Bitumen in Construction: Types, Grades, Uses, Tests, Properties and Selection Guide

Bitumen is one of the most important binder materials used in modern construction, especially in roads, highways, airport pavements, bridge decks, roofing systems, basements, foundations, industrial pavements, waterproofing works and pavement recycling. It is the black, sticky and water-resistant material that helps bind aggregates together in asphalt pavement and protects many structures from moisture damage.

In simple words, bitumen works like a flexible glue in construction. It coats stone aggregates, binds them into a compacted asphalt layer, seals surface voids, resists water entry and allows pavement layers to tolerate small movements caused by traffic and temperature change. But in professional engineering, bitumen is not selected only because it is black, sticky or cheap. It is selected according to grade, penetration value, viscosity, temperature performance, traffic load, climate, ageing resistance, aggregate compatibility, application method and project specification.

A normal city road may use 60/70 penetration grade bitumen or VG-30 bitumen. A hot-climate highway may need VG-40, polymer modified bitumen or a high-temperature Performance Grade binder. A cold-region road may need a softer binder or a low-temperature PG binder. Road maintenance often uses bitumen emulsion, pavement recycling may use foamed bitumen, and roofing or basement waterproofing may use oxidized or polymer-modified bitumen membranes.

This page explains bitumen in construction in a practical, research-based and engineering-focused way so that students, engineers, contractors, buyers and site professionals can understand how bitumen is selected, tested, used and controlled on real projects.

What Is Bitumen?

Bitumen is a dark black or brown, highly viscous, adhesive and waterproof material mainly obtained from crude oil refining. It is the heavy residue left after lighter petroleum fractions are separated. In construction, bitumen is mainly used as a binder, sealant, waterproofing material and protective coating.

A practical definition is:

Bitumen is a petroleum-derived, thermoplastic and water-resistant construction binder used for asphalt paving, road surfacing, waterproofing, roofing, sealing and protective coating.

The word thermoplastic is important. It means bitumen softens when heated and hardens when cooled. This behavior makes it useful in road construction because it can be heated at the asphalt plant, mixed with aggregates, transported to site, laid by a paver and compacted by rollers. After cooling, it helps form a durable asphalt pavement layer.

Bitumen is used in construction for several important functions. In asphalt pavement, it coats and binds aggregates. In waterproofing, it creates a water-resistant barrier. In maintenance, it seals cracks, bonds pavement layers and protects old road surfaces. In industrial works, it can be used as a protective coating for underground structures, pipes and concrete surfaces.

The main point is simple: bitumen is not just a raw material; it is a performance-based construction binder. Its success depends on choosing the right type and grade for the right job.

Bitumen vs Asphalt vs Tar

Many people use the words bitumen, asphalt and tar as if they mean the same thing. Technically, they are different.

In many countries, bitumen means the binder and asphalt means the final road mixture. In North American terminology, the binder may also be called asphalt binder or asphalt cement.

A simple way to remember the difference is:

Bitumen is the binder. Asphalt is the road mix. Tar is a different historical material.

This difference matters on real construction projects. A buyer ordering bitumen is not ordering ready asphalt mix. A contractor laying asphalt is not laying pure bitumen. A project specification may separately define the binder grade, asphalt mix type, aggregate gradation, filler content, layer thickness, compaction requirement and quality control tests.

Why Bitumen Is Important in Construction

Bitumen is still widely used because construction projects need materials that can handle traffic load, moisture, heat, cold, ageing, vibration and movement. Roads face repeated wheel loads, braking force, rainwater, sunlight and temperature changes. Bridges face deck movement and water penetration. Airport pavements face heavy aircraft loads and high tire pressure. Roofs and basements need long-term water protection.

Bitumen performs well in these situations because it can bind, seal, flex and protect. It gives asphalt pavement its cohesion and waterproofing ability. It allows road surfaces to be repaired, overlaid, milled and recycled. It can also be modified with polymers, crumb rubber, rejuvenators and other additives when ordinary paving grade bitumen is not enough.

The quality of bitumen directly affects pavement life. If the binder is too soft for a hot and heavily loaded road, rutting and bleeding may occur. If the binder is too stiff for a cold region, thermal cracking can develop. If the bond between bitumen and aggregate is weak, water can cause stripping, ravelling and potholes.

This is why bitumen selection is an engineering decision, not a visual decision.

How Bitumen Works in Road and Construction Materials

Bitumen performance depends on several connected properties. A good binder must be workable during mixing and compaction, but stable during service. It must bond with aggregate, resist water, tolerate temperature changes and remain durable as it ages.

Adhesion with Aggregate

Adhesion is the bond between bitumen and aggregate. Good adhesion keeps the binder attached to stone particles even when water and traffic are present. Poor adhesion can lead to stripping, ravelling, loose aggregate and potholes.

Adhesion depends on aggregate type, surface cleanliness, dust, moisture, binder chemistry, temperature and anti-stripping additives. Wet or dusty aggregates are a common reason for poor coating and early pavement failure.

Cohesion inside the Binder

Cohesion is the internal strength of bitumen. It helps the binder resist tearing, deformation and aggregate loss. A binder with poor cohesion may not hold the asphalt mix together properly under traffic.

In hot climates, weak or overly soft binders can contribute to rutting. In cold climates, binders that become too stiff may contribute to cracking.

Viscosity and Workability

Viscosity means resistance to flow. During mixing, bitumen must be fluid enough to coat aggregates. During compaction, it must remain workable enough to help the asphalt achieve proper density. During service, it must be stiff enough to resist deformation.

This is why viscosity-controlled binders, such as VG grades, are important in hot mix asphalt work.

Temperature Sensitivity

Bitumen becomes softer in heat and harder in cold. This is one of the biggest reasons grade selection matters.

A harder binder alone does not guarantee better performance. Rutting resistance also depends on aggregate skeleton, air voids, binder content, layer thickness, drainage and compaction quality.

Key Properties of Bitumen

A bitumen sample may look good but still fail if its properties do not match the project requirement. Engineers test bitumen to understand hardness, heat response, flow, flexibility, safety, ageing and rheological performance.

A good project specification should not only say “use good quality bitumen.” It should clearly define the grade, test method, acceptance limits, sampling frequency, delivery temperature, storage requirement and rejection criteria.

Main Types and Grades of Bitumen Used in Construction

Bitumen is available in several types and grading systems. The correct choice depends on project use, climate, traffic, construction method and required performance.

Penetration Grade Bitumen

Penetration grade bitumen is classified by the depth a standard needle penetrates into a bitumen sample under controlled temperature, load and time. The result is measured in tenths of a millimeter. Lower penetration value means harder bitumen. Higher penetration value means softer bitumen.

Penetration grade is easy to understand and still widely used. However, penetration value alone does not fully predict rutting, fatigue cracking or low-temperature performance. For heavy traffic, extreme climate or high-value projects, viscosity grade, performance grade or modified binders may provide better control.

Viscosity Grade Bitumen

Viscosity Grade bitumen, commonly called VG bitumen, is classified by flow behavior. It gives better control of high-temperature performance than penetration grading alone.

VG-30 is commonly used for general paving in many warm regions. VG-40 is selected where heavy traffic, slow-moving loads or high pavement temperatures increase rutting risk.

VG grading is strong for high-temperature flow control, but it does not fully solve every cold-climate issue. In extreme climates, performance grading can provide more temperature-specific selection.

Performance Grade Bitumen

Performance Grade bitumen, or PG binder, is a temperature-based grading system. It is commonly written as PG 58-22, PG 64-22, PG 70-10 or PG 76-22.

The first number represents high-temperature performance. The second number represents low-temperature performance. For example, PG 64-22 is designed for high pavement temperature performance around 64°C and low-temperature performance around -22°C.

AASHTO M 320 covers performance-graded asphalt binders, and its grading designations are related to maximum and minimum pavement design temperatures. (MATEST Russia)

PG binder testing commonly uses DSR, BBR, RTFO, PAV and MSCR to evaluate rheology, ageing, low-temperature stiffness and repeated stress recovery. FHWA’s asphalt binder PG testing material also links PG binder verification with AASHTO M 320, R 29 and related test methods. (Federal Highway Administration)

Polymer Modified Bitumen

Polymer Modified Bitumen, or PMB, is bitumen improved with polymers to increase elasticity, rutting resistance, fatigue resistance and durability.

PMB is commonly used in airports, bridges, expressways, intersections, bus lanes, toll plazas, heavy truck corridors and waterproofing membranes. It costs more than ordinary bitumen but can improve long-term performance where the pavement is under high stress.

Crumb Rubber Modified Bitumen

Crumb Rubber Modified Bitumen, or CRMB, uses processed waste tyre rubber to improve flexibility, elasticity and durability. It can support sustainable pavement construction by reusing waste tyres.

CRMB may be used in overlays, urban roads, flexible pavements, heavy-duty surface layers and sustainability-focused road projects. However, it requires proper blending, storage stability control, temperature management and quality testing. If handled poorly, rubber separation and inconsistent binder behavior may occur.

Bitumen Emulsion

Bitumen emulsion is a mixture of bitumen, water and emulsifying agent. It allows bitumen to be applied at lower temperatures, which makes it useful for maintenance and surface treatment works.

Bitumen emulsion is used for tack coat, prime coat, fog seal, slurry seal, microsurfacing, surface dressing, cold mix, pothole repair and soil stabilization. Its performance depends on weather, surface moisture, aggregate type, curing time and application rate.

Cutback Bitumen

Cutback bitumen is bitumen diluted with solvent to reduce viscosity. It can be used where lower-temperature application is needed, but it has environmental and safety concerns because the solvent evaporates during curing.

Many modern projects prefer emulsions over cutbacks because cutbacks can release volatile organic compounds and create additional fire and health risks. Cutbacks should only be used where local specifications allow them.

Oxidized Bitumen

Oxidized bitumen, also called blown bitumen, is produced by blowing air through hot bitumen. This increases softening point and reduces flow at high temperatures.

Oxidized bitumen is mainly used in roofing membranes, waterproofing sheets, damp-proofing, pipe coating, expansion joints, industrial insulation and protective coatings. It is generally not used as a normal paving binder.

Foamed Bitumen

Foamed bitumen is produced by injecting a small amount of water into hot bitumen. The water rapidly turns into steam and expands the bitumen temporarily into foam. This helps distribute bitumen in cold recycling and stabilization works.

Foamed bitumen is used in cold recycling, full-depth reclamation, base stabilization, pavement rehabilitation and reuse of existing pavement materials. Important parameters include expansion ratio, half-life, moisture content, binder content, aggregate gradation, mixing quality and compaction control.

Natural Bitumen and Specialty Additives

Natural bitumen, such as gilsonite-type materials, and specialty additives are used to improve stiffness, durability, waterproofing or high-temperature performance in selected applications. These materials require compatibility testing and controlled dosage because too much stiffness can create cracking risk.

Bitumen Selection Guide: Which Bitumen Should Be Used Where?

The right bitumen depends on climate, traffic, pavement layer, application method, moisture exposure and performance target. The table below gives a practical selection direction.

For hot and heavily loaded roads, the binder must resist permanent deformation. For cold regions, flexibility and low-temperature cracking resistance become more important. For wet areas, aggregate-binder adhesion and drainage are critical. For recycling work, the binder must be designed with existing aged material, not treated like a completely new mix.

Layer-Wise Use of Bitumen in Road Construction

Bitumen is used in different pavement layers and road treatments. Each layer has a different function, so the same binder or application rate is not suitable everywhere.

Layer bonding is especially important. Poor tack coat application can cause slippage, shoving, delamination and early pavement failure. A good pavement is not only about the top surface; it depends on how all layers work together.

Major Uses of Bitumen in Construction

Road Construction

Bitumen is mainly used in asphalt concrete, dense bituminous macadam, binder course, wearing course and base course. It coats aggregates and helps create a compacted pavement layer that can carry traffic.

Highways and Expressways

Highways need binders that can resist traffic stress, moisture, heat and ageing. Depending on climate and loading, highway projects may use VG-30, VG-40, PMB or PG binders.

Airport Pavements

Airport runways, taxiways and aprons require high-performance binders because aircraft loads, braking stress and tire pressure create severe pavement conditions. PMB and PG binders are often preferred where performance requirements are high.

Bridge Deck Waterproofing

Bridge decks need waterproofing systems that protect concrete and reinforcement from water and chlorides. Modified bitumen membranes are commonly used because they can tolerate movement and provide a continuous barrier.

Roofing and Waterproofing

Oxidized and modified bitumen are used in flat roofs, basements, retaining walls, podium decks, foundations and damp-proof courses. Proper surface preparation, overlap, protection board and drainage are essential for long-term waterproofing.

Industrial Pavements

Ports, container yards, truck terminals, warehouses and logistics parks need bituminous systems that resist slow-moving heavy loads and static pressure. VG-40, PMB or hard grade binders may be used depending on design.

Road Maintenance

Bitumen emulsions and special bituminous products are used for tack coat, prime coat, fog seal, slurry seal, microsurfacing, surface dressing, crack sealing and pothole repair.

Pavement Recycling and Rehabilitation

Foamed bitumen and emulsions are used in cold recycling, full-depth reclamation and base stabilization. FHWA supports the use of recycled highway materials where practical and economical, with the goal of reducing waste, preserving resources and maintaining or improving performance. (Federal Highway Administration)

Step-by-Step Use of Bitumen in Road Construction

Bitumen road construction is a controlled process. A weak step in design, heating, laying or compaction can reduce pavement life.

Step 1: Project Assessment

Engineers first study traffic level, climate, axle loads, subgrade condition, drainage, pavement life and service environment. This information guides binder selection and asphalt mix design.

Step 2: Binder Selection

The binder grade is selected according to project conditions. A normal road may use 60/70 or VG-30. A heavy-traffic or high-temperature road may require VG-40, PMB or a high PG binder.

Step 3: Aggregate Selection

Aggregates must be clean, strong, angular, durable and properly graded. Wet, dusty or weak aggregates can cause poor coating and early failure.

Step 4: Job Mix Formula

The job mix formula defines aggregate gradation, binder content, filler content, air voids, stability, flow, density and volumetric properties. It is the technical recipe for the asphalt mix.

Step 5: Heating and Mixing

Bitumen and aggregates are heated to the required temperature. Overheating can age the binder, while low temperature can reduce coating and compaction quality.

Step 6: Transportation

Hot mix asphalt is transported in clean and insulated trucks to minimize temperature loss and avoid contamination.

Step 7: Laying

A paver spreads the asphalt to the required thickness, slope, camber and level. Continuous paving helps reduce cold joints and weak points.

Step 8: Compaction

Rollers compact the asphalt while it is still hot enough. Proper compaction reduces air voids, improves durability and limits water entry.

Step 9: Quality Control

Quality control includes temperature checks, field density testing, thickness verification, binder content, gradation, smoothness, core samples and surface inspection.

A durable pavement needs correct binder, correct mix, correct temperature, correct compaction and proper drainage.

Bitumen Quality Testing

Bitumen is tested to confirm whether it meets the project specification. These tests help engineers understand hardness, flow, heat response, ageing, flexibility and performance.

Common International Bitumen Test Standards

Different countries and clients may use ASTM, AASHTO, EN, BIS, Austroads or local highway authority standards. The project specification should clearly mention the required test method and acceptance limit.

The Asphalt Institute has also highlighted the rotational viscosity requirement in AASHTO M 320, including the original binder viscosity limit at 135°C, which is important for pumpability and handling of PG binders. (Asphalt Institute)

A strong specification should include:

• Binder grade
• Test standard
• Acceptance limits
• Sampling frequency
• Delivery temperature requirement
• Storage requirement
• Retesting procedure
• Rejection criteria

Asphalt Mix Quality and Strength Tests

Binder testing alone is not enough. A road performs as a complete asphalt mix, not as bitumen alone. Aggregate gradation, binder content, air voids, density and compaction quality all affect performance.

Rutting and fatigue cracking are among the major distresses studied in asphalt pavement performance, and research consistently links pavement behavior to binder properties, aggregate gradation, additives, traffic and mixture design. (UM Research Repository)

Bitumen Acceptance Checklist Before Site Use

Bitumen should not be accepted simply because it arrived on site. It should be accepted only when it matches the project specification.

Document Checklist

Before unloading, site staff should verify supplier name, grade, batch number, certificate of analysis, production date, delivery date, tanker number, quantity, compliance certificate and Safety Data Sheet.

Site Inspection Checklist

The site team should check correct grade labeling, delivery temperature, tanker cleanliness, water contamination, foreign material, unloading safety and storage tank condition. Mixing unknown grades in the same tank should be avoided.

Laboratory Verification Checklist

Depending on project requirements, the laboratory may verify penetration, softening point, viscosity, flash point, water content, elastic recovery, storage stability, DSR, BBR or MSCR.

The site rule should be:

Do not accept bitumen by appearance. Accept it by specification, documentation and test results.

Common Bitumen and Asphalt Failures

Most asphalt failures are not caused by one single issue. They usually result from a combination of wrong binder selection, weak mix design, poor drainage, bad compaction, overheating, water damage or delayed maintenance.

Using more bitumen is not always the solution. Excess binder can cause bleeding and rutting. A durable asphalt pavement needs balanced mix design, suitable binder grade, clean aggregate, controlled temperature and proper compaction.

Causes of Bitumen Failure and How to Prevent Them

Bitumen-related failures are often preventable when quality control starts before construction.

Common causes include wrong binder grade, poor aggregate quality, wet or dusty aggregates, excess binder, insufficient binder, poor drainage, overheating, low compaction temperature, weak tack coat, poor density, inadequate thickness, contamination and delayed maintenance.

Practical prevention includes using harder or modified binders in hot/heavy-traffic areas, softer binders in cold areas, PMB where rutting and fatigue risk is high, dry aggregates, accurate binder content, proper tack coat, correct compaction temperature, good drainage and timely crack sealing.

Good pavement performance begins before construction, not after failure appears.

Storage, Heating, Handling and Safety of Bitumen

Bitumen is often stored and handled hot, so temperature control and worker safety are essential.

Storage Rules

Use clean tanks, prevent water entry, avoid mixing unknown grades, maintain pumps and pipelines, keep sampling points accessible, monitor storage temperature and circulate modified binders when required.

Heating Rules

Heat bitumen only to the required working temperature. Avoid local overheating near heating coils. Do not allow water to enter hot bitumen because it can cause violent foaming and splashing. Follow supplier and project specification limits.

Safety Rules

Workers should use heat-resistant gloves, face shield, eye protection, safety boots and long sleeves. Fire extinguishers should be available near heating and unloading areas. No-smoking zones, proper ventilation, emergency training and Safety Data Sheets are important.

Good handling protects workers, equipment and pavement performance.

Sustainability and Modern Bitumen Technologies

Bitumen is petroleum-based, but asphalt construction can still support sustainability when designed properly. True sustainability means better life-cycle performance, lower waste, efficient material use and safe long-term service.

Reclaimed Asphalt Pavement

Reclaimed Asphalt Pavement, or RAP, uses old asphalt in new pavement. It reduces demand for virgin aggregate and fresh binder. FHWA promotes recycled highway materials where practical and economical, with the goal of reducing waste and preserving natural resources while maintaining performance. (Federal Highway Administration)

Warm Mix Asphalt

Warm Mix Asphalt allows asphalt to be produced and placed at lower temperatures than traditional hot mix asphalt. FHWA notes that the immediate benefit of WMA is reduced energy consumption from heating fuels at the plant. (Federal Highway Administration)

Rejuvenators

Rejuvenators help restore flexibility in aged binder from reclaimed asphalt. They are useful when higher recycled content is used, but dosage must be carefully designed and tested.

Rubberized Asphalt

Rubberized asphalt uses crumb rubber from waste tyres. It can improve flexibility and support waste reuse when properly processed and tested.

Polymer Modified Bitumen

PMB improves rutting resistance, fatigue resistance and durability, especially in heavy traffic and high-temperature pavements.

Bio-Based and Nano-Modified Binders

Bio-based additives and nano-additives are being studied for recycling support, ageing resistance, moisture resistance and durability. These technologies need proper laboratory and field validation before large-scale use.

Low-Carbon Asphalt Approach

A low-carbon asphalt strategy may combine warm mix technology, RAP, efficient plant operation, optimized binder content, local materials, preventive maintenance, long-life pavement design and life-cycle assessment.

A recycled road is not automatically sustainable if it fails early. The best sustainable bitumen project balances durability, recycling, safety, cost, performance and life-cycle impact.

How to Choose the Right Bitumen Supplier

A supplier should be selected by quality, consistency, documentation, logistics and technical support, not only by price.

A good supplier should provide consistent grade quality, complete test certificates, batch traceability, clean tankers, correct delivery temperature, reliable logistics, technical support, third-party testing options and proper packaging.

Important documents include certificate of analysis, batch number, grade confirmation, test report, delivery temperature record, Safety Data Sheet and compliance certificate.

Cheap bitumen can become expensive if it causes rejection, rutting, cracking, water damage or early maintenance.

Expert Comparison Table: Bitumen Types, Grades, Tests, Uses and Limitations

Common Mistakes in Bitumen Construction

Many bitumen failures happen because of simple mistakes that could have been avoided. The most common mistakes are selecting binder only by price, using one grade for every climate, ignoring traffic loading, using wet aggregates, overheating bitumen, applying poor tack coat, using incorrect binder content, accepting poor field compaction, ignoring air voids, using emulsion without curing time, mixing different grades in one tank, skipping lab verification and delaying crack sealing.

A professional project should control bitumen from procurement to placement. Quality should not begin at the road surface; it should begin at specification, supplier selection and material testing.

FAQs About Bitumen in Construction

What is bitumen used for in construction?

Bitumen is used for road paving, asphalt production, waterproofing, roofing, bridge deck protection, basement coating, foundation protection, industrial pavements, maintenance and pavement recycling.

Which bitumen is best for road construction?

For normal roads, 60/70, 80/100, VG-30 or VG-40 may be used depending on climate and traffic. For heavy traffic, PMB or PG binder may be more suitable.

What is the difference between 60/70 and 80/100 bitumen?

60/70 bitumen is harder and is generally used in moderate-to-hot climates and heavier traffic. 80/100 bitumen is softer and is more suitable for moderate or cooler climates and lighter traffic.

What is VG-30 bitumen used for?

VG-30 is widely used in hot mix asphalt for road construction, especially in moderate and hot climate conditions.

What is VG-40 bitumen used for?

VG-40 is used in heavy traffic and high-temperature areas such as intersections, toll booths, bus lanes, truck routes and industrial pavements.

What is Performance Grade bitumen?

Performance Grade bitumen is a temperature-based binder grading system. It classifies binders according to high and low pavement temperature performance.

What is PMB?

PMB means Polymer Modified Bitumen. It improves elasticity, rutting resistance, fatigue resistance and durability.

What is CRMB?

CRMB means Crumb Rubber Modified Bitumen. It uses processed waste tyre rubber to improve flexibility and support sustainable pavement construction.

What is bitumen emulsion?

Bitumen emulsion is bitumen dispersed in water with an emulsifier. It is used for tack coat, prime coat, slurry seal, microsurfacing, surface dressing and maintenance.

Is bitumen waterproof?

Yes, bitumen is water-resistant and widely used in waterproofing. Good surface preparation, correct application thickness, proper overlaps and protection layers are essential.

Can bitumen be recycled?

Yes, bitumen in asphalt pavement can be reused through reclaimed asphalt pavement, cold recycling and full-depth reclamation systems.

Why does asphalt pavement fail?

Asphalt pavement may fail due to wrong binder grade, weak mix design, poor compaction, water entry, poor drainage, overheating, ageing or heavy traffic stress.

Conclusion

Bitumen is not just a black sticky material. It is a performance-based construction binder used in roads, highways, airports, bridges, roofs, basements, industrial pavements, waterproofing systems and recycling works.

Its performance depends on selecting the correct type, grade, test method, application temperature, storage condition and construction process.

A normal road may use 60/70 or VG-30. A hot-climate highway may need VG-40 or a high-temperature PG binder. A cold-region road may need a softer penetration grade or low-temperature PG binder. A heavy-traffic corridor may require polymer modified bitumen. A maintenance project may need emulsion. A recycling project may need foamed bitumen. A roof or basement may need oxidized or modified waterproofing bitumen.

The most important rule is:

Use the right bitumen type, in the right grade, tested by the right method, for the right project condition.

Contact us

Need accurate civil engineering calculations for road materials, asphalt work, concrete quantities or construction cost planning? Use our professional civil engineering calculators to estimate material requirements before starting construction or contact us

References

• Federal Highway Administration, asphalt pavement recycling and reclaimed asphalt pavement resources. (Federal Highway Administration)
• Federal Highway Administration, Warm Mix Asphalt technologies and research. (Federal Highway Administration)
• AASHTO M 320, Performance-Graded Asphalt Binder specification summary. (MATEST Russia)
• FHWA asphalt binder PG testing manual and related AASHTO test references. (Federal Highway Administration)
• Asphalt Institute guidance on AASHTO M 320 rotational viscosity limits. (Asphalt Institute)
• Asphalt pavement performance literature on rutting, fatigue, binder behavior and aggregate structure. (TransResearch Library)