Classification of macadam roads

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Macadam roads, also known as macadamized roads, are a type of road construction method that was popularized by Scottish engineer John Loudon McAdam in the early 19th century. This method revolutionized road construction by introducing a new approach to building durable and cost-effective roads.

Macadam roads are classified based on various factors, including the materials used, the construction process, and the intended use. Here are some common classifications of macadam roads:

1. Water-bound macadam (WBM) roads: Water-bound macadam roads are constructed by placing multiple layers of broken stones or aggregates on a prepared subgrade. The stones are compacted and bound together using water as a binding agent. The water helps to fill the voids between the stones, creating a solid and stable surface. WBM roads are commonly used for low-traffic rural roads and temporary access routes.

2. Bituminous macadam (BM) roads: Bituminous macadam roads are constructed by adding a bituminous binder to the water-bound macadam base. The bituminous binder, typically hot bitumen or tar, acts as an adhesive that binds the aggregates together. This additional layer provides increased strength and durability to the road surface. BM roads are commonly used for medium-traffic urban and rural roads.

3. Asphaltic macadam (AM) roads: Asphaltic macadam roads are similar to bituminous macadam roads but with an additional layer of asphalt concrete on top. The asphalt concrete layer is made up of a mixture of aggregates and asphalt binder, which provides a smooth and durable riding surface. AM roads are commonly used for high-traffic highways and major urban roads.

It is important to note that these classifications may vary in different regions or countries, as road construction practices can differ based on local materials, climate conditions, and engineering standards.

In addition to these classifications, there are other variations and modifications of macadam roads, such as:

– Double-layered macadam roads: These roads consist of two layers of water-bound macadam, with the lower layer acting as a base course and the upper layer serving as a wearing course. This design provides improved strength and longevity.

– Penetration macadam roads: In this type of road construction, a bituminous binder is sprayed on the prepared subgrade, followed by the placement of aggregates. The aggregates are then compacted to form a stable surface. Penetration macadam roads are commonly used in areas with weak subgrades.

– Gravel macadam roads: Gravel macadam roads are constructed by placing a layer of gravel or crushed stone on the prepared subgrade. The gravel acts as both the base and wearing course, providing a relatively simple and cost-effective road surface.

It is worth mentioning that over time, traditional macadam road construction methods have evolved, and modern road construction techniques now incorporate advanced materials and technologies to enhance durability, safety, and sustainability.

In conclusion, macadam roads can be classified into different types based on the materials used, construction process, and intended use. Water-bound macadam (WBM) roads, bituminous macadam (BM) roads, and asphaltic macadam (AM) roads are some common classifications. However, it is important to consult local engineering standards and specifications for accurate classification in specific regions or countries.

Top 3 Authoritative Reference Publications or Domain Names:

1. “Highway Engineering” by S.K. Khanna and C.E.G. Justo
2. “Roads: An Introduction to the Engineering of Roadways” by Richard De Neufville
3. “Transportation Engineering: An Introduction” by C. Jotin Khisty and B. Kent Lall


Arbaj Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

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