As a civil engineer with over 20 years of experience in asphalt materials and roadway construction, I’ve seen firsthand the most effective techniques for building and maintaining asphalt pavements. In this comprehensive guide, I’ll share the key methods and best practices for constructing, repairing, and enhancing asphalt pavement durability and performance.
Overview of Asphalt Pavement Construction
Asphalt pavement consists of multiple layers of asphalt material laid over a graded aggregate base. The top layer is known as the wearing course, which provides a smooth driving surface and absorbs the impact of traffic loads. Underneath are binder and leveling courses that distribute loads and provide stability.
The asphalt mixture is composed of liquid asphalt binder and graded mineral aggregates. Asphalt binder acts as the glue to hold aggregates together, while aggregates provide the pavement’s strength and structure. An asphalt mixing plant combines the hot asphalt cement and dried aggregates in precise proportions to produce the asphalt mixture, which is then transported to the paving site in haul trucks.
Laying asphalt pavement involves spreading, compacting, and smoothing the hot asphalt mixture with specialized equipment like paving machines, rollers, and vibratory compactors. Proper compaction is essential for achieving pavement density and durability. The pavement is allowed to cool and harden before opening to traffic.
Methods for Repairing Asphalt Pavement
Over time, asphalt pavement deteriorates and must be repaired to maintain a smooth, safe driving surface. Here are the main methods of asphalt pavement repair:
Patching
Patching involves removing the damaged pavement area and placing new asphalt mixture to fill potholes, cracks, raveling, or depressions. The repair area is squared off and the patch material compacted for a permanent fix. Patching extends pavement life at low cost but is a short-term solution.
Crack Filling/Sealing
Filling or sealing cracks with asphalt emulsion or rubberized crack sealer inhibits water intrusion and prevents further cracking. Rout and seal involves widening cracks for maximum sealant effectiveness. Filling small cracks <1/4″ helps maintain pavement integrity.
Pothole Repair
Potholes form through surface wear or base failure. After squaring off the area, compacted hot mix asphalt is placed in 2”+ lifts for deep patches. Temporary cold mixes can be used until hot mixes are available. Pothole repair improves ride quality and safety.
Milling and Resurfacing
Milling off worn pavement and overlaying with 1-2 inches of new asphalt surface course restores rideability and skid resistance. Resurfacing is cost-effective for extensively cracked and oxidized surfaces with sound structural bases.
Full-Depth Repairs
Severely distressed areas with base failures require full-depth removal and replacement of asphalt layers. This comprehensive repair restores pavement structure and surface integrity. It’s often done in preparation for resurfacing.
Heater Scarification
Scarifying involves heating the surface with infrared heaters to soften the top 1⁄2 – 1” layer, then scarifying it to a specified depth. New hot mix is overlaid and compacted. This rejuvenation treatment seals cracks, restores friction, and repairs top-down cracking and raveling.
Best Practices for Asphalt Pavement Construction
Adhering to industry best practices for asphalt paving maximizes pavement quality and long-term performance. Here are my top recommendations:
- Use quality materials – Specify Superpave performance-graded (PG) asphalt binders and aggregates that meet state DOT specifications. Conduct quality control testing on binders and mixes.
- Follow mix design procedures – Develop asphalt mixes meeting Superpave volumetrics for optimal asphalt binder content and aggregate structure. Account for traffic, climate, and pavement use.
- Maintain proper temperatures – Heat asphalt binder, aggregates and mixtures to the required temperatures to achieve workability and coating. Prevent overheating binder.
- Compact thoroughly – Use the specified roller patterns and protocols to achieve target density through all pavement depths. Density testing verifies compliance.
- Execute quality construction – Ensure qualified paving crews, proper equipment, adherence to specifications, and consistent paving speed, thickness, and smoothness.
- Inspect finished product – Perform visual inspections and testing to check for defects. Repair any issues like segregation, lack of compaction, raveling, rutting, etc.
- Limit moisture damage – Take precautions to avoid paving on wet surfaces or exposing fresh pavement to moisture. Use anti-stripping additives as needed.
- Prevent overloading – Enforce load restrictions, especially on new pavements, to prevent permanent deformation from overloading.
Following these best practices minimizes premature pavement distresses and maximizes asphalt pavement life and performance.
Enhancing the Sustainability of Asphalt Pavements
In addition to longevity, asphalt pavements can be designed and constructed to minimize environmental impacts. Here are some key strategies:
- Increase reclaimed asphalt pavement (RAP) usage – Adding RAP reduces the need for virgin materials. Standards allow up to 50% RAP in new pavement mixes.
- Use warm mix asphalt (WMA) – WMA uses additives that allow reduced production and paving temperatures, resulting in lower emissions.
- Consider cool pavement technologies – Highly reflective surface mixtures and porous friction courses mitigate urban heat island effects.
- Improve pavement recycling and reuse – Full-depth reclamation and cold central plant recycling create stabilized base layers from old asphalt.
- Monitor plant emissions – Use baghouse particulate controls, scrubbers, and other measures to limit plant emissions. Switch to cleaner fuels when possible.
- Design for traffic demands – Optimized pavement thickness and stiffness prolongs service life and reduces rehabilitation needs.
- Incorporate recycled components –substituting recycled shingles, glass, slag, tire rubber, and other materials conserves resources in asphalt mixes.
With deliberate planning and design, asphalt pavements can be a sustainable infrastructure solution.
Routine Maintenance Extends Asphalt Pavement Life
Consistent, timely maintenance preserves pavement function, safety, and surface quality for the longest possible time. Recommended routine asphalt pavement maintenance includes:
- Crack sealing – Fill cracks yearly to prevent water intrusion and deterioration. Prioritize wide transverse and alligator cracks.
- Pothole repair – Repair potholes as they occur, especially after freeze-thaw cycles, to protect pavement integrity.
- Patching – Patch isolated deep depressions, and raveling areas, and block cracks frequently to maintain smoothness.
- Surface treatments – Apply fog seals, chip seals, or micro-surfacing every 5-7 years to seal, protect, and refresh the top-wearing surface.
- Drainage maintenance – Clean culverts, storm drains, and ditches regularly to prevent pavement and base saturation.
- Mowing and vegetation control – Mow regularly and remove invasive vegetation to maximize visibility and prevent root damage.
- Striping maintenance – Refresh lane and edge striping every 1-2 years for optimal visibility, especially at night.
- Sweeping – Schedule regular street sweeping to remove debris that could clog drainage and accelerate wear.
Proactive, low-cost maintenance maximizes taxpayer investments in asphalt roads and runways. It effectively slows deterioration rates and extends pavement life at the lowest long term cost.
Types of Asphalt Used in Pavement Construction
There are three main types of asphalt binder used in pavement construction, each with applications based on traffic and climate:
1. Asphalt Cement
Asphalt cement is the basic binder produced from petroleum distillation. It is widely used for lower-traffic pavements and secondary roads. Performance grades span from AC-5 to AC-30 based on viscosity and high-temperature grading.
2. Performance-Graded (PG) Asphalt
PG binders are engineered for superior temperature-related performance. PG grades like PG 64-22 meet specific criteria for high and low pavement temperatures. Polymer modification improves elasticity and durability. PG asphalt is ideal for heavily trafficked roads and extreme climates.
3. Modified Asphalt
Modified asphalts incorporate polymer additives like styrene-butadiene-styrene (SBS), ethylene-vinyl acetate (EVA) or ground tire rubber (GTR) to enhance properties. Added at 4-6%, polymers improve resistance to rutting, cracking, and temperature extremes. Modified asphalts suit high-traffic highways, busy intersections and cold regions.
Understanding asphalt binder grades and modifiers helps engineers select the optimal materials to maximize pavement longevity given traffic volumes and environmental conditions.
Selecting the Best Asphalt for Specific Pavement Uses
Choosing the right asphalt type and grade for the pavement use and conditions is critical for optimum performance. Here are asphalt selections for different applications:
Roadways
For heavily trafficked highways and busy urban streets, polymer-modified PG 70-22 provides maximum rutting resistance and durability. In cold climates, PG 58-34 withstands freezing temperatures and resists thermal cracking. PG 64-28 suits many roads in moderate climates.
Parking Lots
Commercial parking areas often use a polymer-modified PG 64-28 for enhanced cracking resistance under heavy stationary loads. For cold regions, PG 58-34 withstands freeze-thaw and plowing stresses. Low-traffic lots can utilize AC-20 asphalt cement.
Driveways
Residential driveways combine economy and performance, with PG 64-22 or AC-20 asphalt suitable for moderate temperatures. Where freezing is common, PG 58-28 withstands cold weather extremes. Polymer-modified asphalt improves driveway longevity.
Airports
Airfield pavements demand extreme rutting resistance. PG 76-22 polymer-modified asphalt with a high stone content withstands jet thrust forces and heavy aircraft gear loads at high temperatures. PG 70-28 flexes at low temperatures.
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Recreational Trails
Hiking, biking, and nature trails need durable, flexible asphalt to handle environmental stresses. PG 64-28 or PG 70-22 asphalt resists cracking and deformation from roots, freeze-thaw, and weathering. Stone mastic asphalt adds stability.
Selecting the right asphalt binder maximizes performance for the unique demands of different pavement uses and conditions.
Differences Between Asphalt and Bitumen
Although often used interchangeably, some key differences exist between asphalt and bitumen:
- Composition – Bitumen is the naturally occurring extra-heavy hydrocarbon found in crude oil deposits. Asphalt is the refined product created after processing and distillation of crude oil bitumen.
- Materials – Bitumen in its pure form is a thick, black, sticky material. Asphalt is the combination of processed bitumen and mineral aggregates engineered to specification.
- Performance – Bitumen alone is brittle with low-temperature cracking resistance. Asphalt binder is modified with polymers to improve viscoelastic properties and performance.
- Uses – Bitumen has limited paving uses and is more often used for waterproofing applications. Asphalt binder is mainly used in flexible pavement construction.
- Specifications – Bitumen composition varies naturally. Asphalt is produced to meet standard specifications for qualities such as viscosity, penetration, and performance grading.
- Availability – Bitumen only occurs naturally in oil deposits. Asphalt is produced commercially at oil refineries to meet global paving needs.
So in summary, bitumen is the raw natural material, while asphalt is the refined and engineered product used to create durable, high-performance pavements.
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Identifying the Strongest Asphalts
The strongest, most durable asphalts contain modified binders engineered for enhanced performance:
- Polymer-modified – Adding polymers like SBS, SBR, EVA, or Elvaloy improves viscosity, strength, flexibility and durability. Used for high-traffic roads and cold climates.
- Rubber-modified – Grinding tire rubber into asphalt binder creates superior resistance to cracking, rutting and thermal stresses. Used in warm climates.
- Fibers and polymers – Combining polymers with reinforcing fibers creates a tough matrix. Fibers combat cracking and improve mix stability.
- Multigrade – Multigrade binders provide both high and low temperature performance. PG 76-22 has exceptional rutting resistance and PG 58-34 resists low temps.
- Stone mastic asphalt – Stone mastic uses a high crushed rock content, polymers, and stabilizing fibers. Extremely rut-resistant and durable. Used on highways and ports.
- High-RAP/RAS mixes – Reclaimed asphalt mixes with high recycled binder contents up to 50% are more sustainable and cost-effective.
Stronger asphalts using modified binders and reinforcing fillers resist distresses and last longer despite heavy traffic loads and temperature swings. Advanced mix designs optimize pavement durability.
Alternative Paving Materials with Benefits Over Asphalt
While asphalt is the predominant paving material, some alternatives offer advantages in certain applications:
- Concrete – More rigid and longer lasting than asphalt, with twice the lifespan. Higher cost but lower maintenance. Used on highways and intersections.
- Pervious concrete/asphalt – Allows drainage through the pavement surface to manage stormwater and recharge groundwater. Provides environmental benefits.
- Recycled plastics – Using recycled plastic bottles, bags and fibers makes eco-friendly, longer-lasting plastics asphalt. Reduces landfilled plastics.
- Cement-stabilized base layers – Mixing dirt or pulverized pavement with cement or lime creates a strong foundation layer under asphalt or concrete.
- Permeable pavers – Interlocking units allow infiltration between joints. Reduces runoff and flooding when used as hardscapes.
- Reclaimed glassphalt – Using recycled crushed glass in the aggregate makes asphalt mixes sparkle while diverting waste glass from landfills.
- Steel reinforcement – Steel meshes and bars add strength and prevent reflective cracking when used in asphalt overlays.
While cost must be considered, alternatives like these offer environmental, structural, or aesthetic benefits in the right scenarios.
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Answering Additional Questions
What are the methods of pavement repair?
The main methods of asphalt pavement repair are patching, crack filling/sealing, pothole repair, milling and resurfacing, full-depth repairs, and heater scarification. The method selected depends on the type and extent of damage.
How can I make my asphalt more environmentally friendly?
Use higher percentages of reclaimed asphalt pavement (RAP), warm mix technologies, porous asphalt, recycled plastics, rubberized asphalt, and other methods to improve the sustainability of asphalt mixes.
What is the routine maintenance of asphalt pavement?
Recommended routine maintenance includes crack sealing, pothole repair, patching, surface treatments every 5-7 years, drainage maintenance, mowing, striping upkeep, and sweeping. This preserves pavement quality between rehabilitation projects.
What are the three types of asphalt used in asphalt pavement construction?
The three main types are conventional asphalt cement, performance graded (PG) asphalt, and polymer modified asphalts. The type used depends on traffic and climate demands.
What type of asphalt is best?
For durability under heavy traffic loads, polymer-modified PG 70-22 provides superior rutting resistance. To withstand cold climates, PG 58-34 resists thermal cracking at freezing temperatures.
What type of asphalt is best for roads?
PG 64-28 or PG 70-22 modified asphalt is optimal for high-traffic urban roads and highways. In cold regions, PG 58-34 withstands freeze-thaw cycles. PG 76-22 has extreme rut resistance for ports and aircraft pavements.
What is the difference between asphalt and bitumen?
Bitumen is the natural raw hydrocarbon material derived from crude oil. Asphalt is a refined product engineered by combining processed bitumen with mineral aggregates to create durable, high-performance paving material.
What is the strongest asphalt?
Polymer-modified asphalt binders such as PG 76-22 and rubberized asphalt create the toughest, most durable asphalt resistant to distress. Multigrade binders like PG 70-28 provide both high and low-temperature performance.
What is better than asphalt?
Materials like concrete, reinforced asphalt, permeable pavements, and recycled plastic-enhanced asphalt can offer improved durability, environmental benefits, drainage, and other advantages over conventional asphalt in certain paving applications.
