Influence of Curing Regimes on the Mechanical Properties, Water Capillary Adsorption, and Microstructure of CSA Cement Mortar Modified with Styrene-Butadiene Copolymer Dispersion

This paper studies the influence of curing regimes on the performance and microstructure of polymer-modified mortar. Mortars with five different ratios (0%, 5%, 10%, 15%, and 20%) of styrene-butadiene copolymer (SB) dispersion to calcium sulfoaluminate (CSA) cement at a constant flowability were investigated. Four temperatures (0°C, 5°C, 20°C, and 40°C) and three relative humidities (RH) varying from low ($32\pm 2\%$), middle ($63\pm 10\%$), to high ($96\pm 3\%$) were considered for mortar specimens curing. The experimental results show that the addition of SB improves the flexural and tensile bond strength development but not the compressive strength. The best performance of CSA cement mortar is achieved with 20% of SB. However, the mechanical properties of CSA cement mortar are significantly degraded when the addition of SB is 5%. High temperature and HRH often lead to the formation of ettringite. The larger size ettringite and polymer film intertwine, which makes the CSA cement mortar denser and thus stronger. Accordingly, the properties of CSA cement mortar including flexural and tensile bond strength are significantly improved. Also, it was found that the CSA cement mortar had very low water capillary adsorption rate even when cured at 0°C, and the addition of SB dispersion provides CSA cement mortar better water resistance.