3DGPR for the Non-Destructive Monitoring of Subsurface Weathering of Sandstone Masonry

Abstract

Remote sensing techniques, such as LiDAR and photogrammetry, are used by researchers exploring the spatial distribution of weathering features in historic masonry. These well-established tools provide users with a perspective of the processes affecting the surface of masonry blocks; however, they cannot provide information on the alteration occurring subsurface. Geophysical tools are being explored as a potential approach to observe the variation in material properties beneath masonry block surfaces and to examine the patterns of deterioration across wall sections. Applying such techniques inform the development of conceptual models of weathering at the block to building wall scale. In this study, ground-penetrating radar (GPR) was selected to inspect the subsurface condition of the wall section of an historic church wall, where areas of granular disintegration and flaking can be observed. 3DGPR was selected for this task, as its use of regular grids during data collection make it better suited for detecting features within an area. Three high-frequency antennas, 1.2 Ghz, 1.6 Ghz and 2.3 Ghz, were run across the study area in a series of 80 cm by 80 cm grids. The data were collated within GIS, where observed features were annotated onto a schematic of the wall surface. The 3DGPR outputs identified anomalies within this structure that could not have been as easily interpreted using a 2DGPR transect. However, as 3DGPR relies upon interpolative techniques to estimate the returns between observation transects, the validity of features detected in these locations need to be tested. The results of this application of 3DGPR identified variable weathering response across the wall section, relative to elevation. These observations were used to develop a conceptual model linking these findings to seasonal variation in the capillary rise of groundwater, upward from the base of the church wall. Through these findings it is possible to see how GPR can assist in developing our understanding of the processes threatening heritage buildings.

Geophysical Surveys for Archaeology and Cultural Heritage Preservation

“…These observations were used to develop a conceptual model linking these findings to seasonal variations in the capillary rise of groundwater, upward from the base of the church wall. Through these findings, it is possible to see how GPR can assist in developing our understanding of the processes threatening heritage buildings [7].…”

Time-Lapse GPR Measurements to Monitor Resin Injection in Fractures of Marble Blocks

“…The GPR method has proved its ability as a valuable geophysical technique to enter the quarrying and construction industries to map the fractures at different stages: during exploration and extraction in quarries to reduce the production costs and wastes [6,7,[10][11][12][18][19][20], and for post-production demands to repair and restore the stones [21]. From various research studies that use the GPR method to study rock fractures, we can mention the theoretical models and laboratory experiments used to characterize rock discontinuities [18][19][20][21][22][23][24][25][26], in situ GPR surveys to detect fractures at different zones of quarries or in historical buildings [7,10,12,15,22,[27][28][29][30], and 3D GPR acquisitions for 3D reconstruction of the fractures and other features [11,12,[31][32][33][34]. Most of these studies are focused on the application of the GPR method to detect rock/stone fractures to optimize the quarrying activities and to preserve the constructions.…”

Adaption of Industrial NDT Protocols Based on Active Infrared Thermography to the Art Conservation World: The Case of the Wall Painting at Herodium

“…Hence, salt crystals as efflorescence or sub-florescence can appear at any location (Arnold and Zehnder, 1989;Charola and Bläuer, 2015). For this reason, fully non-destructive testing (NDT) has been widely preferred for the diagnosis of moisture and salt weathering (Johnston et al, 2019). This study utilized one of the most common and wellestablished NDT methods, Infrared thermography (IRT) for performing a detailed analysis of salt content at the subsurface of Herudiums' wall paintings.…”