compatibility of ultra high performance concrete as repair material

surface treatment applied. In contrast, a general premature failure occurred with thosesamples cast on a concrete substrate with a dry moisture condition. Smooth, sandblasted,brushed and chipped surfaces presented similar strengths which indicates that the surfacetreatment is not a critical factor, at least under this loading configuration. Macrotexturedepths equal or greater than 1.5 mm are often related with good bond strength based onfield experience (Sprinkel 1997), but in this research, the different substrate surfaces hadmacrotexture depths between 0.6 and 1.06 mm, and all of them presented outstandingstrengths. Therefore, it can be concluded that when UHPC is used as overlay material ona saturated substrate, a simple surface treatment that removes the dust from the concretesurface is enough to achieve a good bond that satisfies the bond strength ranges given by((ACI 546.3R-06 2006), (Sprinkel and Ozyildirim 2000)).In all cases, 300 freeze-thaw cycles have a beneficial effect on the bond strength. Whilethe prolongation of the freeze-thaw cycles did not drastically affect the bond strength,having slightly greater or lower strengths that those obtained with 300 freeze-thawcycles.The low COV for the monolithic samples (from 6.7% to 12.9%) confirms the consistencyof the splitting tensile test. Whereas the COV for the composite specimens was greater(from 7.1 to 29.4%) but still can be considered as consistent. They are in the same range(2.4 to 29.5 %) as obtained by Santos and Julio et al. (2011) in his study of the bondbetween two concretes.Comparing the tensile strength attained by the composite prisms with respect to thatobtained by the monolithic samples and taking into consideration that the compressivestrength tests showed that NSC mix used to cast the monolithic samples had higherstrength than the rest of NSC mixes, it is reasonable to state that most of the compositeprisms failed due to they have reached the maximum tensile capacity of the NSCsubstrate. The summary of the failure modes as well verifies the latter: most of thefailures were in the concrete substrate or a mix failure of bond and concrete. Therefore, itcan be drawn that the tensile strength of the bond interface is equal or greater than that ofthe substrate.82