Deciphering the functional mechanism of polycarboxylate superplasticizers in seawater concrete: Insights from molecular dynamics simulation.

The prevailing view holds that polycarboxylate ether-based (PCE) superplasticizers exhibit diminished efficacy in seawater concrete, yet the underlying mechanisms remain obscure. This study employs molecular dynamics simulation to investigate the conformational changes of water-reducing and slump-retaining superplasticizers in concrete. The reliability of the model is validated by comparing the simulation results with experimental data. In addition to analyzing concentration distribution, gyration radius, and backbone end-to-end distance, this study examined the radial distribution function and conducted pull-out simulations to reveal the differences in adsorption conformation and performance between tap water and seawater environments, elucidating the mechanisms of PCE in seawater concrete. Compared to tap water, in seawater, the carboxyl groups on the PCE backbone form a cationic layer, which reduces the gyration radius and backbone end-to-end distance of PCE, leading to a more spherical adsorption conformation. Radial distribution function analysis indicates that cations present in seawater alter the PCE adsorption mode from combined adsorption of the backbone's carboxyl and the side chain's hydroxyl groups to adsorption relying solely on the backbone's carboxyl groups. This shift results in a decreased adsorption strength during pull-out simulations. The conformational coiling and shift in adsorption mode contribute to the attenuated efficacy of PCE in seawater. This study may provide a mechanistic explanation for the PCE behaviors in seawater concrete. • Reveal the reasons behind the reduced effectiveness of PCE in seawater concrete. • The adsorption mechanisms of PCE in seawater differ from those in tap water. • Cations both promote and hinder the adsorption of PCE. • The multi-layer ion layer on the surface of C-S-H makes PCE easier to detach. [ABSTRACT FROM AUTHOR]