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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.

This paper investigated the effect of two types of PCE superplasticisers, including water-reducing and slow-releasing types, on the workability and rheological behaviour of cement mixed with tapwater and seawater. In addition to rheology and minislump tests, the characterisation of PCE on chemical structure and hydrodynamic radius was conducted and the adsorption behaviours were also examined to reveal the underlying mechanisms. The results showed that for the water-reducing type PCE, the seawater led to an obvious decrease in the fluidity of the PCE-superplasticised cement paste whereas it did not significantly change the fluidity of cement with slow-releasing PCE. The addition of both PCEs changed the rheological behaviour of the cementitious materials. Although the mix of seawater decreased the minislump of PCE-superplasticised cement, the adsorption amount of both types of PCE in seawater was increased due to the complexation between the carboxylate group in PCEs and the divalent Mg2+ from the seawater. The reduced dispersion could be attributed to the shrinkage of the PCE backbone and the decreased thickness of the adsorption layer.

Due to the complexity of the interior of a rubber-cement composites, its internal stress/strain is very complex. In this study, a digital volume correlation based on X-ray computed tomography was used to obtain the interior volumetric displacement and volumetric strain of the rubber-cement composites under uniaxial compression. The results showed that the particle size and spatial distributions of the rubber particles could be obtained by image processing. The calculation parameters were optimal when the subset sizes were 43 voxels (three times the speckle particle size) and 5 voxels. The inconspicuous microcracks and their cracking patterns could be satisfactorily reflected in the three-dimensional volumetric displacement. The three-dimensional volumetric strain could be used to predict the cracking position inside the sample and the direction in which the crack extended.