Mechanical and damage mechanisms of reinforced ultra high performance concrete under tensile loading

Understanding the tensile mechanism of reinforced ultra high performance concrete (RUHPC) is important for structural design and application of ultra high performance concrete (UHPC). In this study, the direct tensile test accompanied with crack width detection and acoustic emission (AE) source locating were conducted on RUHPC specimens with the longitudinal reinforcement ratios of 0%, 2.3% and 4.6%. Two types of RUHPCs were studied: high strain hardening RUHPC (HSH-RUHPC) and strain softening RUHPC (SS-RUHPC). Experimental results included the tensile stress (load)-strain curves, the crack width-strain curves and the AE source distribution maps under tensile loading. The tensile mechanisms were elaborated from two aspects. From the view of mechanical mechanism, during Stage I (the elastic stage) and Stage II (the elastic-plastic stage): (1) HSH-RUHPC had a globally uniform stress distribution while the steel rebar in SS-RUHPC changed from total elastic state to partial yielding and finally to partial strain hardening; (2) the reduction of the tensile strength of UHPC was observed in RUHPC, which was more obvious with the higher reinforcement ratio. From the view of damage evolution mechanism based on AE analysis method at the micro level: (1) HSH-RUHPC exhibited a homogeneous damage distribution owing to its multiple-micro-cracking mode before steel yielding; (2) SS-RUHPC showed several damage concentrations at crack positions after UHPC softening due to its several-macro-cracking mode. Meanwhile, Gini index was proved to be an effective parameter to evaluate the distribution non-uniformity of the internal damages of RUHPC. (C) 2019 Elsevier Ltd. All rights reserved.