Ans :Bitumen is available in a variety of types and grades. To judge the suitability of these binders various physical tests have been performed. The common tests to assess the properties and requirement of paving grade bitumen are the viscosity test, penetration test, ductility test and the softening point test. Penetration test is one such indirect test to determine the consistency of paving grade bitumen, which is very simple test. Thus the basic principle of the penetration test is the measurement of the penetration (in units of one tenth of a mm) of a standard needle in a bitumen sample maintained at 250 C during five seconds, total weight of the needle assembly being 100 g . Penetration test apparatus consists of a penetration needle assembly which is attached to a calibrated dial. On release, the penetration needle penetrates into the bitumen specimen without appreciable friction. The bitumen is softened to a pouring consistency, stirred thoroughly and poured into containers to a depth at least 15 mm in excess of the expected penetration. The sample containers are then placed in a temp. controlled water bath at a temp. of 25 0C for one hour. The sample with container is taken out, placed under the penetrometer and the needle is adjusted to make contact with surface of the sample. The dial is set zero or the initial readings is taken and the needle is released for 5 second. The final reading is taken on dial gauge.