MARSHALL METHOD OF BITUMINOUS MIXES

Bruce Marshall, formerly Bituminous Engineer with Mississippi State Highway Department, USA formulated Marshall Method for designing bituminous mixes. Marshall’s test procedure was later modified and improved upon by U.S. Corps of Engineer through their extensive research and correlation studies. ASTM and other agencies have standardized the test procedure. Generally, this stability test is applicable to hot-mix design of bitumen and aggregates with maximum size 2.5 cm. In Bangladesh, bituminous concrete mix is commonly designed by Marshall Method.

In this method, the resistance to plastic deformation of cylindrical specimen of bituminous mixer is measured when the same is loaded at the periphery at a rate of 5 cm per minute. The test procedure is used in the design and evaluation of bituminous paving mixes. The test is extensively used in routine test programmers for the paving jobs. There are two major features of the Marshall method of designing mixes namely,

i) Density-voids analysis
ii) Stability-flow test.

The stability of the mix is defined as a maximum load carried by a compacted specimen at a standard test temperature of 60⁰C. The flow is measured as the deformation in units of 0.25mm between no load and maximum load carried by the specimen during stability test. In this test an attempt is made to obtain optimum binder content for the aggregate mix type and traffic intensity.

LABORATORY TEST FOR BITUMINOUS MATERIAL

Laboratory Test on Bitumen

Crude petroleum obtained from different sources contains different proportions of different constituents. Hence its properties may differ. Therefore to judge their suitability as binders, following tests are recommended;

i)                    Penetration test

ii)                   Ductility test

iii)                 Softening point test

iv)                 Specific gravity test

v)                  Flash point and fire point test

vi)                 Float test

vii)               Viscosity test

viii)              Loss on heating test

ix)                 Solubility test

 

To determine all of these properties, a variety of tests have been specified by Institutions like ASTM, I.S.I., Asphalt institute and B.S.I. Here ASTM is followed. Prepared samples are tested to determine some of above properties.