Effects of transition zone densification on fiber/cement paste bond strength improvement

This paper investigates the effectiveness of transition zone densification on the fiber-cement paste system. By controlling the water: cement (w:c) ratio and the condensed silica fume content, environmental scanning electron microscopy studies confirm that transition zone densification can be achieved in all brass, steel, and polyethylene fiber-cement systems. However, single fiber pullout tests indicate that densification only enhances the brass-cement paste interface bond strength and not the other systems. Further microscopy investigation of the surface of fibers peeled off from a composite fracture surface and of the groove left by the fiber on the cement paste suggests that bond failure for the brass-cement system is of a cohesive type, whereas bond failure for the other two systems is of an adhesive type. It is concluded that the transition zone densification technique should be effective in fiber-cement systems in which bond strength is controlled by cohesive failure of the transition zone material.