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[Display omitted] • MD simulation can reveal the effect of moisture on interfacial behaviors of geopolymer-aggregate interaction; • Wetting characteristics of aggregate surfaces were elucidated and compared. • The interfacial mechanism of geopolymer-aggregate with the participation of moisture was explained. • Mechanical behaviors of geopolymer-water-aggregate interface were investigated using peeling and shearing simulation. The interaction between geopolymer and aggregate largely determines the mechanical properties and durability of the geopolymer concrete. The effects of moisture on interfacial behavior of geopolymer-aggregate interaction are poorly understood, especially at molecular level. Herein, molecular dynamics (MD) simulation was employed to reveal the interactive behaviors of geopolymer-aggregate interfacial system with the participation of moisture. Full atomistic models adopted for MD simulations were constructed using the sodium aluminum silicate hydrate (N -A S H) gel model and the main chemical components of the aggregates, SiO 2 and CaCO 3. Then the wetting characteristics of aggregate surfaces, interfacial characteristics and mechanical behaviors of the geopolymer-aggregate interfacial systems containing interfacial moisture were elucidated and compared. It is found that the SiO 2 surface is hydrophobic while the CaCO 3 surface exhibits hydrophilic characteristics. Interfacial moisture participates in electrostatic interaction, H-bond interaction and coordination interaction in geopolymer-aggregate interface area. Appropriate interfacial water is beneficial to the interfacial interaction of geopolymer-aggregate system, but excessive water will increase the risk of interfacial failure. The interfacial moisture affects the diffusion behavior of water molecules and Na+ ions in geopolymer to the interfacial region, and the formation of H-bonds and coordination bonds at the interface. Mechanically, with the participation of interfacial moisture, the geopolymer-SiO 2 interfacial system possesses stronger tensile strength, and a greater risk of shear failure than that of geopolymer-CaCO 3. The above atomic-level findings may facilitate a better design and fabrication of geopolymer concrete in engineering. [ABSTRACT FROM AUTHOR]

As a promising sustainable building material, geopolymer/steel-slag composite materials have been poorly known in the field of the interfacial characteristics of geopolymer/steel-slag interface, especially at the molecular level. Herein, in this work, molecular dynamics simulation was employed to reveal the interfacial characteristics and mechanical behaviors of geopolymer binder with steel slag aggregate. The molecular models of two geopolymer binders (C-A-S-H and N-A-S-H) and three main minerals of steel slag aggregate (Ca 2 SiO 4 , Ca 2 Fe 2 O 5 and CaCO 3) were constructed and carried out. Then the wetting characteristics of different mineral surfaces, interfacial characteristics, interaction mechanisms and mechanical behaviors of various geopolymer/steel-slag interfacial systems were elucidated and compared. It is found that the Ca 2 SiO 4 , Ca 2 Fe 2 O 5 and CaCO 3 of steel slag aggregate show strong hydrophilicity, attracting water molecules to accumulated on its mineral surface and promoting the diffusion of Ca2+ and Na + at the interface. The interaction energy of geopolymer/steel-slag systems is mainly composed of electrostatic interaction energy. Thanks to the accumulation of water molecules on the mineral surface, the stronger hydrogen bond interaction occurs at the interface of the geopolymer/steel-slag system. The free metal cations from mineral surfaces and geopolymer binder respectively are coordinated with the accumulated water molecules to emerge hydrated ions, forming composite ionic clusters to stabilize the interfacial interaction. Mechanically, the interaction systems with C-A-S-H binder possess stronger interfacial tensile strength and shear strength. Steel slag with higher Ca 2 SiO 4 content can effectively form strong interfacial bonding, lowering the risk of interfacial tensile failure, whereas steel slag containing more Ca 2 Fe 2 O 5 can reduce occurrence possibility of shearing damage. CaCO 3 formed by carbonization of steel slag, is conductive to strengthening the interfacial interaction with geopolymer binder. [Display omitted] • MD simulation can reveal the interfacial behaviors of geopolymer/steel-slag. • The interfacial interaction of geopolymer/steel-slag is mainly composed of electrostatic interaction. • The water molecules at the interface produce hydrogen bond interaction. • The water molecules, Ca2+ and Na + migrate to the interface to form hydrated ions. [ABSTRACT FROM AUTHOR]