compatibility of ultra high performance concrete as repair material

days failed at UHPC or B(UHPC). While the failures at 3 days took place in the concretesubstrate for all specimens with an interface angle of 55°, the least demanding angle forthe interface, and in the bond, UHPC or a general failure for all specimens with interfaceangle of 60° and 70°. Notice that the compressive strength at 2 days of UHPC cured inambient conditions is still considered weak and is less than the 40% of the ultimatecompressive strength at 28 days.The assessment of the failure modes gives remarkable information about the quality ofthe bond and highlights the importance of the joint angle in the slant-shear test. Allspecimens at the age of 8 days with an interface angle of 60° failed in the concretesubstrate. Consequently, the bond capacity obtained only establishes a minimum of theactual strength of the bond. As shown in Figure 4.12, the highest shear stress wasobtained with the sandblasted surface. This might lead to the wrong conclusion that thegreater strength bond is attained with the sandblasting treatment. However, this deductioncannot be taken due to fact that the concrete substrate of the sandblasted specimens hadhigher compressive strength (8112 psi) than those of the other surfaces (6460 and 6607psi). In contrast, the specimens with an interface angle of 70° provide more informationabout the quality of the bond. All specimens with brushed surface failed in the bond.Hence, the bond capacity estimated is the actual one for this surface. The rest ofspecimens failed, mostly, in the concrete substrate, signifying that these bond interfacesmight have resisted greater stresses. Figure 4.12 shows the bond capacity at 8 days for60°. It is observed that the bond strength, at the age of 8 days, is well beyond the ACI546.3R-06 requirements at 7 days and even satisfies the minimum bond strength at 28days.87