Bionic repair protective coatings with high toughness and bond strength based on anionic waterborne polyurethane-modified cement

Protection and repair of surface cracks play pivotal roles in enhancing their effective service life. Inspired by the bionic shell principle, an anionic waterborne polyurethane (WPU) was designed. The Synthetic WPU was applied to sulphoaluminate (SAC) and ordinary Portland (OPC) cements to prepare composite coatings. The results showed that with the increase in polymer-to-cement ratio (P/C), attributable to the electrostatic adsorption and complexation of R-COO-, the content of CH, AH3 and AFm increased, while the content of AFt decreased due to the inhibitory effect of WPU on hydration reactions. The molecular dynamics model indicated that the oxygen atoms in WPU can not only form ion pairs with Ca2+ in AFt but also form strong hydrogen bonds with the H in the hydroxyl group of AFt and the H in water molecules. Hence, for P/C exceeding 10 %, combined with FloryHuggins theory, a continuous interpenetration polymer network (IPN) comprising multiphase composites was successfully demonstrated, bolstered by the macromolecular structure composed of -OH, -COOH, Ca2+ and Al3+ serving as a bridge. The network was more pronounced in coatings with SAC than in those with OPC due to synergistic effects caused by rapid hydration reactions. Due to the presence of IPN and the Si-O-Si bonds caused by the hydrolysis condensation reaction of silane coupling agent, the tensile and bond strengths exhibited an upward trend with increasing P/C, surging by up to 326 % and 180 %, respectively. The value reached 6.81 MPa and 2.2 MPa. And the addition of WPU enhanced crack resistance.