compatibility of ultra high performance concrete as repair material

At the same time as this research was going on, (Sritharan et al. 2012) published anexperimental investigation about the bond between UHPC and normal concrete. A totalof 60 slant shear specimens were cast. The inclination angle chosen was 53.1°. Fivedifferent textures for the concrete surface (from 1.3 mm to 5 mm) and three differentconcrete strengths (5000, 7500 and 10000 psi) were used. The bond capacity obtainedvaried, approximately, from 4250 psi with a concrete substrate of 10000 psi compressivestrength to 2175 psi with a concrete substrate of 5000 psi. These results are similar to theobtained in this research for an angle of 60°: from 3143 psi with a concrete substrate of8112 psi compressive strength to 2339 psi with a concrete substrate of 6460 psicompressive strength. It should be recalled that a greater angle from the horizontalproduces a more critical situation with a lower bond capacity as previously stated.4.3 Pull-off testThe pull-off test consists in applying a direct tensile force to a core advanced intoconcrete substrate until failure takes place. Although an estimation of the tensile strengthwas obtained by means of the splitting tensile test, this method was carried out due to thefact that can be used in situ or in laboratory, making possible the future correlation of thebond strength between different loading tests.4.3.1 ResultsTable 4.10 summarizes the pull-off results. Equation 3.2 was used to estimate the directtensile strength, f t . A 2 in diameter was utilized to calculate the area of the cores. TheNSC compressive strengths presented are those of the day of testing, however UHPCcompressive strengths were estimated by testing two cylinders from each mix 2 or 3 daysbefore the direct tensile test, exactly at 8 days after casting; therefore, the UHPCcompressive strengths given have to be considered as a minimum of the true ones. Allcores failed in the concrete substrate, except one that failed in the bond. Figure 4.15shows these two different failure modes. All cores after failure can be found in theAppendixes. It should be emphasized that the averages of the tensile strengths shown inTable 4.10 do not represent the actual tensile bond strength due to the fact that the91