AASHTO PP 103:2021 StandardI Practice for Sample Preparation and Polishing of Unbound Aggregates for Dynamic Friction Testing.
5.1. Three- Wheel Polishing Device—A polishing device that has three patterned pneumatic
tires and is capable of exerting 0.65 ± 0.02 kN (146 ± 5 ibs) through the tires to the test surfaces.
The device’s height shall be adjustable to accommodate sample heights of 25 mm (1.0 in.) to 50 mm (2.0 in.). The device shall be capable of accommodating a 508 mm x 508 mm (20 in. x 20 in.) sample holder (Figures 1, 2, and 3).
5.1.1. The tire size shall be 2.80/2.50-4 and shall maintain a pressure of 240 ± 34 kPa (35 ± 5 psi) and a tread depth of no less than 2 mm (0.1 in.). The tire tread shall have a ribbed pattern. The tire tread shall be free of any visible contamination. When replacement is necessary, all tires shall be replaced at the same time.
Note 1—Several tire manufacturers supply a 2.80/2.50-4 pneumatic tire. The rubber compound chemistry and tread style are unique for each manufacturer. For consistent polishing for each test surface, always replace the tires with the same tire from the same manufacturer. To validate whether performance will be comparable between batches of tires from the same manufacturer, it is suggested to perform comparison tests prior to exhausting supply of the previous batch.
5.1.2. The driving mechanism for the vertical shaft shall be an electric motor geared to rotate the shaft and wheel assembly at a speed of 6.28 ± 0.5 rad./s (60 ± 5 rpm).
Note 2 The path of polishing should coincide with the direction of friction testing.
5.1.3. The device shall be equipped with an automatic counter that can shut off the machine at a predetermined number of revolutions.
Bonding Agent—A supply of polyester resin and catalyst (or another suitable bonding material, such as an epoxy resin) having a pot life of 20 to 30 mm and a curing time of 3 to 6 h. This bonding agent shall not be so fluid as to flow through the glass beads. A bonding agent conforming to the requirements of T 279, Appendix Xl has been found suitable for this purpose.
6.1.1. Extender Pigment—A supply of Wollastonite (or another suitable extender pigment). An extender pigment conforming to the requirements of T 279, Appendix Xl.
6.1.2. Gelling Agent—A supply of amorphous fumed silica conforming to the requirements of T 279, Appendix X 1.
6.1.3. Hardener—Methyl ethyl ketone peroxide.AASHTO PP 103 pdf download.