Using Acoustic Emissions to Detect Damage in Historical Stone Masonry

Abstract

Numerous historical structures were built with structural walls of stone masonry and mortar. Many have not survived the test of time. Some have had obvious signs of distress such as bowing, bulging, and cracking. Others have had catastrophic failures occur without warning. As part of a research project sponsored by the National Center of Preservation Technology and Training [Biggs, Healy, 2007] Ryan-Biggs Associates, P.C., as a consultant to Fort Ticonderoga, investigated using acoustic emission technology as a means of monitoring historical stone structures, detecting damage, and predicting impending failure. This paper presents some of the findings of the research project. Acoustic emission technology has been successful in structural health monitoring in materials such as composites, steel, and concrete and has the potential to be an effective economical tool to monitor the structural integrity of stone-masonry walls. BACKGROUND An acoustic emission is an elastic wave that propagates through a specimen caused by a sudden, inelastic, localized change of stress such as cracking. This wave can be detected at the specimen surface by an acoustic emission sensor and converted into electrical voltage. The electrical voltage is then amplified and processed into an acoustic emission signal, which can be analyzed to potetially deduce the magnitude, nature, and location of damage in the material. Figure 1 shows an acoustic emission signal recorded as part of this research.