Early-age autogenous shrinkage, tensile creep, and restrained cracking behavior of ultra-high-performance concrete incorporating polypropylene fibers

Ultra-high-performance concrete (UHPC) as a kind of progressive cement-based material has attracted wide attention in the field of concrete engineering due to its superior performance. Nonetheless, the high early-age cracking potential of UHPC under restrained conditions due to the considerable autogenous shrinkage (AS) becomes one major impediment. Polypropylene fibers have been added to UHPC for increasing the tensile strength. However, the influence of polypropylene fibers on the cracking potential of UHPC under restrained conditions is not well studied. The restrained cracking behavior of UHPC incorporating polypropylene fibers was examined by the temperature stress test machine tests in the present study. To study the influencing mechanism of polypropylene fibers on the cracking potential of UHPC, workability, mechanical properties, shrinkage-induced stress, AS, and tensile creep were investigated. Results indicated that the incorporation of polypropylene fibers improved the tensile strength and flexural toughness, decreased the elastic modulus and AS, and increased the tensile creep of UHPC. The shrinkage-induced tensile stress obtained from test was reduced by 64.9%, 65.9%, 67.8%, and 67.5% attributed to creep when compared to the calculated theoretical stress for UHPC incorporating 0%, 1%, 2%, and 3% volume proportion of polypropylene fibers, respectively. As a result, the cracking potential of UHPC under uniaxial restrained condition estimated by the integrated criterion decreased by 21.7%, 60.7%, and 44.1% with the increasing volume proportion of polypropylene fibers from 0% to 1%, 2%, and 3%, respectively.