Identification of the stress-crack opening behavior of HPFRCC: the role of flow-induced fiber orientation

a High Performance Fiber Reinforced Cementitious Composite (HPFRCC), containing 100 kg/m3 straight steel fibers (lf = 13 mm; df = 0.16 mm), has been designed for precast roof elements and thin slabs where fibers act as the sole reinforcement. With this material, 1m x 0.5m x 30 mm thick slabs were cast according to different procedures. Beam specimens, further tested in 4-point bending (4pb), have been sawn from them, in such a way that the direction of the principal tensile stresses resulted respectively parallel, transverse or randomly oriented with respect to the casting flow direction, along which fibers are likely to be aligned, thanks to the viscosity of the fluid mixture balanced at the purpose. From the undamaged portions of the tested beams, double edge notched square tiles were then obtained and tested according to a novel “Double-Edge Wedge Splitting” (DEWS) technique, which is deemed to provide the tensile stress-crack opening law, as an alternative to direct tension tests. The correlation between the thus identified law and the one obtained through inverse analysis from bending tests will be assessed, also in the sight of calibrating suitable crack opening limits for the definition of residual strengths. Furthermore, due to the above described specimen manufacturing process, quantitative correlation will be assessed between relevant material constitutive parameters, as above, and fiber orientation, suitably detected through image analysis.