Compressive properties of polypropylene fiber reinforced seawater sea-sand recycled aggregate concrete under different strain rate loading

Polypropylene fibers possess high strength and excellent abrasion resistance, and have been used to enhance concrete materials. This study investigated the influence of polypropylene fibers on the dynamic compressive properties of seawater sea-sand recycled aggregate concrete (SSRAC) under three strain rates (10- 5 , 10-4, and 10-3/s). 90 specimens were prepared, with fiber lengths of 9, 13.5, and 18 mm (the corresponding aspect ratio of 357, 536, and 714, respectively), and fiber contents of 0.6, 0.9, and 1.2 kg/m3. The test results indicate that the polypropylene fiber reinforced SSRAC specimens are more sensitive to strain rate in terms of peak stress and peak strain, and the incorporation of fibers generally increases the peak stress. Furthermore, the microscopic morphology and nanoindentation analysis are conducted on the interfacial transition zone (ITZ) of the polypropylene fiber reinforced SSRAC. The addition of polypropylene fibers increases the local porosity of the ITZ, and reduces the bonding area between mortar and aggregates, resulting in a decrease in the elastic modulus of the ITZ. This reduction effect varies with different lengths and contents of fibers, which has a significant impact on the peak stress, peak strain, and elastic modulus of specimens, leading to some degree of dispersion in the corresponding strain effect. Finally, a dynamic prediction model for fiber-reinforced SSRAC is derived, which provides a theoretical basis for the study of the dynamic mechanical properties of fiber reinforced SSRAC.