FROST DURABILITY OF HIGH-STRENGTH CONCRETE - EFFECT OF INTERNAL CRACKING ON ICE FORMATION

Ice formation measurements using low temperature calorimetry (CAL) wer e made on non-air entrained high strength concretes (HSC) before and a fter exposure to rapid freeze/thaw cycles in water (ASTM C666 proc. A) . The purpose was to explore the relationship between water absorption during test, changes in ice formation and deterioration, to investiga te the deterioration mechanism of non-air entrained HSC in the ASTM C6 66 test. CAL results showed zero or very little ice formation in the c oncretes (w/b = 0.40 and 0.35, 0, 5 and 8 % silica fume) before C666 t esting in the temperature range of the test (-20 degrees C). After the test (DF = 10 - 11) significant water absorption had taken place. Onl y one half or less of the absorbed water was freezeable to - 20 degree s C, i.e. only part of the absorbed water goes into the created cracks and contributes to the deterioration by freezing there. The rest of t he water is feezeable at lower temperatures or so tightly bound that i t does not freeze at all to -55 degrees C. The freezeable water to -20 degrees C after test constitutes 3 - 7 vol-% of the cement paste. CAL measurements at intermediate stages of deterioration show very rapid transitions between no and significant amount of feezeable water, and indicate a progressive mechanism of deterioration, starting at the sur face in contact with water and moving inward. Apparently very little i ce formation can initiate the process and result in major damage. Wate r storage after freeze/thaw testing results in self healing characteri zed by significant recovery of dynamic E-modulus and decreased amounts of ice formation. However, compressive strength recovery is much smal ler than the recovery of E-modulus.