Visual evidence of deterioration is often apparent in the form of cracking and spalling of the concrete surfaces.
However, an experienced, specialist engineer can often recognise more subtle evidence before the appearance of more severe defects.
The spalling of cover concrete may be an obvious visual clue to the current condition of the reinforcement and substrate, although the quantification of such visual defects does not always allow for the underlying latent problems. The expansive pressure caused by reinforcement corrosion products may produce localised hollow spalls with no obvious debonding of cover at the time of inspection. Where necessary a sounding hammer should be used to confirm the extent of visual defects.
When cast, the alkali nature of the concrete offers adequate protection to the reinforcing within, however as the pore water within the surface matrix evaporates, carbon dioxide diffuses from the atmosphere to form a mild acid. The acid negates the effects of the alkali and so the protection to the reinforcement is lost. Carbonation depth measurements are made in accordance with BRE information paper IP 6/81 by spraying phenolphthalein, on freshly broken concrete. The mean depth of carbonation is measured as the distance between the concrete surface and the boundary of the uncoloured zone.
Structural investigations are undertaken to confirm the construction type, structural arrangement and condition of reinforced concrete elements. These investigations often include localised breakouts to expose reinforcement, allowing the measurement of reinforcement diameters, spacing and identification of bar type and configuration. Measured surveys may also be carried out to verify structural dimensions and detailing where original drawings are unavailable or require confirmation.
Where deterioration is suspected, corrosion assessments and reinforcement section loss measurements can be undertaken to establish the extent of damage and inform appropriate repair strategies.
Reinforcement mapping is carried out using non-destructive techniques such as ferroscan and Ground Penetrating Radar (GPR) to identify reinforcement location, spacing and depth within concrete members. The data obtained can be used to produce accurate CAD drawings of structural elements, including reinforcement layouts and structural member sections, supporting engineers, designers and asset owners in the assessment and management of existing structures.
The depth of cover to reinforcement is vital to establish the general trends in the construction techniques employed as well as giving indications of quality control and design. Covermeter depth measurements are carried out in accordance with BS 1881: Part 204: 1988 guidelines. The recording of maximum and minimum cover depths allows the interpretation of the relevance of carbonation depths and moisture or chloride ingress.
The Assessment of fire damage is carried out in line with the Concrete Society Technical Report No. 68 and includes both on site and laboratory based techniques to fully assess the significance of any extreme heat and correctly specify concrete repairs.
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