EFFECT OF SUPPLEMENTARY CEMENTING MATERIALS ON THE SPECIFIC CONDUCTIVITY OF PORE SOLUTION AND ITS IMPLICATIONS ON THE RAPID CHLORIDE PERMEABILITY TEST (AASHTO T277 AND ASTM C1202) RESULTS

AASHTO T277 and ASTM C1202 have specified a rapid test method to rank the chloride penetration resistance of various concretes by applying a potential of 60 V DC to a concrete specimen and measuring the charge passed through the specimen during sh hours of testing. The method is essentially a measurement of electrical conductivity of concrete, whic h depends on both the pore structure and the chemistry of the pore sol ution. Analyses based on published results have indicated that the rep lacement of portland cement with supplementary cementing materials, su ch as silica fume, can reduce the electrical conductivity of concrete more than 90 percent due to the change in pore solution composition in the concrete. Chemical composition of pore solution has little to do with the transport of chloride ions in the concrete; thus, it is not c orrect to use passed charge to rank the chloride penetration resistanc e of concrete made with supplementary cementing materials.