An investigation into marine biofouling and its influence on the durability of concrete sea defences

Hughes, Peter (2014) An investigation into marine biofouling and its influence on the durability of concrete sea defences. Doctoral thesis, University of Central Lancashire.

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This research has investigated marine biofouling and its influence on the durability of concrete sea defences using on-site and laboratory-based studies. The study was divided into three main phases namely: the surface analysis of armour concrete, the study of algal colonisation within the matrix and investigations into the presence of a bacterial biofilm within freshly hardened armour concrete. The effectiveness of photocatalytic coatings as a non-toxic anti-fouling strategy and cell attachment to synthetic fibres was also studied.
It was found that algal growth quickly developed at the interface of inclusions within the matrix and that power washing with the use of Dairy Hypochlorite to remove this accelerated wear, leading to significant mass loss. It was also observed that bacterial growth within local beach sand, which was used in the production of the revetment armour units, survived the concrete manufacturing process. Bacteria were cultured from the sand and were found to match the Actinomycete like growth in the freshly hardened matrix of armour concrete.
This thesis proposes a holistic model for biofouling of fibre reinforced marine concrete in which algal growth around inclusions facilitates a complex process of biodeterioration. Bacterial filamentous growth around and through synthetic fibres embedded in the new concrete mix, appears to be detrimental to the long term durability of synthetic fibres. Subsequent algal colonisation on the surface of newly placed units appeared to quickly penetrate the surface through exposed fibres and percolated interfaces of inclusions, subsequently weakening their bond. During the manufacture of the armour units, aggregate segregation in the 90° corners in the bottom of the form created a weaker matrix in the surface region most exposed to biodeterioration, the full force of wave action and power washing.
The main conclusions from this study are:
• Synthetic fibres used at the study site are inappropriate for marine concrete, particularly in algal rich waters, within the inter-tidal zone where beach sand is used in the concrete mix. Amendments to Concrete Society Technical Report No. 65: Guidance on the use of Macro-synthetic-fibre-reinforced concrete have been recommended.
• Bacterial loaded beach sand is detrimental to the durability of marine concrete in the inter-tidal zone and amendments are recommended to PD 6682-1:2013 Aggregates for concrete (BSI, 2013a) in order to highlight this concern. This UK guidance suggests limiting values for aggregate properties within the ranges permitted in BS EN 12620 (BSI, 2013) but does not place any limits on microorganisms present in beach sand. Further work is needed into the susceptibility of synthetic fibres to crystal growth. Alterations in the manufacture of armour units have been recommended by this author.

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