compatibility of ultra high performance concrete as repair material

5.1.4 Overall performancea. For this formulation (Ductal®JS1000), better bond performance is expected witha saturated concrete substrate. A dry condition of the concrete substrate cannegatively affect the development of the bond strength while a saturated conditionof the concrete substrate is beneficial for obtaining an excellent bondperformance. If the appropriate wetting condition of the substrate takes place, theroughness degree of the concrete substrate (friction) is not a critical factor toobtain a good bond strength due to the high adhesion that is developed betweenboth materials.b. The bond performance between UHPC and NSC is considered successful, as thestrength, regardless the different loading configurations, is greater than that of theconcrete substrate and largely satisfies the requirements of ACI 546.3R-06.c. It is not possible to draw a failure envelope of the bond between UHPC andconcrete due to the fact that in most cases the failure occurred in the concretesubstrate. Therefore, it was only possible to have a lower bound of the realcapacity.d. When UHPC has achieved a strength greater than 14,500 psi and theconcrete substrate had an adequate wetting condition at the day of placingthe overlay, the NSC substrate, designed according to MichiganDepartment of Transportation (2009) for concrete overlays, will be theweakest part of the composite system and the bond will offer a performancethat accomplish with the ACI 546.3R-06 requirements.e. The compressive strength obtained under ambient condition for UHPC (22.5 ksi)is considerably lower than the typically expected under thermal treatment (30 ksi)for this specific formulation (Ductal JS1000). Despite this, UHPC offered goodperformance under freeze-thaw cycles and its strength widely surpasses to that ofNSC.98