Abstract
The paper presents the results of integrated ground penetrating radar (GPR) and ultrasonic testing (UT) measurements conducted on a historical floor in St. Nicholas’ Church, Gdańsk, Poland. The described inspection was the first stage of the technical state assessment of the building. The aim of the study was the detection of underfloor air gaps, which were observed in a few trial pits. The condition of the ground under the floor was determined by localizing other inclusions such as rubble, human remains, brick walls and pipes. To identify the phenomenon of electromagnetic and ultrasonic wave propagation within the air gap, laboratory tests were conducted on physical models consisting of two concrete slabs stacked on top of each other and gradually moved apart to simulate a slot of varying thickness. The conducted research was supported by the numerical models of electromagnetic wave propagation. The obtained results showed that the integration of the GPR and UT methods provided an effective imaging of the floor and the area under it. Ultrasonic testing was proved to be a good technique for identifying air voids, while the GPR method allowed detecting concentrated anomalies and determining the degree of ground homogeneity under the floor.
Highlights
Non‐destructive testing (NDT) is commonly used for assessing the condition of components of engineering structures
The identified gaps thicknesses were slightly different from the actual ones because the depth axis in Figure 11 was calculated for the velocity of the electromagnetic wave in concrete (15 cm/ns)
The integrated ground penetrating radar (GPR) and ultrasonic testing (UT) inspection was conducted on the floor of a historical church
Summary
Non‐destructive testing (NDT) is commonly used for assessing the condition of components of engineering structures. It is a quick and efficient approach, the main advantage of which is the ability to examine a structure in a non‐invasive way, without damaging or changing the composition or shape of the inspected object. Non‐destructive testing is suitable in the case of historical objects. Such an approach is more and more often applied in cultural heritage buildings due to the necessity to preserve such structures in an untouched condition for future generations. Non‐invasive testing conducted within the flooring area allows detecting crypts, tombs and hidden rooms, as well as evaluating the technical
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