There are different stages of road development. But among all of them, Macadam road is the most successful type of road. Some detail features about macadam road are:
–John Loudon Macadam (1756 -1836 AD) was the surveyor of general of a road in England who put forward an entirely new method of road construction.
-The macadam method is the first method based on scientific thinking.
-It realized that the stresses due to wheel load get decrease at the lower layers & so it is not necessary to provide large layer pavement.
-The importance of subgrade, drainage and compaction was recognized so the subgrade was compacted and was prepared with a slope of (1 in 36 ).
Construction of Macadam Road
The standard size of the road was taken as 4.5 m in macadam road. The total thickness of the base, sub-base and surface course was taken as 25 cm. The construction of the macadam road consists of the following steps:
a. Sub Grade Preparation
Compacted subgrade having cross-slope 1 in 36 was prepared.
b. Sub Base Preparation
It was the layer above subgrade which was constructed using stones passing through 5 cm sieve. Its thickness was 10cm.
c. Base Course Preparation
The base course was prepared from broken stones passing through 3.75 cm sieve. Its thickness was 10 cm.
d. Surface Course Preparation
It was prepared using broken stones passing through 1.9 cm sieve. Its thickness was 5 cm.
It is the process of construction when it was introduced by John Macadam.
With time; use of binding materials like bitumen, stone dust and cement was introduced to bind materials together. Flexible Pavement and Rigid Pavement are also the modified form of macadam road.
Types of Macadam Road
Over time, different modified macadam roads were developed and using binding materials in macadam roads become more popular because of the increased durability and life of the road.
Macadam road can be classified into four types.
In this type, broken stones are bounded with the help of stone dust and water during the construction process. It is also used recently in rural areas of African and Asian Countries because it can be constructed at a very low cost.
b.Traffic Bound Macadam
Broken stones or gravels are generally used as a wearing. Multi-layers of stones and gravels are provided in this type. It is used in rural as well as urban areas.
Bitumen is used as a binding material to bind stone chips and also to bind base and sub-base courses. Flexible pavement is a little modified type of Bituminous Macadam.
d. Cement Macadam
Cement macadam is quite similar to bitumen macadam. Cement is used as a binding material instead of bitumen. Rigid Pavement is a modified type of Cement Macadam.