Influence of fiber shapes on the compressive behaviors of ultra-high performance concrete containing coarse aggregate

The addition of coarse aggregate in ultra-high performance concrete (UHPC-CA) has the potential to reduce autogenous shrinkage and improve mechanical properties. However, it also affects the fiber distribution and crack propagation, thereby compressive relationship of UHPC. This study investigated the effects of different fiber shapes on the compressive behaviors of UHPC-CA. Three fiber shapes (straight fiber, hooked fiber, and hybrid fiber) and six coarse aggregate content (0-1200 kg/m3) are the main variables. The test results have indicated that the addition of coarse aggregate in UHPC rendered wider main cracks. Hybrid fiber was preferred over the hooked-end and straight fibers to optimize ductility in UHPC-CA. An increase in compressive strength of up to 17.7 % and elastic modulus of UHPC of up to 23.7 % after moderate addition of coarse aggregate contents, The fiber shape affected peak strain and ultimate strain values for UHPC-CA. Their peak and ultimate strains were improved by 12.8 %-15.3 % and 38.2%-127.4 % with the inclusion of 2 % hooked and hybrid fibers. Based on the experimental data and relevant equations, a proper rational equation from the existing literature is used to generate the complete compressive stressstrain curves of UHPC-CA with different fiber shapes. In summary, this study establishes that hybrid fiber shapes significantly enhance the compressive properties of UHPC-CA. The high elastic modulus and ductility of the UHPC-CA with hybrid fiber are particularly promising for blast and impact applications.