A wide range of types and grades of roofing bitumen have been subjected to bulk heating, pressure oxidation, solar exposure and water immersion separately, and the resulting changes in rheological properties determined. Particular attention was given to the use of a sliding plate microviscometer and the means of overcoming complexities of non‐Newtonian behaviour and shear rupture to develop evaluations, oxidation resistance and solar exposure resistance, involving initial viscosity, rate of increase of viscosity and a critical viscosity at rupture. Results of these tests are discussed in relation to the performance of the bitumens when exposed outdoors for 2 years as model roofs with various surfacings and evaluated by visual rating, microviscometry, and solvent analysis. Agreement is good and the advantage in durability by using as low a softening point bitumen as possible is indicated except for aluminium‐painted coatings.
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K. G. Martin (1964) studied this question.
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