A thorough investigation must be performed to determine the extent and magnitude of concrete distress. The typical investigation begins with a condition survey based on visual examination and soundings to identify delamination and deterioration. Frequently the evaluation includes obtaining concrete cores and examining them microscopically in the laboratory. These techniques, however, do not detect the full extent of unseen, early stage corrosion that may be going on in the concrete, and electrical measurements are commonly made to supplement the condition survey.
STANDARD HALF CELL TEST METHOD
Corrosion of reinforcing steel is an electrochemical process: that is, both a flow of electricity and a chemical change are involved. Detecting and measuring this electric current flow helps us assess the degree of unseen corrosion activity. To record this information, half cell procedures standardized in ASTM C 976 have been developed. A copper-copper sulfate half cell connected to the positive terminal of a voltmeter is placed in contact with the concrete surface, and the negative terminal of the voltmeter is electrically connected to the reinforcing steel mat. A reading of electrical potential (voltage) is taken at each point.
COMPUTER-ASSISTED HALF CELL EQUIPMENT
Computer-aided half cell equipment not only addresses the shortcomings of conventional half cell procedures, but also adds a valuable dimension to corrosion assessment in concrete. The computer concurrently measures and records electrical resistance in addition to potential.