Utveckling av Prallmetoden

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The Prall test is one of several laboratory methods for determining the wear of asphalt pavements. It was initially developed in the U.S. as a method for testing the adhesion properties. In the 1980s the method it was introduced in Sweden, where it became known as FAS Method 471. Comparative tests between road wear and Prall wear showed that the Prall test very well equals the wear of asphalt pavement on Swedish roads with high use of studded tires in the winter.

The method is today, together with the Finnish PWR (SRK) method, a European standard known as EN 12697-16. A weakness of the method is that it has proven poor repeatability and reproducibility. The studies in this report aim to improve the method's accuracy. Different parameters affecting Prall value have been investigated to determine which factors have the greatest impact and thus need to be addressed in order to get a method with better precision. These parameters are stroke length, water temperature, the weight and the diameter of the balls and frequency. Measurements with an accelerometer with the aim of assessing imbalances in the equipment and tests with different types of reference samples have been conducted. A summary of round robin tests conducted since the early 1990s are presented in the report, too.

The report provides suggestions for modification of the method that hopefully will give the method increased accuracy. The most important of these are:

  • always to test on cut surfaces
  • to treat the stones that come loose in the test in a similar way
  • to specify a minimal weight for the sets of balls
  • to introduce narrower tolerance for frequency (stroke/min) and time

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