compatibility of ultra high performance concrete as repair material

such test configuration, this upper bound is represented by point u b1 in Figure 2.8.Another way to explain it, if the bond failure envelope intercepts with the τ/σ ratiostraight line outside the Mohr’s circle in compression, the bond strength cannot bedetermined due to the fact that the failure will occur in the material instead of the bondinterface. The same concept can be applied to the Mohr’s circle in direct tension or pureshear, represented by points u b2 and u b3 .Morh’s circles from: 1 compressive strength, 2 direct tensile test, 3 pure shear. Bond/material failurecriterion (ub1, ub2, ub3, upper bounds for failure at the joint plane). Bond failure envelope (*) can bedefined while Bond failure envelope (**) cannot be defined due to its strength its greater than that of thematerial.Figure 2.8 Upper bounds to determine the bond failure envelope. Modified from Robins and Austin (1995)Robins and Austin (1995), and Austin et al. (1999) carried out the slant-shear test withthree different interface angles, the direct tension test (pull-off), patch test and the tensileshear test in order to accurately understand the bond strength of cementitious materials.The authors stated that the Mohr criterion in its basic shear-compression relationship witha tensile cut-off overestimates the shear strength area as it was demonstrated in the studyof rock mechanics and the better fits to the experimental data achieved from the different32