Impact of Macro-Polypropylene Fiber on the Mechanical Properties of Ultra-High-Performance Concrete

Steel fibers are frequently used in ultra high-performance concrete (UHPC) due to their superior properties, but they also have disadvantages, such as corrosion exposure, high specific gravity and high cost. Although synthetic fibers have emerged as an alternative, the focus has generally been on hybrid use with steel fibers in UHPC. This study investigates the applicability of macro-polypropylene (PP) fibers for UHPC in terms of mechanical properties. An experimental campaign was conducted for UHPC mixtures containing macro-PP fibers with varying volumetric ratios. The effects of macro-PP fiber on the mechanical properties of UHPC were investigated in terms of compressive strength, splitting tensile strength and flexural behavior. The two-dimensional digital image correlation (2D-DIC) method was adopted to examine the cracking behavior. In addition, tensile constitutive law for UHPC mixtures was obtained with inverse analysis based on Model Code 2020 (MC2020). The results showed that the use of macro-PP fibers had no significant impact on compressive and splitting tensile strength. However, residual flexural tensile strength and fracture energy increased by up to 2.8 and 2.5 times, respectively, compared to UHPC without fiber. It was determined that macro-PP fibers could exhibit effective crack control in UHPC.