Interlayer bonding improvement of 3D printed concrete with polymer modified mortar: Experiments and molecular dynamics studies

The inherent weak interfaces between adjacent layers by the laminate stacking process of 3D concrete printing hinder this advanced technique for general engineering applications. In this study, polymer-modified mortars were fabricated to improve the weak interlayer bonding performances. The effects of the setting time of the printed concrete and changes of the interlayer moisture were tested. Both epoxy resin- and chloroprene latex-modified mortars were prepared and used as interlayer interface enhancement materials according to different interlayer intervals. The direct tensile and shear strengths of the polymer mortar-strengthened interfaces were tested and evaluated by the crossover test. Moreover, the effects of the moisture released from the surface of the cement-based composite materials on the interlaminar bonding properties and the enhancing mechanism of the epoxy resin- and chloroprene latex-modified mortars were simulated through molecular dynamics and density functional theory. The results demonstrate that the electrostatic interaction (Coulomb force) between the epoxy resin and calcium ions from hydrated calcium silicate counteracts the weakening effect of water molecules (surface moisture) on the interlaminar bonding, thus improving the interface bonding of printed concrete. The optimal polymer mortar that strengthens the interfaces most effectively was identified.