Comparative interpretation of results after application of different non-destructive and portable techniques on historic concrete in the Centennial Hall in Wrocław

Many concrete buildings erected during the 20th century are assuming a cultural and historical value, and their conservation against the climate changes and the urban impact represent a major challenge for the heritage science for the future. A key aspect for their preservation is the development/application of innovative testing approaches based on non-destructive and portable techniques (NDPT) for diagnostics and monitoring the state of conservation. This research activity has been conducted on the case study of the Centennial Hall exhibition centre in Wroclaw (Poland), where the physical and mechanical characteristics of cementitious materials were estimated through indirect methods and therefore compared to prove their efficiency and usefulness in the limitation of invasive inspections. These methods were focused to control the hardness and compactness of the material (by ultrasonic pulse velocity and rebound tests), the surface permeability (by sponge test method), the water and salts content of the material (by Evanescent Field Dielectrometry - EFD), and the change of colour (by colorimetric measurements). In order to test the strength of the proposed approach, all these techniques (except the EFD) were made in duplicate by two different teams, using different instruments but following a similar protocol. The data were compared in between, and the environmental conditions were also considered. The results showed a good repeatability, furnishing useful information about the quality of concrete and its state of conservation, as well as possible forethoughts for a proper interpretation. This multi-technique approach could support the conservation decisions making process for the management of historic concrete building.