Molecular dynamics simulation study on the hydrophobic mechanism of ettringite nanoporous channels modified by silane and silane/graphene oxide

Sulfoaluminate cement, as an important repairing material in engineering, plays an irreplaceable role in the urgent repair of important engineering facilities. Under the coastal environment, the waterproof demand for concrete is urgent. Silane series coatings are widely used in the waterproofing of concrete. In this paper, the MD method is used to study the multiple interface interaction in the ettringite nanopore, the Isobutyltriethoxy silane(IBTS) and IBTS/graphene oxide(GO with oxidation degree of 5%,10%, and 20%) modified ettringite nanopore under the water erosion. The bonding mechanism of IBTS, GO and ettringite interface and the hydrophobic mechanism of the coatings are analyzed. The hydrophobic efficiency of coatings is IBTS/GO10%≥IBTS/GO20%>IBTS/GO5%>IBTS > Ettringite. IBTS and GO interact with ettringite by hydrogen bonds and Ca-O ionic pairs. The interaction between GO and ettringite substrate is more stable due to its functional groups and larger specific surface area. During water transmission, the IBTS/ettringite interface interaction failed, IBTS desorbed and resulting in coating failure. But GO with a higher oxidation degree can capture the desorbed IBTS to form GO-IBTS hydrophobic network and further reduce the nanopore size and significantly hinder water invasion. This study provides a nano-perspective for the application of IBTS, IBTS/GO coatings in cement-based repair materials.