Flow Chart - Construction of WMM Layer

Wet Mix Macadam (WMM) Construction Methodology

Standard Operating Procedure, Plant Mixing Standards & Quality Control Protocol

1. Executive Summary & Base Course Dynamics

Wet Mix Macadam (WMM) is a superior unbound granular base course layer used in flexible pavement construction. Unlike traditional Water Bound Macadam (WBM), WMM premixes clean crushed aggregates, screenings, and moisture in predetermined proportions inside a specialized pugmill plant. This plant-mixed approach ensures homogeneous blending, prevents aggregate segregation during transit, and allows rapid field laydown via mechanical pavers to achieve high density and load transfer capabilities.

flowchart TD %% --- PRE-CONSTRUCTION STAGE --- A(["Start"]) --> B["Identification of Quarry Source by Contractor"] B --> C["Collection of Certificates about Quarry Source"] C --> D["If all materials are OK, use them for mixing in plant"] D --> E["Collection of coarse & fine aggregates, quarry dust, and binding material"] E --> F["Test on coarse aggregates:\nImpact Value, Flakiness, Elongation, Gradation, Abrasion Value, etc."] F --> G["Send sample to lab"] H["Test blended sample for sieve analysis, LL, PL, and PI"] G --> H H --> I["Check for MDD"] I --> J["Construction of subgrade/subbase/lower layer completed?"] J --> K{"Is subbase/lower layer completed?"} K -- No --> J K -- Yes --> L["Construction of trial test for lateral confinement\nwith approved material after testing"] %% --- CONSTRUCTION STAGE --- L --> M{"Test field compaction pass?"} M -- Fail --> N["Scarify, loosen, recompact"] N --> L M -- Pass --> O["Brooming till all loose material & dust removed"] O --> P["Very light sprinkling of water\n(for damp condition) before application of emulsion"] P --> Q["Spreading of WMM material over prepared GSB"] Q --> R["Spread uniformly in one layer to required thickness\nby paver or motor grader"] R --> S["Check with templates or survey levels"] S --> T{"Levels OK?"} T -- No --> U["Scarify and relevel"] U --> S T -- Yes --> V["Rolling and compaction"] V --> W["Check for MDD (Field Density Test)"] W --> X{"Meets required density?"} X -- No --> N X -- Yes --> Y["Approved for next layer / surface course"] Y --> Z(["End"]) %% --- STYLE DEFINITIONS --- classDef process fill:#e7f0fd,stroke:#4682b4,stroke-width:1px; classDef decision fill:#fff5b7,stroke:#b8860b,stroke-width:1px; classDef fail fill:#fcd5ce,stroke:#d22b2b,stroke-width:1px; classDef pass fill:#d4f8e8,stroke:#2e8b57,stroke-width:1px; class A,B,C,D,E,F,G,H,I,J,L,O,P,Q,R,S,V,W,Y process; class K,M,T,X decision; class N,U fail;

2. Sequential Execution Guidelines

Phase 1: Material Evaluation & Job Mix Formula (JMF)

Coarse and fine aggregates together with quarry dust binder are sourced from certified quarries and subjected to rigorous physical test protocols:

• Coarse Aggregate Quality: Aggregate Impact Value (AIV), Los Angeles Abrasion Value, Flakiness and Elongation Index, and Water Absorption testing.
• Blended Fraction Testing: Sieve Analysis to match designated grading curves, along with Liquid Limit (LL), Plastic Limit (PL), and Plasticity Index (PI) determinations on fine fractions.
• Compaction Standards: Heavy Compaction (Modified Proctor) testing to fix laboratory Maximum Dry Density (MDD) and Optimum Moisture Content (OMC).

Phase 2: Underlying Surface Preparation & Trial Length Verification

Prior to WMM laydown, the underlying Granular Sub-Base (GSB) or lower course must be verified for structural completeness and levels. Lateral confinement bunds are constructed to support compaction edges.

Surface Preparation Protocol: The underlying bed must be thoroughly broomed to clean all loose dust, silt, and foreign matter. A light water spray is applied immediately before spreading WMM or applying prime/tack coats to maintain a moist, non-absorptive interface.

Phase 3: Spreading, Leveling & Compaction

WMM material mixed at OMC (or OMC + 0.5% to account for field evaporation) is transported to the site via tipper trucks and laid using a sensor paver finisher or motor grader.

Compaction & Level Acceptance Loops: Surface elevations are cross-checked with templates and optical levels. If level checks fail, the uncompacted layer is scarified and releveled. Rolling starts from the outer edges and progresses towards the centerline (or low side to high side on superelevated curves) using vibratory rollers. If Field Dry Density (FDD) fails to reach minimum criteria (≥100% MDD), the layer must be scarified, loosened, re-moistened, and re-rolled.

3. Quality Control & Material Testing Specifications

Quality Assurance Parameter	WMM Technical Specification Limit	Testing Frequency / Reference
Aggregate Impact Value (AIV)	≤ 30% Maximum	IS: 2386 (Part 4) / 1 per 1,000 m³
Combined Flakiness & Elongation	≤ 35% Maximum	IS: 2386 (Part 1) / 1 per 500 m³
Los Angeles Abrasion Value	≤ 40% Maximum	IS: 2386 (Part 4) / 1 per source
Plasticity Index (PI) of Fines	≤ 6% (Non-plastic preferred)	IS: 2720 (Part 5) / 1 per 500 m³
Compaction Moisture Range	OMC to (OMC + 1.0%)	Field Moisture Test per truck load/lift
Minimum Field Compaction	≥ 100% Maximum Dry Density (MDD)	Sand Replacement / 1 set per 1,000 m²
Surface Level Tolerance	± 10 mm	Cross-section survey every 20 meters

Yogendra Gopal Borse

Civil Engineer | Assistant Engineer Grade-I, Maharashtra PWD

B.Tech (Civil) from VJTI Mumbai. Experienced in bridge design, road works, estimation, project monitoring and digital engineering tools. Creator of YogiPWD – practical technical resources for civil engineers.

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