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Determination of the Friction Coefficients of Icy Pavements Under Different Amounts of Snowfall
Chapters
Summary January 6th, 2023
Here, we present a method for determining the friction coefficient of pavements with different ice thicknesses indoors. The complete procedure includes the preparation of the equipment, the calculation and analysis of the snowfall, equipment calibration, friction coefficient determination, and data analysis.
Transcript
This video is aimed to show the process of determining the coefficient of friction of an icy road surface. Using the pendulum friction coefficient meter. Ice on the road surface can lead to a significant reduction in the coefficient of friction and thus endanger driver safety.
We want to establish a complete and scientific experimental procedure indoors to determine the coefficient of friction of icy road surfaces. A pendulum friction tester was used to conduct in the experiment and asphalt slabs and water layers were frozen simultaneously to simulate road icing. Different levels of snowfall was also simulated on asphalt slab with varying ice thickness to make the results more intuitive.
Preparation of the equipment. First, the pendulum friction coefficient meter, during the experiment ensure that B P T is within its surface life and that surface is clean and undamaged. Its components are base, leveling spiral, leveling bubble, pointer, pendulum, lifting spiral, fastening spiral, huddle, and dial.
Then the asphalt slab, ensure that asphalt mixture sample size use for experiment is 30 centimeters by 30 centimeters by five centimeters. The right figure shows the asphalt slab wrapped with molds. Next the freezing equipment, ensure that this equipment used in the experiment can freely regulate the temperature between subzero 20 centigrade to zero centigrade.
Other equipment used in the experiment includes, tripod, measuring cylinder, rubber sheet, pavement thermometer, sliding length ruler and brush. The size of the rubber sheet used in the experiment is 6.35 millimeters by 25.4 millimeters by 76.2 millimeters and should meet the quality requirements given in the following table. During the experiment, ensure that the rubber sheet has no following defects:First, there are oil stains;Second, rubber sheet width edge wear is greater than 3.2 millimeters.
Third, rubber sheet length direction wear is greater than 1.6 millimeters. Before using a new rubber sheet, ensure that the rubber sheet is measured 10 times on a dry surface before employed for official testing. Calculation and analysis of snowfall the table gives the snowfall class classification to consider extreme cases takes 24 hours of snowfall at the condition for the study.
Moreover, to ensure the ease of experimentation the upper limits of each level of snowfall division as used for the corresponding calculation and analysis. After calculation, different levels of snowfall test at the corresponding water volume of the samples as provided in the table. Experiment does not consider the influence of the extraordinary snow storms and number the very light snow to big blizzard from 1 to 6.
Equipment calibration Place the BPT in a suitable position. A suitable position means that the ground is flat and free of potholes, rotate the leveling spiral on the base of the BPT to keep the leveling bubble in the middle position. Loosen the fastening spiral, rotate the lifting spiral to make the pendulum lift and swing freely.
Then tighten the fastening spiral. Place the pendulum arm on the right cantilever of the pendulum table keeping the arm in the risen toe position while rotating the pointer to the right side flush with the arm. Press the release button to let the pendulum arm swing freely and then the pendulum crosses the lowest point.
To reach the highest point, hold it by hand. The pointer should indicate zero at this time. If the pointer does not show the zero point loosen and tighten the narrowing nut to make it show the zero point.
Place the asphalt slab directly under the pendulum while loosening the fastening spiral so that the lowest edge of the rubber sheet touche the surface of the asphalt slab. Prepare the sliding length ruler and bring it close to the rubber sheet. Lift the carrying handle to make the left scale mark of the sliding length ruler flush with the lowest edge of the rubber sheet.
Lift the carrying handle and move the pendulum to the right again so that the lowest edge of the rubber sheet only touches the surface of the asphalt slab. Observe further, the sliding length jeweler is flush with the edge of the rubber sheet. If flush, the sliding length meets a requirement of 136 millimeters.
Otherwise, continue the following operation. Turn the lifting spiral to adjust the height of the pendulum to make the sliding length meet the requirements. Vital tan is needed.
Twist the level spiral on the base. The level in bubble needs to remain centered during an adjustment. Friction coefficient determination.
Select seven pieces of asphalt slabs. Clean their surface with a brush and dry naturally at room temperature. Number the asphalt slabs in turn place the asphalt slabs into modes and simultaneously coup and freeze with the water layer.
The sevens samples were placed into the freezer at a controlled temperature in a sub zero 10 centigrade for 24 hours. After freezing, turn down the samples in turn, remove the modes and place them on the BPT centers, which have been leveled and zero use the pavement centimeter to measure the surface temperature of the sample and record, perform sliding length calibration. To ensure sliding distance of 126 millimeters press the pendulum arm release switch and when the pad arm crosses the lowest point and swings to the highest one held by hand, read and recorded restore both the pendulum arm and the pointer to the zero and horizon positions respectively.
The sliding length should be re calibrated each time a new sample is tested. Repeat the steps for 10 times. Measure seven samples in sequence.
Each sample has 10 measurement results and both the minimum and the maximum value difference should be less than three. Data analysis recorded data in the table and the average measurement results to get average values bring the temperature value measured into the equivalent. To obtain the temperature compensated value subtract the compensated BPN value from average BPN value in the table to obtain the final temperature compensated BPN value plot the final BPN values in table four and the bar graph for more intuitive results.
Representative results:When comparing sample seven and the other six groups, I think it is observed to significantly reduce the friction coefficient of the pavement. Based on sample one very light snow force is not to have a serious impact on the road friction coefficient. With respect to sample two, three, and four the surface friction coefficient was observed to gradually decrease for sample four, five and six.
The average final BPM values are identical. This may indicate that the road friction coefficient of the ice layer tends to stabilize and another measure of a thicker ice layer is not necessary. The bar graph can better reflect the wide ratio of friction coefficient.
Sample one represents very light snow that adhere to the pavement surface after icing resulting the reduction in the pavement friction coefficient and its BPM value decreased by approximately 43%compared to the dry sample. Sample two, three and four correspond to light medium and heavy snow respectively. Among them the BPM value of medium snow is only one half that of light snow because the thickness of the iced layer corresponding to little snow is of like two minimum.
The micro structure of the sample surface still affects the friction coefficient value and the BPN is larger. The BPNs of the heavy snow, blizzard and large blizzard samples are the same, which may stop an ice thickness reaches 11 minimum. The rubber sheets can no longer deformed the ice layer by compacting it.
Conclusion:The friction coefficients of seven asphalt slabs were determined by means of a pendulum friction coefficient tester, and the final results were corrected for temperature. It can be seen that, the effect of pavement icing on the coefficient of friction is indeed significant, with even slightly light snow resulting in patches of ice reducing the pavement of friction coefficient by about 40%The final results can provide a reference for road design and winter pavement maintenance.
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