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

DBM Construction Methodology – MORTH Specifications, Plant & QA Guide

Q: What is the minimum compaction requirement for DBM?

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

Q: Can DBM be laid in rainy conditions?

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

Q: What is the difference between DBM and BC?

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

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: Raise RFI for sampling of aggregates for DBM/BC mix design.

2: Sample the cold bin individual aggregates jointly.

3: Conduct individual gradation for aggregate as mentioned in MoRTH 500-10.

4: Blend the aggregate to meet the specified limits as mentioned in MoRTH 500-10.

5: Conduct the tests for aggregate to confirm its suitability for asphalt mix works:

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: Feed the cold bin blending aggregate proportion in the Hot Mix Plant & take the individual hot bin aggregates.

8: Conduct specific gravity & water absorption test in the hot bin aggregates.

Sl. No. 9: Conduct the individual gradation for aggregate & blend the aggregate to achieve the limit specified in MoRTH Table 500-10.

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: Conduct the following tests for bitumen: Softening Point Test, Penetration Test, Viscosity Test from the approved bitumen source.

12: Prepare the mix with different binder content & find the Maximum Specific Gravity of the mix as per ASTM D-2041.

13: Cast the Marshall moulds with different binder content to check VMA, VFB, GSA, Air Voids, Stability & Flow of the mix.

14: With the obtained result plot the graph for Bulk Density, Marshall Stability, Air Voids, Flow, VMA & VFB.

15: All test data are interpreted & marked at which % all criteria passes.

16: Optimum Binder Content (OBC) has been found from chart.

17: Retained Stability Test conducted at OBC.

18: Refusal Density of the BC mix to be checked at 75, 150, 300 blows.

19: Marshall Quotient found for BC as per Table 7 of IRC SP:53-2002.

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.

MoRTH Clause 505.3.3 – Job Mix Formula (JMF)

Detailed Practical Example for DBM (Dense Bituminous Macadam)

1. Material Sources

Material	Source	Location
26.5 mm Aggregate	ABC Stone Crusher	Roorkee
13.2 mm Aggregate	ABC Stone Crusher	Roorkee
Stone Dust	ABC Stone Crusher	Roorkee
Mineral Filler	UltraTech Cement	Roorkee
Bitumen	VG-40	IOCL Refinery

2. Aggregate Blend Proportions

Material	Percentage of Total Aggregate
26.5 mm Aggregate	35%
13.2 mm Aggregate	30%
Stone Dust	30%
Mineral Filler	5%

3. Combined Gradation

Sieve Size	% Passing
26.5 mm	100
19 mm	95
13.2 mm	79
9.5 mm	68
4.75 mm	52
2.36 mm	38
1.18 mm	28
0.60 mm	20
0.30 mm	14
0.15 mm	9
0.075 mm	5

4. Marshall Mix Design Results

Property	4.0%	4.5%	5.0%
Marshall Stability (kN)	12.8	15.4	14.0
Flow (mm)	2.6	3.1	4.0
Air Voids (%)	6.0	4.2	2.5
VMA (%)	14.2	15.1	16.0
VFB (%)	58	72	84

5. Optimum Binder Content

Selected Optimum Binder Content (OBC)

4.5% VG-40 Bitumen

6. Volumetric Properties

Property	Value
Maximum Specific Gravity (Gmm)	2.520
Bulk Density (Gmb)	2.398
Air Voids (Va)	4.84%
VMA	15.1%
VFB	67.9%

7. Moisture Susceptibility Test (AASHTO T 283)

Parameter	Value
Dry Strength	1050 kPa
Wet Strength	910 kPa
TSR	86.7%
Status	PASS

8. Temperature Requirements

Activity	Temperature
Aggregate Heating	170–180°C
Bitumen Heating	150–165°C
Mixing Temperature	155–165°C
Laying Temperature	140–155°C
Compaction Temperature	130–150°C

Final Approved JMF Summary

Parameter	Approved Value
Mix Type	DBM Grading-2
Binder Grade	VG-40
Optimum Binder Content	4.5%
Marshall Stability	15.4 kN
Flow	3.1 mm
Air Voids	4.84%
VMA	15.1%
VFB	67.9%
TSR	86.7%
Mixing Temperature	155–165°C
Compaction Temperature	130–150°C

Next Step After JMF Approval

Once the Job Mix Formula (JMF) is approved by the Engineer, the Contractor shall conduct a Plant Trial in accordance with MoRTH Clause 505.3.4 to verify that the hot mix plant can consistently produce a mix conforming to the approved JMF.

After successful completion and approval of the Plant Trial, a Laying Trial shall be carried out as per MoRTH Clause 505.3.5 to demonstrate that the approved mix can be laid and compacted satisfactorily under field conditions.

Only after successful approval of both the Plant Trial and Laying Trial shall full-scale production and paving operations commence on the project.

Detailed Example – Plant Trial Verification as per MoRTH Clause 505.3.4

Approved Job Mix Formula (JMF)

Assume the approved JMF for DBM is as follows:

Sieve Size	JMF (% Passing)
26.5 mm	100
19.0 mm	95
13.2 mm	78
9.5 mm	68
4.75 mm	48
2.36 mm	36
1.18 mm	27
0.60 mm	20
0.30 mm	14
0.15 mm	9
0.075 mm	5
Binder Content	4.5%
Mixing Temperature	160°C

Step 1: Calculate Permissible Limits

Parameter	JMF Value	Tolerance	Permissible Range
19 mm	95%	±8%	87% – 100%
13.2 mm	78%	±7%	71% – 85%
9.5 mm	68%	±7%	61% – 75%
4.75 mm	48%	±6%	42% – 54%
2.36 mm	36%	±5%	31% – 41%
1.18 mm	27%	±5%	22% – 32%
0.60 mm	20%	±5%	15% – 25%
0.30 mm	14%	±4%	10% – 18%
0.15 mm	9%	±4%	5% – 13%
0.075 mm	5%	±2%	3% – 7%
Binder Content	4.5%	±0.3%	4.2% – 4.8%
Mixing Temperature	160°C	±10°C	150°C – 170°C

Step 2: Actual Plant Trial Results

Parameter	Actual Result
19 mm	91%
13.2 mm	80%
9.5 mm	70%
4.75 mm	52%
2.36 mm	34%
1.18 mm	28%
0.60 mm	19%
0.30 mm	13%
0.15 mm	8%
0.075 mm	4.5%
Binder Content	4.6%
Mixing Temperature	158°C

Step 3: Compliance Check

Parameter	Permissible Range	Actual Result	Status
19 mm	87–100%	91%	✅ Pass
13.2 mm	71–85%	80%	✅ Pass
9.5 mm	61–75%	70%	✅ Pass
4.75 mm	42–54%	52%	✅ Pass
2.36 mm	31–41%	34%	✅ Pass
1.18 mm	22–32%	28%	✅ Pass
0.60 mm	15–25%	19%	✅ Pass
0.30 mm	10–18%	13%	✅ Pass
0.15 mm	5–13%	8%	✅ Pass
0.075 mm	3–7%	4.5%	✅ Pass
Binder Content	4.2–4.8%	4.6%	✅ Pass
Temperature	150–170°C	158°C	✅ Pass

Example of Failure

Suppose the extracted binder content is 5.0%.

Permissible Range = 4.2% to 4.8%

Actual Result = 5.0%

Difference from JMF = +0.5%

Result: ❌ Non-Conforming

The Contractor must:

Check calibration of bitumen pump.
Verify bitumen flow meter.
Inspect plant controls.
Produce a fresh trial mix.

Practical Site Note

During Plant Trial, engineers generally perform:

Hot Bin Analysis
Extraction Test (Binder Content)
Gradation After Extraction
Temperature Monitoring
Marshall Specimen Preparation
Stability and Flow Verification
Comparison with Approved JMF

Only after successful Plant Trial compliance can the Contractor proceed to Laying Trial under Clause 505.3.5.

Detailed Example – Plant Trial Verification as per MoRTH Clause 505.3.4

Approved Job Mix Formula (JMF)

Assume the approved JMF for DBM is as follows:

Sieve Size	JMF (% Passing)
26.5 mm	100
19.0 mm	95
13.2 mm	78
9.5 mm	68
4.75 mm	48
2.36 mm	36
1.18 mm	27
0.60 mm	20
0.30 mm	14
0.15 mm	9
0.075 mm	5
Binder Content	4.5%
Mixing Temperature	160°C

Step 1: Calculate Permissible Limits

19 mm Sieve (Tolerance ±8%)

JMF = 95%
Upper Limit = 95 + 8 = 103% → Maximum possible = 100%
Lower Limit = 95 − 8 = 87%
Permissible Range = 87% to 100%

13.2 mm Sieve (Tolerance ±7%)

JMF = 78%
Upper Limit = 85%
Lower Limit = 71%
Permissible Range = 71% to 85%

9.5 mm Sieve (Tolerance ±7%)

JMF = 68%
Upper Limit = 75%
Lower Limit = 61%
Permissible Range = 61% to 75%

4.75 mm Sieve (Tolerance ±6%)

JMF = 48%
Upper Limit = 54%
Lower Limit = 42%
Permissible Range = 42% to 54%

2.36 mm Sieve (Tolerance ±5%)

JMF = 36%
Upper Limit = 41%
Lower Limit = 31%
Permissible Range = 31% to 41%

1.18 mm Sieve (Tolerance ±5%)

JMF = 27%
Upper Limit = 32%
Lower Limit = 22%
Permissible Range = 22% to 32%

0.60 mm Sieve (Tolerance ±5%)

JMF = 20%
Upper Limit = 25%
Lower Limit = 15%
Permissible Range = 15% to 25%

0.30 mm Sieve (Tolerance ±4%)

JMF = 14%
Upper Limit = 18%
Lower Limit = 10%
Permissible Range = 10% to 18%

0.15 mm Sieve (Tolerance ±4%)

JMF = 9%
Upper Limit = 13%
Lower Limit = 5%
Permissible Range = 5% to 13%

0.075 mm Sieve (Tolerance ±2%)

JMF = 5%
Upper Limit = 7%
Lower Limit = 3%
Permissible Range = 3% to 7%

Binder Content (Tolerance ±0.3%)

JMF = 4.5%
Upper Limit = 4.8%
Lower Limit = 4.2%
Permissible Range = 4.2% to 4.8%

Mixing Temperature (Tolerance ±10°C)

JMF Temperature = 160°C
Upper Limit = 170°C
Lower Limit = 150°C
Permissible Range = 150°C to 170°C

Step 2: Actual Plant Trial Results

Parameter	Actual Result
19 mm	91%
13.2 mm	80%
9.5 mm	70%
4.75 mm	52%
2.36 mm	34%
1.18 mm	28%
0.60 mm	19%
0.30 mm	13%
0.15 mm	8%
0.075 mm	4.5%
Binder Content	4.6%
Mixing Temperature	158°C

Step 3: Compliance Check

Parameter	Permissible Range	Actual Result	Status
19 mm	87–100%	91%	✅ Pass
13.2 mm	71–85%	80%	✅ Pass
9.5 mm	61–75%	70%	✅ Pass
4.75 mm	42–54%	52%	✅ Pass
2.36 mm	31–41%	34%	✅ Pass
1.18 mm	22–32%	28%	✅ Pass
0.60 mm	15–25%	19%	✅ Pass
0.30 mm	10–18%	13%	✅ Pass
0.15 mm	5–13%	8%	✅ Pass
0.075 mm	3–7%	4.5%	✅ Pass
Binder Content	4.2–4.8%	4.6%	✅ Pass
Temperature	150–170°C	158°C	✅ Pass

Example of Failure

Suppose the extracted binder content is 5.0%.

Permissible Range = 4.2% to 4.8%

Actual Result = 5.0%

Difference from JMF:

5.0 − 4.5 = +0.5%

Since the allowable variation is only ±0.3%, the result is:

❌ Non-Conforming

The Contractor must:

Check calibration of bitumen pump.
Verify bitumen flow meter.
Inspect plant controls.
Produce a fresh trial mix.

Practical Site Note

During Plant Trial, engineers generally perform:

Hot Bin Analysis
Extraction Test (Binder Content)
Gradation After Extraction
Temperature Monitoring
Marshall Specimen Preparation
Stability and Flow Verification
Comparison with Approved JMF

Only after successful Plant Trial compliance can the Contractor proceed to Laying Trial under Clause 505.3.5.

MoRTH Clause 505.3.5 – Laying Trials (Dense Graded Bituminous Macadam)

Purpose of Laying Trial

After successful completion and approval of the Plant Trial under Clause 505.3.4, the Contractor shall conduct a Laying Trial to demonstrate that:

The approved Job Mix Formula (JMF) can be laid satisfactorily in the field.
The proposed paver can achieve the required thickness, line, level, and profile.
The selected rolling pattern can achieve the specified density.
The proposed construction methodology is suitable for large-scale production work.

The laying trial serves as a field validation of the approved mix and plant production process before commencement of actual paving works.

Requirements of Laying Trial

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 regarding the proposed method for laying and compacting the material shall be provided to the Engineer. The laying trial shall establish whether the proposed laying plant, compaction equipment, and methodology are capable of producing satisfactory results under actual field conditions.

The density of the finished paving layer shall be determined by taking cores no sooner than 24 hours after laying, or by any other method approved by the Engineer.

For Dense Graded Bituminous Macadam (DBM), the compacted layer shall achieve a minimum field density equal to or greater than 92% of the Theoretical Maximum Specific Gravity (Gmm) determined in accordance with ASTM D 2041.

Once the laying trials have been approved, the same plant, equipment, rolling pattern, and methodology shall be applied to the laying of the material on the project. No variation shall be permitted unless approved in writing by the Engineer.

The Engineer may, at his discretion, require additional laying trials if significant changes are proposed in the paving equipment, compaction equipment, construction methodology, or Job Mix Formula (JMF).

Tack Coat

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 to achieve the specified rate of spray and ensure proper bonding between the existing surface and the subsequent bituminous layer. The tack coat shall be applied uniformly over the entire surface without streaking, pooling, or missed areas.

The treated surface shall be allowed to break and cure appropriately before placing the overlying bituminous layer to ensure effective adhesion and long-term pavement performance.

The trial section shall satisfy the following requirements:

Trial Area

Be located on a suitable area approved by the Engineer.
Not form part of the permanent works.
Have a minimum area of 100 m².
Be constructed using the same materials, equipment, layer thickness, and methodology proposed for the project road.

Example

For a DBM layer of 100 mm thickness:

Trial Length = 25 m
Trial Width = 4 m
Area = 100 m²

This satisfies the minimum MoRTH requirement.

Contractor's Responsibilities Before Trial

Before starting the laying trial, the Contractor shall submit the following details to the Engineer:

Paver Details

Make and model of paver.
Screed type.
Operating width.
Sensor arrangement.

Roller Details

Tandem Roller.
Pneumatic Tyred Roller (PTR).
Vibratory Roller.

Rolling Pattern Example

Roller Type	Number of Passes
Vibratory Roller	4 Passes
Pneumatic Tyred Roller (PTR)	6 Passes
Finish Roller	2 Passes

Construction Methodology

Hauling arrangement.
Temperature control measures.
Paving sequence.
Rolling sequence.
Joint construction method.

Objectives of Laying Trial

1. Uniform Laying

The mix shall be laid without:

Segregation.
Dragging.
Surface tearing.
Excessive temperature loss.

2. Thickness Control

The paver shall achieve the specified compacted thickness.

Example:

Required DBM Thickness = 100 mm

Core Location	Measured Thickness
Core 1	101 mm
Core 2	98 mm
Core 3	100 mm

Result: Thickness acceptable.

3. Surface Regularity

Smooth riding quality.
Correct camber.
Correct cross fall.
Proper longitudinal profile.

4. Compaction Capability

The rolling pattern shall achieve the required field density. This is the most important objective of the laying trial.

Density Requirement for DBM

MoRTH specifies that the compacted DBM layer shall have a minimum field density equal to or greater than 92% of the Theoretical Maximum Specific Gravity (Gmm).

Gmm Determination

Gmm is determined as per ASTM D 2041.

Example:

Gmm = 2.520

Required Density = 92% × 2.520 = 2.318 g/cc

Minimum Acceptable Field Density = 2.318 g/cc

Density Verification by Core Test

Cores shall be extracted at least 24 hours after paving.

Core Density Results

Core No.	Bulk Density (g/cc)
1	2.340
2	2.332
3	2.325

Average Density:

(2.340 + 2.332 + 2.325) ÷ 3 = 2.332 g/cc

Percent Density Calculation

Density (%) = (Field Density ÷ Gmm) × 100

= (2.332 ÷ 2.520) × 100

= 92.54%

Result: ✅ PASS

Because 92.54% > 92%

Example of Failure

Assume:

Field Density = 2.280 g/cc
Gmm = 2.520

Density (%) = (2.280 ÷ 2.520) × 100

= 90.48%

Result: ❌ FAIL

Because 90.48% < 92%

Possible Reasons for Failure

Insufficient roller passes.
Delayed rolling.
Low mix temperature.
Inadequate roller weight.
Excessive layer thickness.
Improper rolling pattern.

Corrective Measures

Modify rolling sequence.
Increase roller passes.
Increase compaction effort.
Adjust paving temperature.
Improve hauling arrangements.
Conduct a fresh laying trial.

Approval of Laying Trial

Parameter	Requirement
Thickness	As per drawing
Density	≥ 92% of Gmm
Surface Finish	Satisfactory
Regularity	Acceptable
Segregation	Nil
Construction Method	Acceptable

Only after satisfactory compliance shall the laying trial be approved.

Requirement After Approval

Same JMF shall be used.
Same hot mix plant shall be used.
Same paver shall be used.
Same roller combination shall be used.
Same rolling pattern shall be used.
Same construction methodology shall be used.

Any change requires written approval from the Engineer.

When a New Laying Trial May Be Required

JMF changes.
Aggregate source changes.
Bitumen source changes.
Paver changes.
Roller combination changes.
Layer thickness changes.
Significant construction problems occur.

Workflow After JMF Approval

JMF Approval
      ↓
Plant Trial (Clause 505.3.4)
      ↓
Plant Trial Approval
      ↓
Laying Trial (Clause 505.3.5)
      ↓
Density & Thickness Verification
      ↓
Engineer Approval
      ↓
Full Scale DBM Production

Interview Question

Q. What is the minimum field density requirement for DBM during Laying Trial as per MoRTH Clause 505.3.5?

Answer: The compacted DBM layer shall achieve a field density equal to or greater than 92% of the Theoretical Maximum Specific Gravity (Gmm) determined as per ASTM D 2041, verified through core cutting or another approved method.

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.

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

Bitumen Grade	Bitumen Temp (°C)	Aggregate Temp (°C)	Mixing Temp (°C)	Laying Temp (°C)	Rolling Temp (Start ≥ °C)
VG-40	160 - 170	160 - 175	160 - 170	150 - 165	150 Min
VG-30	150 - 165	160 - 175	150 - 165	145 - 165	140 Min
VG-20	145 - 165	150 - 165	145 - 165	140 - 160	135 Min
VG-10	140 - 160	150 - 165	140 - 160	130 - 150	130 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

Spreading in restricted areas shall be done manually.
Hot joints shall be executed before earlier material cools to 100°C. No laying in standing water.
During rain, laying shall stop when water accumulates; rollers may continue compaction.
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:

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

COMPOSITION OF DENSE GRADED BITUMINOUS MACADAM

Grading	1	2
Nominal aggregate size	37.5 mm	26.5 mm
Layer Thickness	75-100 mm	50-75 mm
45.00	100	-
37.50	95-100	100
26.50	63-93	90-100
19.00	-	71-95
13.20	55-75	56-80
9.5	-	-
4.75	38-54	38-54
2.36	28-42	28-42
1.18	-	-
0.600	-	-
0.300	7-21	7-21
0.150	-	-
0.075	2-8	2-8
Bitumen Content	Min 4.0%	Min 4.5%

QUALITY CONTROL INSPECTION & FREQUENCY OF TESTING:

Layer

Inspection Stage

Test / Parameter

Standard

Frequency

Acceptance Criteria

Dense Bituminous Macadam (DBM)

Inspection at Source – Properties of Binder & Aggregate

Quality of Binder

IS:1201 to IS:1220 & IS:15462

1 Sample / Lot

Ordinary Bitumen complying with IS:73 (2013)
Modified Bitumen complying with IRC:SP:53 (2010)

Aggregate Impact Value

IS:2386 (Part 4)

1 Test / 350 m³

27% (Max)

Los Angeles Abrasion Value

IS:2386 (Part 4)

As & when Required

35% (Max)

Combined Flakiness & Elongation Index

IS:2386 (Part 1)

1 Test / 350 m³

35% (Max)

Stripping Value

IS:6241

1 Test / Source

Minimum retained coating 95%

Soundness Test

IS:2386 (Part 5)

1 Test / Source

12% max with Sodium Sulphate
18% max with Magnesium Sulphate

Water Absorption Value

IS:2386 (Part 3)

1 Test / Source

2% (Max)

Sand Equivalent Value

IS:2720 (Part 37)

1 Test / Source

50% (Min)

% Age of Fractured Face

IS:2386 (Part 1)

As & when Required

90% of material retained on 4.75 mm sieve shall have at least 2 fractured faces

Plasticity Index

IS:2720 (Part 5)

1 Test / Source

4% (Max)

Inspection at Source – Properties of Mix

Aggregate Grading (Mix Aggregates)

IS:2386 (Part 1)

1 Test / 400 MT of Mix
Minimum 2 Tests / Plant / Day

IS Sieve	Grading-I	Grading-II
45 mm	100	-
37.5 mm	95-100	100
26.5 mm	63-93	90-100
19 mm	-	71-95
13.2 mm	55-75	56-80
4.75 mm	38-54	38-54
2.36 mm	28-42	28-42
300 micron	7-21	7-21
75 micron	2-8	2-8

MoRTH Spec (5th Rev.) Table 500-10

Marshall Stability

ASTM D-1559 / AASHTO T245