compatibility of ultra high performance concrete as repair material

a) C: Concrete failure b) B: Bond failureFigure 4.15 Failure modes in the pull-off testThe bond performance between UHPC and NSC can be considered successful, as thetensile strength of the bond and the overlay material are greater than that of the concretesubstrate. As shown in Figure 4.16, the tensile strength obtained at 10-11 days, reach therequirements at 7 and 28 days.600Minimun direct tensile strength (psi)4002000318331Brushed, 10-11 days Sandblasted, 10-11days352370Rough, 10-11 days Grooved, 10-11 daysAcceptablebondstrength a28 days (ACI546.3R-06 )Acceptablebondstrength a 7days (ACI546.3R-06 )Figure 4.16 Tensile strength per case study obtained in pull-off test at 10-11 daysHowever, it should be noted that the failure stresses of the concrete substrate are lowerthan expected. By using Equation 4.1, given by ACI318-11, an estimation of the splittingtensile strength of the concrete substrate can be obtained from the compressive strength.The expected splitting tensile strength for the concrete substrate is between 526 and 598psi. Momayez et al. (2005) demonstrated that the splitting tensile strength is equal orslightly greater than the direct tensile strength. The experimental results gave noticeablylower average tensile strengths, 318 to 370 psi. It is well known that the tensile strength93