Effects of polycarboxylate superplasticiser on hydration characteristics and hardened properties of cement blended with seawater

The manufacturing of concrete using seawater provides a promising method to overcome shortages of fresh water and provides both economic and environmental benefits. However, the effects of superplasticiser on seawater-blended concrete, particularly from fresh to hardened properties, have not been thoroughly explored, which hinders the performance-based design of seawater-blended concrete. In this study, based on the water-film theory, the effects of two typical polycarboxylate superplasticisers (PCEs) on the hydrated characteristics and hardened properties of seawater-blended cement were systematically investigated. Water film thickness (WFT) was first analysed to determine the dispersion performance of the PCEs in seawater. The hydration heat was monitored using isothermal conduction calorimetry, and the products were analysed using X-ray diffraction, thermogravimetric analysis, and derivative thermogravimetry. Microstructures were investigated using scanning electron microscopy with energy-dispersive spectroscopy. In addition to compressive strength testing, the pore structures of the seawater-blended cementitious materials were analysed using mercury intrusion porosimetry. The results indicated that the incorporation of PCEs slightly increases the WFT in cement mixed with tap water and seawater. Furthermore, although seawater increased the hydration heat and densified the microstructures of the specimens with both PCEs, the hydration products were not influenced. Additionally, the compressive strength of cement with tap water and seawater decreased as a result of the increase in the proportion of capillary pores induced by incorporating PCEs.