Interfacial characteristics and mechanical behaviors of geopolymer binder with steel slag aggregate: Insights from molecular dynamics

Abstract

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 Ca 2+ 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. • 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, Ca 2+ and Na + migrate to the interface to form hydrated ions.