1.6 History of road development

  

1. Early development

• The oldest mode of travel obviously was on the foot tracks.
• Animals were used to transport mean and material.
• Later, simple animal drawn vehicle were developed and this became a common and popular mode of transportation fora long period, which brought up the necessity of providing hard surface for this wheeled vehicle to move on.
• Such hard surface is believed to have existed in Mesopotamia in period about 3500 B.C.

2. Roman Roads

• During the period of the Roman Empire, roads were constructed in large scale. Romans constructed the roads radiating in many directions from Rome, mainly for military operations.
• During roman’speriod many roads were built of stone blocks of considerable thickness.
• Appian Way was built in 312 B.C extending over 580 km.

The following are the main features of roman roads

• They were built straight regardless of gradients.
• The soft soil was excavated and removed till hard stratum was reached.
• The total thickness of construction was 0.75m to 1.2m at some places even though the magnitude of wheel load of animal drawn vehicles was very low.
• Some of these roman roads are still in existence after over 2000 years.

3. Tresaguet construction

Until the eighteen century, there is no evidence of any new road construction method except the concept used by romans. Pierre Tresaguet developed an improved method of construction in 1764 AD in France. His construction was much cheaper than the roman roads.

The main features of his constructions are

• The thickness of construction need be only in the order of 30cm.
• Consideration was given by him to subgrade moisture condition and drainage of surface water.
• The sub-grade was prepared and a layer of foundation stones were laid on edge by hand. At two edge of pavement, large stone were embedded edge wise to serve as submerged kerb stones.
• The corners of these heavy foundation stones were hammered and then the interstices filled with smaller stones. Broken stones were packed to a thickness of about 8 cm and compacted.
• The top wearing course was made of smaller stones and compacted to a thickness about 5 cm at the edge and gradually increased towards the centre, giving a cross slope of 1 in 45 to surface, to provide surface drainage.
• The shoulderswere also provided cross slope to drain surface water to side drain.

4. Telford Construction

Thomas Telford began his work in early 19th century in England. He also believed in using heavy foundation stones above soil subgrade. He insisted on providing definite cross slope for the top surface of pavement by varying the thickness of foundation stones.

The main features of his construction are

• A level subgrade was prepared to design width of about 9 meters
• The stones of lesser thickness (17cm) were placed towards edge and stones of increasing thickness up to 22cm were laid towards the centre such that these stone of varying thickness provides the cross slope.
• The interstices between foundation stones were filled with smaller stone and properly beaten down.
• The central portion of about 5.5 metre width was covered with two layers of angular broken stones to compacted thickness of 10 and 5cm.
• A binding layer of wearing course 4cm thick was constructed on top using gravel. The finished surface has a cross slope of about 1 in 45.

5. Macadam construction

Johan macadam, a Scottish road builder is considered as the pioneer of modern road construction. He was the first man to realize the importance of subgrade drainage in addition to its surface drainage. He was also first person to realize the baseless use of hard and strong stones in road base. The total thickness of road pavement suggested by him is just 25 cm.

Construction steps

• Sub-grade is compacted and prepared with a cross-slope of 1 in 36 upto a desired width.
• Broken stones of strong variety, all passing through 5 cm sieve were compacted to a uniform thickness of 10cm.
• A second layer of strong broken stones of sizes 3.75cm was compacted to thickness of 10cm.
• The top layer consisted of stones of size less than 2cm compacted to a thickness of about 5cm and finished so that the cross slope of pavement was about 1 in 36.

6.Modern Roads

All of the modern roads are improvements over the macadam construction. Bituminous binders were made use of instead of soil binder in the surface course of road pavements. Apart from flexible pavements with bituminous layers, rigid pavements using cement concrete were also developed.

Some examples of modern road are

• Roads with surface dressing. Surface treatments at top with various granular base below.
• Bituminous bound macadam road
• Asphalt concrete roads
• Cement concrete roads