chapter  13
A study of properties of the paste-aggregate interface
Pages 10

Abstract The properties of the interfacial zone between aggregate and cement paste was studied. A newly developed push-out method was used to evaluate the interfacial properties of transition zone including the stiffness, strength, friction and fracture energy of the interface. A closed loop controlled set-up was used to continuously measure force and slip-displacement during loading. The experimental data were analyzed by using a recently proposed theoretical model. The transition zone was further investigated by using backscattered electron imaging and energy dispersive analysis of x-rays to characterize the microstructure of the interface. The relationship between mechanical properties and microstructure of interfacial zone was studied. Type of aggregate, treatment of aggregate surface, mixing process and incorpo­ ration of silica fume were investigated. It was found that the microstructure of the interfacial zone can be significantly improved by aggregate pretreatment and mixing methods, and thus the mechanical interfacial properties can be enhanced. Keywords: Interfacial zone, Bond-slip relationship, Fracture energy, Silica fume, Aggregate, Shear bond strength

A number of studies have been conducted to characterize the chemical nature, morphology and mechanical properties of interfacial zone. The microstructure of the interface has been investigated using a scanning electron microscope(BSE) . The formation of a calcium hydroxide film adjacent to the aggregate surface has been observed. By using EDAX, the presence of ettringite and the preferentially oriented calcium hydrox­ ide crystals in the interfacial zone has been demonstrated . BSE imaging has been used to quantify the transition zone . It was found that the porosity at the interface decreases towards the bulk paste.