Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

(i) Screenings
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Quality Assurance Handbook for Rural Roads
The use of screenings shall be omitted in the case of soft aggregates like brick metal, kankar,
laterite etc.
(a) Physical Requirements
Screenings should normally consist of same material as the coarse aggregate. However, where
economic considerations so warrant, non-plastic material such as moorum or gravel with
LL less than 20 and PI less than 6 may be used. Fraction passing 75 micron should not
exceed 10 percent.
(b) Grading
TABLE 405.2: GRADING REQUIREMENTS OF COARSE AGGREGATE FOR WBM
Grading No. Size Range IS Sieve Designation Per cent by weight passing
1. 90 mm to 45 mm 125 mm 100
90 mm 90-100
63 mm 25-60
45 mm 0-15
22.4 mm 0-5
2. 63 mm to 45 mm 90 mm 100
63 mm 90-100
53 mm 25-75
45 mm 0-15
22.4 mm 0-5
3. 53 mm to 22.4 mm 63 mm 100
53 mm 95-100
45 mm 65-90
22.4 mm 0-10
11.2 mm 0-5
Note: The compacted thickness for layer with Grading 1 shall be 100 mm while for layer with Grading 2 and 3, it shall be 75 mm.
Grading 1 shall be used for sub-base only. For base course, Grading 2 or 3 shall be used. For surfacing, Grading 3 shall be used.
The screening shall conform to the grading specified in Table 405.3.
TABLE 405.3: GRADING FOR SCREENINGS
Grading Classification Size of Screenings IS Sieve Designation Per cent by weight
passing the IS Sieve
A. 13.2 mm 13.2 mm 100
11.2 mm 95-100
5.6 mm 15-35
180 micron 0-10
B. 11.2 mm 11.2 mm 100
5.6 mm 90-100
180 micron 15-35
Approximate quantities of coarse aggregate and screenings required for 100 mm compacted thickness
of WBM Grading 1, and 75 mm compacted thickness of WBM Grading 2 and 3 are given in Table 405.4.