Material Required For Construction of Water Bound Macadam (W.B.M) Road
The pavement made of crushed or broken aggregates, mechanically interlocked by Rolling and filling the voids with screening and binding material with the assistance of water is called water bound macadam(W.B.M)Road.
The W.B.M can be used as a sub-base, base course or surface course. The thickness of each compacted layer of W.B.M ranges from 10 cm to 7.5 cm depending on the size and gradation of aggregates used.
Materials required for the construction of Water Bound Macadam (W.B.M.) roads are as follows:
a) Coarse Aggregates
The coarse aggregates used in W.B.M. generally consist of hard varieties of crushed aggregates or broken stones. However, soft aggregates like over burnt bricks metal, kankar and laterite may be used.
The screening is used to fill up the voids in the compacted layer of coarse aggregates. The screening consists of aggregates of smaller sizes, generally of the same materials as the coarse aggregates. From the economic considerations, kankar, moorum or gravel can be utilized as screening materials.
c) Binding Materials
Binding materials consist of fine-grained materials. Kankar nodules or limestone dust etc. are used as binding materials in W.B.M construction.