compatibility of ultra high performance concrete as repair material

4 Results and DiscussionThis chapter presents the results obtained from different loading configurations. Theexperimental program was made up of three different bonding test methods, including,splitting tensile test combined with freeze-thaw cycles, slant-shear test and pull-off test.The failure stress and the failure mode were taken from each composite sample. Thelocation of the failure provides valuable information about the quality of the bondbetween the repair and substrate materials. In general, if the failure takes place in thesubstrate, it can be stated that the bond strength is at least as high as that of the concretesubstrate. If the failure occurs at the bond interface, the failure strength estimated is thebond strength. Therefore, a failure that occurs in the concrete substrate indicates that thebond strength is greater than that of the substrate concrete. The failure mode of eachtested sample was visually examined and classified as the bond, concrete substrate,overlay or a mixture failure of these. ACI specified a bond strength range to select therepair materials in Guide for the Selection of Materials for the Repair of Concrete (2004)(ACI 546R-04) depending on the bond testing, as shown in Table 4.1. These values areconsidered as the minimum acceptable bond strength.Table 4.1ACI bond strength range for different bond test configurations. Adapted from ACI 546R-04DescriptionBond strength1 days: 400 to 1,000 psi 3 to 7 MPaSlant-Shear Bond7 days: 1,000 to 1,800 psi 7 to 12 MPa28 days: 2,000 to 3,000 psi 14 to 21 MPa1 days: 70 to 150 psi 0.5 to 1 MPaDirect Tensile Bond7 days: 150 to 250 psi 1 to 1.7 MPa28 days: 250 to 300 psi 1.7 to 2 MPa1 days: 150 to 300 psi 1 to 2 MPaDirect Shear Bond7 days: 300 to 400 psi 2 to 3 MPa28 days: 400 to 600 psi 3 to 4 MPaThe highest bond strength expected is that of the slant-shear in which a combined state ofshear and compression stresses is produced along the bond interface. While the loweststrength is obtained under direct tension (the most severe loading condition). Thiscoincides with the experimental results provided by Momayez et al. (2005) that rankedthe different tests according to the bond strength average obtained, from the greatest69