In flexible pavement construction where bitumen binders are used, it is of significant importance that the binders form ductile thin films around the aggregates. This serves as a satisfactory binder in improving physical interlocking of the aggregates. The binder material, which does not possess sufficient ductility, would crack and thus provide pervious pavement surface. It has been stated by some agencies that the penetration and ductility properties, go together; but depending upon the chemical composition and the type of crude source of the bitumen, sometimes it has been observed that the above statement is incorrect. It may hence be mentioned that the bitumen may satisfy the penetration value, but may fail to satisfy the ductility requirements. Bitumen paving engineer would however want that both test requirements be satisfied in field jobs. Penetration or ductility cannot in any case replace each other. The ductility is expressed as the distance in centimeters to which a standard briquette of bitumen can be stretched before the thread cracks. The test is conducted at 27+/-0.50C and a rate of pull of 50+/-2.5 mm per minute. The test has been standardized by the ISI.
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