PVA fiber/cement-based interface in silane coupler KH560 reinforced high performance concrete – Experimental and molecular dynamics study

PVA fiber reinforced cementitious composites are becoming more and more popular. Due to the difference in physical and chemical properties of the materials, there is a problem of weak interfacial properties between PVA and cement. In order to solve this problem, this study adopts the means of pretreatment of PVA fibers with silane coupler KH560 (KH560), and the strengthening mechanism of KH560 is systematically investigated by means of multi-scale analysis. From the macroscopic test data, it was found that the flexural strength of PVA fiber concrete at 28 days was enhanced by 16% maximally when the PVA fiber content was 0.9%. A series of microscopic tests (Scanning Electron Microscope-SEM, X-ray Diffraction- XRD, Fourier Transform Infrared Spectrometer-FTIR) characterizing the interfacial properties of the KH560-modified material revealed the reason why the pretreated PVA could be better embedded in the cementitious base. Because the addition of KH560 not only generates more gel material and increases the tightness of the interfacial structure between the fiber and the cementitious base, but also reacts with the cement to produce Si-O-Si chemical bonds. A molecular model of PVA and a gel model of calcium silicate hydrate (C-S-H), the main product of cement, were constructed using the method of molecular dynamics (MD) simulation technique. The interaction between fibers and C-S-H was found to be not only mechanical occlusion, but also unstable hydrogen and ionic bonds between PVA molecules and C-S-H. The Si-O-Si bond is very important. In summary, the strengthening mechanism of KH560 and PVA synergistically on concrete is summarized by the analysis of different scales. It also provides theoretical and experimental support for the application of KH560 and PVA fibers in composite materials.