Advancing understanding of polymer-based superplasticizers for diverse concrete applications: Insights from quantum chemistry and nanoscale adsorption behavior

Abstract

Polycarboxylate superplasticizers (PCEs) are the most commonly used admixture in the concrete industry. Their premise for work is often considered to be the adsorption of the cement particles through the anchoring groups. Here we suggest a nanoscale perspective to understand the effects of anchoring groups on the adsorption of PCEs by employing the density functional theory (DFT) method. The electronic structural analyses consider various typically anchoring groups of (COO−, PO42−, PO32−, Silanol, and SO3−). The findings indicate that anchoring adsorption predominantly occurs at apex calcium and silicon hydroxyl (Si–OH) sites on the C–S–H surface. Specifically, PCEs containing the PO32− groups exhibit the highest degree of chemical adsorption at the apex cacium site, whereas those with COO− groups show the most pronounced chemical adsorption affinity at the Si–OH site. This observation suggests that varying calcium content in cementitious materials may necessitate the use of different anchoring groups for optimal PCE performance. Further analyses of the Reduced Density Gradient (RDG) indicate that PCE with the COO− and PO32− groups demonstrate the most robust adsorption with the corresponding site. Furthermore, quantitative examination of the peak value at the intersection of the electron localization function (ELF) curve derived an inference that aligns with the findings from the RDG analysis. This study provides a robust framework for understanding the adsorption mechanisms of PCEs with various anchoring groups and offers valuable insights for evaluating the performance of PCEs in more complex cementitious systems.