Setting time and flowability of accelerated Portland cement mixed with polycarboxylate superplasticizer.

Introduction: Important limitations of mineral trioxide aggregate for use in clinical procedures are extended setting time and difficult handling characteristics. The removal of gypsum at the end stage of the Portland cement manufacturing process and polycarboxylate superplasticizer admixture may solve these limitations.

Methods: Different concentrations of polycarboxylate superplasticizer (0%, 1.2%, 1.8%, and 2.4% by volume) and liquid-to-powder ratios (0.27, 0.30, and 0.33 by weight) were mixed with white Portland cement without gypsum (AWPC-experimental material). Type 1 ordinary white Portland cement mixed with distilled water at the same ratios as the experimental material was used as controls. All samples were tested for setting time and flowability according to the International Organization for Standardization 6876:2001 guideline. The data were analyzed by two-way analysis of variance. Then, one-way analysis of variance and multiple comparison tests were used to analyze the significance among groups.

Results: The data are presented in mean ± standard deviation values. In all experimental groups, the setting times were in the range of 4.2 ± 0.4 to 11.3 ± 0.2 minutes, which were significantly (p < 0.05) lower than the control groups (26.0 ± 2.4 to 54.8 ± 2.5 minutes). The mean flows of AWPC plus 1.8% and 2.4% polycarboxylate superplasticizer groups were significantly increased (p < 0.001) at all liquid-to-powder ratios compared with control groups.

Conclusions: Polycarboxylate superplasticizer at concentrations of 1.8% and 2.4% and the experimental liquid-to-powder ratios reduced setting time and increased flowability of cement, which would be beneficial for clinical use.