Characterization of the Bond Strength between Ultra-High Performance Concrete and Normal Strength Concrete in accordance with Split Prism and Freeze-Thaw cycling tests

Abstract

[ES] Un trabajo experimental fue llevado a cabo para evaluar la unión de UHPC con el hormigón convencional para aplicaciones de rehabilitación de estructuras del hormigón. Las condiciones de saturación del substrato, la preparación de la superficie, ciclos de hielo y deshielo y la resistencia a tracción indirecta fueron tomadas en consideración para estudiar el rendimiento de la unión. Un total de 67 muestras fueran ensayadas en tracción indirecta. Los resultados experimentales mostraron que las muestras sometidas a ciclos de hielo-deshielo tenían una unión superior que aquellas muestras sin ciclos de hielo-deshielo. La unión entre UHPC y hormigón normal aumenta considerablemente si el substrato de hormigón está saturado antes de colocar el UHPC sobre él.

[EN] Currently, civil engineers have to face a new issue in the concrete industry: the increasing need for rehabilitation of many concrete structures that were constructed in the second part of the last century. Thus far, most of the efforts of the engineers were addressed to design new infrastructures. However, after the construction boom in developed countries over the last few decades, the repair of structures is becoming increasingly necessary. The latter represents an important environmental concern: if we are able to design successful repairs, the material and cost saving can represent a significant achievement for the sustainability of the concrete industry, increasing the service live of the existing concrete structures with the lowest consumption of material. The experimental results show that UHPC would have an excellent performance under severe environmental conditions due to its negligible permeability. This makes UHPC have almost no penetration of chlorides and sulphides. Further, its high abrasion and freeze-thaw resistances make this material suitable as overlay that protects the rest of the structure from extreme environmental conditions. Nonetheless, for widespread use of UHPC as repair material, the bond between UHPC and Normal Strength Concrete (NSC) needs to be assessed. It is essential that the bond offers enough strength to resist the stress due to mechanical loading or thermal effects, while also maintaining an extended service-life performance. An experimental study was performed to assess the bond performance of UHPC for overlay applications. Pre-wetting conditions, surface preparation, freeze-thaw cycling and indirect tensile strength were variables taken into account to study such performance. A total of 60 composite and 7 monolithic concrete specimens, 102x76x394 mm, were cast to test in indirect tension. Experimental results showed that samples subjected to 300 freeze-thaw cycles present greater bond strength than samples of the same age without freeze-thaw cycles, and all samples in which the moisture condition of the substrate is saturated before placing UHPC achieves excellent bond strength which amply satisfies the range specified in the ACI Selection of Materials for the Repair of Concrete (2004).