MECHANICAL DAMAGE AND FATIGUE EFFECTS ASSOCIATED WITH FREEZE-THAW OF MATERIALS

摘要

In a traditional freeze-thaw test, in which the specimen is exposed to water during freezing and/or thawing, it is often observed that damage increases progressively with increasing number of freeze-thaw cycles. Sometimes a certain "incubation" number of cycles is required before frost damage occurs. This behaviour is often believed to be an effect of fatigue. In the paper it is shown that the progression of damage observed probably is caused by a gradual water absorption during the test. Therefore, each new freeze-thaw cycle is performed with a somewhat higher moisture content in the specimen than in the cycle before. This means that progressive destruction is not an effect of fatigue of tradi-tional type, but is caused by gradually increased internal stresses due to the increased inner moisture level. No damage occurs until the number of cycles has become big enough to cause damage which explains the existence of "incubation" cycles. It is shown that a certain low-cycle fatigue exists and that this has an influence on the progression of damage. But, this effect is limited to rather few freeze-thaw cycles fol-lowing the the one that caused the first damage. Experiments with different materials in-dicate that an upper limit for low-cycle frost damage fatigue exists and that this limit is a function of the moisture content. Results of an investigation of concrete on the effect of frost and high moisture levels on compressive strength, tensile strength, bond strength, and E-modulus are presented.