Comparative biaxial flexural behavior of ultra-high-performance fiber-reinforced concrete panels using two different test and placement methods

In order to investigate the effects of fiber length, placement method, and test method on the biaxial flexural behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC), several UHPFRC panels with two different fiber lengths (L_f of 13 and 19.5mm) were fabricated using two different placement methods (placing concrete at the center and the edge) and were then tested by two different test methods (ASTM C1550-12a and a novel biaxial flexure test (BFT)). Image analysis was also performed to quantitatively investigate the fiber distribution characteristics according to the fiber length and placement method and to thoroughly analyze the experimental results. The first cracking strength and corresponding toughness were found to be insignificantly influenced by the fiber length, placement method, and test method, but the panels with longer fibers and with concrete placed at the center (in the maximum moment region) were found to have higher biaxial flexural strength, deflection capacity, and toughness after a deflection of 2.5mm (d2.5). The panels tested by the BFT method showed lower flexural strength, more cracks with a random distribution, and higher deviation in flexural performances than those tested by ASTM C1550. These test results were verified by evaluating the fiber distribution characteristics (i.e., the number of fibers per unit area, fiber orientation, and fiber dispersion) at localized crack surfaces by using the image analysis technique.