Durability enhancement of cement-based repair mortars through waterborne polyurethane modification: Experimental characterization and molecular dynamics simulations

Abstract

With the rapid development of society and economy, more and more concrete structures are facing severe damage and deterioration, requiring repair. However, traditional cement repair materials generally suffer from brittleness, poor durability, and other deficiencies, failing to meet the demands for durable repair materials. In this study, we designed and synthesized an anionic waterborne polyurethane (WPU) emulsion for cement-based materials, characterized its performance, and applied it to modify cement mortars, evaluating the durability of the WPU-modified cement composite repair materials. The experimental results showed that the cured WPU exhibited good radiation resistance, tensile properties, and alkali resistance, and the WPU emulsion demonstrated good compatibility with cement mortars. The WPU-modified cement mortars exhibited improved resistance to drying shrinkage, thermal expansion, freeze-thaw cycles, and water penetration, with increasing WPU content further enhancing the durability of mortar. Simultaneously, the organic-inorganic phase distribution and microstructure of the WPU-modified cement-based composites were investigated. WPU can interact with the cement paste, forming an interpenetrating network structure and increasing the material's density. Finally, molecular dynamics simulations were employed to study the adsorption behavior of WPU on calcium silicate hydrate (CSH) and the transport of water molecules in WPU-modified CSH nanopores. The study found that WPU spontaneously adsorbed onto the CSH surface through hydrogen bonding and weakened the transport efficiency of water molecules in CSH nanopores. Overall, the WPU modification enhanced the density and durability of the cement repair mortars, and the MD method provided molecular-scale insights into the improved water penetration resistance. This study hopes to aid in the design and practical application of polymer-modified cement-based repair materials.