An appraisal of a historic reinforced concrete structure : the naval reservoir

Abstract

This study is based on the Historic Naval Reservoir built in Hal Luqa between 1905 and 1909. The objective of the dissertation is to conduct a detailed appraisal of the structure and its components based on scientific methods, including the appraisal of the structure through inspection, Scanning, and Photogrammetry, Non-Invasive assessment through non-destructive tests on the structure and materials assessment based on experiments to define the properties of materials in the structure. The Naval Reservoir was constructed at the beginning of the 20th century. It consists of a vast underground space excavated in Globigerina limestone, with masonry block columns resting on concrete bases, supporting spandrel parabolic arches, which in turn support a thin reinforced concrete shell structure. The naval reservoir has been associated with the drydocks in the Grand Harbour, Malta. The Naval Reservoir exhibits various defects, including spalling of concrete and cracking in different shell elements, which may be attributed to different sources. In addition, its water retaining properties have been impaired over the years. The dissertation aims to identify the degradation mechanisms based on documentation and visual inspection of the structure, which was further supported through photogrammetry, non-destructive tests, and materials analysis on the extracted samples. NDTs included Cover Meter, Schmidt Hammer, Ultrasonic Pulse Echo, Ground Penetrating Radar, and Resistivity Meter. Findings from the cover meter measurements indicated that the structure offer sufficient protection to the steel reinforcements buried inside it. This finding was further substantiated since the resistivity measurements demonstrate negligible likelihood of corrosion. The Ultrasonic Pulse Echo, Ground Penetrating Radar, and Thermal Camera, all indicate a structure that is generally consistent and has few indications of delamination. The concrete shell exhibits indications of degradation and weathering. Conversely, the other structural components, such as the arches, seem to be generally well-preserved. The examination of the core samples offers insights about the various aggregates and materials used. As a result of these particular properties, the maximum compression strength achieved of a core with globigerina aggregate was that of just 8.80 N/mm2. Other tests were also conducted on the cores to determine the Carbonation, Density, Vacuum Saturation Porosity, Chloride ion with depth, and UPV. The appraisal shall form part of a more comprehensive assessment of the structure and informs additional studies leading to its restoration and exploitation as an asset for the storage of water. Nonetheless, the collected data was examined to confirm the assessment methodology for the masonry / concrete and reinforced concrete structural elements, which aids in conservation efforts. The findings shed light on the state of the structure and the possible causes of degradation. The Getty Publication, The Burra Charter, and the Declaration of San Antonio, among other conservation documents, were used and discussed the possible intervention on this industrial heritage structure following the appraisal conducted. It was determined that the Naval Reservoir could be effectively repaired using engineering techniques without violating conservation guidelines. The proposed strategy includes patch repairs, crack sealing epoxies, and the use of water sealant materials. The methodology was reviewed with respect to case studies in reinforced concrete conservation, conservation charters, and frameworks for restoring historic reinforced concrete structures. The appraisal methodology gives a solid foundation to outline a preliminary repair approach.