AbstractThis paper presents the results of an experimental investigation on the interface bond strength between reinforcing fibers embedded in a calcium sulfoaluminate (CSA) cement matrix, utilizing the single-fiber pullout test. Bonding at the fiber–matrix interface plays an important role in controlling the mechanical performance of cementitious composites. To examine the fiber–matrix bond within the CSA and portland cement system, fibers with differing elastic modulus strengths were selected, including polyvinyl-alcohol (PVA), polypropylene, coated steel, and plain steel. The fibers were embedded in three different matrices: two sulfate-based cements including a commercially available CSA cement and a CSA cement fabricated from coal-combustion byproducts. The third matrix was a silicate-based ordinary portland cement. In this study, the single-fiber pullout test was employed to examine the fiber–matrix interface and the effect of cement type on interfacial bond strength. Experiments show the more rigid-dense morphology of the CSA cement paste related to the ettringite crystal structure yielded higher shear-bond strengths for both steel and synthetic fibers. Results suggest the primary way to increase the effectiveness of reinforcing fibers is to decrease the modulus of elasticity ratio of fiber to matrix.