CHLORIDE PENETRATION AND THE EFFECT ON POROSITY IN A PAVEMENT

A concrete pavement 230 mm (9 in.) thick was studied for chloride penetration and porosity. The pavement was subjected to an estimated 4600 kg/km (16,000 lb/mi) of deicer annually. Three types of cores were removed from the pavement: cores through sound areas, through sealed joints, and through cracks. Cores were taken in 1985 and 1990. Chloride concentrations were measured in the cores at depths of 25, 76, 127, and 178 mm (1, 3, 5, and 7 in.). The chloride concentrations in whole cores--that is, the cores taken from intact areas of the pavement containing no visible cracks or joints--fall under the corrosion limit at depths below 76 mm (3 in.), although higher chloride contents were detected near the surface. The steel mesh [located between 76 mm (3 in.) and 102 mm (4 in.) below the surface of the concrete] showed no indication of corrosion in these cores. Cores taken through cracks and joints showed much higher chloride concentrations than cores taken from sound concrete. The chloride in the cracked and joint cores was usually above the corrosion limit for steel, and the mesh in the cracked areas had completely corroded, showing that the chloride penetration is mainly through cracks and joints and not through sound concrete. Data from literature suggest that flexural cracks may be enough to admit chlorides. The porosity of the samples was measured using mercury porosimetry. There was no correlation between porosity and chloride content, confirming that damage is more important than porosity in chloride intrusion.