ارزيابي عريان شدگي مصالح سنگي در رويه هاي بتن آسفالتي با روش هاي آزمايشگاهي

Evaluation of Stripping in Asphalt Concrete Pavement by Experimental Methods

عريان شدگي مصالح سنگي يكي از خرابي هاي رويه هاي آسفالتي است كه دقيقا به چسبندگي بين قير و مصالح سنگي بستگي داشته و عامل اصلي پايداري و دوام آسفالت مي باشد. اين خرابي مي تواند زمينه را براي بروز ساير خرابي ها فراهم نمايد. هدف از انجام اين تحقيق بررسي خرابي عريان شدگي در مخلوط هاي آسفالتي، با تكيه بر عامل مصالح سنگي و انتخاب روشي مناسب جهت كنترل و بررسي اين معضل در شرايط آزمايشگاهي است. مطالعه موردي بر روي آزادراه زنجان قزوين كه اين پديده در برخي از قطعات آن ديده شده است نشان داد كه، از معدن مصالح سنگي قطعاتي كه عريان شدگي در آنها شديدتر از ساير قسمتها بود، مصالح جهت ساخت آسفالت انتخاب گرديد. با آزمايشهاي XRF و XRD استعداد عريان شدگي مصالح آزادراه بدليل فزوني كاني سيليس در آنها مشخص گرديد. با استفاده از روش طرح اختلاط مارشال نمونه هاي استوانه-اي بتن آسفالتي تهيه شدند. همچنين طبق استاندارد AASHTO T283-85 دوام آنها در برابر عريان شدگي مورد بررسي قرار گرفت. در اين روش نمونه ها تحت آزمايش كشش غيرمستقيم قرار گرفتند؛ درصد عريان شدگي نمونه ها نيز توسط آزمايش آب جوشان تخمين زده شد. براي پيشگيري از بروز اين خرابي آهك هيدراته به عنوان عمده ترين افزودني ضدعريان شدگي شناسايي شده و نحوه ارزيابي از طريق آزمايشات بصري مانند آزمايش استاندارد آب جوشان و آزمايشات كمي از جمله آزمايش لاتمن اصلاح شده صورت گرفت. از اين تحقيق نتيجه گرديد كه چنانچه آهك هيدراته بعنوان مصالح فيلر در مخلوط بكار رود اولا موجب تقليل عريان شدگي شده و ثانيا باعث افزايش انسجام، استحكام و دوام روسازي آسفالتي مي شود.

Adhesion of bitumen to Aggregates is the basis of the strength of the asphalt pavements. The term "stripping" is used for hot mix asphalt (HMA) mixtures to show the separation of asphalt binder film from aggregate surfaces, due primarily to the action of moisture and/or vapor. If this phenomenon is eliminated for any reason, stripping will be occurred. This problem not only is as a distinct distress but also can cause other asphalt distresses which are finally resulted in the overthrow of road. Mainly because this distress either results from or is dominated by moisture, it is usually called “moisture damage” or “moisture susceptibility”. The main goal in this research is to study stripping in asphalt mixtures. The key factors which must be considered in this research are aggregates and selecting the suitable approach for controlling and assessment of this distress in laboratory conditions. the most recent approach introduced is the rehabilitation and modification of asphalt mixtures against stripping, whether asphalt concrete or surface treatment. Thus, in this study on "Zanjan-Qazvin" freeway where this distress have usually been observed, the aggregates for constructing the asphalt was selected from sections of the aggregate the stripping intensity of which is higher than the others. First, the sensitivity of stripping was specified by XRF & XRD analysis. There is a requisite to do a realistic laboratory test method to predict moisture susceptibility of HMA mixtures. It was observed in the case histories that the asphalt pavements were saturated with water (55-80% saturated as specified in ASTM D4867 or AASHTO T283). Thereafter, in order to calculate the tensile strength ratio, it is required to consider unsaturated specimens some of which remained with no conditions. A laboratory test procedure that simulates such conditions will be more realistic. The cylindrical asphalt concrete specimens are constructed by marshal method. Thus, their durability is evaluated according to AASHTO-T283. In this method, those stabilities are measured by indirect tensile test; the amount of their stripping was previously estimated by boiling test. Results showed that according to literature boiling test method is not reliable enough to be accurate. On the other hand, the result of laboratory test of AASHTO-T283 is quantitative and much more technical. Also, using hydrated lime 3% for this material can be useful to reduce the adverse effect of stripping, and it can be used as a suitable anti-stripping. Based on the probabilistic analysis, all the specimens result either in Indirect Tensile Test, or in the TSR results. This showed the improvement of the strength. Also, the rate of increasing is close to that of the parabolic curve. WTAT test was carried out over the surface treatment specimens constructed using these aggregates. Hydrated lime was utilized as the most important anti-stripping additive for prevention and rehabilitation of this distress in all of the experiments.