Wet Mix Macadam (WMM) Construction – MoRTH 5th Revision

Wet Mix Macadam (WMM) Construction Methodology

Quick Summary:
MoRTH Table 400-12 specifies the physical requirements of coarse aggregates used in WMM for sub-base and base courses. Los Angeles Abrasion ≤ 40%, Aggregate Impact Value ≤ 30%, and combined Flakiness + Elongation ≤ 35%. These limits ensure strong, durable, and well-interlocked aggregate structure for long-lasting pavement performance. Read full details →

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Scope

This work consists of laying and compacting clean, crushed, graded aggregate premixed with water to a dense mass over a prepared GSB sub-base. Layers should follow approved lines, grades, and cross-sections.

Minimum single compacted layer thickness: 75 mm
Maximum single compacted layer thickness: up to 200 mm with AE approval

References

Contract Agreement
IRC: SP: 84-2014
MoRTH Specifications (5th Revision)
Relevant drawings

Materials

1. Aggregates

a) Physical Requirements

Coarse aggregates shall be crushed stone. At least 90% of pieces retained on 4.75 mm sieve must have two or more fractured faces. Follow MoRTH Table 400-12.

b) Grading Requirements

Follow MoRTH Table 400-13 for continuous gradation.

2. Lateral Confinement

Lay adjoining shoulders with WMM and follow Clause 404.3.3 to prevent lateral spread.

3. Preparation of Mix

Mix aggregates in an approved plant with controlled water dosing, forced mixing (pug-mill/pan), vibrating screens, conveyor, and centralized control. Determine Optimum Moisture Content (OMC) per IS:2720 Part 8 and ensure uniform wetting.

MoRTH Tables

Table 400-12 — Physical Requirements of Coarse Aggregates

S. No.	Test	Method	Requirement
1	Los Angeles Abrasion / Aggregate Impact Value	IS:2386 Pt 4 / IS:5640	LA ≤40%, AIV ≤30%
2	Combined Flakiness & Elongation	IS:2386 Pt 1	≤35%

Table 400-13 — Grading Requirements

IS Sieve	% Passing
53 mm	100
45 mm	95–100
26.5 mm	—
22.4 mm	60–80
11.2 mm	40–60
4.75 mm	25–40
2.36 mm	15–30
600 μ	8–12
75 μ	0–5

Material finer than 425 μ shall have PI ≤6%. Gradation must be continuous without large jumps between adjacent sieves.

Table 900-3 — QC Test Frequency

Item	Test	Frequency
WMM	Aggregate Impact Value	1 per 1000 m³
	Grading	1 per 200 m³
	Flakiness & Elongation	1 per 500 m³
	PI (425 μ)	1 per 200 m³
	Field Density	3 tests per 1000 m²

Spreading of Mix

Spread aggregates immediately using self-propelled paver with hoppers, screed (tamping & vibration), and electronic leveling. Motor grader may be used for small jobs. Avoid segregation.

Compaction

≤100 mm: Smooth wheel roller 80–100 kN
Up to 200 mm: Vibratory roller 80–100 kN, adjustable frequency/amplitude
Roller speed ≤5 km/h

Setting & Drying

Allow WMM to dry for 24 hours before traffic.

Quality Control & Surface Finish

Follow MoRTH Section 900. Surface tolerances: longitudinal ±15 mm, cross slope ±0.3%, evenness ≤12 mm per 3 m straightedge.

Rectification of Surface Irregularities

Scarify full thickness if irregularities occur, reshape or replace with fresh mix, and recompact. Minimum treated area: 5 m × 2 m.

Quick Reference: WMM Quality Control

Layer thickness: 75–200 mm
Grading: MoRTH Table 400-13
Material: LA ≤40%, Flakiness & Elongation ≤35%, PI ≤6%
OMC mixing: ±1%
Compaction: ≥98% MDD
Surface: Longitudinal ±15 mm, Cross ±0.3%, Evenness ≤12 mm
QC frequency: Table 900-3
Testing standards: IS:2386, IS:2720, IS:5640

Top 10 FAQs – WMM

What is WMM? Base layer of flexible pavement, mixed with water, compacted to dense mass per MoRTH 406.
Purpose of WMM? Stable, well-drained foundation for bituminous layers.
Materials? Crushed stone aggregates, LA ≤40%, Flakiness ≤35%.
Grading? MoRTH Table 400-13, continuously graded.
OMC? Determined by modified Proctor (IS:2720 Pt 8).
Mixing method? Mechanical plant with controlled water, uniform mixing.
Compaction requirement? ≥98% MDD using vibratory roller.
QC tests? Aggregate impact, grading, flakiness, PI, field density per Table 900-3.
Surface tolerance? Longitudinal ±15 mm, Cross slope ±0.3%.
Minimum layer thickness? 75–200 mm per lift; multiple lifts if thicker.

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