The twin Chillon Viaduct, situated next to world-famous Chillon Castle on the A9/E27, was conceived by Jean Muller, designed by Jean-Claude Piguet, and built in the late 1960s. This chapter focuses on full-scale failure tests on specimens representing zones between and above the webs of the box girder. The primary goal was to verify the expected increase in ultimate resistance due to the R-UHPFRC layer, as expected through analytical models. The full-scale tests confirmed that also an unstrengthened slab undergoing strength reduction due to Alkali-Silica Reaction would not fail by punching of a wheel load. Casting of the R-UHPFRC strengthening on the 2.1 km long Chillon Viaduct was performed during five weeks, ending in September 2014. Structural design of the strengthening layer was performed using analytical resistance models which were validated by non-linear finite element modelling, calibrated to the present test results.