Bituminous Mix Design (BM, DBM, BC, SMA)
Marshall method mix design for all hot-mix asphalt layers per MoRTH Section 500
Bituminous mix design determines the optimum proportion of aggregates and bitumen binder to produce a hot-mix asphalt (HMA) that meets strength, durability, and workability requirements. The Marshall method — the most widely used procedure in India — establishes the Optimum Binder Content (OBC) for each layer type: BM, DBM, BC, and SMA.
What Is Bituminous Mix Design?
Test Parameters & Acceptance Criteria
The following parameters are evaluated during Marshall mix design. Acceptance values vary by layer type (BM, DBM, BC, SMA) and traffic category as specified in MoRTH Section 500 Tables 500-12 through 500-19.
| Parameter | Value / Range | Unit | Standard |
|---|---|---|---|
| Marshall Stability (at 60 degrees C) | >= 9.0 kN (DBM/BC), >= 6.25 kN (SMA) | kN | MoRTH Cl. 500 / MS-2 |
| Marshall Flow | 2-4 mm (DBM/BC), 2-4 mm (SMA) | mm | MoRTH Cl. 500 / MS-2 |
| Air Voids (Va) | 3-5% (DBM/BC), 4% target (SMA) | % | MoRTH Table 500-18 |
| Voids in Mineral Aggregate (VMA) | >= 12-16% (depends on NMAS) | % | MS-2 Table 5.3 / MoRTH |
| Voids Filled with Bitumen (VFB) | 65-75% (DBM/BC) | % | MoRTH Table 500-18 |
| Optimum Binder Content (OBC) | 4.5-6.5% (varies by layer and gradation) | % | MS-2 / MoRTH |
| Retained Stability (after 24-hr water immersion) | >= 75% | % | MoRTH Cl. 500 |
| Drain Down (SMA only) | <= 0.3% | % | MoRTH Table 500-19 |
| Aggregate Gradation | Within MoRTH grading envelope for specified NMAS | MoRTH Tables 500-12 to 500-17 |
Applicable Standards
Mix Design Methods for Asphalt Concrete and Other Hot-Mix Types (Marshall Method)
Specifications for Road and Bridge Works — Section 500 (Base, Surface, and Special Courses)
Standard Test Method for Marshall Stability and Flow of Asphalt Mixtures
Standard Test Method for Bulk Specific Gravity and Density of Non-Absorptive Compacted Asphalt Mixtures
Standard Test Method for Percent Air Voids in Compacted Asphalt Mixtures
Methods of Test for Aggregates for Concrete — Particle Size, Shape, Specific Gravity, Mechanical Properties
Equipment Used
Marshall Stability Testing Machine
AIMIL AIM-305
50 kN capacity with digital load and deformation readout
CalibratedMarshall Compaction Pedestal & Hammer
Standard 4.54 kg hammer, 457 mm drop height
75 blows per face (heavy traffic) / 50 blows (medium traffic)
CalibratedThermostatically Controlled Water Bath
AIMIL / Humboldt
60 +/- 1 degrees C, accommodates 24 Marshall specimens
CalibratedBitumen Mixing and Heating Oven
Hot air oven, 50-200 degrees C range
Capacity for aggregate and binder heating to mixing temperature
CalibratedSpecific Gravity Apparatus
Pycnometer and vacuum setup
For Gmm (theoretical maximum specific gravity) per ASTM D2041
CalibratedIS Sieve Set (for Aggregate Gradation)
Standard IS sieves 26.5 mm to 75 micron
Full set with mechanical shaker for JMF verification
CalibratedMix Design Process
Material Collection & Aggregate Characterisation
Day 1-2Representative samples of all aggregate fractions (coarse, fine, and filler) are collected from the project hot-mix plant stockpiles — typically 50-60 kg total. Bitumen (VG-30, VG-40, or modified binder) is sampled as well. Aggregates are tested for gradation, specific gravity, water absorption, flakiness/elongation index, Los Angeles abrasion, aggregate impact value, and stripping resistance as per IS 2386 and MoRTH requirements.
Job Mix Formula (JMF) Development
Day 2-3Individual aggregate fractions are proportioned using trial-and-error or graphical methods to achieve a combined gradation that falls within the MoRTH grading envelope for the specified layer type (BM/DBM/BC/SMA) and Nominal Maximum Aggregate Size (NMAS). For SMA, the coarse aggregate skeleton must satisfy the VCA (Voids in Coarse Aggregate) requirement. The proportioned blend becomes the Job Mix Formula (JMF).
Specimen Preparation at Varied Binder Contents
Day 3-4Aggregates are heated to 150-170 degrees C and mixed with bitumen heated to the specified mixing temperature (based on viscosity-temperature chart). Five sets of Marshall specimens are prepared at binder contents of OBC-1.0%, OBC-0.5%, estimated OBC, OBC+0.5%, and OBC+1.0%. Each specimen is compacted with 75 blows per face using the Marshall hammer at the specified compaction temperature. Three specimens are prepared per binder content — a total of 15 specimens.
Volumetric Analysis
Day 4-5Each compacted specimen is weighed in air and water to determine bulk specific gravity (Gmb) per ASTM D2726. Theoretical maximum specific gravity (Gmm) of the loose mix is measured at the estimated OBC using the rice method per ASTM D2041. Air voids (Va), VMA, and VFB are calculated for each binder content. These volumetric properties are plotted against binder content to assess compliance with MoRTH limits.
Marshall Stability & Flow Test
Day 5Specimens are conditioned in a water bath at 60 +/- 1 degrees C for 30-40 minutes. Each specimen is then placed in the Marshall testing head and loaded at a deformation rate of 50.8 mm/min. The maximum load at failure is recorded as Marshall stability (kN), and the corresponding deformation is recorded as flow (mm). For MoRTH compliance, stability must be >= 9.0 kN and flow must be 2-4 mm for DBM and BC layers.
OBC Determination & Retained Stability
Day 5-6Stability, flow, unit weight, air voids, VMA, and VFB are plotted against binder content. The Optimum Binder Content is selected as the binder percentage at 4% air voids (or the average of binder contents at maximum stability, maximum unit weight, and target air voids, per MS-2). A retained stability test is conducted by comparing the Marshall stability of specimens immersed in water at 60 degrees C for 24 hours against standard 30-minute conditioned specimens — the ratio must be >= 75%.
Report Generation & JMF Certification
Day 6-7The final mix design report includes aggregate characterisation results, JMF with blending proportions, all volumetric and Marshall test data at each binder content, graphical plots, recommended OBC, and retained stability results. For SMA mixes, drain-down test results are also included. The NABL-accredited report serves as the certified Job Mix Formula for hot-mix plant production and is delivered in both hard copy and digital format.
Where Bituminous Mix Design Is Used
Detailed Information
-
Bituminous Macadam (BM)
- Bituminous Macadam (BM)is commonly used for the base course of road construction. It provides a stable foundation for the subsequent surface layers.
- Components:
- Bitumen: The bitumen used in BM typically has a penetration grade of 60/70. The content of bitumen in the mix generally ranges between 5% and 4.5%by weight of the total mix. The bitumen serves as the binder that holds the aggregates together.
- Aggregates: The aggregates are usually a combination of coarse and fine aggregates. The coarse aggregates, typically ranging from 10mm to 20mm, provide strength and stability, while fine aggregates fill the gaps between larger particles.
- Filler: Filler materials such as hydrated lime, cement, or fly ash may be added to enhance the stability of the mix, improve bonding, and reduce air voids.
- Marshall Stability Test:
- Objective: To determine the stability (resistance to deformation) and flow (deformation under load) of bituminous mixtures.
- Test Procedure: A compacted specimen of the bituminous mix is subjected to a standard load at 60°C. The stability is the maximum load that the specimen can withstand before failure. Flow measures the deformation that occurs under the load.
- Criteria: A minimum stability of 8 kNand a flow value of 2 to 4 mm is typically considered ideal for BM mixes.
- Reference: IS 1201 – 1978 (Methods for testing bituminous materials).
- Gradation Test:
- Objective: To determine the size distribution of aggregates, which affects the compactness, stability, and durability of the mix.
- Test Procedure: The sample of aggregates is passed through a series of sieves with known aperture sizes. The amount of material retained on each sieve is weighed, and the gradation curve is plotted.
- Reference: IS 2386 (Part 1) – 1963 (Methods for testing aggregates).
- Criteria: The aggregate grading must meet the prescribed limits for coarse and fine aggregates to ensure good performance and durability.
- Bitumen Content Test:
- Objective: To determine the percentage of bitumen in the mix, which affects its workability, adhesion, and performance.
- Test Procedure: The bitumen content is determined by heating a sample of the mix to remove the bitumen and calculating the percentage of bitumen by weight.
- Reference: IS 1203 – 1978 (Methods for testing bitumen).
- Criteria: The content of bitumen should fall within the range of 5% to 4.5%for BM.
- Bulk Density and Specific Gravity Test:
- Objective: To determine the compactness and void content of the mix, as well as the specific gravity of the aggregates used.
- Test Procedure: The compacted mix is weighed in both its dry state and submerged in water to calculate its bulk density and specific gravity.
- Reference: IS 2386 (Part 3) – 1963 (Methods for testing aggregates).
- Criteria: A high bulk density ensures the mix has good compaction, reducing voids and enhancing stability.
-
Dense Bituminous Macadam (DBM)
- Dense Bituminous Macadam (DBM)is an advanced mix compared to BM, offering better durability, higher stability, and superior performance under heavy traffic conditions.
- Components:
- Bitumen: DBM typically uses 0% to 5.0%bitumen by weight, often using higher penetration grade bitumen (60/70 or 80/100).
- Aggregates: The aggregate grading is finer compared to BM. DBM requires a more uniform blend of coarse and fine aggregates, ensuring a dense mix with minimal air voids.
- Filler: As with BM, fillers such as lime or cement are used to improve bonding and reduce voids in the mix.
- Marshall Stability and Flow Test:
- Objective: To determine the stability and flow of DBM, similar to BM but with higher bitumen content and improved aggregate grading.
- Reference: IS 1201 – 1978.
- Criteria: Stability of 9 to 14 kNand flow value of 2 to 4 mm are generally acceptable for DBM.
- Aggregate Impact Value (AIV) Test:
- Objective: To assess the toughness and resistance of the aggregates to impact.
- Test Procedure: Aggregates are subjected to a standardized number of impacts, and the percentage of material that fails to pass through a sieve is calculated.
- Reference: IS 2386 (Part 4) – 1963.
- Criteria: Lower AIV indicates better resistance to crushing and impact, improving the overall durability of the mix.
- Skid Resistance Test:
- Objective: To evaluate the ability of the surface to resist skidding and ensure road safety.
- Test Procedure: A standardized vehicle tire is used to simulate vehicle movement on the road surface, and the skid resistance is measured.
- Reference: IS 11059 – 1984.
- Criteria: A minimum skid resistance value of 50 BPN (British Pendulum Number)is generally required.
- Void Content Test:
- Objective: To determine the air voids in the compacted mix, which affects the durability, strength, and moisture resistance of the mix.
- Test Procedure: The void content is measured by determining the volume of air pockets in a compacted sample.
- Reference: IS 2386 (Part 3) – 1963.
- Criteria: The void content should typically be in the range of 4% to 6%for optimum performance.
-
Bituminous Concrete (BC)
- Bituminous Concrete (BC)is typically used for the wearing course due to its superior smoothness, strength, and durability.
- Components:
- Bitumen: BC requires higher bitumen content than BM or DBM, usually 0% to 6.0%by weight. Modified or polymerized bitumen is often used for superior performance.
- Aggregates: A blend of coarse and fine aggregates with higher fine aggregates is used to provide a smooth, dense surface. The aggregate grading is carefully controlled to provide the required stability.
- Filler: Filler materials, like hydrated lime or cement, are used to improve the cohesion between aggregates and reduce voids.
- Marshall Stability and Flow Test:
- Objective: To assess the stability and flow of BC under load.
- Reference: IS 1201 – 1978.
- Criteria: Stability should be 12 kN or higher, and the flow should fall within 2 to 4 mm.
- Wheel Tracking Test:
- Objective: To measure the rutting resistance of the mix by simulating traffic loading.
- Test Procedure: The specimen is subjected to repeated wheel loads at 60°Cto simulate the effect of traffic on the mix.
- Reference: ASTM D 7240 (Standard Guide for Wheel Tracking).
- Criteria: Low rut depth indicates higher resistance to deformation, with a rutting depth of less than 10 mmconsidered ideal.
- Density and Compaction Test:
- Objective: To ensure proper compaction, which influences the durability and strength of the mix.
- Test Procedure: The mix is compacted in a mold, and the density is measured to assess compaction.
- Reference: IS 2386 (Part 3) – 1963.
- Criteria: The density should be maximized to minimize air voids and improve resistance to wear.
- Water Sensitivity Test:
- Objective: To assess the moisture susceptibility of the BC mix and determine how it behaves under wet conditions.
- Test Procedure: Samples of BC are immersed in water, followed by a Marshall Stability test to evaluate the mix’s performance after water exposure.
- Reference: IS 6241 – 1971.
- Criteria: The mix should show minimal reduction in stability after immersion, demonstrating resistance to moisture-induced damage.
-
Stone Matrix Asphalt (SMA)
- Stone Matrix Asphalt (SMA)is designed for high-load, heavy-traffic roads due to its superior rutting resistance, durability, and high binder content.
- Components:
- Bitumen: SMA generally requires a high bitumen content, ranging from 0% to 7.5%by weight, often using polymer-modified bitumen for enhanced performance.
- Aggregates: SMA requires a higher proportion of coarse aggregates, ensuring that the mix has a dense stone skeleton. A significant proportion of filler material is also used.
- Filler: The higher proportion of filler ensures better binder retention, improving the mix's stability.
- Marshall Stability Test:
- Objective: To evaluate the stability of SMA under heavy traffic loads.
- Reference: IS 1201 – 1978.
- Criteria: Stability values typically range from 16 kN to 18 kNor higher for SMA mixes.
- Rutting Test (Wheel Tracking Test):
- Objective: To determine the rutting resistance under repeated traffic loads at high temperatures.
- Test Procedure: The mix is subjected to repeated loading at a temperature of 60°C, and the rut depth is measured.
- Reference: ASTM D 7240.
- Criteria: The rut depth should be less than 5 mm, indicating good resistance to rutting.
- Void in Mineral Aggregate (VMA):
- Objective: To determine the volume of air voids in the compacted mix, which impacts its durability.
- Test Procedure: The VMA is calculated by measuring the volume of air voids and dividing it by the total volume of the sample.
- Reference: ASTM D 3203.
- Criteria: Higher VMA values are typically desired for SMA, contributing to better performance under heavy traffic.
- Moisture Susceptibility Test:
- Objective: To assess the ability of the SMA mix to resist moisture damage and stripping.
- Test Procedure: The sample is immersed in water and then tested for stability after exposure.
- Reference: IS 6241 – 1971.
- Criteria: Minimal loss in stability indicates high resistance to moisture damage, which is critical for SMA's performance.
Conclusion of Bituminous Mix Design
The design mixes for Bituminous Macadam (BM), Dense Bituminous Macadam (DBM), Bituminous Concrete (BC), and Stone Matrix Asphalt (SMA) play a crucial role in modern pavement engineering. Each layer is meticulously designed to address specific functional requirements and environmental conditions, ensuring the longevity and safety of road infrastructure.- Bituminous Macadam (BM): Serves as a cost-effective base course with coarse aggregates and moderate bitumen content, designed to provide structural stability for roads with moderate traffic. However, it is less durable compared to other mixes and requires a proper surface course to protect it from weathering and wear.
- Dense Bituminous Macadam (DBM): Acts as a durable base layer for high-traffic roads, offering enhanced resistance to deformation and cracking. Its denser composition minimizes voids, which reduces water ingress, a primary cause of road failure.
- Bituminous Concrete (BC): Designed for surface layers, BC ensures smoothness, skid resistance, and durability. Its fine grading and high bitumen content provide superior performance under heavy traffic loads and adverse weather conditions.
- Stone Matrix Asphalt (SMA): A premium mix that excels in rutting resistance and durability, SMA is particularly suitable for highways and roads experiencing heavy traffic and extreme conditions. Its stone skeleton structure, coupled with high binder content, offers exceptional performance in terms of stability and fatigue resistance.
- Marshall Stability and Flow Testsevaluate the load-bearing capacity and deformation characteristics.
- Wheel Tracking Testsmeasure rutting resistance under simulated traffic conditions.
- Aggregate Impact, Gradation, and Specific Gravity Testsensure the durability, quality, and compatibility of materials.
- Moisture Susceptibility Testscheck the resistance of mixes to water damage, a critical factor for long-lasting pavements.
- Enhance Pavement Life: Reduce maintenance costs by minimizing failures such as rutting, cracking, and potholing.
- Improve Traffic Safety: Provide skid-resistant surfaces and smooth rides, reducing accidents.
- Support Sustainability: Optimized material usage and the inclusion of reclaimed asphalt pavement (RAP) in mixes can reduce resource consumption and environmental impact.
- IS 1201 – 1978 (Marshall Stability Test)
- IS 2386 (Part 1-6) – 1963 (Aggregate Testing)
- IS 6241 – 1971 (Moisture Susceptibility Test)
- ASTM D 3203 (Void in Mineral Aggregate)
- ASTM D 7240 (Wheel Tracking Test)
Why Choose NKMPV for Bituminous Mix Design?
NABL Accredited Results
Our Marshall mix design reports carry NABL accreditation (ISO/IEC 17025:2017), accepted by NHAI, state PWDs, independent engineers, and hot-mix plant auditors without additional verification.
All Layer Types Covered
We design mixes for BM, DBM (Grading 1 and 2), BC (Grading 1 and 2), and SMA in a single laboratory setup — no need to engage separate labs for different layer types on your project.
Complete Aggregate Characterisation
Every mix design includes full aggregate testing — gradation, specific gravity, Los Angeles abrasion, flakiness, elongation, stripping, and water absorption — eliminating the need for separate aggregate test orders.
24-Specimen Water Bath Capacity
Our thermostatically controlled water bath holds 24 specimens simultaneously, enabling us to test all binder content levels and retained stability specimens in a single conditioning cycle — faster results for your project.
Hot-Mix Plant Coordination
We work directly with hot-mix plant operators to ensure the laboratory JMF translates effectively to plant production, including mixing temperature, compaction temperature, and aggregate stockpile management recommendations.