The Structure
Tolaga Bay Wharf is a protected historical structure. The wharf was built in the early 1920’s using unwashed aggregates off Napier Beach and the local water supplies are very salty. Serious corrosion became evident within 7 or 8 years following construction.
The Challenges
Remedials are currently funded by local efforts and lottery donations. The objective therefore was to remediate and/or preserve the concrete structural elements, within a budget that reflected the minimal funds available. Pieces of the original steel were extracted which displayed milling scale, or in many cases complete corrosive destruction.
Steel below lowest tide level was all sound, and mostly still with mill scale, due to having very little oxygen to sustain corrosion, along with some protection by cathodic activity associated with aggravated corrosion in the adjoining wet/dry section of piles.
How could MARKHAM help preserve the ageing structure, within the limited budget?
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The Solutions
New concrete throughout incorporated concrete hydrogel waterproofing treatment into the mix. Existing headstock concrete was treated with advanced spray-applied hydrogel treatment, atomized onto the surface and also used as substrate preparation for cementitious repairs.
The Results
The waterproofing admixture provides long-term protection for the new concrete, blocking the entrance or movement of water-borne reactants. This hydrogel admixture also provided a remarkable benefit on site while the works were proceeding, by delaying the mix from setting while it was being manually transported to the far end of the wharf, as motorised vehicle traffic on the old structure was not possible.
The spray-applied treatment to the existing concrete penetrates deep into the porosity of the structure, protecting the reinforcing zone and, again, block the entrance of contaminants. This treatment also prevents the development of Incipient Anode Formation, which is a high risk where cementitious patching has taken place.
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