compatibility of ultra high performance concrete as repair material

concrete or bond/concrete while for brushed surface, all failures took place on theconcrete substrate for 0 and 300 freeze-thaw cycles, however, the main failure mode forthe 600 and 900 freeze-thaw cycles conditions was bond. In the case of grooved surface,the mixture failure on the concrete/grooved was the predominant one.Number of failures, case study121086420Sb w/oSb 300 FTSb 600 FTSb 900 FTBr w/oBr 300 FTBr 600 FTBr 900 TSm w/oCB/C or B/GB or GSm 300 FTSm 600 FTSm 900 FTCh w/oCh 300 FTCh 600 FTCh 900 FTGr w/oGr 300 FTGr 600 FTGr 900 FTFigure 4.8 Failure modes per case study in the splitting tensile test under wetting conditionsFigure 4.9 represents the final average bond strength for each case study and Figure 4.10gives the COV of the bond strength for each case study. It was decided not to include thefour specimens that gave high values of COV and that are highlighted in Table 4.6 due tothe fact that a potential error in the preparation of the samples could have taken place. Sbw/o 3 specimen is a clear example of the latter; two prisms obtained high values of tensilestrength that surpass widely the requirements given by ACI 546.3R-06, however, notensile bond strength was developed in the other two prisms. The authors can not specifythe reason whereby this happened due to the large number of steps needed to prepare thesplitting tensile samples. Further research needs to be done to understand the chemicalprocess that takes place on the interface and provokes this high cohesion between bothUHPC and NSC materials. A microanalysis of the transition zone between UHPC andNSC materials by using Scanning Electron Microscope (SEM) could help to understandthe necessary conditions to obtain good bond strength. This study has concluded that asaturated concrete substrate have a strong beneficial effect on the development of thebond strength. However, additional research have to carry out in this aspect due to the80