بررسی تاثیر جریان آب و مواد یخ زدا بر خرابی بتن آسفالتی تحت سیکل های یخ زدن و ذوب شدن

روسازی راه از مهمترین سرمایه های هر کشوری می باشند و سالانه هزینه های قابل توجهی صرف تعمیر و نگهداری آنها می شود. با توجه به کاهش مقاومت لغزشی راه‌ها در هنگام وجود برف و یخ، مقادیر زیادی ماده یخ زدا برای آب نمودن برف و یخ راه ها استفاده می شود. مواد یخ‌زدا، باعث ذوب برف و یخ شده و آب حاصل که حاوی ماده یخ‌زدا می‌باشد تحت شیب بر سطح راه جریان می‌یابد. حضور مواد یخ‌زدا اثرات مخرب زیادی بر روسازی دارد و توجه بسیاری از محققین را به خود جلب نموده است. اما آنچه به خوبی بررسی نشده است، اثرات جریان آب حاوی ماده یخ‌زدا می‌باشد. لذا این تحقیق به بررسی اثرات توامان جریان آب و مواد یخ‌زدا در سیکل های یخ زدن و ذوب شدن بر خرابی های بتن آسفالتی پرداخته است. در این راستا نمونه های آسفالتی ساخته ‌شده تحت اثر پنج حالت مختلف از سیکل‌های یخبندان و دو ماده یخ‌زدا شامل نمک یخ‌زدا و استات کلسیم قرار داده شدند. همچنین به منظور بررسی دوام بتن آسفالتی، یک دستگاه سایش طراحی گردید تا نمونه های آسفالتی را تحت بارگذاری عمودی و اصطکاکی قرار دهد. میزان درصد افت وزن و مقاومت مارشال نمونه‌ها به عنوان شاخص‌های خرابی بتن آسفالتی در نظر گرفته شدند. نتایج این آزمایشات نشان می دهد که جریان محلول‌های یخ زدا در دوره یخبندان باعث افزایش شدت خرابی آسفالت می‌شود. به علاوه استفاده از نمک یخ زدا تاثیر به مراتب مخرب تری نسبت به استات کلسیم از خود نشان می دهد.

Study of the effects of water flow and deice materials on asphalt concrete deterioration under freezethaw cycles

Roads and pavements are one of the most important assets in any country and considerable amount of money is paid for their rehabilitation or maintenance annually. Pavement surface is the most expensive and susceptible layer as it is in direct contact with traffic and also it experiences different environmental conditions during different seasons. Harsh weather condition and winter maintenance is another parameter that can increase the annual maintenance cost significantly. Winter snow and the resulting ice, can reduce pavement surface friction and therefore, deicing material such as deicing salt or calcium acetate are used to melt the ice and snow. Deicing material decrease the frost temperature and melt the remaining ice and snow and the resulting water flows due to the longitudinal and transverse grade over the pavement surface. The flowing water goes through longer distances in locations were the drainage system is not adequate. Although several researchers and scientists have studied the effects of deicing material on asphalt and concrete pavement deterioration, but what has not been fully studied is the simultaneous effects of deicing material and water flow on the rate of pavement deterioration under freezethaw cycles. Therefore, the focus of this study is to evaluate the combined effects of flowing water and deicing material on the deterioration of asphalt pavements under freezethaw cycles. Two types of asphalt samples were prepared and subjected to five different freezethaw exposure conditions. Deicing salt and calcium acetate were used as the deicing material in this study. The samples were also tested in an abrasion test apparatus and subjected to normal and frictional forces. This abrasion test apparatus was built based on the concepts used in Hamburg WheelTracking Device. Marshall strength loss and weight loss of the samples were measured and used as a measure of asphalt deterioration. Results showed that the combined effects of water flow and deicers increases the deterioration of asphalt concrete samples under freeze–thaw conditions. Furthermore, deicing salt has more deteriorative effects on asphalt concrete in comparison to calcium acetate. In addition, results indicated the water flow has significant effects on asphalt concrete pavement stripping and strength loss. Water flow slows down the formation of ice during freezing cycles by not allowing or slowing the formation of ice crystals and their agglomeration. In still plain water freezethaw chamber, a thin ice layer was formed in zero degrees of centigrade and its depth increased during the freezing cycles but in the flowing plain water freezing condition, where the water flow was present, small ice particles started to form in areas in the chamber where the water flow was in its lowest level. Then, the ice formation gradually expanded to the area with the highest level of water flow. Besides the mentioned effects of water flow, the presence of water flow decreases the freezing temperature of water in the asphalt concrete pores and, consequently, the hydrostatic pressure inside the asphalt concrete increases significantly. Therefore, the asphalt concrete deterioration process becomes faster and more severe when water flow is present in the freezethaw cycles.