The effect of processing on the bond and interfaces in steel fiber reinforced cement composites

The object of the present work was to study the influences that processing may have on the pullout resistance of a steel fiber from a normal cementitious matrix, consisting of portland cement binder cast as paste or mortars with varying sand content. In order to determine the mechanisms by which the processing affects the pull-out resistance, the nature of the interfacial transition zone (ITZ) was evaluated simultaneously by microhardness testing and characterization of its microstructure by SEM. It was found that processing of the matrix and modifications in its composition by changing the sand content had a considerable influence on the steel fiber-matrix average bond, which was increased by a factor of two. The influences are due to changes in the interfacial microstructure and the content of sand. In pastes, the interfacial microstructure seems to be the dominant mechanism controlling bond, and processing which leads to densening results in higher average bond. The influences in mortars are more complex; average bond is less sensitive to processing and is more influenced by the sand content.