Table of Contents

    Dense Bituminous Macadam (DBM) Construction Methodology | MoRTH Clause 507

    DBM Construction Methodology – MORTH Specifications, Plant & QA Guide

    Author: Kishor Kumar | Category: Bituminous Works | As per MoRTH Clause 507

    Quick Overview:
    Dense Bituminous Macadam (DBM) is a dense-graded hot mix bituminous layer used as a binder or base course in flexible pavements. Proper DBM construction is critical to ensure load distribution, durability, and bonding between pavement layers.

    Why DBM Quality Is Critical

    The Dense Bituminous Macadam (DBM) layer forms the primary structural course in flexible pavement construction. It provides load distribution, structural strength, and surface uniformity before the Bituminous Concrete (BC) wearing course is laid.

    This field-ready guide covers MoRTH specifications, asphalt plant requirements, mix design parameters, layer thickness criteria, temperature control, compaction standards, and complete QA/QC procedures—making it practical for site engineers, QA/QC professionals, and highway contractors.

    Most premature pavement failures—such as rutting, fatigue cracking, shoving, and delamination—originate from poor DBM execution. Incorrect binder content, inadequate compaction, segregation during laying, improper joint construction, or temperature loss during transportation and paving can significantly reduce pavement service life.Since DBM acts as the structural backbone of flexible pavements, strict compliance with MoRTH specifications, proper mix design control, and systematic field quality checks are essential to ensure long-term pavement performance.

    Quick Technical Reference

    • Nominal Aggregate Size: 37.5 mm (Grading 1), 26.5 mm (Grading 2)
    • Layer Thickness: 50–100 mm
    • Binder Type: VG-30 / VG-40 / PMB (as per climate & traffic)
    • Minimum Binder Content: 4.0% (Gr-1), 4.5% (Gr-2)
    • Compaction Requirement: ≥ 98% of Marshall Density

    Applicable Codes & Specifications

    • MoRTH Specifications for Road & Bridge Works – Section 500 (Clause 507)
    • IRC: SP: 84 – Manual of Specifications & Standards
    • IS: 73 – Paving Grade Bitumen
    • IS: 2386 (Parts I–IV) – Aggregate Testing
    • ASTM / AASHTO and MS-2 7th Rev– Marshall Mix Design
    • Top Level Sheet – DBM (Dense Bituminous Macadam): Approved Mix Design & Approved GFC Drawings

    Materials & Job Mix Design

      Test Procedure of DBM & BC Mix Design (as per MoRTH & IRC Specifications)

      1. 1: Raise RFI for sampling of aggregates for DBM/BC mix design.
      2. 2: Sample the cold bin individual aggregates jointly.
      3. 3: Conduct individual gradation for aggregate as mentioned in MoRTH 500-10.
      4. 4: Blend the aggregate to meet the specified limits as mentioned in MoRTH 500-10.
      5. 5: Conduct the tests for aggregate to confirm its suitability for asphalt mix works:
      6. 6: AIV or LAAV, FI & EI, Stripping value, Water Absorption, Sand Equivalent value test to meet its suitability for DBM & BC as mentioned in MoRTH.
      7. 7: Feed the cold bin blending aggregate proportion in the Hot Mix Plant & take the individual hot bin aggregates.
      8. 8: Conduct specific gravity & water absorption test in the hot bin aggregates.
      9. Sl. No. 9: Conduct the individual gradation for aggregate & blend the aggregate to achieve the limit specified in MoRTH Table 500-10.
      10. 10: Feed the obtained blending proportion in the Hot Mix Plant and take the combined mix sample and check the combined gradation tests as mentioned in MoRTH 500-10.
      11. 11: Conduct the following tests for bitumen: Softening Point Test, Penetration Test, Viscosity Test from the approved bitumen source.
      12. 12: Prepare the mix with different binder content & find the Maximum Specific Gravity of the mix as per ASTM D-2041.
      13. 13: Cast the Marshall moulds with different binder content to check VMA, VFB, GSA, Air Voids, Stability & Flow of the mix.
      14. 14: With the obtained result plot the graph for Bulk Density, Marshall Stability, Air Voids, Flow, VMA & VFB.
      15. 15: All test data are interpreted & marked at which % all criteria passes.
      16. 16: Optimum Binder Content (OBC) has been found from chart.
      17. 17: Retained Stability Test conducted at OBC.
      18. 18: Refusal Density of the BC mix to be checked at 75, 150, 300 blows.
      19. 19: Marshall Quotient found for BC as per Table 7 of IRC SP:53-2002.
      20. 20: Confirmatory moulds casted & tested for Stability, Flow, VFB, VMA.
    • Job Mix Formula (JMF): The Job Mix Formula (JMF) for Dense Bituminous Macadam (DBM) shall be developed and approved for use in the works in the presence of the Authority Engineer. The JMF shall include the following details:
      • Source and location of all materials (bitumen, aggregates, filler)
      • Proportions of all constituent materials
      • Binder type and percentage by weight of total mix
      • Coarse aggregate, fine aggregate, and mineral filler percentages
      • Combined grading curve with specific sieve passing limits as per specification
      • Marshall test results including stability, flow, density, and air voids as per Table 500-10 / 500-11 (as applicable)
      • Compliance of aggregates with MoRTH Clause 507 requirements
      • Mixing, laying, and compaction temperature ranges
      • Optimum Bitumen Content (OBC) and volumetric properties (VMA, VFB, Air Voids)

    • Job Mix Design for DBM shall be conducted in the Field Laboratory using Marshall Method. The materials shall be collected directly from the stockyard / storage tank and shall be checked for various physical requirements.

      The testing shall be carried out in the presence of the Consultant and submitted for approval.

      Approval of JMF: Approval shall be based on witnessed testing by the Independent Engineer. Samples shall be tested in in-house QC lab. Any change in material source requires submission of new JMF for approval prior to execution.

    • Plant Trials: After laboratory approval, plant trials shall be conducted to ensure uniform mix production. Permissible variations shall comply with Table 500-13 limits.
    • Laying Trials:

      Once the plant trials have been successfully completed and approved, the laying trials are executed to demonstrate that the proposed mix can be successfully laid and compacted in accordance with Clause 501. The laying trial shall be carried out on a suitable area which is not to form part of the works. The area of the laying trials shall be a minimum of 100 sq. m. of construction similar to that of the project road, and it shall be in all respects, particularly compaction, the same as the project construction, on which the bituminous material is to be laid.

      Information to AE is given of the proposed method for laying and compacting the material. The density of the finished paving layer shall be determined by taking cores, no sooner than 24 hours after laying. Once the laying trials have been approved, the same plant and methodology shall be applied to the laying of the material on the project.

      Tack Coat shall consist of the application of a single coat of low viscosity liquid bituminous material on the existing bituminous surface using a calibrated boom pressure sprayer, ensuring uniform and continuous coverage. The application shall be carried out at a controlled speed of approximately 45 km/hour to achieve proper bonding between existing surface and subsequent bituminous layers.

    Transportation, Paving & Compaction Methodology (Enhanced)

    1. Transportation of Bituminous Mix

    Hot Mix shall be transported in rear tipping dumpers of minimum 10T capacity or higher, ensuring uninterrupted supply to the paver. All vehicles shall be clean, leak-proof, and properly insulated where required.

    To prevent heat loss, each dumper shall be fully covered with heavy-duty tarpaulin immediately after loading. The mix temperature shall be monitored at plant, dispatch, and site to ensure compliance with MoRTH specifications.

    2. Paving Operations

    Paving shall be carried out using a high-performance Asphalt Paver equipped with hydraulically extendable screed capable of maintaining precise longitudinal and transverse profiles, gradients, and levels.

    Pavers of approved make shall be deployed, capable of paving up to 11.0 m width for full carriageway laying. For service roads and restricted areas, pavers capable of paving up to 5.5 m width shall be used.

    Continuous and uniform paving shall be ensured without segregation, with automatic sensor control wherever applicable to maintain specified thickness and smooth riding quality.

    3. Temperature Control

    The temperature of the mix at the time of laying shall be strictly maintained as per approved Job Mix Formula (JMF). Any material outside permissible temperature limits shall be rejected at site.

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    Table 500-2: Mixing, Laying and Rolling Temperatures for Bituminous Mixes (°C)

    Bitumen GradeBitumen Temp (°C)Aggregate Temp (°C)Mixing Temp (°C)Laying Temp (°C)Rolling Temp (Start ≥ °C)
    VG-40160 - 170160 - 175160 - 170150 - 165150 Min
    VG-30150 - 165160 - 175150 - 165145 - 165140 Min
    VG-20145 - 165150 - 165145 - 165140 - 160135 Min
    VG-10140 - 160150 - 165140 - 160130 - 150130 Min

    Note: Rolling must be completed before the mat cools down to the specified minimum rolling temperatures to ensure proper compaction and interlocking of aggregates.

    4. Rolling & Compaction Sequence

    Breakdown rolling shall commence immediately behind the paver and shall start only when the mix temperature is below 120°C and stable enough to avoid displacement or cracking.

    Rolling shall be completed before the mix temperature falls below 80°C to ensure optimum density and interlocking of aggregates.

    Compaction shall be achieved using a combination of:

    • 10T Double Drum Vibratory Roller (Primary Compaction)
    • Pneumatic Tyre Roller (Secondary Compaction / Kneading Effect)

    Final rolling shall ensure elimination of roller marks and achievement of uniform density across the entire surface width.

    5. Quality Control & Testing

    Finished surface levels shall be jointly verified with the Consultant and compared with approved design levels and tolerances.

    Field density shall be checked using Sand Replacement Method or Nuclear Density Gauge at specified frequency as per QA/QC plan.

    Core samples shall be extracted using a calibrated core cutting machine. All laboratory tests including thickness, density, and bitumen content shall be carried out to ensure compliance with approved specifications and JMF.

    6. Opening to Traffic

    The newly laid bituminous surface shall be opened to traffic only after complete cooling to ambient temperature or after a minimum curing period of 24 hours, whichever is later, and subject to approval of the Engineer.

    7. Safety & Environmental Management

    • Caution boards shall be installed at entry, exit, and all hazardous locations of work zone.
    • Continuous barricading with reflective tape shall be provided along active work areas.
    • Trained flagmen / signalmen shall be deployed at high traffic density locations.
    • Reflective signage and blinking lights shall be provided during night operations.
    • Hot mix plant shall be operated with valid pollution control measures in place.
    • Noise control and emission control devices shall be maintained in working condition.
    • Construction waste shall be disposed of in designated approved locations only.
    • All necessary precautions shall be taken to avoid public inconvenience and environmental impact.

    8. Contractor’s Technical Remarks

    • Manpower and machinery deployment is indicative and may be adjusted based on site requirements and progress.
    • Any modification in execution methodology shall be implemented only after prior approval from the Consultant/Engineer.
    • Full compliance with MoRTH, IRC, and project-specific specifications shall be ensured at all stages of execution.

    Additional Items

    1. Spreading in restricted areas shall be done manually.
    2. Hot joints shall be executed before earlier material cools to 100°C. No laying in standing water.
    3. During rain, laying shall stop when water accumulates; rollers may continue compaction.
    4. All tippers shall be covered with tarpaulin during rain.

    Daily Progress Reports

    • Date of operation with RFIs
    • Material quantity records
    • Laydown records (location, layer, time, temperature)
    • Plant and labour deployment
    • Laboratory and field test records

    DAILY PROGRESS REPORTS SHALL RECORD:

    1. Date of Operation with RFIs
    2. WMM/DBM used within PCC operations to weighed prior to dispatch.
    3. Lay down Record Sheets indicating location, layer, lane, time, load, temperature.
    4. Plant/Labor used.
    5. Appropriate Laboratory/Field Test records.

    COMPOSITION OF DENSE GRADED BITUMINOUS MACADAM

    Grading12
    Nominal aggregate size37.5 mm26.5 mm
    Layer Thickness75-100 mm50-75 mm
    45.00100-
    37.5095-100100
    26.5063-9390-100
    19.00-71-95
    13.2055-7556-80
    9.5--
    4.7538-5438-54
    2.3628-4228-42
    1.18--
    0.600--
    0.3007-217-21
    0.150--
    0.0752-82-8
    Bitumen ContentMin 4.0%Min 4.5%

    QUALITY CONTROL INSPECTION & FREQUENCY OF TESTING:

    LayerInspection StageTest / ParameterStandardFrequencyAcceptance Criteria
    Dense Bituminous Macadam (DBM) Inspection at Source – Properties of Binder & AggregateQuality of BinderIS:1201 to IS:1220 & IS:154621 Sample / Lot Ordinary Bitumen complying with IS:73 (2013)
    Modified Bitumen complying with IRC:SP:53 (2010)
    Aggregate Impact ValueIS:2386 (Part 4)1 Test / 350 m³27% (Max)
    Los Angeles Abrasion ValueIS:2386 (Part 4)As & when Required35% (Max)
    Combined Flakiness & Elongation IndexIS:2386 (Part 1)1 Test / 350 m³35% (Max)
    Stripping ValueIS:62411 Test / SourceMinimum retained coating 95%
    Soundness TestIS:2386 (Part 5)1 Test / Source 12% max with Sodium Sulphate
    18% max with Magnesium Sulphate
    Water Absorption ValueIS:2386 (Part 3)1 Test / Source2% (Max)
    Sand Equivalent ValueIS:2720 (Part 37)1 Test / Source50% (Min)
    % Age of Fractured FaceIS:2386 (Part 1)As & when Required 90% of material retained on 4.75 mm sieve shall have at least 2 fractured faces
    Plasticity IndexIS:2720 (Part 5)1 Test / Source4% (Max)
    Inspection at Source – Properties of MixAggregate Grading (Mix Aggregates)IS:2386 (Part 1) 1 Test / 400 MT of Mix
    Minimum 2 Tests / Plant / Day
    IS SieveGrading-IGrading-II
    45 mm100-
    37.5 mm95-100100
    26.5 mm63-9390-100
    19 mm-71-95
    13.2 mm55-7556-80
    4.75 mm38-5438-54
    2.36 mm28-4228-42
    300 micron7-217-21
    75 micron2-82-8

    MoRTH Spec (5th Rev.) Table 500-10
    Marshall StabilityASTM D-1559 / AASHTO T245 Set of 3 Specimens / 400 MT of Mix
    Minimum 2 Sets / Plant / Day    		As per Table 500-10 of MoRTH Specification
    Marshall FlowASTM D-1559 / AASHTO T245 Set of 3 Specimens / 400 MT of Mix
    Minimum 2 Sets / Plant / Day    		As per Table 500-10 of MoRTH Specification
    Air VoidsASTM D-2726 Set of 3 Specimens / 400 MT of Mix
    Minimum 2 Sets / Plant / Day    		As per Table 500-10 of MoRTH Specification
    Voids in Mineral Aggregate (VMA)ASTM D-2726 Set of 3 Specimens / 400 MT of Mix
    Minimum 2 Sets / Plant / Day    		As per Table 500-10 of MoRTH Specification
    Voids Filled by Bitumen (VFB)ASTM D-1559 Set of 3 Specimens / 400 MT of Mix
    Minimum 2 Sets / Plant / Day    		As per Table 500-10 of MoRTH Specification
    Binder ContentASTM D-2172 1 Test / 400 MT of Mix
    Minimum 2 Tests / Plant / Day    		 4% (Min) for Grade-I
    4.5% (Min) for Grade-II
    Maximum Specific Gravity of Mix (Gmm)ASTM D-2041 1 Test / 400 MT of Mix
    Minimum 2 Tests / Plant / Day    		As per Approved Mix Design
    Water Sensitivity Test
    (if retained coating in stripping test is less than 95%)    		AASHTO T2831 Test / Mix (When Source of Material Changes)80% (Min)
    Control of Temperature Control of Temperature of Binder in Boiler & Aggregate in DryerMoRTH SpecificationsEvery Day Prior to Production Starts Aggregate Temp: 150°C–170°C
    Binder Temp: 150°C–165°C
    Discharge Temp: 150°C–165°C

    Modified Bitumen:
    Aggregate Temp: 150°C–185°C
    Binder Temp: 165°C–185°C
    Discharge Temp: 150°C–170°C
    Permissible Variations of Plant Mix from Job Mix FormulaAggregate GradingMoRTH SpecificationsNA
    Passing Sieve Size (mm)Variation
    19 & Above±8%
    13.2 & 9.5±7%
    4.75±6%
    2.36, 1.18 & 600 micron±5%
    300 & 150 micron±4%
    0.075 mm±2%
    Inspection and Acceptance Criteria Table
    CategoryItemReference / StandardFrequencyRequirement / Criteria
    In-process InspectionCheck level control of paverMORTH SpecificationsAt regular close intervals-
    Temperature of mix before laying and rollingMORTH SpecificationsAt regular close intervals Laying Temp. 140°C (Min)
    Rolling Temp. 90°C (Min)
    Acceptance CriteriaControl of Compaction (Field Density)ASTM-D 27261 Test / 700 m²As per MORTH Cl 903.4.2
    Tolerance in Surface LevelStandard survey practiceAs per Specification+6 mm or -6 mm
    Surface RegularityIRC-SP-16As & when RequiredBituminous Base Course 6 mm
    Binder Tolerance± 0.3%
    Mixing Temperature Tolerance± 10°C

    INSPECTION PLAN:

    1. Approval of WMM TOP layer – Inspection & Testing required
    2. Spreading / fill layers – Inspection required
    3. Final Layer – Inspection & Testing required
    4. Density checks – Inspection & Testing required

    SAFETY MEASURES:

    • All safety measures shall be as per approved EHS Plan.

    Common Field Problems & Remedies

    • Segregation: Improve handling, reduce drop height
    • Low Density: Increase rolling passes or temperature
    • Fatty Surface: Reduce binder content, improve gradation
    • Cold Joints: Proper joint heating and rolling

    Safety & Best Practices

    • Mandatory PPE for all personnel
    • Proper traffic diversion and barricading
    • Safe handling of hot bituminous materials
    • Maintain complete QC documentation

    Frequently Asked Questions (FAQ)

    What is the minimum compaction requirement for DBM?

    DBM must achieve at least 98% of Marshall Density as per MoRTH.

    Can DBM be laid in rainy conditions?

    No. DBM shall not be laid during rain or on wet surfaces.

    What is the difference between DBM and BC?

    DBM acts as a binder/base course, while BC is the wearing course with finer gradation.

    Prepared by Highway Quality Engineers | For educational & site-reference use

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