Specification for Dense Bituminous Macadam

IRC 94: Dense Bituminous Macadam (DBM) - Introduction & Key Specifications

1. Mix Preparation & Plant Requirements

• Use hot-mix plants (batch or continuous) with:
  • Aggregate dryer, grading & batching units.
  • Bitumen heating & metering units.
  • Paddle mixer for uniform coating.
  • Filler feeder.

2. Base Preparation & Tack Coat (Clause 7.5)

• Granular surfaces must be primed per IRC:16-1965 before tack coat.

3. Spreading & Compaction

• Use mechanical pavers for uniform thickness.
• Longitudinal joints offset by ≥150 mm from base joints.
• Compaction sequence:
  • Breakdown rolling: 8-12 t 3-wheel steel roller.
  • Intermediate rolling: 15-30 t pneumatic roller.
  • Finished rolling: 8-10 t tandem or vibratory roller (vibration off).
• Rolling speed ≤ 5 km/h; wheels moist (no fuel/oil).

4. Quality Control & Testing

• Aggregate gradation & physical tests (impact, abrasion, flakiness, stripping).
• Bitumen penetration & softening point as per IS 1203, 1205.
• Mix temperature: 120°C to 160°C.
• Bitumen viscosity: 150-300 cSt at 150-177°C.
• Marshall tests for stability, flow, voids, density.
• Permissible variation from job-mix formula (Table 4):

IRC 94: Key Materials Specifications & Formulas for Dense Bituminous Macadam (DBM)

1. Aggregate Gradation (Table 4)

2. Aggregate Quality Requirements (Table 3)

• Coarse aggregate: Retained on 2.36 mm sieve, angular, clean, durable.
• Fine aggregate: Passing 2.36 mm and retained on 75 µm sieve, clean and uncoated.
• Filler: Material passing 75 µm sieve, inert (stone dust, cement, lime, fly ash).

3. Job Mix Formula

• Blend aggregates by weight or volume to meet gradation.
• Optimum bitumen content: **4.5% to

IRC 94: Design Criteria for Dense Bituminous Macadam (DBM)

Key Specifications (from Table 3: Design Criteria)

Aggregate Quality Requirements (Clause 2.36, Table 4)

• Coarse Aggregate: Crushed, angular, clean, durable, hydrophobic preferred.
• Fine Aggregate: Passing 2.36 mm sieve, clean and durable.
• Filler: Passing 600 μm sieve, inert (stone dust, cement, lime, fly ash).

Job Mix Formula

• Blend aggregates by weight or volume to meet gradation and optimum bitumen content from lab design.
• Ensure materials used on-site match lab sample properties.

Summary Diagram of DBM Mix Design Process

flowchart TD
    A[Sample Aggregates] --> B[Lab Mix Design]
    B --> C[Determine Optimum Bitumen Content]
    C --> D[Job Mix Formula]
    D --> E[Field Blending & Compaction]
    E --> F[Quality Control & Testing]

Use these criteria strictly for quality, durability, and performance of DBM layers as per IRC 94.

Job Mix Formula - IRC 94 Key Points & Specifications

Definition:
The Job Mix Formula (JMF) is the optimized combination of coarse aggregate, fine aggregate, filler, and bitumen content determined in the laboratory, used for actual field mixing.

Key Specifications from IRC 94:

• Aggregate gradation: Must satisfy limits as per Table 2 (not provided here, but essential for mix design).
• Bitumen content: Optimized for stability, voids, and durability.
• Aggregate types:
  • Coarse aggregate: >2.36 mm, angular, clean, tough, max 2% water absorption.
  • Fine aggregate: 75 µm to 2.36 mm, clean and durable.
  • Filler: Passing 600 µm sieve, inert material (stone dust, cement, lime, fly ash).

Permissible Variations from Job Mix Formula (Table 4):

Quality Control Tests (Clause 7.7):

• Marshall Test: Stability, flow, voids, and density.
• Bitumen content: Extraction and determination.
• Sieve analysis: After bitumen extraction for gradation check.
• Temperature control: Mix temperature between 120°C and 160°C.

Summary of Job Mix Formula Preparation:

flowchart TD
    A[Laboratory Testing of Aggregates] --> B[Determine Aggregate Gradation]
    B --> C[Optimize Bitumen Content]
    C --> D[Formulate Job Mix Formula]
    D --> E[Field Production Control]
    E --> F[Quality Control Tests & Adjustments]

Note: The JMF must be based on representative samples and strictly adhered to during production for durable pavement performance.

IRC 94: Key Specifications & Formulas for Construction of Dense Bituminous Macadam

1. Materials Specification

• Coarse Aggregate: Crushed, angular, clean, durable; retained on 2.36 mm sieve.
• Fine Aggregate: Passing 2.36 mm, retained on 75 μm sieve; clean and durable.
• Filler: Passing 600 μm sieve; inert (stone dust, cement, lime, flyash).

Physical Limits for Aggregates:

2. Job Mix Formula

• Aggregate proportions (coarse, fine, filler) blended by weight or volume.
• Optimum bitumen content: 4.5% to 6.0% by weight of total mix.
• Marshall Stability ≥ 340 kg; Flow 2-4 mm; Voids 5-10%; Voids filled with bitumen 55-75%.

3. Gradation (Typical Percentage Passing)

Preparation of the Base - Key Specifications (IRC 94)

1. Tack Coat Application (Clause 7.5):

• Dry, hungry bituminous base: 6 to 7.5 kg bitumen/10 m²
• Normal bituminous surface: 5 to 5.5 kg bitumen/10 m²
• Non-bituminous surface: 7.5 to 10 kg bitumen/10 m²
• Granular surface must be primed as per IRC:16-1965 before tack coat.

2. Base Preparation (Clause 6.1):

• Prepare base to specified line, grade, and cross-section.
• Clean surface thoroughly (remove dust, mud, deleterious materials).
• Repair potholes/ruts with premixed bituminous material, compacted well.
• For irregular bases, provide profile corrective course before laying.

3. Mix Preparation & Spreading:

• Use hot-mix plant for uniform quality (Clause 6.2).
• Spread mix with mechanical paver to achieve uniform thickness (Clause 6.3).
• Longitudinal joints offset by ≥150 mm from base course joints.

4. Compaction (Clause 6.4):

• Breakdown rolling: 8-12 tonnes, 3-wheel steel roller.
• Intermediate rolling: 15-30 tonnes pneumatic roller (tyre pressure 7 kg/cm²).
• Finished rolling: 8-10 tonnes tandem or vibratory roller (vibration off during finishing).
• Roll from edges to center; keep wheels moist (no oil/fuel).

5. Quality Control:

• Aggregate gradation, bitumen penetration, and temperature checks.
• Mix temperature at laying: 120°C to 160°C (Clause 7.8).
• Bitumen viscosity: 150-300 centistokes at 150-177°C.
• Permissible variations from job-mix formula (Table 4):

Key Specifications & Formulas for Preparation of Dense Bituminous Macadam Mix (IRC 94):

1. Mix Preparation (Clause 6.2)

• Use a hot-mix plant (batch or continuous) with:
  • Dryer for aggregates (max temp. 163°C ±10°C)
  • Grading & batching units
  • Bitumen heating & metering (viscosity 150–300 cSt at 150–177°C)
  • Paddle mixer for uniform coating
  • Filler feeder

2. Tack Coat Application (Clause 7.5)

3. Permissible Variations in Mix (Table 4)

4. Marshall Test Design Criteria (Table 3)

5. Temperature Control (Clauses 7.3, 7.4, 7.8)

• Aggregate temp: ≤ 163°C (±10°C tolerance)
• Bitumen temp: 150–177°C (vis

Spreading of the Mix (IRC 94 Key Points)

• Mix Transport & Spreading: Use tipper trucks to carry hot mix from the plant to site. Spread preferably by self-propelled mechanical paver with screeds for uniform thickness and correct grade.

• Thickness Control: After compaction, check thickness via hot steel scale penetration correlated with surface area and total mix quantity.

• Joints:

  • Longitudinal joints offset by ≥150 mm from base course joints.
  • Joints cut vertically, painted with hot bitumen before laying fresh mix.

• Compaction Rolling Sequence:

  • Breakdown rolling: 8-12 tonnes 3-wheel steel roller
  • Intermediate rolling: 15-30 tonnes pneumatic roller (tyre pressure 7 kg/cm²)
  • Finished rolling: 8-10 tonnes tandem roller or vibratory roller (vibration off during finish)
  • Roll longitudinally from edges to center; on superelevated sections, roll from lower to upper edge.
  • Roller speed ≤ 5 km/h; wheels kept moist (no oil/fuel).

• Temperature for Rolling: Complete rolling before mix temperature drops below 80°C.

• Field Density: One test per 500 m²; density ≥ 95% of laboratory density.

Permissible Variation in Mix Constituents (Table 4)

Design Criteria for Mix (Marshall Test)

Key Specifications & Formulas for Compaction (IRC 94)

1. Marshall Specimen Compaction

2. Rolling & Compaction Procedure

• Rolling speed: ≤ 5 km/h
• Breakdown rolling: 8-12 tonnes, 3-wheel steel roller
• Intermediate rolling: 15-30 tonnes pneumatic roller (tyre pressure ~7 kg/cm²)
• Finished rolling: 8-10 tonnes tandem roller
• Vibratory roller (8-10 tonnes) can replace above; vibratory mode off during finishing
• Rolling sequence: from edges to center; on superelevated sections, from lower to upper edge
• Roller wheels kept moist (no fuel/oil), overlap passes by 50%

3. Field Density Control

• Field density test after every 500 m² compacted area
• Density ≥ 95% of laboratory density

4. Temperature Control

• Mix laying temperature: 120°C to 160°C
• Rolling completed before mix temperature drops below 80°C
• Aggregate temperature ≤ 163°C
• Bitumen temperature: 150-177°C (viscosity 150-300 cSt)
• Max temperature difference between aggregate and bitumen: 14°C

5. Permissible Variation from Job-Mix Formula

IRC 94 - Opening to Traffic: Key Specifications & Controls

• Opening to Traffic:
  Traffic is allowed only after final rolling when the mix has cooled to ambient temperature. However, a wearing course must be laid before regular traffic or rain exposure.

• Compaction Temperature:

  • Rolling must finish before mix temperature drops below 80°C.
  • Mix laying temperature: 120°C to 160°C.

• Density Requirement:
  Field density should be ≥ 95% of laboratory density (tested every 500 m²).

• Quality Control:

  • Aggregate gradation, bitumen penetration, softening point, and mix stability must be regularly tested.
  • Permissible variations from job-mix formula (Table 4):

• Rolling Sequence:
  Breakdown (8-12t steel roller) → Intermediate (15-30t pneumatic roller) → Finishing (8-10t tandem or vibratory roller without vibration).

flowchart LR
    A[Mix Laid (120-160°C)] --> B[Breakdown Rolling (8-12t)]
    B --> C[Intermediate Rolling (15-30t pneumatic)]
    C --> D[Finishing Rolling (8-10t tandem/vibratory)]
    D --> E[Mix Cooled to Ambient Temp]
    E --> F[Opening to Traffic (After Wearing Course)]

Summary: Ensure proper temperature, compaction, and quality control before opening to traffic as per IRC 94 Clause 6.5 and related clauses.

Quality Control - IRC 94 Key Points

1. Aggregate Control:

• Periodic sieve analysis at cold feeder.
• Tests: Aggregate Impact Value, Los Angeles Abrasion, Flakiness Index, Stripping Value (1 test/50-100 m³).
• Aggregate temperature: max 163°C (±10°C tolerance).
• Aggregate-bitumen temperature difference ≤ 14°C.

2. Bitumen Control:

• Penetration & softening point tests as per IS 1203 & IS 1205.
• Bitumen temperature: 150-177°C.
• Viscosity: 150-300 cSt.
• Bitumen content variation ±0.5% (Table 4).

3. Mix Control:

• Mix temperature at laying: 120°C to 160°C.
• Plant checks on aggregate gradation and proportion.
• Sample every 100 tonnes or once daily for:
  • Marshall stability (≥ 340 kg), flow (2-4 mm), voids (5-10%).
  • Bitumen content and sieve analysis after extraction.

4. Permissible Variations (Table 4):

Marshall Test Design Criteria (IRC 94)

flowchart TD
    A[Aggregate Sampling] --> B{Tests}
    B -->|Impact, Abrasion, Flakiness|

Permissible Variations as per IRC 94 (Clause 7.7 & Table 4)

Key Specifications Summary:

• Mix temperature at laying: 120°C to 160°C
• Bitumen viscosity: 150 to 300 centistokes (at 150-177°C)
• Aggregate temperature: Not to exceed 163°C (±10°C tolerance allowed on lower side)
• Difference between aggregate & bitumen temp: ≤ 14°C
• Compaction: Breakdown rolling with 8-12 t steel roller, intermediate with 15-30 t pneumatic roller, finished with 8-10 t tandem or vibratory roller (vibration off during finishing)
• Longitudinal joint offset: ≥ 150 mm from base course joints
• Marshall Test Criteria:
  • Stability ≥ 340 kg
  • Flow 2-4 mm
  • Voids in mix 5-10%
  • Binder content 4.5-6.0% by weight

Practical Notes:

• Ensure gradations conform to job-mix formula within above tolerances.
• Use hot bitumen tack coat rates as per surface type (Clause 7.5).
• Maintain quality control with periodic sieve analysis, penetration, softening point, and Marshall tests.

flowchart TD
    A[Aggregate Preparation] --> B[Heating & Drying (≤163°C)]
    B --> C[Batching & Mixing with Bitumen (Viscosity 150-300 cSt)]
    C --> D[Transport to Site]
    D --> E[Spreading by Mechanical Paver]
    E --> F[Compaction]
    F --> G[Quality Control Checks]
    G --> H

IRC 94: Testing Requirements - Key Specifications

Marshall Mix Design Criteria (Table 3)

Aggregate Grading (Table 4) - % Passing

Field Testing & Rolling

• Rolling temperature: Complete before mix cools below 80°C to avoid shoving/hair cracks.
• Thickness check: Use hot steel scale penetration correlated with surface area and plant output.
• Field density test: One test per 500 m² compacted surface; density ≥ 95% of lab density.

flowchart TD
    A[Mix Preparation] --> B[Compaction with 50 blows each end]
    B --> C[Marshall Stability & Flow Test]
    C --> D[Check Voids & Binder Content]

IRC 94: Joint and Edge Construction Key Points

Joint Construction

• Longitudinal joints: Offset at least 150 mm from base course joints.
• Joints must be vertical, cut back to full thickness of the previously laid mix.
• Vertical cut face must be painted with hot bitumen before fresh mix placement.

Edge Construction

• Edges should be true to delineating lines parallel to pavement centerline.
• Rolling of joints and edges with 8-10 tonnes static roller to ensure compaction.
• Rolling starts from the edge progressing towards center (reverse on superelevated sections).

Compaction Rolling Sequence

Tack Coat Application (Clause 7.5)

Temperature Control

• Aggregate temperature: ≤163°C (±10°C tolerance allowed)
• Bitumen temperature: 150°C to 177°C (viscosity 150-300 cSt)
• Max temp difference between aggregate & bitumen: 14°C
• Mix laying temperature: 120°C to 160°C

flowchart TD
    A[Prepare Base Surface] --> B[Apply Tack Coat]
    B --> C[Heat & Mix Aggregates & Bitumen]
    C --> D[Transport & Spread Mix]
    D --> E[Construct Joints & Edges]
    E --> F[Compaction Rolling Sequence]
    F --> G[Cooling & Opening to Traffic]

This ensures durable, well-bonded joints and edges crucial for pavement integrity as per IRC 94.

IRC 94: Surface Profile Requirements for Dense Bituminous Macadam (DBM)

Key Specifications:

• Rolling Temperature: Rolling must be done before mix temperature drops below 80°C to avoid shoving or hair cracks (Clause 7.9).
• Thickness Check: Thickness is verified by depth of penetration of hot steel scale, correlated with surface area and total mix output (Clause 7.10).
• Density Requirement: One field density test per 500 m² compacted surface minimum; density ≥ 95% of laboratory density (Clause 7.11).

Gradation Table for DBM Mix (Percentage Passing):

Additional Notes:

• Bitumen content and finer gradations like 1.18 mm and 600 µm are critical for mix stability (Clause 1.18).
• Proper compaction and rolling sequence ensure surface smoothness and durability.

flowchart LR
    A[Mix Preparation] --> B[Mix Temperature > 80°C]
    B --> C[Rolling Operations]
    C --> D[Compaction & Thickness Check]
    D --> E[Field Density Test (≥95% lab density)]
    E --> F[Surface