ABSTRACT
The selection of UHP-FRCC samples used in this study is based on results from previous studies (Kwon et al., 2014, Kwon et al., 2015). To improve
1 INTRODUCTION
Ultra-High-Performance Fiber-Reinforced Cementitious Composites (UHP-FRCC) fall under the is category of Strain Hardening Cementitious Composites (SHCC) and show excellent mechanical properties even under tensile stress. In particular, strain hardening behavior has been achieved by formation if multiple cracks rather than by the widening of a single crack. The number of cracks increases during strain hardening but generally, the widths of multiple cracks can be controlled within a very narrow range of less than 0.1 mm. Due to the very dense micro-structure and the extremely low water-binder ratio (0.15 in this study), UHPFRCC shows excellent resistance to the penetration of aggressive substances into the matrices (Tanaka et al., 2010). On the other hand, even if the crack widths are very small, the presence of multiple cracks is mandatory to achieve a high mechanical performance. In other words, in order to exploit the excellent mechanical properties of UHP-FRCC, these should be designed with the presence of cracks. Thus, the durability of cracked
the tensile performance of UHP-FRCC, the factors that influence their tensile behavior have been identified and a material design based on a multiscale fiber-reinforcement system is proposed (Fig. 1(a)). According to fracture mechanics criteria for concrete, micro-scale cracks initiate in the so-called fracture process zone, in the form of a large number of very fine and invisible cracks, which are formed in the area where the tensile stress is concentrated. With further increase in stress, these cracks join and propagate into the concrete matrix. This process progresses to the meso-scale and macro-scale, which finally leads to failure. Fibers with appropriate sizes can bridge cracks and restrain their widening at the early stage of crack formation. This multi-scale fiber-reinforcement is the key mechanism by which UHP-FRCC can be obtained while reinforcing a very high strength matrix. The typical mechanical performance of UHP-FRCC employed in this study is shown in Fig. 1(b), which describes the relationship between strain and tensile stress under a uniaxial tension. Strain hardening behavior and high tensile strength are observed in UHP-FRCC.
