What is the required compaction for a WMM layer?

The compacted density must be at least 98% of the Maximum Dry Density (MDD) determined by heavy compaction test IS 2720 (Part 8).

What is the maximum allowed Los Angeles Abrasion value for WMM aggregates?

The LA Abrasion value should not exceed 40% as per Table 400-12 of MORTH specifications.

What are the plasticity requirements for the fine material in WMM?

The material passing the 425-micron sieve must have a Plasticity Index (PI) of not more than 6.

What is the maximum thickness of a single compacted WMM layer?

A single compacted layer thickness should not exceed 250 mm and is typically laid in 100mm or 200mm layers.

IS 11991

: 1987

Specification for Wet Mix Macadam (WMM) - Aggregates

CurrentEssentialSpecificationTransportation · Roads and Pavement

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This specification details the requirements for Wet Mix Macadam (WMM), a pavement base course material. It defines the physical properties of the crushed stone aggregates, the mandatory particle size distribution (grading), and the requirements for mixing, laying, and compaction to achieve a dense, stable layer.

Specifies requirements for aggregates and general guidelines for the construction of wet mix macadam (WMM) as a base or binder course.

Quick Reference Values

Maximum Los Angeles Abrasion Value40%

Maximum Aggregate Impact Value (AIV)30%

Maximum Combined Flakiness and Elongation Index35%

Maximum Water Absorption2%

Plasticity Index of material passing 425 micron sieveLess than 6

Minimum compacted density98% of MDD

Permissible variation in Optimum Moisture Content (OMC) for mixingOMC ± 1%

Practical Notes

The user-provided code IS 11991 is incorrect for this topic. The authoritative specification for WMM is Clause 406 of the MORTH 'Specifications for Road and Bridge Works' (5th Revision), on which this data is based.

Control of moisture content is critical. The mix must be compacted at Optimum Moisture Content (OMC) to achieve the required 98% of Maximum Dry Density (MDD).

Ensure segregation of aggregates is avoided during transport and laying. The surface regularity after compaction is crucial and checked with a 3m straight edge.