compatibility of ultra high performance concrete as repair material

substrate while the scarifying method has a high risk of introducing microcraks(International Concrete Repair Institute 1997).• Pulverization (steel shotblasting, abrasive blasting)Shot-blasting treatment is a useful surface treatment to remove concrete up to a depth of¼ inch, providing a roughed surface without dust. The treatment consists of blasting steelshot at high velocity onto the concrete surface. Based on bonding tests in the field, amacrotexture of 1.5 mn suggests that the surface has been enough shot-blasted to providean adequate roughness (International Concrete Repair Institute 1997; Sprinkel 1997).Sandblasting or abrasive blasting methods use compressed air mixed with an abrasivemedium to remove damaged concrete surfaces or to clean the steel bars. Shot-blastingand sand blasting have a low risk of producing microcracks in the remaining concrete(International Concrete Repair Institute 1997).• Expansive pressure (steam: flame blasting, water: high-pressure water jetting)Flame scaling or flame blasting method consists in creating tensile stress near theconcrete surface that fracture both matrix and aggregate by means of the expansive forceof superheated pore water. This method might cause a bruised layer in the remainingconcrete (International Concrete Repair Institute 1997).2.3.3 Failure Envelope of the Bond InterfaceAustin et al. (1999) stated that each different bonding test provides a narrowrepresentation of bond behavior, therefore, in order to fully understand the characteristicsof bonded materials, diverse bonding tests that produce different stress states should beapplied. A bond failure envelope can be drawn from the different states combinationsobtained by means of the different loading configurations. For this purpose, Robins andAustin (1995) proposed a simplified failure envelope of straight line based on anadhesion-friction relationship, where the adhesion is the tensile adhesive strengthbetween the new and old materials and the friction is a degree of the shearing resistance,namely, friction and interlock effects. It can be noted that the compressive stress normal30