Molecular dynamic simulations of interfacial interaction mechanism between the NASH gels and the polyethene fibre

Cementitious materials suffer from their inherent brittleness, and thus much research has been devoted to circumventing this problem. A promising approach is incorporating polymeric fibre to enhance the ductility of cementitious materials. Therefore, fibre-reinforced geopolymer composite (FRGC) has attracted much attention due to its ultra-high ductility and environmentally friendly characteristics. The bonding between the fibre and matrix plays a critical role that impacts the FRGC's performance. However, the structure–property relationship of the composite is still unclear. In particular, the effect of matrix compositions, i.e., sodium aluminosilicate hydrated (NASH) gel, on the frictional bonding remains a mystery. In this paper, we employ molecular dynamics simulations to obtain a fundamental understanding of the interfacial interactions between NASH gels and polyethene (PE) fibre – a commonly found FRGC. The dynamic pull-out and the interfacial property characterisations are conducted for several NASH/PE models with different Si/Al ratios and internal moisture contents. Our results reveal that the adhesive bonding between the NASH and PE is influenced by the interfacial interaction and the mechanical interlocking between the two materials. The interfacial interaction energies between NASH and PE are dominated by the short-range van der Waals interactions and the hydrogen bonding between hydrogen atoms in the polyethene chains and oxygen atoms in the NASH. In addition, the Si/Al ratio can significantly impact the shear bonding strength between PE and NASH. Moreover, the degradation of the adhesive properties of NASH/PE composite strongly correlates to the internal moisture of the NASH. Thus, our work reveals the sources of frictional bonding between PE fibre and NASH gels, and relates the bonding performances with the Si/Al ratio and the internal moisture content of the matrix. Our results will provide valuable insights into the material design of FRGC and optimize their performances.