The scratching test for on-site determination of historical mortars: method and preliminary results

Since the civil authorities have understood the necessity to preserve the old building heritage, important budgets are allocated to finance heavy restoration campaigns. Many historical masonry buildings, forgotten for decades, are affected by structural pathologies and the restoration campaigns have to be preceded by stabilization operations. In order to precise the structural behaviour of the old masonry buildings and to propose effective solutions for the future, the engineers need a correct knowledge of the constitutive materials (rock, mortar, ...) Several on-site determination techniques exist, showing their own advantages and disadvantages. This paper presents a scratching device, daily used by the petroleum industry for the determination of mechanical properties of rocks. This test has already shown its suitability on rocks (Suarez-rivera et al., 2002 ; Mitaim et al. 2004, Dagrain et al., 2004) and the paper proposes to adapt it for the on-site determination of the compressive strength of historical mortars. It presents the method, the adaptations needed and the use of the technique on a practical case : the masonry foundations of a cathedral recognized by UNESCO as part of the World Heritage.