The North Forts Complex at Manly is part of the pre-World War II military fortifications complex on North Head at the entrance to Sydney Harbour.
The military reinforced concrete structures needing repair comprised a Command Post, Battery Observation Post and two auxiliary engine rooms.
The Sydney Harbour Federation Trust commissioned Remedial Technology to carry out a condition assessment of the four buildings, prepare a methodology for rectification work and carry out supervision of the repairs.
The key aspect of the repair methodology was to restore the structural integrity of the buildings while performing minimal concrete breakout and repairs to conserve the original historical aesthetics of the buildings. The repair strategy included the removal of all spalled and cracked concrete, cleaning of the rebar to bright metal condition using grit blasting and the application of a steel coating and high resistivity repair mortar to provide the highest possible long-term durability for the repair.
For the embedded rebar in the original concrete at the perimeter of the concrete repair areas, targeted corrosion protection using SPA Smart Zinc 130 Edge galvanic anodes encapsulated with low resistivity mortar were used to ensure incipient anode prevention and uniform corrosion protection along the edge of the repair areas.
For areas with low concrete cover, a surface repair polymer modified mortar was used to enhance concrete cover protection to the embedded rebar. A highly resistant clear coating (providing an effective barrier to chloride and carbon dioxide) was applied to all concrete surfaces.
The detailed electrochemical testing combined with the targeted selection of the latest technologies in repair materials and corrosion prevention products were used to give a new lease of life to the historic WW2 Fortifications at North Head in Manly, NSW. The next stage of the work includes reinstatement of replicate windows and doors before the opening of these buildings to the public.
The contracting company for the work was Eptec Pty Ltd and the design of the repair methodologies and technical supervision and testing were performed by Remedial Technology Pty Ltd. The Sydney Harbour Federation Trust provided logistic support and guidance throughout all stages of the work.
Battery observation post building before and after repairs