There are different stages of road development. Among all of them, Macadam Road is the most successful type of road.
John Loudon Macadam (1756 -1836 AD) was the surveyor-general of the road in England who put forward an entirely new method of road construction. The macadam method was the first method based on scientific thinking. It realized that the stresses due to wheel load get decrease at the lower layers and so it is not necessary to provide large layer pavement.
The importance of subgrade, drainage and compaction was also 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 road construction when it was introduced by John Macadam.
Types of Macadam Road
Over time, different modified macadam roads were developed. 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.
Over time, different road building technology was applied to roads by several engineers. One of them is Richard Edgeworth. He filled the gaps between the surface stones using the mixture of stone dust and water to make the surface more smooth. This method of construction is named as water bound macadam.
The macadam road whose wearing coarse is constructed with clean crushed aggregates which are mechanically interlocked by rolling and bounded together with the mixture of filler material(sand or clay) and water that is laid on a prepared base course. It is abbreviated as WBM road.
a. Made from local materials and labours.
b. It is economical to construct.
c. No skilled manpower is required.
a. They are permeable.
b. Short life.
c. Production of dust during service.
b.Traffic Bound Macadam
In this macadam, broken stones or gravels are generally used at a wearing course. Multi-layers of stones and gravels are provided in this type.
This road is consolidated by the action of traffic. It is used in rural as well as urban areas. The compacted thickness of each layer may vary from 2.5 to 5.0 cm
In bituminous macadam, bitumen is used as a binding material to bind stone chips and also to bind base and sub-base courses. It is also called as Tar Bound Macadam.
Dust become a serious problem on macadam roads; so bituminous macadam was introduced. 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.
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