Lessons Learnt from the Shotcrete Repair of the Powell River Concrete Hulks, and their Applicability to other Marine Structures

摘要

Background: Concrete structures can be damaged by many chemical or physical processes. Where such damages affect appearance, serviceability or structural integrity, repair may be required. 10 decommissioned concrete ships form a massive floating breakwater on the Malaspina Strait in the City of Powell River in British Columbia, Canada. The ships are subjected to extremely onerous conditions, namely in the salt water splash zone under seasonal freeze-thaw cycling. This paper provides anecdotal evidence based on condition assessments after repairs were carried out, on how a well-matched repair concrete can significantly extend the service life of these and similar sorts of marine structures. Methods: Condition assessment was carried out using sounding, visual examination, photo and video documentation, compressive strength testing, splitting tensile strength testing, chloride ion concentration testing, and half-cell potential testing. Results: It was found that the areas which had been repaired had fared very well, with no observable deterioration. The non-repaired areas of the structures had continued to deteriorate, particularly in non-submerged areas, close to the waterline, along with new impact damage. Conclusion: Durable concrete repairs can be achieved even for concrete exposed to extreme environmental conditions. Key conditions for such repairs are: complete removal of the deteriorated portions of the original concrete, removal of all loose corrosion products from exposed reinforcing steel, preparation of a clean, firm, rough, surface dry but partially or fully water saturated, substrate surface, selection of a compatible repair material, use of an application technique which facilitates high bond strength between substrate and repair material, adequate curing, and protection of the repair material while immature.