Marshall Stability

The Marshall test measures the stability and flow of a compacted cylindrical bituminous-mix specimen: stability is the maximum load the specimen carries at 60 °C before failure, and flow is the deformation at that load. By moulding specimens at a range of bitumen contents and plotting stability, flow, density, air voids and voids in mineral aggregate, the Marshall mix-design method determines the Optimum Bitumen Content (OBC) that satisfies all the specified criteria simultaneously.

It is the standard job-mix-formula design and acceptance method for dense bituminous mixes (DBM, bituminous concrete) in Indian road practice, with the stability/flow/voids limits set by IRC 111 / MoRTH for the relevant mix and traffic. Too little bitumen gives a dry, ravelling, fatigue-prone mix; too much gives an unstable mix that ruts and bleeds — so the volumetric properties (air voids typically ~3–5% in the design mix) are as important as the stability number itself, and the field-produced mix is checked against the approved job mix.