What are the main physical tests required for WBM aggregate as per IS 6579?

The main tests are Los Angeles Abrasion Test, Aggregate Impact Test, Flakiness and Elongation Index, and Water Absorption, with limits specified in Table 2.

What are the standard grading sizes for coarse aggregate in WBM?

Table 1 specifies two primary gradings: Grading 1 (63 mm to 45 mm) and Grading 2 (53 mm to 22.4 mm).

What is the maximum permitted value for the Aggregate Impact Value (AIV)?

The Aggregate Impact Value shall not exceed 30 percent, according to Table 2.

Is a high water absorption value acceptable for WBM aggregates?

No, a high value is undesirable. The water absorption should not be more than 2 percent as per Table 2.

IS 6579

: 1981

Coarse Aggregate for Water Bound Macadam

CurrentFrequently UsedSpecificationTransportation · Stones

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This standard lays down the requirements for coarse stone aggregates used in the construction of water-bound macadam (WBM) for road pavements. It specifies the material's physical properties such as strength, hardness, toughness, shape, and water absorption, along with the required size gradations to ensure proper mechanical interlocking and stability.

Coarse Aggregate for Water Bound Macadam

Quick Reference Values

Maximum Los Angeles Abrasion value40%

Maximum Aggregate Impact Value30%

Maximum Combined Flakiness and Elongation Index30%

Maximum Water Absorption2%

Grading 1 Size Range63 mm to 45 mm

Grading 2 Size Range53 mm to 22.4 mm

Practical Notes

WBM's stability comes from the interlocking of graded aggregates and the binding action of screenings and water. Ensuring the specified grading from Table 1 is critical for performance.

The physical requirements in Table 2, especially abrasion and impact values, are crucial for durability under traffic. Always insist on a material test report from an accredited lab.

This standard is often used in conjunction with Ministry of Road Transport and Highways (MoRTH) specifications, which provide detailed construction methodology.