT) and flowability of the cementitious paste could be improved. However, there have been few studies on the effects of SP type on the packing density and WFT. This study aims to evaluate the roles of SP type in the packing density, WFT and flowability of cementitious paste. In the study, cementitious paste samples with three cementitious material compositions, two SP types (namely, a naphthalene-based SP and a polycarboxylate-based SP) and increasing SP dosages were tested. The test results showed that the addition of either type of SP would significantly increase the packing density and WFT, but the polycarboxylate-based SP is more effective than the naphthalene-based SP. Besides, the combined effects of SP and WFT on the flowability of cementitious paste were analyzed.

Different types of superplasticizer have different effects on the packing density, water film thickness and flowability of cementitious paste, as illustrated in the diagram below, where SP means superplasticizer, SP1 is a naphthalene-based superplasticizer and SP2 is a polycarboxylate-based superplasticizer.Figure optionsDownload as PowerPoint slide