Effect of polycarboxylate superplasticisers on the fresh properties of cementitious materials mixed with seawater

•Performance of two PCEs in tapwater and seawater mixed cement were investigated.•No chemical changes occurred in both PCEs in seawater.•Rheological behaviour of cement with PCEs in seawater differed to that in tapwater.•Seawater significantly affected the dispersion performance of water-reducing PCE. 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.