AASHTO TP 143:2021 Standard Method of Test for Continuous Measurement of Sideway-Force Friction Number for Highway Pavements.
3.2. A controlled slipping condition is achieved through a freely rotating test wheel mounted mid- machine in line with the wheel path and angled at 20 degrees. pointing towards the center of the vehicle, in the direction of travel3. The test wheel is titted with a special pneumatic, smooth rubber tire.
3.3. When the vehicle is in motion, the test wheel is applied to the pavement surface under a measured vertical load. A controlled flow of water wets the pavement surface immediately in front of the test wheel, so that when the vehicle moves forward, the test wheel rotates, but due to the inclined angle there is slippage in the transverse direction (i.e., in line with the test wheel axle).
3.4. The force generated by the resistance to sliding is related to the wet-pavement skid resistance. The ratio of the measured sideway component of force (H) to the measured vertical load (V) multiplied by 100 provides the sideway-force friction number (SFN).
3.5. The SFN is affected by the speed of the test vehicle, so testing speed shall be measured on a continuous basis to make the necessary SFN speed correction.
3.6. The friction analysis is displayed on the in-cab monitor and can be downloaded to other devices as required by the client for analysis.
4.1. The knowledge of sideway-force friction serves as an additional tool in characterizing pavement surfaces. Sideway-force friction data alone may be of limited value in determining the suitability of paving materials or finishing techniques. However, when used in conjunction with other physical and chemical tests, the sideway-force friction may contribute valuable information about the interaction of tires and the pavement surface.
4.2. The values measured with the equipment and procedures stated herein do not necessarily agree or correlate directly with those obtained by other paved surface friction measuring methods.
5.1. The test equipment shall include the following features:
5.1.1. Test wheel assembly,
5.1.2. Testtire,
5.1.3. Water supply and flow control mechanism, and
5.1.4. Electronic recorder and measurement control system.
5.2. Test Wheel Assembly:
5.2.1. The test wheel assembly is mounted on a frame within the wheelbase of the vehicle. The two vertical shafts are attached to the frame and position the test wheel assembly in the appropriate wheel path.
5.2.2. The assembly shall be free to move vertically when the test wheel is in contact with the surface (to minimize the effects of vehicle chassis movements). The test wheel assembly shall be comprised of a back plate for location on the vertical shafts, a swinging arm, hub, test wheel and tire, and electrical load cells to measure the horizontal (i.e. perpendicular to the test wheel) and vertical loads.AASHTO TP 143 pdf download.