Experimental study on time-dependent behavior of cracked UHP-FRCC under sustained loads

Ultra-high-performance fiber-reinforced cementitious composite (UHP-FRCC) has been successfully developed over the last decade. UHP-FRCC shows very high strength and high durability because of its very low water binder ratio and dense microstructures. Moreover, by incorporating a combination of steel and mineral fibers with different sizes in the mixture design, UHP-FRCC also exhibits high ductility and high energy absorption capacity, even under uniaxial tensile stress. The high ductility of UHP-FRCC materials shows strain hardening behavior with multiple cracking after the occurrence of the first crack. While extensive research on the tensile and bending behavior of this composite under short-term loading is reported, only limited results can be found on time-dependent behavior of UHP-FRCC under sustained long-term loading, which is strongly related to the situation of real structures. This paper presents experimental results concerning the time-dependent behavior of cracked UHP-FRCC specimens under sustained bending load. In bending creep test, sustained load with 50% of the pre-cracking load was applied to a pair of prismatic specimens of 50×100× 400 mm under a 4-point bending setup. The performance of UHP-FRCC is compared with those of conventional fiber reinforced cementitious composites (FRCC) using steel and synthetic fibers, which are investigated within the Round Robin Test (RRT) organized by RILEM TC 261-CCF. The results showed that UHP-FRCC exhibited smaller creep deformation at the sustained loading condition than the conventional FRCC, even when the initial deformation of the UHP-FRCC is much larger than the conventional FRCC. Cracking pattern, in terms of crack width and number of cracks, was also studied in both composites under sustained loads. As a result, the superior resistance of UHP-FRCC was obtained with respect to conventional FRCC.