Topological effects on the concrete transportation inhibitors: Nano-mechanisms and design principles

The durability of reinforcement concrete is greatly threatened by the chloride ions (Cl⁻) in marine environments, which is attributed to the good permeability of concrete pores where the fluids with Cl⁻ can easily transport in. Recent studies have been focusing on designing admixtures that can significantly inhibit the transportation of fluids in concrete, but their mechanism of inhibition and designated principle need to be further clarified. Herein, the surfactant-like concrete transportation inhibitors (CTI) with different molecular topologies were investigated to reveal the inhibition mechanism and structural effectiveness by employing molecular dynamics simulations. The increase in nanoscale interfacial tension (IFT) inside the concrete pores is considered to be the origin of transport inhibition. The topological effects of inhibitors on the IFT are also revealed as follows: DTA > DIA > SUA > STA > DBA in which the bola-type structures are recognized as the most competitive ones. Further studies of the nanoscale characteristics from free energy and bonding aspects indicate that the stronger adsorption and stable tails of bola-type structures ensure the best barrier between C-S-H and water, and thus facilitate the highest IFT. Detailed information on the adsorption structures, phase distribution and kinetics properties were also calculated to support this conclusion. This work not only supplies a positive method that can effectively evaluate the properties of CTI in the nanoscale but also can be considered as the beginning of developing concrete admixtures from the molecular design.