Influence of polycarboxylate superplasticizer and calcium sulfoaluminate cement on the rheology, hydration kinetics, and porosity of Portland cement pastes

• Published in: Journal of Building Engineering 2023-06, Vol.68, p.106120, Article 106120
• Main Authors: Tambara Júnior, Luís Urbano Durlo, dos Santos Lima, Geannina Terezinha, Silvestro, Laura, Ruviaro, Artur Spat, Gleize, Philippe Jean Paul, de Azevedo, Afonso Rangel Garcez
• Format: Article
• Language: English
• Subjects: Calcium sulfoaluminate cement; Hydration; Portland cement; Rheology; Superplasticizer
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2023.106120

Binary systems composed of Portland cement (PC) and calcium sulfoaluminate (CSA) cement have stood out for applications requiring high early strengths. Nevertheless, the application of these systems may be limited due to their properties in the fresh state, which requires a better understanding of the rheological behavior of these materials. Thus, this study evaluated the incorporation of different polycarboxylate-based superplasticizer (SP) contents (0.15, 0.20, and 0.25 wt%) on PC and PC-CSA binary cement pastes. Rotational rheometry, isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption and desorption tests to assess the pore size distribution of cement pastes were conducted. While the SP incorporation reduced the dynamic yield stress of PC pastes, it progressively increased the yield stress of PC-CSA systems. The increase in SP content increased the main heat flow peak of PC-CSA pastes, although it did not significantly affect the cumulative heat after 160 h of hydration. FTIR and XRD confirm higher ettringite contents in the binary systems and indicate the presence of carboaluminates phases after 7 d of hydration in both PC and PC-CSA and hemicarboaluminate in PC-CSA pastes. The CSA incorporation reduced the cumulative pore volume by up to 32% compared to PC pastes, while the SP content evaluated did not significantly affect the porosity of PC-CSA pastes. •SP reduced the dynamic yield stress of PC and increased the yield stress of PC-CSA.•PC-CSA tends to form AFt and hemicarboaluminate instead monocarboaluminate.•Herschel-Bulkley's model presented a good fit for the PC-CSA rheological data.•Higher C–S–H gel formation was observed for PC and only monocarboaluminate as AFm.•The increased ettringite formation reduced the pore volume to 32% in PC-CSA systems.