Effect of polypropylene fibers on the fracture behavior of heated ultra-high performance concrete

Abstract

In this work we assess the effect of the addition of polypropylene (PP) fibers in a heated ultra-high-performance fiber reinforced concrete (UHPFRC). To this end, three sets of specimens with identical cementitious materials were manufactured: plain concrete, a concrete reinforced exclusively with steel fibers and a concrete reinforced with steel and polypropylene fibers. The mechanical and fracture properties of each concrete at temperatures ranging from room temperature to 300∘C were determined. A thorough appraisal of the thermal effect on the microstructure was also carried out by means of an X-ray scan analysis. Based on the testing data, the relation between the macroscopic response, including mechanical and fracture behavior, and the microscopic structure, i.e., size and number of pores and their distribution, is ascertained. The results show that the addition of PP fibers significantly increases the maximum pore size and slightly increases the total porosity. Furthermore, the partial melting of polypropylene fibers at 300∘C, in combination with the rise in porosity, reduces thermal damage and results in similar behavior at low and high temperatures, room temperature and 300∘C, respectively.