EFFECT OF CRACKING AND HEALING ON CHLORIDE TRANSPORT IN OPC CONCRETE

The effects of cracking and self healing on chloride migration and com pressive strength were investigated on w/c = 0.40 concrete. Internal c racking due to rapid freeze/thaw exposure resulted in a compressive st rength reduction of 68 - 40 % and a reduced Ultrasonic Pulse Velocity (UPV) to 78 - 45 % of undamaged values. The rate of chloride migration through 15 mm thick slices under a 10 volt electric field was increas ed by 2.5 - 8 times, and the chloride penetration time through the sli ces was reduced from 64 to 0 hours for the most severe cracking. The i ncreased chloride transport due to cracking could be predicted fairly well by characterizing the cracks using a square grid crack pattern mo del. Self healing by storage of cracked specimens in lime saturated wa ter at 20 degrees C for three months after stop of freeze/thaw exposur e gave recovery in UPV of 50 - 100 %, but compressive strength recover ed only 0 - 10 % of the initial value. Rate of chloride migration in t he self-healed concretes was reduced by 28 - 35 %, and penetration tim e was increased compared to newly cracked concrete. The chloride migra tion through an air entrained concrete with the same w/c ratio (no int ernal cracking after more than 300 cycles of rapid freeze/thaw exposur e), was unaffected by freeze/thaw.