Almost all types of pavement require to be paved with varying thicknesses of asphalt depending on the expected traffic volume. Stone base consist of mixture of quarry dust and aggregates. This material is mostly used as base course for pavements with expected high volume of traffic. For low trafficked pavements low cost laterite with CBR value greater than 80% can be used for the same purpose.
Asphalt and Stone base are very costly materials and their cost contribute most to the materials cost of constructing flexible pavement. The materials are usually spread using asphalt pavers. Owing to the high cost of these materials, care is taking during the paving process to ensure there is minimum losses.
To control the use of these materials, weighbridge is necessary in the yard of every construction company. When the materials are loaded in trucks to be moved to site, their tonnage are recorded at the weigh bridge. At the end of a day’s work, the total tonnage of asphalt or stone base moved to site for paving is cumulated.
The section on the site that those materials were layed would also be measured (length, width and thickness) and the volume of such determined. Using the compacted density of either of the materials, the mass and then the tonnage laid is also determined. It is expected that the difference between the tonnage moved to site and the tonnage laid should be within 5%.
Example 1
Assuming that stone base was layed over a road section, 50 m x 7.3 m x 0.2 m, determine the tonnage of stone base that was layed
Volume of stone base = 50 x 7.3 x 0.2 = 73 m3
Compacted density of stone base = 2.2 Ton/m3
Tonnage of stone base laid and compacted = 73 x 2.2 = 160.6 Ton
Example 2
Assuming the same area is paved with asphalt of thickness of 60 mm, determine the tonnage of asphalt that was laid
Thickness of asphalt = 60 mm = 0.06m
Volume of asphalt laid = 50 x 7.3 x 0.06 = 21.9 m3
Compacted density of asphalt = 2.35 Ton/m3
Tonnage of asphalt laid = 21.9 x 2.35 = 51.465 Ton
It is very important to control all quantities on site especially these two among other factors to ensure minimal expenditure in road construction projects.
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