An equation for determining freeze-thaw fatigue damage in concrete and a model for predicting the service life

摘要

The present study uses the dynamic modulus of elasticity as the damage variable and derives an equation that can be used to determine the freeze-thaw fatigue damage in concrete under water and deicing salt freeze-thaw conditions based on the mechanical fatigue damage theory. The present study derives a model for predicting the service life of concrete subjected to freeze-thaw cycles under different freeze-thaw systems. Accumulative model is also presented for predicting the service life of concrete subjected to freeze thaw cycles under a combination of different freeze-thaw systems in natural environmental conditions; this model uses the fatigue damage accumulation theory along with the fact that the mechanism of freeze-thaw damage in concrete is the same in the natural freeze-thaw environment as it is under standard laboratory rapid freeze-thaw conditions. The equation for determining the freeze-thaw fatigue damage in concrete and the model for predicting the service life of concrete subjected to freeze-thaw cycles are verified based on a large amount of test data. The relationship between the number of freeze-thaw cycles concrete undergoes under laboratory condition and natural environmental conditions is recalculated. In addition, applying the cumulative model for predicting the service life of concrete subjected to freeze thaw cycles under natural environmental conditions is discussed. The results show that the curves of the freeze-thaw fatigue damage for different types of concrete obtained from the proposed equation have the same trends and are in good agreement with the curve of the measured relative dynamic modulus of elasticity. Furthermore, the relative errors between the values calculated from the model for predicting the service life of concrete subjected to freeze-thaw cycles and the values measured under different cooling rates are less than 3%; this result indicates that the model for predicting the service life of concrete subjected to freeze-thaw cycles and its cumulative model can satisfactorily predict the natural fatigue life of concrete subjected to freeze-thaw cycles in an actual freeze-thaw environment. The analysis and calculation of the measured laboratory condition and natural environmental conditions data shows that the ratio of the standard fatigue life of concrete subjected to freeze-thaw cycles under rapid laboratory freeze-thaw conditions to the natural fatigue life of the same concrete subjected to freeze-thaw cycles in the actual environment is approximately 1:8-1:9, instead of the previously reported range of 1:10-1:15. (C) 2017 Elsevier Ltd. All rights reserved.