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IS 6579:1981 is the Indian Standard (BIS) for coarse aggregate for water bound macadam. 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.
! 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.
coarse aggregatestonecrushed stonemacadamroad base
International Equivalents
Similar International Standards
BS EN 13242:2002+A1:2007BSI / CEN, United Kingdom / Europe
HighCurrent
Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction
Specifies properties for aggregates in unbound pavement layers, which is the modern functional equivalent of a WBM course.
AASHTO M 147-17AASHTO, USA
HighCurrent
Standard Specification for Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses
Covers requirements for aggregate base courses that serve the same structural purpose as WBM layers in a pavement structure.
ASTM D1241-15ASTM International, USA
MediumCurrent
Standard Specification for Materials for Soil-Aggregate Subbase, Base, and Surface Courses
Defines materials for unbound aggregate layers, but focuses on well-graded soil-aggregate mixtures rather than the open-graded stone of WBM.
AS 2758.5-2015Standards Australia, Australia
HighCurrent
Aggregates and rock for engineering purposes - Part 5: Aggregates for unbound and recycled pavement base and sub-base
Details requirements specifically for unbound base aggregates, directly aligning with the application described in IS 6579.
Key Differences
≠IS 6579 specifies open-graded coarse aggregates (e.g., 63-45mm) intended for mechanical interlock, with voids filled later by smaller screenings. Modern international standards (e.g., AASHTO M 147) typically specify continuously-graded or well-graded materials that achieve density through compaction of a pre-mixed aggregate.
≠The Indian standard is prescriptive for the 'Water Bound Macadam' construction technique itself. International equivalents like BS EN 13242 are material specifications for 'unbound mixtures', which is a broader category not tied to a single construction method.
≠BS EN 13242 uses a category-based system for properties (e.g., Los Angeles Abrasion categories LA₂₀, LA₃₀, etc.), allowing designers to select aggregate quality based on traffic loads. IS 6579 provides a single limiting value (e.g., LAAV max 40%) for most applications.
≠International standards frequently mandate durability tests like Sodium or Magnesium Sulfate Soundness to assess resistance to weathering, which is not a mandatory requirement in IS 6579.
Key Similarities
≈Both IS 6579 and its international counterparts aim to specify a durable, load-bearing unbound aggregate layer to form the base or sub-base of a pavement structure.
≈All standards control key mechanical properties of the aggregate, including resistance to abrasion (Los Angeles Abrasion Value) and particle shape (Flakiness/Elongation).
≈The types of permitted source materials are similar, including crushed rock, crushed slag, and crushed gravel, provided they meet the specified physical and chemical requirements.
≈All standards place limits on deleterious materials such as clay lumps, soft fragments, and organic matter to ensure the long-term integrity of the pavement layer.
Parameter Comparison
Parameter
IS Value
International
Source
Los Angeles Abrasion Value
Maximum 40%
Varies by class; e.g., Class A/B max 40%, Class C max 50%.
AASHTO M 147-17
Aggregate Impact Value (AIV)
Maximum 30%
This test is not commonly used in US/EU standards; L.A. Abrasion is the preferred method for assessing toughness.
N/A (Concept replaced by LAAV)
Combined Flakiness & Elongation Index
Maximum 30%
Specified separately. E.g., Flakiness Index by category (FI₂₀, FI₃₅) and Shape Index by category (SI₂₀, SI₄₀).
BS EN 13242:2002
Water Absorption
Maximum 2.0%
Varies; often specified by category, e.g., WA₂₄ 2 (≤2%). Not always a mandatory requirement in all unbound specs.
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.