Construction Site Surveys
In addition to laboratory testing, we can offer comprehensive on-site sampling and testing services, which include:
Half cell potential
The electrical potential of reinforcing steel with respect to a standard copper/copper sulphate half cell, can give a measure of the extent to which corrosion has occurred. Testing is carried out in accordance with ASTM C876 modified slightly to UK standard practice. Results are presented in the form of a contour map indicating areas of risk.
The resistivity of a concrete can provide a measure of the possible rate of corrosion of steel embedded in it. A highly permeable concrete will probably have high conductivity and low resistivity. Hence if concrete is in an environment where reinforcement corrosion is likely to occur it will be more rapid if the resistivity is low and conductivity is high.
The results of a half cell survey and resistivity survey can be interpreted in conjunction with the chloride content of the concrete.
A covermeter survey is invaluable when investigating durability of concrete. It is essential to relate the depth of carbonation and chloride concentrations to the depth of steel.
Uncarbonated concrete shows a bright pink colour when a freshly exposed surface is sprayed with a phenolphthalein solution. The test is quick and easy to carry out and indicates areas of alkalinity above about pH 9.5. For an accurate assessment of the carbonation profile it is necessary to use X-ray diffraction, preferably on a core sample.
Samples are taken by either drilling or coring – depending upon the subsequent testing. Cores are required for compressive strengths and are preferable for investigating carbonation by X-ray diffraction. Drilled samples are suitable for X-ray spectrometry, X-ray diffractometry and most other methods of analysis. By sampling at increasing depths, a profile can be obtained to determine if corrosive salts are inherent of from an external source.
The method of access required for site surveys is dependent on the structure and the sample locations. Abseiling, scaffolding or cradles are used, whichever is most suitable.