AbstractConcrete has been one of the most prevalent construction materials from ancient times to the present. Its ubiquitous application during the 20th century has brought interest in it as a heritage material.
Historic concrete structures should be regularly monitored to detect changes and deterioration caused by natural phenomena, such as ageing and weathering. There is an increasing demand for the advancement of reliable non-destructive testing techniques (NDT) for the assessment of concrete deterioration, such as laser scanning. Conservation and restoration of historic structures are among the main applications of laser scanning.
This research was aimed at investigating the role and effectiveness of laser scanning as a non-destructive technique as well as its application in the growing field of monitoring and conserving historic concrete structures. For the investigation, the effect of weathering/deterioration on concrete and associated cementitious repair mortars was studied through the use of laser scanning application to detect small-scale changes via the use of the environmentally simulated conditions using chemical reagents, including sodium chloride (freeze-thaw cycle), sodium sulphate and acetic acid (room temperature), and distilled water (freeze-thaw cycle). The research also examined the performance of different types of cementitious repair mortars.
The objectives were achieved through laboratory and field experiments. The laboratory experiments were conducted on concrete and repair mortar cube specimens (100 x 100 x 100) mm. The main variables included two concrete substrates (0.5 and 0.6 water-cement ratios) mixes, three cementitious mortars (two were laboratory-produced and one pre-packed), and two types of concrete moulds (steel and timber to provide smooth and rough textures) and chemical solutions. The analysed variables included compressive strength, density, shear bond strength, freeze-thaw test, and the 3D laser scanning results.
The results show that the water-cement ratios had an effect on the bond strengths in that a concrete substrate with a 0.5 water-cement ratio resulted in higher bond strengths (almost more than 50 % higher). In addition, polymer-modified (Monolite) mortar resulted in better adhesion and performed better under the freeze-thaw cycles compared to the laboratory-based mortars.
In terms of laser scanning, the results show that it is possible to detect small-scale topographic surface changes and to quantify erosion rates when the specimens are subjected to various environmental conditions. The effect of sodium chloride and distilled water resulted in a surface volume increase. Moreover, the specimens that were made of timber moulds resulted in higher volumes, which could be attributed to the high porosities caused by rough surfaces. In addition, the effect of acetic acid at room temperature resulted in gradual volume loss (erosion). However, the results of sodium sulphate showed variability in surface volume estimations. Furthermore, specimens made from timber moulds resulted in higher local surface roughness.
This research also involved a case study of Boathouse 4, Portsmouth Historic Dockyard, UK. The outcomes demonstrated a successful approach to monitoring historic concrete and associated repairs as well as dealing with site form and complexity. Three small patches of concrete located in the undercroft of Boathouse 4 were chosen to be monitored using a 3D laser scanner. These patches were scanned to obtain a high resolution of the concrete surface so that gradual changes to the appearance and texture of that surface and associated repairs could be detected. However, only a relative measurement can be made in the form of a standard deviation measurement to quantify surface roughness. The results show that Patch 3, which was closer to the seawater, had the most topographic change, and the roughness was higher compared to the other patches.
Whilst the use of laser scanning technology is not new within the domain of monitoring, the novelty of this research lies in the application of this technology to the specific area of assessing and monitoring the weathering/deterioration of historic concrete and associated cementitious repair mortars.
|Date of Award||10 Jul 2023|
|Supervisor||Stephanie Barnett (Supervisor), Rob Inkpen (Supervisor) & Amanda Thomas (Supervisor)|