Monotonic and cyclic compressive behavior of ultra-high performance concrete with coarse aggregate: Experimental investigation and constitutive model

This paper presents a systematic investigation on the compressive stress-strain behavior of ultra-high performance concrete with coarse aggregate (UHPC-CA) subjected to monotonic and cyclic loading. A total of eight groups of UHPC specimens considering different coarse aggregate (CA) and steel fiber (SF) contents were tested, with a synchronous monitoring and acquisition of acoustic emission (AE) signal releasing process. The mechanical properties and performance degradation of UHPC were analyzed. The damage mechanism of UHPC under compression and synergy of CA and SF were discussed. The results show that the inclusion of CA and SF has notable positive synergetic effect on the compressive behavior of UHPC, in spite of deformability. Moreover, obvious elastic stiffness degradation of UHPC with loading cycles is observed, which is alleviated by the incorporation of CA and SF. The failure pattern of UHPC is changed from tensile cracks to shear cracks with the increase of SF and CA contents. In addition, SEM observations demonstrate that CA in matrix acts as the 'skeletons' of UHPC, although the microstructures of UHPC are broken because of more pores caused among the inclusions and 'wall effect' of CA. Finally, a semi-empirical elastoplastic damage constitutive model is developed to generate the compressive response of UHPC-CA under monotonic and cyclic loading.