compatibility of ultra high performance concrete as repair material

3.7.1.2 Indirect tensile loadingOnce the freeze-thaw test was completed, the samples were stored under ambientlaboratory conditions until one week before the loading test. At this point they were cutinto four small prisms, 4x3x3 in, discarding approximately 1.75 in of each end, asdescribed by Li et al. (1999) and Geissert et al. (1999) and shown in Figure 3.2.Compression loading was applied using the 55-kip 810 Material Test System (MTS)machine at a constant rate of 1800 lbf/min (8 kN/min) until the sample was split, asshown in Figure 3.13.a. This loading rate would produce an indirect tensile stress ofabout 95 psi/min in a monolithic NSC sample which is the same as that applied byGeissert et al. (1999) and slightly lower than that recommended by ASTM C 496 (100-200 psi/min). All samples were exposed to the same environmental conditions when theywere not in the freeze-thaw chamber. As shown in Table 3.8, the differential shrinkagebetween samples was kept constant between 0 and 300 cycles and as well between 600and 900 cycles, with the purpose of minimizing the introduction of a new variable intothe test matrix (Julio et al. 2005). To estimate the indirect tensile stress along the bondinterface, Equation 3.1 was applied despite the fact that the prisms were made up of twodifferent materials. The nominal area, 4x3 in, was used for the samples subjected to 0 and300 cycles while the real area was measured for those samples subjected to 600 and 900cycles. Figure 3.2.c shows the dimension of the steel bars and plywood strips used to heldthe prisms and transmit the stress evenly along the bond interface during the loading test.Figure 3.2.d gives an approximately distribution of indirect tensile stress along theinterface based on Geissert et al. (1999).3.7.2 Slant-shear testAfter demoulding, the composite samples were cured under ambient conditions (68-77°Fand 25-40% RH) until the day of testing. If the surface of NSC was not perfectly flat, asmall cut in the corner was made to obtain a regular surface. Different measures of thecross area of all prisms were taken. The load rate was 35 psi/s according to ASTM C 39.A calibrated Baldwin CT 300 hydraulic load frame was utilized to apply the load.65