What is the maximum permissible Los Angeles Abrasion value for aggregates in a WBM surface course?

The maximum value is 40% as per Table 1.

What is the maximum allowed combined Flakiness and Elongation Index for coarse aggregates?

The combined index shall not exceed 30% according to Table 1.

What are the three standard grading sizes for coarse aggregates in WBM?

Grading 1 (90-45mm), Grading 2 (63-45mm), and Grading 3 (53-22.4mm) as specified in Table 2.

What test determines the toughness of the aggregate for WBM?

The Aggregate Impact Value (AIV) test is used, and its value should not exceed 30% for surfacing courses (Table 1).

IS 11990 Part 1

: 1987

Specification for Water Bound Macadam: Part 1 Aggregates

CurrentFrequently UsedSpecificationTransportation · Roads and Pavement

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This standard specifies the physical and grading requirements for coarse aggregates, screenings, and binding materials used in the construction of Water Bound Macadam (WBM) road layers. It provides limits for strength, durability, shape, and size distribution to ensure a stable and well-compacted pavement structure.

Specifies requirements for aggregates used in the construction of water bound macadam (WBM) as a sub-base or base course in pavement layers.

Quick Reference Values

Max Los Angeles Abrasion Value (Surfacing Course)40%

Max Aggregate Impact Value (Surfacing Course)30%

Max Combined Flakiness and Elongation Index30%

Max Water Absorption2%

Grading 1 Coarse Aggregate Size Range90 mm to 45 mm

Grading 2 Coarse Aggregate Size Range63 mm to 45 mm

Grading 3 Coarse Aggregate Size Range53 mm to 22.4 mm

Practical Notes

The choice of aggregate grading (1, 2, or 3) is dependent on the total thickness of the WBM layer being constructed.

Ensure screenings are from the same parent rock as the coarse aggregate to maintain material compatibility and achieve proper interlocking.

This standard focuses only on aggregates for WBM. The construction methodology is detailed in other codes and specifications like MORTH.