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Basement, Tunnels, Tanks and Pools – Water Retaining and Excluding Structures

Although reinforcement corrosion may be the typical outcome of deterioration in water retaining or excluding structures there are a range of mechanisms that may occur.

  • cracks may leak leading to corrosion of reinforcement at cracks
  • water flowing over the concrete surface from leaks at cracks and joints occur runs over the atmospheric surface and evaporative concentration leads to a high build-up of chlorides at the surface which diffuse back into the concrete and cause corrosion in the run off area
  • if there is a high pressure head of water and the concrete is not high performance  water penetrates the concrete under a pressure head. Evaporation of the water arriving at the atmospheric concrete face and chlorides or sulphate ions back diffuse to the reinforcement. The process is referred to as transpiration.
  • carbonation of the concrete due to carbon dioxide level in the atmosphere in the basement can lead to corrosion activation and then the dampness leads to rapid corrosion

In all these case reinforcement corrosion may be the main problem and this is solved by application of cathodic protection although leakage will need to be stopped as part of the repair process.

corrPRE Galvanic Anodes for Corrosion at Cracks or Joints

Leakage at a construction joint. Where sealed corrosion protection  can be applied locally using ZLA or Roll Anodes. Leakage at a construction joint. Where sealed corrosion protection can be applied locally using ZLA or Roll Anodes.
Transpiration. Water penetrates under a pressure head. Contaminants are deposited at the air face. Chlorides diffuse back to the reinforcement. Transpiration. Water penetrates under a pressure head. Contaminants are deposited at the air face. Chlorides diffuse back to the reinforcement.
Cassettes installed at Billingham forum. The Cassettes were easily installed in the confined space behind pipework. Cassettes installed at Billingham forum. The Cassettes were easily installed in the confined space behind pipework.
Cassettes installed on the soffit of a conveyor tunnel at Dalrymple Bay Coal Terminal. Cassettes installed on the soffit of a conveyor tunnel at Dalrymple Bay Coal Terminal.

Where corrosion at cracks or joints is a risk ZLA or Roll Anodes can be used to provide durable localised cathodic protection. These galvanic anodes require no monitoring or wiring and are uniquely design to give true cathodic protection meeting the 100mv 24 hr decay criteria in the codes. 

corrPRE Galvanic Anodes for Evaporative Concentration at Leaks

Where the concrete surface is continuously or repeatedly wetted due to leaks, where the water evaporates it deposits the salts in the water. These salts can build to high concentrations over time even where the concentration in the water is quite low. Even though the defects causing the leakage may be quite small the concrete area affected can be very large. A poor construction joint has a small area but leakage can affect many square meters below the joint. If the area affected by leaks is small and isolated then corrPRE galvanic anodes can be used in a similar fashion to that used for cracks and joints. If the area affected is widespread then Potector’s Cassettes can be applied in a similar fashion to more general corrosion.

Cassette for General Corrosion Due to Leakage, Transpiration or Carbonation

Because of the speed of installation and low cost Cassette is recommended wherever it is aesthetically acceptable and wide spread corrosion is an issue due to leaks or transpiration. ZLA could be used and might be lower cost if it’s a dry basement but that is often not the case.

Basement car parks in commercial and residential buildings are more likely to be solely a carbonation problem and in that case ZLA is a potentially a sound and economic solution, particularly if the basement is above the water table. If below the water table then water vapour migration has the potential to cause issues with the ZLA adhesive which is water soluble.

Freyssinette have detailed the repairs at Billingham forum. A condition survey was carried out and corroded reinforcement was noted. Concrete repairs alone were considered inadequate to provide the clients desired 20-year design life.

Mott McDonald were commissioned to design a suitable economic cathodic protection system applied via the pool face in the confined space service tunnels. This meant minimising dust producing activities such as chasing of concrete. Repairs using Cassette were specified and completed in 6 weeks in full accordance with the relevant sections of EN 1504 Products and Systems for the Protection and Repair of Concrete Structures. The system was commissioned in May 2011 and is performing to the full requirements of BS EN 12696:2000 Cathodic Protection of Steel in Concrete.

At Dalrymple Bay Coal Terminal a conveyor terminal was suffering from corrosion. Various cathodic protection systems were considered but they could not be installed due to the density of reinforcement and the low cover. Cassette proved the ideal solution. SRCP arranged for a tailor made Cassette system to be fabricated and delivered from Norway in 2 weeks. The system was installed during a shut down in one week. 

If you do not wanting to worry about leaking tanks, you should check out Heritage Tanks, who provide tuff water tanks built in Australia, and are well respected and qualified manufacturers. 

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