بررسي تاثير جريان آب و مواد يخ زدا بر خرابي بتن آسفالتي تحت سيكل هاي يخ زدن و ذوب شدن

Effects of Water Flow and De-Ice Materials on Asphalt Concrete Deterioration Under Freeze-Thaw Cycles

روسازي راه از مهمترين سرمايه هاي هر كشوري مي باشند و سالانه هزينه هاي قابل توجهي صرف تعمير و نگهداري آنها مي شود. با توجه به كاهش مقاومت لغزشي راه ها در هنگام وجود برف و يخ، مقادير زيادي ماده يخ زدا براي آب نمودن برف و يخ راه ها استفاده مي شود. مواد يخ زدا، باعث ذوب برف و يخ شده و آب حاصل كه حاوي ماده يخ زدا مي باشد تحت شيب بر سطح راه جريان مي يابد. حضور مواد يخ زدا اثرات مخرب زيادي بر روسازي دارد و توجه بسياري از محققين را به خود جلب نموده است. اما آنچه به خوبي بررسي نشده است، اثرات جريان آب حاوي ماده يخ زدا مي باشد. لذا اين تحقيق به بررسي اثرات توامان جريان آب و مواد يخ زدا در سيكل هاي يخ زدن و ذوب شدن بر خرابي هاي بتن آسفالتي پرداخته است. در اين راستا نمونه هاي آسفالتي ساخته شده تحت اثر پنج حالت مختلف از سيكل هاي يخبندان و دو ماده يخ زدا شامل نمك يخ زدا و استات كلسيم قرار داده شدند. همچنين به منظور بررسي دوام بتن آسفالتي، يك دستگاه سايش طراحي گرديد تا نمونه هاي آسفالتي را تحت بارگذاري عمودي و اصطكاكي قرار دهد. ميزان درصد افت وزن و مقاومت مارشال نمونه ها به عنوان شاخص هاي خرابي بتن آسفالتي در نظر گرفته شدند. نتايج اين آزمايشات نشان مي دهد كه جريان محلول هاي يخ زدا در دوره يخبندان باعث افزايش شدت خرابي آسفالت مي شود. به علاوه استفاده از نمك يخ زدا تاثير به مراتب مخرب تري نسبت به استات كلسيم از خود نشان مي دهد.

Roads and pavements are among 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 freeze-thaw 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 freeze-thaw cycles. Two types of asphalt samples were prepared and subjected to five different freeze-thaw 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 Wheel-Tracking 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 that 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 freeze-thaw chamber, a thin ice layer was formed in zero degrees of centigrade and its depth increased during the freezing cycles, while 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. Thereafter, 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 freeze-thaw cycles.