ASTM D2746 Test Method for Staining Tendency of Asphalt (Stain Index)
3. Summary of Test Method
3.1 A horizontal disc of asphalt, cast in a brass retaining ring, is placed on a sheet of filter paper supported on a flat plate and heated at 80°C (175°F) for 120 h. The diameter of the resulting stained circle on the paper is compared to the inside diameter of the brass ring to determine the staining characteristic of the asphalt. The stain index is the difference between the diameter of the stained circle and the initial disc diameter measured to the nearest 0.5 mm (1/64 in.).
4. Significance and Use
4.1 This test method measures the tendency for oil components to separate spontaneously from asphalt. The separation of oil components can cause staining in asphalt roofing products and adjacent materials in storage and use.
4.2 The stain index is related to the thermal stability of the asphalt. Higher stain index values indicate lower stability and greater tendency for staining.
4.3 Use this procedure to determine the staining tendency of asphalt and to compare the results against a material for which the staining tendency is known.
