Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

3. Section-400
14. In case the screenings are not of crushable type such as moorum or gravel, it is necessary to add
binding material (PI between 4 and 6) after application of screenings. The binding material should
be applied in two or more layers at a slow and uniform Generally, the quantity required for 10 m 2
of 75 mm thickness of WBM is 0.06 to 0.09 m 3 and for 100 mm thickness, the corresponding quantity
would be 0.08 to 0.10 m 3 .
In case WBM surface is not to be covered with Bituminous surfacing, PI of binding material shall
be between 4 and 10.
15. The process of water sprinkling, sweeping and rolling should continue till the resulting slurry
forms a wave ahead of roller.
16. The compacted WBM course should be allowed to completely dry and set before the next pavement
course is laid or traffic is allowed.
17. The earthen shoulders should be constructed simultaneously with the WBM construction in
accordance with Sub-Section 407.
18. The finished surface of WBM should conform to the prescribed tolerances given in Para B. Where
the surface irregularity exceeds the tolerances, the WBM layer should be scarified to its full depth
over the affected area and corrected by adding or removing and replacing with fresh material.
B Quality Control Requirements
1. Materials
(i) Coarse Aggregate
(a) Physical requirements
Physical requirements of coarse aggregate for water bound macadam for sub-base, base and
surfacing should conform to the requirements given in Table 405.1. If the water absorption
of aggregate is greater than 2 per cent, Soundness test should be carried out.
TABLE 405.1: PHYSICAL REQUIREMENTS OF COARSE AGGREGATES FOR WBM
Test Sub-base Base Surfacing
Aggregate Impact value Less than 50 Less than 40 Less than 30
Flakiness index Less than 30 Less than 25 Less than 20
Soundness test
-Loss with Sodium Sulphate Less than 12% Less than 12% Less than 12%
-Loss with Magnesium Sulphate Less than 18% Less than 18% Less than 18%
Aggregates like brick bats, kankar, laterite etc. which get softened in presence of water shall be
tested for Aggregate Impact Value under wet conditions in accordance with IS:5640.
(b) Grading :
The coarse aggregates should conform to the grading specified in the Contract and meet the
requirements given in Table 405.2.
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