The rapid chloride permeability test (RCPT) determines chloride permeability by measuring the number of coulombs able to pass through a sample. The rapid chloride permeability test consists of two parts:To obtain consistent chloride permeability values for a concrete batch each slice is conditioned to start at the same moisture content. Then the concrete is tested by measuring the charge passed through the slice when one side of the specimen is in contact with a sodium chloride solution and the other side is in contact with a sodium hydroxide solution.

Chloride permeability decreases the longer concrete cures. To avoid the suggested 28-day cure time, some testing laboratories are using accelerated cure methods on the concrete specimens. However, there are no test results that indicate how to accelerate concrete curing to obtain the same coulomb value as for a 28-day moist-cured specimen. Contractors and ready mix producers should be cautious of test results that are provided before the concrete is 28 days old. Also note that tests have shown that significantly different coulomb test results are obtained at the top and bottom of a cylinder. Use the average of three specimens to obtain a representative value.