As a civil engineer with over 25 years of experience working with asphalt materials and roadway construction, I am often asked to explain the key differences between asphalt concrete and bituminous concrete. While the terms are sometimes used interchangeably, some distinct variations in their composition and usage are important to understand. In this article, I will provide an overview of asphalt and bituminous concrete materials, compare their key characteristics, and discuss the optimal applications for each pavement type.
Differences Between Asphalt and Bitumen
From my 25+ years working with asphalt and bituminous materials in pavement construction, here are the key differences between asphalt concrete and bitumen:
| Parameter | Asphalt Concrete | Bitumen |
|---|---|---|
| Composition | Well-graded aggregates + engineered asphalt cement binder | Aggregate + basic bitumen binder |
| Layer Thickness | 25-40 mm typically | 10-20 mm typically |
| Lifespan | 20+ years | 5-10 years |
| Surface Characteristics | Smooth, skid resistant | Loose fragments, more friction |
| Fuel Efficiency | Lower rolling resistance improves fuel economy | Higher friction reduces Fuel Efficiency |
| Permeability | Impermeable – does not leach | Can leach into soil and groundwater |
| Temperature Sensitivity | Performs well across typical temperature range | Softens at high temperatures |
| Installation Cost | Higher initial cost | Lower initial cost |
| Maintenance | Lower long-term cost with periodic maintenance | Requires more frequent maintenance and repairs |
Asphalt Concrete vs. Bitumen – Detailed Comparison
| Parameter | Asphalt Concrete | Bitumen |
|---|---|---|
| Production Process | Hot mix – heated and precision-engineered | Variable production methods |
| Placement Method | Laid hot and compacted | Variable methods including spraying |
| Curing Time | Fast cooling and curing | Slower curing depending on the application |
| Mix Consistency | Consistent, engineered mixture | Variable consistency |
| Environmental Resistance | Withstands weathering, oxidation | More prone to environmental damage |
| Optimal Use | Structural layers like roads | Surface treatments mostly |
| Repairability | Can be overlaid; patches blend in | Repairs are more noticeable |
| Traffic Volume | Withstands any traffic level | Only low to moderate traffic |
| Viscosity | Asphalt cement viscosity can be controlled | Wide variability in bitumen viscosity |
To summarize, asphalt concrete provides consistent engineering, quality control, durability, and performance across a wide range of parameters. It is clearly the superior material for major structural paving projects. Bitumen offers variability and economy for some thinner surfacing applications.
As an experienced civil engineer, I recommend asphalt concrete over bitumen for most structural pavement applications like roads and parking lots. The precisely engineered composition of aggregates and asphalt cement in asphalt concrete provides a stronger, longer-lasting pavement surface.
While bitumen can be used for some thin surface treatments, its durability is lower compared to asphalt concrete. The smooth, impermeable surface of asphalt concrete improves safety, reduces tire wear noise, and increases fuel efficiency – critical factors for roadways. And asphalt concrete’s lifespan of 20+ years minimizes life cycle costs with proper periodic maintenance.
For major projects, the higher initial cost of asphalt concrete is offset by lower maintenance expenses and extended pavement life compared to bitumen. Asphalt concrete’s superior engineering makes it the best choice where performance and durability are priorities.
Asphalt vs Bituminous Concrete: Design Considerations
| Design Aspect | Asphalt Concrete | Bituminous Concrete |
|---|---|---|
| Step-Back Distances | Precise calculations required to transition lanes | Less stringent requirements for temporary surfaces |
| Adapted Circulation Flow | Engineered for smooth, continuous traffic flow | May require circulation adaptations during application |
| Structural Reconfiguration | Existing structural sections must be evaluated | Less involved structural analysis needed |
| Traffic Flow | Maintains consistent capacity; minimal disruptions | Reduced lanes or diversions may be required |
| Material Staging Areas | Large equipment and material staging areas needed | Typically smaller equipment requirements |
| Inspection Checklists | Extensive quality control testing and inspection | Less stringent inspection requirements |
As an experienced civil engineer, I recommend asphalt concrete for most structural paving projects because it requires more involved design, traffic control planning, materials coordination, quality control, and structural considerations. The precise engineering of asphalt concrete necessitates greater attention to detail during design and construction compared to basic bituminous surfacing applications
What is Asphalt Concrete?
Asphalt concrete, also known as bituminous concrete, is a composite material commonly used in pavement construction. It consists of mineral aggregate bound together with asphalt cement, a dark brown or black petroleum-based substance. The aggregate gives the asphalt concrete its strength and stability, while the asphalt cement binds it together into a cohesive whole.
The most commonly used type of asphalt concrete is hot mix asphalt (HMA). This is produced by heating the asphalt cement to decrease its viscosity, then mixing it with dried aggregate in a mixing facility. Hot mix asphalt concrete is appropriately named because it is mixed and placed at high temperatures.
Composition of Asphalt Concrete
Asphalt concrete contains:
- Aggregate – This makes up over 90% of asphalt concrete by weight. The aggregate should be high quality crushed stone, gravel, or sand. It provides the load-bearing component and gives the asphalt concrete its stability. Common aggregate sizes used are 3/8 to 1 inch.
- Asphalt Cement – Usually makes up 4-8% of the asphalt concrete mix. This petroleum-based binder comes from the residue left after crude oil is refined into gasoline and other fuels. Asphalt cement is a dark, sticky substance that holds the aggregate together when compacted.
- Additives – Small amounts of additives may be included to modify the properties of the asphalt concrete. Polymer modifiers can be added to improve elasticity and durability. Anti-stripping agents help prevent water damage. Fillers like stone dust may be used to improve cohesion.
The exact proportions, grade of asphalt cement, and aggregate specifications are determined by the required pavement performance criteria. Asphalt concrete can be engineered and designed to withstand specific traffic loads and environmental conditions.
Applications of Asphalt Concrete
The primary use of asphalt concrete is in flexible pavement construction, including:
- Roads
- Parking lots
- Driveways
- Airfields
- Walking trails
Asphalt concrete provides a smooth, durable driving surface that is versatile enough for a wide range of applications. It can be placed over any type of base material to create a paved surface. Asphalt concrete is especially suited for road construction because it is economical, can be paved quickly, and is easy to repair.
The hot mix asphalt concrete placement process allows flexibility in working conditions. It can be placed in cold weather and does not require a long curing time like concrete. Traffic can drive on new asphalt concrete pavements as soon as it has cooled and compacted.
What is Bituminous Concrete?
Bituminous concrete is a broad term used to describe any composite paving material made with a bitumen binder. This encompasses a wide variety of mixture designs used in asphalt paving. Bituminous comes from the Latin word bitumen, referring to naturally occurring asphaltic substances like asphalt or tar.
All asphalt concrete is bituminous, but not all bituminous concrete is considered asphalt concrete. The term bituminous concrete may refer to seal coats, surface treatments, and asphalt emulsion applications in addition to hot mix asphalt. However, when it comes to structural pavement layers, bituminous concrete is essentially synonymous with asphalt concrete.
Key Differences Between Asphalt and Bituminous Concrete
While bituminous concrete is a more general term, there are a few key differences between traditional hot mix asphalt concrete and other bituminous pavement materials:
- Composition – Asphalt concrete contains well-graded, high quality mineral aggregates. Some bituminous applications like seal coats have limited aggregates. Emulsified asphalt mixes also contain water.
- Consistency – Asphalt concrete has a stable, consistent mixture that is engineered to specification. Bituminous seal coats and surface treatments have wide variability in application.
- Structure – Asphalt concrete provides structural strength as part of a pavement system. Some bituminous applications like fog seals are non-structural surface treatments.
- Usage – Asphalt concrete is primarily used for structural pavement layers. Bituminous materials may be used for surface treatments, waterproofing, and a range of specialty applications.
So in summary, all asphalt concrete fits under the umbrella of bituminous concrete, but not all bituminous products meet the composition and consistency standards to be considered asphalt concrete mix for structural paving purposes. Asphalt concrete is a high quality, precisely engineered bituminous paving material.
Asphalt Concrete vs Bituminous Concrete: Safety Comparison
| Safety Factor | Asphalt Concrete | Bituminous Concrete |
|---|---|---|
| Skid Resistance | Excellent – uniform surface provides good traction | Fair – loose fragments reduce skid resistance |
| Visibility | Good – uniform black color provides good visibility at night | Fair – loose chips can temporarily reduce visibility after application |
| Noise | Low – very smooth surface minimizes tire noise | Moderate – loose fragments increase noise from tire friction |
| EVENNESS | Excellent – can be paved to a smooth, even surface | Fair – some applications leave an uneven surface |
| Repairs | Seamless repairs maintain smooth surface | Repairs may leave uneven patches |
| Rutting Resistance | Excellent – distributed loads minimize rutting | Poor – susceptible to rutting from concentrated loads |
| Cracking Resistance | Excellent – flexible, resistant to cracks | Poor – more prone to cracking over time |
Optimal Use Cases
Asphalt and bituminous concrete each have optimal applications based on their composition and characteristics:
Asphalt Concrete Best Uses:
- Structural pavement layers for roads, parking lots, driveways, etc.
- Any application requiring a thick (over 2 inches), stable paving material
- Areas with heavy traffic loads or environmental stresses
- Places where durability and low maintenance are priorities
Bituminous Concrete Best Uses:
- Surface treatments like fog seals, chip seals, slurry seals
- Waterproofing layers and vapor barriers
- Specialty applications like tennis courts or runways
- Thin pavement overlay or leveling course
- Temporary patches or low-traffic areas
My Professional Insights
While asphalt concrete and bituminous concrete are often confused as interchangeable terms, there are important differences between these two paving materials. Asphalt concrete is a precisely engineered composite of aggregates and asphalt cement that provides structural integrity and durability. Bituminous concrete is a more general term for any pavement material made with a bituminous binder, which encompasses a wide variety of asphalt and tar-based products beyond just hot mix asphalt concrete.
Understanding these key differences allows civil engineers like myself to select the optimal paving material for each application, based on traffic, environment, budget and performance requirements. With over 25 years of experience working with asphalt and bituminous materials, I can recommend the right pavement solution for each unique project.
Through this article, I have aimed to provide a helpful overview comparing asphalt concrete and bituminous concrete materials. Please feel free to reach out if you have any other questions!
About the Author
Steve Axton is a licensed civil engineer with over 25 years of experience specializing in asphalt materials, specifications, and roadway construction. He has worked on paving projects ranging from highways to commercial parking areas throughout his career. Steve stays up to date on the latest technologies and best practices in asphalt concrete and bituminous materials to provide optimal, cost-effective pavement design solutions for his clients. He is passionate about sharing his extensive knowledge and experience to help educate others in the engineering and construction industries.
Common Concerns About Asphalt Concrete and Bituminous Concrete
What is the main difference between asphalt concrete and bituminous concrete?
The main difference is that asphalt concrete is an engineered composite material with specific proportions of well-graded aggregates and asphalt cement binder. Bituminous concrete is a more general term for any paving material made with a bitumen binder, which has a wider variability.
Why is asphalt concrete better for heavy-traffic areas?
Asphalt concrete is designed and engineered specifically to withstand heavy traffic loads. The aggregates interlock and the asphalt cement binds them into a strong, durable, weather-resistant pavement.
Can bituminous concrete be used for structural road paving?
While bituminous concrete can refer to any asphalt or tar pavement, typically it does not have the precise mixture design and quality control necessary for heavy-duty structural paving layers on major roads. Asphalt concrete is preferred.
What type of bituminous concrete is optimal for driveways?
For most residential driveways, a standard hot mix asphalt concrete will provide an affordable, low-maintenance pavement with good durability. Asphalt concrete driveways are designed for moderate traffic loads.
Why does asphalt concrete last longer than some bituminous products?
Asphalt concrete pavements are more resistant to cracking, rutting, and weathering because the aggregates strongly bond together with the properly formulated asphalt cement. Some bituminous seal coats have lower durability.
Can polymer-modified asphalt concrete be considered a bituminous concrete?
Yes, polymer-modified asphalt is still asphalt concrete, which falls under the umbrella of bituminous concrete materials. The polymers improve the performance characteristics.
How are open-graded and dense-graded asphalt concretes different?
Open-graded asphalt concrete contains little fine aggregate, which leaves air voids for drainage. Dense-graded asphalt concrete is designed with a fuller gradation of aggregates that form a tighter pavement.
Why are some asphalt emulsions classified as bituminous materials instead of asphalt concrete?
Asphalt emulsions contain water, require different mixing and curing processes, and result in different pavement performance than hot mix asphalt concrete.
For cold climates, which is better – asphalt concrete or bituminous concrete?
Asphalt concrete holds up best to freeze-thaw cycles in cold climates. The aggregates and asphalt cement are less prone to cracking compared to some bituminous products.
Can warm-mix asphalt concrete be considered bituminous concrete?
Yes, warm-mix asphalt concrete is still fundamentally an asphalt concrete mix produced at lower temperatures. It has similar properties to hot mix asphalt concrete.
What type of bituminous concrete is used for tennis courts?
Acrylic-coated asphalt concrete provides a durable, flexible surface for tennis courts and similar recreational applications. These specialty bituminous mixes contain additives.
Why is compaction important for asphalt concrete?
Proper compaction of hot mix asphalt concrete removes air voids, maximizing pavement density and strength. Insufficient compaction can reduce asphalt concrete durability.
Is tar considered a type of bituminous material?
Yes, tar and asphalt are both bituminous binders derived from petroleum processing. Coal tar was used more historically in bituminous concrete, while asphalt cement dominates today.
For parking lots, should bituminous or asphalt concrete be used?
Asphalt concrete is preferred for parking lot construction to provide a durable, low-maintenance surface able to withstand moderate traffic loads from vehicles. The smooth surface and flexibility of asphalt concrete fits parking lot needs.
