Experimental study on the mechanical properties and the microstructure of hybrid-fiber-reinforced concrete under an early stage

Based on the fixed aspect ratio of 650 for carbon fiber (CF) in hybrid-fiber-reinforced concrete (HFRC), this study investigated the effect of polypropylene fiber (PPF) and the aramid fiber (AF) aspect ratio on the mechanical properties of HFRC under the early stage. For this purpose, compressive, splitting tensile, and flexural tests were carried out to obtain the optimal hybridization parameters with respect to the aspect ratio of polypropylene fiber (PPF-AR) and aramid fiber (AF-AR) in HFRC. Additionally, the microstructure of HFRC was also examined by scanning electron microscope method to investigate the bond properties between fiber and a concrete matrix. It can be found from the results that the failure modes of overall tests are a ductile failure. The enhancement of tensile strength is attributed to PPF-AR, whereas AF-AR mainly tends to improve the performance in compressive and flexural strength. Meanwhile, the aspect ratio of fibers has little effect on the tensile-to-compressive-strength ratio (TC-R) or the flexural-to-compressive-strength ratio (FC-R) of early-stage HFRC.