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Interview with John John Drewett - Director of Concrete Repairs Ltd.
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| 21 Feb 2012 |
Why is corrosion control knowledge particularly important for concrete structures in Saudi Arabia?
Concrete on its own does not present a corrosion problems but it is often used in construction with steel reinforcement to provide strength in tension. This steel is protected from corrosion when embedded in highly alkaline concrete with low levels of chloride ions. However the environment in Saudi Arabia can be quite saline due to the marine environment and soil conditions. Over a period of time chlorides can penetrate the concrete and initiate rapid corrosion of the steel reinforcement which leads to a reduction in the structural capacity. It is important to understand the corrosion process to reduce the risk of steel reinforcement corrosion in new concrete and deal with the problem when it does occur.
How can corrosion monitoring benefit asset managers in Saudi Arabia?
All concrete structures will deteriorate with time and this will lead to steel corrosion. In Saudi Arabia the warm climate and high chloride levels can lead to very rapid corrosion pitting of the steel. When there is visual evidence of corrosion on the surface of the concrete the steel will often require replacement to restore the structural integrity. This is an expensive exercise and may require temporary closure of the structure while the work is undertaken. By using buried probes in the concrete asset managers can remotely monitor the condition of the concrete and install a corrosion control system before it becomes necessary to undertake expensive repairs.
Why are FRP composites successfully used to reinstate structural integrity in concrete structures?
There are many reasons why concrete structures need to be strengthened such as concrete deterioration, increased loading, change of use and poor construction. Steel has traditionally been used to strengthen concrete but this increase the dead load and there is an on-going problem protecting the steel from corrosion. FRP composites are a combination of high strength fibres and resins fixed to the surface of the concrete with an adhesive which act like an external reinforcement system. These materials are lightweight, thin and very durable so they are ideally suited for use in the Saudi Arabian construction sector.
Why is it important for asset managers in Saudi Arabia to regularly inspect their concrete buildings and structures?
The aggressive environment in Saudi Arabia can cause concrete structures to fail prematurely because it makes it difficult to achieve high quality concrete on site and the saline environment can lead to corrosion of the reinforcement. This makes it important to undertake regular surveys of the concrete to identify any deterioration before it becomes a major problem. There are a variety of NDT survey techniques available to enable asset managers to report on the condition of the concrete and by comparing results over a number of years the rate of deterioration can be identified which can they be used to predict when repairs will become necessary.
Why is cathodic protection often used in the Saudi Arabian market for corrosion control in concrete?
Corrosion control is an electrochemical process where the corrosion site is the anodic site and the passive areas of steel are the cathodic sites. The anodic sites are acting like sacrificial anodes so if traditional concrete repairs are undertaken at the anodic site where the steel is corroding the corrosion will start again on steel nearby. The only effective way to deal with this problem is to use an electrochemical solution called cathodic protection which utilises an anode installed on or in the concrete making the steel reinforcement cathodic and thus in a passive state. Cathodic protection has been used very effectively for new and existing structures in Saudi Arabia to stop corrosion of the steel reinforcement.
What changes have taken place in international guidance notes which will be of benefit to asset managers in Saudi Arabia?
Over the last two years there have been a number of new documents issued which will assist in the management of concrete structures.
The Concrete Society in the UK has published a new document Technical Report No. TR73 “Cathodic Protection of Steel in Concrete” which includes a model specification. At the same time it is about to publish revision 3 for Technical Report No. 55 “Design Guidance for Strengthening Concrete Structures using Fibre Composite Materials”.
There is also the new European Standard EN 1504 “Products and Systems for the Protection and Repair of Concrete Structures” which covers the inspection, repair specification, execution of the works, quality control and on-going maintenance.
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