Understanding the role of coarse aggregate on tensile fatigue behaviors of ultra-high performance concrete

This work investigated the tensile fatigue behaviors of ultra-high performance concrete containing coarse aggregate (UHPC-CA), with an emphasis on exploring the underlying mechanisms induced by CA incorporation. Upon constant-amplitude fatigue tests at four different stress levels, CA incorporation-induced variations in fracture morphology, deformation capacity, and fatigue life of UHPC-CA were analyzed, which were further revealed through multiscale characterization of hydration products, pore structures, and stress state alterations within UHPC matrix. The results showed that despite the considerable enhancement in elastic modulus in comparison with CA-free UHPC, weakened fatigue deformability and accelerated damage evolution are observed for UHPC-CA. As the CA content increased, the performance degradation was continually exacerbated, and it was experimentally evidenced to be highly linear with the loss of bound water and the increase in macropore volume. Compared to CA-free UHPC, the premature fatigue failure of UHPC-CA was primarily attributed to the magnified stress concentration within the matrix.