If the asphalt overlay is thicker than 30 mm, it is necessary to remove it in certain areas to perform the test. Differentiation between debonding of an overlay and delamination in the concrete can be made by coring in the dull-sounding areas. The reinforcing steel in parking garage decks should be protected with a 50 mm thick concrete cover, a minimum requirement which is unfortunately seldom met. To obtain reasonably long service life for the repaired deck, those areas where the cover is less than 25 mm have to be identified and corrective measures taken. The thickness of the concrete over the steel can be measured with a cover meter, also known as pachometer.
Several types are available.
Measurement of corrosion potentials Corrosion of metals is an electrochemical process in which the deteriorating area of the metal is the anode, the positively charged electrode of the galvanic cell. Positive potential of the metal indicates corrosion activity, i.e., the metal in this region is converting from the metallic to the ionic state. The value of the potential depends on the tendency of the metal to go into solution and, based on the concentration of ions around the electrode, is a good measure of the corrosion that has taken place. If a water-proofing membrane is present, it has to be punctured to establish electrical continuity before the test can be performed. With galvanized steel, interpretation of the results is difficult and, if epoxy-coated, the measurement cannot be made at all for lack of electrical continuity.