In older reinforced concrete structures, particularly those in coastal locations with a prevalence of salty air, or ones exposed long-term to pollutants in towns and cities, some form of corrosion is inevitable. However, the visual signs of carbonisation and chlorides, such as cracks or spalling, can take months, possibly even years before appearing. By then, of course, serious damage could be done and repairs could prove costly.
To protect and prolong the life of a structure, early corrosion diagnosis is vital. But how is this achieved when the surface gives no indication of a problem? A concrete condition survey offers a reliable test as to how a building is reacting to its surrounding environment. BS EN 1504 Standards stipulate a survey and interpretation of results is a prerequisite prior to work starting on concrete repair projects. This will reveal the overall state of the concrete and determine the type of remedial action required.
Sika is in the process of launching an investigation service. In conjunction with our partner, Vector, the survey will identify the most appropriate corrosion management system to employ. This offering further demonstrates our all-round commitment to quality concrete refurbishment.
A survey could include the following depending on the structure and condition of the concrete:
Visual inspection: This offers a flexible and powerful form of testing. It can provide an immediate assessment of a concrete structure’s condition and identify causes of stress or other debilitating conditions. A visual inspection, however, is dependent on the competence and experience of the survey team carrying it out, therefore surveys of this kind should only be made by those qualified and experienced to do so.
Hammer testing: A hammer test identifies hollow or spalled areas of concrete by assessing the sound difference using either a hammer or chain.
Carbonation: A solution called Phenolphthalein is used to indicate levels of alkalinity which triggers the corrosion process. The substance, which is spray-applied, turns pink when it contacts alkaline in concrete.
Break out: Break out testing sees areas of concrete broken away to assess the condition of the steel. This test acts as a validation measure against the other tests such as carbonation, chloride and half-cell measurements.
Concrete cover: A cover meter survey identifies and records the minimum and average depths of concrete cover to the embedded steel to help determine the risk of corrosion. It is also used to identify where the steel is.
Chloride analysis: This involves collecting concrete dust samples to test for the presence of chlorides.
Half-cell potential mapping: Corrosion of reinforcing steel is an electro-chemical process and the deterioration of the steel can be assessed by measuring its half-cell potential. The greater the potential, the higher the risk that corrosion is taking place.
Corrosion rate measurement: An electrochemical test carried out on the surface of the corroding metal to assess the causes of corrosion and predict the rate it will occur.
Once a survey has taken place, results will determine the most suitable corrosion management system to employ. For example, where high levels of chlorides are detected within the concrete, the Sika® Galvashield® system, comprising embedded galvanic anodes, is recommended. The sacrificial anodes prevent the formation of new corrosion sites either adjacent to the refurbished concrete or to concrete which is visually sound but from the survey information identified as high risk.
This simple, innovative anode system involves a small, circular-shaped cementitious shell encasing a zinc core which is quickly and easily fastened to exposed steel reinforcement. Once installed, the anode’s zinc core corrodes sacrificially to the surrounding rebar to therefore protect it.
A concrete conditioning survey can help identify a potential problem before it takes hold, tying-in with the well-known saying, ‘prevention is better than cure’. The good news is, with the launch of our investigation service, alongside our existing Total Corrosion Management System, Sika has the means to provide both the prevention and a long-term cure.
from The UK Construction Blog http://ukconstructionblog.co.uk/2017/05/30/concrete-condition-check-key-to-structural-wellbeing/