Ultra-high performance concrete under direct tension: Investigation of a hybrid of steel and synthetic fibers

Abstract

Ultra-high performance concrete (UHPC) offers superior tensile properties in comparison to normal and high-strength concrete. This is known to largely depend on the fibers included in the UHPC mixtures. Among the available types of fiber, steel fibers have been commonly used in the current practice. However, given the price and availability issues associated with steel fibers, there has been growing interest in benefiting from synthetic fibers in UHPC. This was the motivation for the current study to investigate the potential of five synthetic fibers by evaluating how the tensile properties of the UHPC mixtures made with a hybrid of steel and synthetic fibers are influenced under direct tension. The synthetic fibers of choice consisted of nylon, polypropylene, polyvinyl alcohol, alkali-resistant glass, and carbon fibers. By using a dog bone test setup, the main tensile properties of the developed mixtures (i.e., direct tensile strength, elastic modulus, and stress–strain relationship) were systematically determined. The results extracted from direct tension tests were then further processed in conjunction with digital image correlation analyses to investigate the formation and propagation of cracks, as well as the post-cracking response. The original findings reported from this study are expected to pave the way to broaden the fiber types that can be considered for the structural applications of UHPC, especially where high tensile stresses/strains are anticipated.