تحليل اصطكاك و بافت روسازي آسفالتي با استفاده از دستگاه آونگ انگليسي و آزمايش پخش ماسه

Analysis of Friction and Texture of Asphalt Pavement by British pendulum Tester And Sand patch Test

لغزنده شدن سطح راه‌ها يكي ازعواملي است كه احتمال وقوع تصادفات را افزايش مي‌دهد. لغزش زماني اتفاق مي‌افتد كه ضريب اصطكاك بين لاستيك و سطح راه براي حفظ چسبندگي بين اين دو كافي نباشد. با افزايش سرعت وسيله نقليه و حجم ترافيك كه دو عامل اساسي در مسيله سرخوردگي است، اين موضوع اهميت زيادي پيدا كرده است. به شكلي كه امروزه كنترل مقاومت سرخوردگي‌ روسازي ها در كشورهاي پيشرفته صنعتي امري مهم بوده و در طرح روسازي‌ها بدان توجه كامل مي‌شود. اصطكاك راه با تغيير عوامل متعددي از جمله مشخصات سطح آسفالت، مشخصات لاستيك، درجه رطوبت راه و شرايط عملكردي وسيله نقليه تغيير مي‌كند. در اين پژوهش با مطالعه موردي خياباني با ترافيك سنگين واقع در منطقه بيست شهر تهران و بررسي اطلاعات آماري مربوط به ترافيك و تصادفات آن، آزمايش‌هاي مربوط به آسفالت در بزرگراه شهيد رجايي تهران مسير شمال به جنوب حد فاصل پل آزادگان تا بيمارستان شهداي هفتم تير انجام و سپس آزمايش‌هاي ميداني به وسيله دستگاه آونگ انگليسي براي تعيين مقاومت لغزشي و آزمايش پخش ماسه براي تعيين بافت درشت روسازي انجام شد در پايان با بررسي ارتباط بين داده‌ها و نتايج آزمايش‌ها، نمودارهاي چگونگي تغييرات مقاومت لغزشي نسبت به زمان بر اثر عبور ترافيك ارايه شده است. با مقايسه نتايج با استانداردها مي‌توان نتيجه گرفت كه پس از گذشت 7 ماه نياز به بهبود مقاومت لغزشي روسازي آسفالتي است.

It has been well proven that as the friction of a road surfacing decreases, the number of loss of control type crashes increases, causing road death and injuries. Slipperiness of the road surface is one of the factors which increase the risk of accident. In fact slip occurs when the coefficient of friction between the tire and road surface is not enough to keep the adherence between the two. Skid should not be considered as a separate issue, but to solve this problem, we should optimize properties of tire and road which leads to decrease in possibility of skid. This is a fact that the less the skid resistance value, the more accidents in fall and winter which have more rain. Road friction changes with change of many factors such as properties of pavement surface, properties of tire, moisture of road and performance of vehicle. This field study has been performed by examining the statistical information related to traffic and accidents and case study of a street with heavy traffic in Tehran. Hot mix asphalt was provided from factories of municipality of Tehran and was distributed and tests of hot mix asphalt were done by Marshal test . After that British pendulum method was used to determine the microtexture, and sand patch test was used to determine mean surface macrotexture depth. Finally by repeating the test in time intervals within 18 months and investigating the relationship between the data and test results, charts of state of changes of skid resistance over time were presented which indicated that slip resistance of asphalt pavement decreases by time and traffic crossing. First this decrease is more and then gradually declines. By comparing the results with standard it is concluded that the skid resistance of asphalt pavement should be improved after 7 months. Also In order to survey the influence of execution of the new asphalt overlay, all the information about traffic volume and accidents in the said street gathered and investigated. Furthermore the result from each part compared with other researches. Results have shown that number of accidents decreased sensibly by modifying asphalt overlay and this decrease would be more at higher speeds. Therefore the method of modifying asphalt overlay is recommended in risky points to preventing or decreasing the accidents. Also by investigating the statistical reports given by the road police in the aforesaid street it was found that about 50% of the accidents are related to function of brakes of vehicles and friction resistance and comparing the statistics reveals that after the road surface is improved by asphalt, accidents in case study street decreased by 25% . After that with comparing the number of accidents in the studied street in the second 6-month of year and during the year especially in accident prone points it was found that number of accidents in the second 6-month is 70% of the whole year. This indicates the particular effect of weather condition in rainy season and decrease of skid resistance of pavement due to roads surface wetting on number of accidents.