One of the most important points towards obtaining a good metalled road is to ensure a proper foundation for the metal to be consolidated on, and to see that the sides are well confined or tied in. Where bricks are used for this foundation they should be whole ones, not bats, be tightly packed together and then rammed with a wooden rammer. The edging should consist of bricks-on-end well backed up with earth on the out, or berm side. The same applies where stone is used for the soling. These must have flat surfaces, be of fair size, and be well hand-packed together and rammed. It is not much use doing metalling work on a raised road until the embankment has at least 2 rains over it to properly consolidate it. This equally applies to the approaches to bridges on a kutcha road where the metalled portion should be extended to a length of at least 10 feet beyond the toe of the approach slope.
Stone Metal.
In most municipalities it is financially impossible to thoroughly repair all the roads each year, nor is it necessary to do so, if the work has been properly done. A system of biennial or triennial repairs should therefore be evolved. A diagram showing how this can be arranged is shown in Fig. [11], page [19].
In the selection of stone metal it is of great importance to see that stone of equal grade and hardness is used, and that surface, or weathered rock, is not mixed up with the harder material lying underneath it in the quarries. The stone should be broken to the size that the largest piece shall pass freely through a 1½″ diameter ring. When repairing existing metalled roads it is essential that all old metal be picked up, and any rounded, or traffic-worn portions re-broken, as it is impossible to ensure good consolidation unless the edges and corners of the stone metal be sharp. Consolidation should be done by a heavy roller. A steam roller for preference. The cost of a 6–ton steam roller is about Rs. 6,000 and the working cost about Rs. 4 per day, but this must necessarily vary considerably in different localities, depending on the cost of fuel and labour.
Diagram
FIG. 11.
For Oiling Roads.
Oiling Roads.
The roadway must first be swept clear of dust and foreign material, when the mixture composed of one part of coal-tar to 20 parts of oil (liquid fuel), mixed cold, must be sprinkled on through a watering cart. Men with hard long handled brushes follow the cart, and brush the mixture into the roadway, and repeat this operation for the second time in the reverse direction, when ¼ of a mile has been done. The oiling lasts for about 2 months, and costs about Re. 1 per hundred square feet.
Tar-Macadam.