The Researching About Evaluation Methods That Concrete Resists Sulfate Erosion Under The Freeze Thaw-Dry Wet Cycling Condition

The concrete material used in three north areas of China are under the effect of freeze-thaw cycles, dry-wet cycles, sulfate attack, and lead to a quick degradation process of concrete material’s performance. In this paper, the concrete’s performance of anti-sulfate attack under freeze thaw- dry wet cycling is studied, based on the tentative study results, the concrete material’s performance is evaluated and the service life is predictedThis paper summarizes the mechanism of sulfate attack in concrete material. Based on the test of concrete’s freeze-thaw cycles and dry-wet cycles, the main test method of freeze thaw- dry wet cycling is determined, and use four evaluation index to evaluate the concrete’s performance: quality change fraction, compressive strength change fraction, flexural strength change fraction and dynamic elastic modulus change fraction. The results show that using freeze thaw- dry wet cycling can speed up the erosion rate of the sulfate significantly. After six freeze thaw-dry wet cycles, each performance of the C40 concrete is than or close to the critical value, and its damage rate is about 1.5 times faster than freeze-thaw cycles and 4 times faster than dry-wet cycles. Through the analysis between this paper and former paper, the test results is almost the same, and shows that the test results can be the basic data of concrete’s comprehensive performance evaluation and service life prediction, which provides a good support to the application of comprehensive evaluation method and service life prediction model.This paper use Analytic Hierarchy Process(AHP) system to determine the weight of each evaluation index, and get the functional weight through extension judgment matrix, entropy method’s weight correction. By Grey Relation Analysis’(GRA) advantage on study of "small sample", "poor information", use grey correlation model’s grey correlation to evaluate the concrete’s comprehensive performance quantitatively, combining with calculated index weight. On the basis of correlation degree, concrete’s performance is divided into five grades: good, preferably, normal, poor and very poor, and determine the correlation degree’s range of each grade by extension evaluate model. Through the verification, evaluation results of concrete’s comprehensive performance of GRA fit well with extension theory, assessment level of concrete improve 1~2 level with the content of fly ash from 0% to 20%, which match the test results of this paper and references, shows the practicability of comprehensive evaluation method in this paper.Using the advantage of Weibull distribution on service life prediction, this paper use two parameter Weibull distribution, taking dynamic elastic modulus as the sign of concrete’s damage, calculating the parameter value of Weibull distribution by least squares estimation method, taking freeze thaw- dry wet cycling damage equivalent to freeze thaw cycling damage by concrete damage superposition principle, getting the service life prediction of concrete according to the relationship between the number of indoor and outdoor concrete’s freeze thaw cycling. Through the equal relation between concrete damage and damage level, the number of indoor freeze thaw cycling and freeze thaw-dry wet cycling that should achieve can be inverse computational, when concrete design working life is 20~120 years and the rate of outdoor freeze thaw cycling is 50~120 per year. The predictive value and inverse computation value are equal and the contrast of them shows the rationality of service life prediction method in the paper, and it has a certain reference value.