A large scale test on concrete joints subjected to constant compressive confinement and reverse cyclic shear load is performed. Shear strength, dilatancy degradation, and overall response are reported. A description of roughness as composed by two orders of asperities with different sizes is used to analyze the results and prompts the extension of an existing generalized joint model. The validity of the interpretation and the role of the proposed extension are pointed out by means of comparisons between numerical simulations and experimental results.