بررسي آماري چقرمگي شكست مخلوط هاي آسفالتي در دماي پايين براساس مدل پيش بيني وايبول

Statistical analysis of mode I fracture mechanics of asphalt mixtures at low temperature based on Weibull prediction model

ترك هاي دماي پايين در روسازي آسفالتي يكي از عوامل تخريب و واماندگي راه ها مي باشد. لذا بررسي رفتار شكست و مقاومت ترك خوردگي روسازي آسفالتي بسيار مهم ارزيابي مي شود. به دليل ساختار چند جزيي مخلوط هاي آسفالتي، پراكندگي داده هاي آزمايشگاهي براي اين مواد از ساير مواد همگن و تك فازي بيشتر مي باشد و در نتيجه براي بررسي رفتار ترك خوردگي مخلوط هاي آسفالتي بايستي از تعداد بيشتري از نمونه هاي آزمايشگاهي و نيز مدل هاي آماري استفاده نمود.در اين پژوهش براي بررسي رفتار شكست مخلوط هاي آسفالتي تعداد زيادي آزمايش چقرمگي شكست مود I بر روي نمونه هاي نيم ديسك خمشي آسفالتي در دو فضاي خالي 4 و 7 درصد در دماي 10- درجه سيليسيوس انجام شد. با بررسي نتايج حاصل از آزمايش هاي چقرمگي شكست و با استفاده از مدل توزيع تجمعي وايبول، به تحليل آماري و ارائه مدل پيش بيني نمونه هاي ترك دار در دو فضاي خالي آزمايش شده پرداخته شد. نشان داده شد كه با استفاده از مدل آماري وايبول دو و سه پارامتري مي توان مشخصات شكست مخلوط هاي آسفالتي با درصد فضاي خالي مختلف را تنها با انجام آزمايش شكست بر روي يك نمونه آسفالتي و با فضاي خالي مشخص پيش بيني نمود.

This paper describes an evaluation of low temperature cracking of asphalt pavement and its propagation agents. Low temperature cracking is one of the noticeable deterioration of asphalt pavement in cold climate regions. This work employed a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixtures, additionally a large number of edge cracked semi circular bend specimens containing 4% and 7% air voids are used and subjected to symmetric three-point bending load at -10 °c to measure fracture toughness. The effect of air voids on pure mode I asphalt fracture are investigated experimentally and Linear Elastic Fracture Mechanics, its assumptions and effective crack tip parameters introduced, which is used in asphalt fracture mechanics. Then fracture toughness as a main parameter of fracture in the asphalt mixtures is calculated and various methods with different specimen types for determining the fracture toughness of asphalt has been viewed and Asshto suggested method has been discussed, which applied to the experimental part of this work. According to the statistical principle, the experimental results were analyzed by Weibull statistical distribution model in order to present the prediction models for each asphalt mixture with different air voids. The two-parameter and the three-parameter Weibull distribution function was applied to air voids data, Thus compared these two functions. Within the statistical analysis, the probability function for brittle fracture suggested by Wallin using a Weibull analysis that have the three parameters, Kmin, m and K0 ,all of which predicted in this study. The analysis of the results also revealed that Weibull distribution model is one of the most appropriate function for disscussing the volumetric properties of asphalt mixtures.Furthermore, a statistical analysis illustrated that Weibull model is also able to predict the statistical parameters for each set of test data, By preliminary data from the tests and also a well- defined Transfer Coefficient from the previous experimental data that the other researchers obtained through their studies, can be predicted the three-parameter and the two-parameter of Weibull statistical model such as Kmin and K0 which have significant role for asphalt fracture mechanics. In addition to the parameters of Weibull distribution, the average fracture toughness or the average stress intensify factor for asphalt specimens can be predicted from this type of the statistical analysis. In conclusion, this paper emphasises on the statistical and the experimental aspect of asphalt fracture mechanics that has investigated Weibull distribution model and the ability of this model to predict the important fracture parameters and the average stress intensify factor from a determined experimental data based on volumetric properties such as air voids. Finally, by investigating the errors for different models that suggested in this paper, indicatin the suitability of this model to predict the actual values of asphalt fracture.