The structural masonry has been showing an excellent option for civil engineering structures, mainly of developing countries. High-rise buildings are more and more necessary and compressive strength of masonry and quality of structures has to meet high requirements. Testing of blocks of different shapes and materials and testing of masonry structures of the same blocks have always given different results. Destructive testing of blocks and walls has been, until now, the most reliable mechanism for evaluation of compressive strength and quality of masonry structures. However, this approach demands a great number of specimens for obtaining statistically valid results, and is a very labor, time, and money-consuming task.An alternative solution has been searched, in order to determine masonry compressive strength by nondestructive testing. Some acoustic methods of nondestructive testing of masonry are briefly discussed. A new ultrasonic measuring technique (ultrasonic surface wave technique) using dry point contact (DPC) transducers is introduced. This technique allows to make a point by point ultrasonic measurements. The obtained results give the opportunity to analyze acoustic fields of materials and structures. The following specimens have been investigated: hollow concrete blocks, concrete cylinders (of the same concrete), mortar cylinders, prisms of two blocks and wallettes (140 mm wide x 790 mm high x 790 mm long). Correlation among compressive strength of these components and elements is presented, as well as graphs of the time propagation of the ultrasonic surface waves on three different wallettes. The experimental results of the differential approach application to analysis of masonry structures demonstrated high sensitivity of the ultrasonic surface wave technique to variations of properties of masonry components.
Key words: masonry, nondestructive testing, ultrasonic technique.
