compatibility of ultra high performance concrete as repair material

Only those specimens with a grooved substrate surface were fully successful in the drysubstrate condition, due to the fact that the bond was achieved by fitting UHPC in thegrooves rather than any adhesive mechanism since no dust removal treatment was appliedin the grooved surface, as shown in Figure 3.6.f. The tensile strength of prisms withgrooved substrate surface and the COV are given in Table 4.5.Gr300FTGrw/oTable 4.5Results of grooved surface under dry concrete substrate conditionPrism (strength+failure mode)Meanstrength,COVN A B C D specimen1 638 G 839 G 981 G 872 G 833 17.22 743 G/C 672 G/C 1048 G 872 G 834 19.83 734 G 733 G 723 G 318 G 627 32.81 761 G 714 G 765 G 824 G 766 5.92 615 G/C 748 G 621 G/C 555 G 635 12.8Meanstrength,casestudyCOV,casestudy764 24.43 730 G/C 784 G 755 G 766 G 759 3.0 712 11.2Note: N: number of the specimen, Gr: grooved, w/o: without freeze-thaw cycles, FT: freeze-thaw cycles, G:failure in the grooves, G/C: mixture failure between bond and concrete. Strength in psi.However, excellent bond performance was achieved under saturated concrete substrate,with the exception of four composite specimens that presented scattered results. The testresults for the saturated substrate samples are presented in Table 4.6 along withdescriptions of the failure modes. The four specimens with high COV were highlighted ingrey. The rest of the samples widely satisfied the range of 250 to 300 psi (1.7 to 2 MPa)at 28 days specified in the ACI 546.3R-06 for acceptable bond strength and 300 psi (2.1MPa) that (Sprinkel and Ozyildirim 2000) defined as an excellent bond. These valuesrefer to direct tensile bond. This comparison with indirect tensile strength is based onresults from Momayez et al. (2005) that demonstrated the bond strength obtained with thepull-off test (direct tensile strength) to be equal or slightly lower than that of the splittingtest (indirect tensile strength).76