Experimental investigation on the damage behavior of ultra-high performance concrete subjected to cyclic compression

This study deals with the compressive response and damage evolution of ultra-high performance concrete (UHPC) subjected to uniaxial monotonic and cyclic compressive loadings. A total of 36 prismatic specimens are tested for different fiber aspect ratios and volume fractions. The acoustic emission (AE) technique is applied to monitor the damage progression and unravel the failure mechanism of UHPC. The test results demonstrate that the incorporation of steel fibers improves the mechanical properties of UHPC in terms of peak stress, peak strain and elastic modulus, and in particular the ultimate strain and toughness for cyclic loading scenarios. The cyclic envelope curve is noted to conform with the corresponding monotonic response. The plastic strain accumulation is linearly proportional to the envelope unloading strain. Moreover, significant stiffness degradation with increasing loading cycles is observed during the cyclic loading process, which can be alleviated by inclusion of steel fibers. Results from AE show that after the peak stress, a concentrated AE signals are released accompanied with an abrupt stress drop implying that a significant amount of fiber pullout, sliding and fracturing events are occurring during the loading process that significantly prohibit the damage process. The cumulative AE counts increase with an increase in fiber volume fraction, whilst the mixture with medium fiber aspect ratio of 60 shows the most AE counts. It is also found from the AE parametric analysis that the failure of UHPC with steel fibers is predominately induced by the accumulation of shear cracks, which differs from the failure of UHPC without fiber where tensile cracks are dominant. Finally, an elastoplastic damage model is proposed to describe the uniaxial monotonic and cyclic stress-strain behavior. The prediction yields a close estimation to the experimental results from both current study and literature.