Conservation of the granite cladding of the Sydney Harbour Bridge: a comparison of femtosecond and nanosecond laser cleaning approaches

Abstract

The Sydney Harbour Bridge is a nearly century-old bridge made of a steel arch flanked by two massive concrete towers faced with Moruya granite, located in a heavily urbanised and populated city in a coastal area of Sydney in Australia. Despite this long exposure to a harsh environment, the materials are original and still in good condition overall. However, cleaning has been identified as a maintenance need, both for the metal of the arch and the granite of the pylons. The granite is affected by various contaminants ranging from biofilm to rust staining that should be removed for aesthetic purposes.
The government agency managing the Bridge, Transport for New South Wales, has been testing different cleaning methods, including sandblasting, water pressure, and short pulse laser cleaning. This thesis explores the use of innovative femtosecond and high-power lasers to restore the Bridge’s appearance and preserve it, as an alternative to most common cleaning techniques investigated so far. The operating parameters offering the most effective laser regime to remove various contaminants without inducing any damage to the stone substrate are determined. The research then compares the femtosecond pulse lasers to more conventional nanosecond pulse lasers widely used in conservation, in terms of cleaning effectiveness and effects on the underlying stone substrate. The findings will help increase the understanding of the application of femtosecond pulse lasers to heritage stonework, paving the way for more widespread adoption of this new technique.
This PhD is undertaken as part of an Australian Research Council (ARC) Linkage Project led by Em/Prof. Andrei Rode from the Australian National University (ANU), which includes collaborators from the ANU, the University of Canberra (UC), the University of Sydney (USYD), the Australian Nuclear Science and Technology Organization (ANSTO), and the New South Wales state government branch, Transport for New South Wales.

Date of Award	2024
Original language	English
Supervisor	Alison WAIN (Supervisor), John TING (Supervisor) & Andrei Rode (Supervisor)