Advanced Concrete Testing Service
Concrete Durability Test
- Water Permeability
- Chloride Penetration
Durability test of concrete is done to determine the resistance to physical or chemical deterioration of concrete resulting from interaction with the environment (physical deterioration) or interaction between constituents (chemical deterioration) of concrete. A durable concrete ensures corrosion resistance of embedded steel which in turn ensures better longevity of the structure as a whole. Concrete structures in the coastal areas are the most susceptible to chemical deterioration as seawater, with a high concentration of chloride ions, has quite a detrimental effect on the durability of concrete. In these cases, the lower the chloride permeability, the better the durability of concrete.
Rapid Chloride Permeability Test (RCPT)
This is the only permeability (chloride diffusion) test recognized as a standard test method, ASTM C120210. The test involves applying a potential of 60V DC across a 100mm diameter x 50mm thick slice of concrete conditioned by vacuum saturation. One end of the samples is immersed in Sodium Chloride and the other in Sodium Hydroxide. The full test would take about three days to complete, with 6 hours required for the actual test. The total electric charge passed (coulombs) is a measure of the chloride ions migrating through the concrete under the described conditions. However, this method has been criticized as not really measuring permeability (movement of chloride ions) but the resistivity of the water-saturated sample. In addition, ASTM C1202 states that the rapid test should not be used unless proper correlations are made with long-term ponding tests (such as the 90-day chloride ponding test, AASHTO T259). The RCPT may also suffer from possible interferences (as indicated in ASTM C1202) and should be considered in the interpretation of results. Interferences affect the resistivity (conductivity) of the concrete and this in turn the coulomb value. Interferences may include the degree of moisture in the specimens, presence of reinforcing steel or ions other than chlorides, use of SCMs and other admixtures, etc. Another more serious problem associated with the method is the potential overheating of test samples, particularly with younger concrete, which would result in damage and therefore distortion of the test data. At younger ages high-performance concrete is so conductive, it would not survive the RCPT due to overheating. As such for quality assurance this test is normally conducted when the concrete is 1 to 3 months old. The method may have to be modified with lower voltages to enable accurate testing for younger concrete. It should also be noted that as part of the SHRP program in the USA (high-performance concrete project), a more rapid and less expensive resistivity method (i.e. AC Impedance Test) was investigated as an alternative to the RCPT for the reasons mentioned above. It was also suggested that RCPT initial Current (amps), may be a better indication of permeability than charge passed (Coulombs) because it avoids possible distortion of the data caused by overheating of the specimen.