compatibility of ultra high performance concrete as repair material

5.1.1 Combination of Splitting Tensile Test with Freeze-Thaw CyclesFor the UHPC-NSC specimens exposed to 0, 300, 600 and 900 freeze-thaw cycles andsubjected to a splitting tensile load scenario, the following conclusions were derived:a. The moisture condition of the concrete substrate is a critical factor for attainingacceptable bond performance. A large number of composite specimens cast withthe dry concrete substrate failed before applying the load. In contrast, excellentbond performance was obtained under saturated concrete substrate.b. The exposure to a lengthy freeze-thaw cycling process does not decrease theindirect tensile strength of the bond. In all cases, the specimens with 300 freezethawcycles have greater strength than those without cycles. While the strength ofthose samples subjected to 600 and 900 cycles had slightly greater or lower valuesthan those without cycles.c. The bond performance at old age (greater than 185 days) gives excellent resultsunder splitting tensile stress, regardless of the degree of roughness of the concretesubstrate or the exposure to freeze-thaw cycles. The bond strength broadlyovercomes the minimum requirements specified by ACI 546.3R-06, even most ofthe specimens obtained more than the double.d. The predominant failure modes were tensile rupture of the substrate and a mixtureof bond/concrete failure or shearing of the grooves (grooved surfaces only). Thisis a sign that the bond strength was greater than that of the concrete substrate.Besides this, most of the composite specimens failed at tensile stress range similarto failure stress of concrete estimated by the relationship between compressivestrength and splitting tensile strength given by ACI 318-11.e. The evolution of the fundamental transversal frequency does not seem to be agood indicator of the bond strength evolution. All samples subjected to 300freeze-thaw cycles and cast under surface saturated conditions showed an increasein bond strength as well as fundamental transverse frequency. However, somespecimens cast under dry concrete substrate also experienced an increase infundamental transverse frequency after freeze-thaw cycling, but failed during the96