Asphalt pavements make up over 90% of paved roads and highways in the United States. They rely on asphalt cement binders to hold aggregates together and resist deformation from traffic loads. However, conventional asphalt binders have limitations in terms of low-, intermediate- and high-temperature performance. Adding nanomaterials is a promising solution to enhance asphalt properties.
What are Nanomaterials?
Nanomaterials refer to substances with at least one dimension on a nanometer scale, which is one-billionth of a meter. At this tiny scale, materials exhibit unique physical, chemical, and mechanical behaviors. Nanoscale additives can be leveraged to modify the characteristics of conventional paving materials.
Benefits of Nano Asphalt Additives
Introducing nanomaterials into asphalt binder provides significant benefits:
- Improved resistance to rutting and deformation
- Better protection against cracking in cold climates
- Increased durability against aging and weathering
- Higher strength and fracture resistance
- Enhanced adhesion between binder and aggregate
- More flexibility and elasticity at low temperatures
Overall, nanoengineered asphalt materials offer superior performance properties compared to standard paving-grade asphalts.
Types of Nanomaterials for Asphalt
Multiple nanoscale additives have been researched for asphalt applications, including:
- Nano carbon – Carbon black, activated carbon nanoparticles
- Nanoclay – Montmorillonite, organoclay, Kaolin clay
- Nanosilica – Fumed silica, silica nanoparticles
- Nanometal oxides – Zinc oxide, titanium dioxide, iron oxide
- Nanopolymers – Styrene-butadiene-styrene (SBS)
Of these options, nanocarbon offers distinct advantages as an asphalt modifier.
Why Use Nano Carbon in Asphalt?
Nanocarbon is an excellent nanomaterial choice to enhance asphalt binder properties. Key benefits include:
- Extremely high tensile strength and durability
- Large specific surface area for better aggregate bonding
- Stiffening effects to resist rutting and deformation
- Flexibility improvements to prevent cracking
- Rheology modification for better workability
- Enhanced electrical and thermal conductivity
Nanocarbon provides multi-dimensional property enhancements using a sustainable, abundant material derived from biomass.
Nano Carbon Production
Nanocarbon is produced industrially by:
- Extracting natural graphite
- Purifying and micro-milling to nano-size
- Oxidation and exfoliation techniques
- Surface functionalization (adding molecules)
This yields carbon nanoparticles 20-60 nm in diameter. They are blended into asphalt binder at less than 10% by weight of the total binder content.
Asphalt Testing Results
Multiple research studies have evaluated the effects of adding nanocarbon on asphalt binder properties with excellent results:
Rutting Resistance
- 45% increase in unaged G*/sin(delta) parameter from dynamic shear rheometer testing
Fatigue Cracking Resistance
- 30% reduction in creep stiffness (S) based on bending beam rheometry
Workability
- Increased rotational viscosity within the acceptable range
Thermal Cracking
- Lowered -12°C bending beam stiffness by 15%
Aging Resistance
- Reduced aging index and improved elastic recovery
Moisture Susceptibility
- Higher tensile strength ratio indicating improved moisture resistance
This data demonstrates nano carbon significantly enhances asphalt binder properties for improved pavement performance.
Field Performance
Full-scale pavement test sections using nano-carbon modified asphalt mixes showed excellent results:
- Rutting: 45% less rut depth after 2 years
- Cracking: 75% increase in fatigue life from beam fatigue testing
- Texture: Better surface frictional properties throughout life
- Moisture: No moisture-related damage after freeze-thaw cycles
- Workability: Consistent properties during paving operations
The superior lab binder results translated directly into better field performance.
Cost Analysis
At present production levels, nano carbon pricing results in a moderate cost increase compared to conventional asphalt:
- Base asphalt cost: $500 per ton
- Nano carbon cost: $20 per lb
- Nano carbon usage: 6 lb per ton of asphalt
- Total cost: $740 per ton of modified binder
With anticipated improvements in nano carbon manufacturing economics, costs are projected to become competitive with polymer-modified asphalts at scale production.
Environmental Benefits
Nano-carbon modified asphalt provides sustainability benefits:
- Raw Materials: Derived from renewable biomass sources
- Energy Usage: Lower production temperatures conserve energy
- Lifespan: Extended pavement life reduces maintenance needs
- Recycling: Fully compatible with RAP and recycled asphalt
The enhanced performance properties also enable pavements to be designed thinner for resource efficiency.
Implementation Strategies
To shift toward broader adoption of nanoengineered asphalts, key approaches include:
- Partnerships between materials suppliers, contractors, and owners
- Ongoing field validation of long-term performance
- Development of material specifications and standards
- Improved economics of scale production
- Effective measurement of sustainability benefits
- Incentives for pilots and initial projects
Last Words
Nano carbon modification has significant potential to create asphalt binders with superior performance properties. With continued research and field implementation, nanoengineered asphalt materials can become a standard component of high-performance, sustainable pavements.
FAQ
What is the performance of an asphalt mixture with nanoparticles?
Research shows that adding nanocarbon, nano clay, nano-silica, and other nanoparticles improves the performance of asphalt mixes by enhancing rutting resistance, fatigue life, moisture susceptibility, thermal cracking resistance, and workability compared to conventional mixtures. The nanomaterials provide multi-dimensional binder property improvements.
What are the nanomaterials in asphalt?
Common nanomaterials used in asphalt include nanocarbon (carbon black, activated carbon), nanoclays (montmorillonite, Kaolin), nanosilica (fumed silica), and nanopolymers like Elvaloy. These nanoscale additives typically make up less than 10% by weight but provide significant binder enhancements.
What is nanocarbon used for?
Nanocarbon is used to improve the properties of materials like asphalt binders. Benefits when added to asphalt include better rutting resistance, fatigue life, thermal cracking resistance, moisture resistance, and workability. Nanocarbon also enhances the electrical conductivity of asphalt.
Why are polymers added to asphalt?
Polymers like SBS and SBR are added to asphalt to improve the temperature sensitivity, rutting resistance, and cracking resistance. The long polymer chains improve asphalt’s elasticity for better flexibility and durability. Polymer modification is a widely used method but can be expensive.
What are the advantages of polymer-modified asphalt?
Polymer-modified asphalts have reduced temperature susceptibility, better-rutting resistance, enhanced cracking resistance, and improved adhesion and ductility. This leads to increased pavement life. The improved workability also allows lower mix production and compaction temperatures.
What are the polymer additives for asphalt?
Common polymer additives to modify asphalt binder include styrene-butadiene-styrene (SBS), styrene-butadiene rubber (SBR), ethylene-vinyl acetate (EVA), polyphosphoric acid (PPA), polyolefins like polypropylene, and engineered plastics such as polyurethane. SBS is the most widely used polymeric modifier.
How strong is nanocarbon?
On a molecular level, nanocarbon has extremely high strength properties. Its tensile strength can reach 150 GPa. This is over 100 times greater than steel. When added to materials like asphalt binder, nanocarbon provides dramatic strength enhancements even at low dosages such as 5% by weight.
How strong is carbon nano?
Carbon nanomaterials like carbon nanotubes (CNTs) are among the strongest known materials, with tensile strength up to 200 GPa, 100-400x greater than steel. Even after combining just 1-2% by weight of CNTs into materials like polymers and epoxy, large strength increases result. This makes carbon nanomaterials ideal reinforcements.
What is the difference between nanocarbon and carbon nanotubes?
Nanocarbon refers to engineered carbon particles on the nanometer size scale. Types include carbon black, activated carbon nanoparticles, and graphene nanoplatelets. In contrast, carbon nanotubes are tubular structured carbon molecules on the nanoscale typically under 100 nm in diameter but micrometers long. Both offer advantages as nanoscale additives.
What is the most commonly used polymer for asphalt modification?
Styrene-butadiene-styrene (SBS) is the most widely used polymer modifier added to asphalt binder. SBS improves asphalt’s temperature sensitivity, rutting resistance, and flexibility. Between 2-7% SBS by weight is typical. Other common polymers include styrene-butadiene rubber (SBR), polyphosphoric acid (PPA), and ethylene-vinyl acetate (EVA).
What is new asphalt made of?
New asphalt paving mixes consist mainly of aggregate (95%) and asphalt cement (5%). The aggregates are virgin natural rock or recycled asphalt pavement (RAP). Asphalt cement is a petroleum-based binder produced from crude oil distillation. Polymer additives are often used to improve properties. The materials are combined and heated to produce HMA.
Is asphalt a natural polymer?
No, conventional paving-grade asphalt is not a natural polymer. It is a complex mixture of hydrocarbons derived as the residue from petroleum crude oil distillation. At ambient temperatures it behaves viscoelastically, giving it some polymer-like qualities, but asphalt binder itself does not contain long-chain polymer molecules.
What makes asphalt strong?
Asphalt’s strength comes from cohesive molecular interactions between the long hydrocarbon components, primarily polar aromatic compounds. These provide thermal and oxidative resistance. Asphalt’s heterogeneous composition creates a microstructure that adds mechanical strength. Polymer modification enhances the viscoelastic properties further for additional strength.
What is the most commonly used asphalt mix?
For major pavement projects, the most commonly used asphalt mix is hot mix asphalt (HMA) made with paving-grade asphalt cement. Within HMA, there are different types including dense-graded Superpave mixes, open-graded friction courses, stone matrix asphalt, and porous asphalt. But traditional HMA with paving asphalt makes up the vast majority of asphalt paving.
What is the mixing material for asphalt?
Asphalt mixtures consist primarily of paving grade asphalt cement as the binder, virgin aggregates or reclaimed asphalt pavement (RAP), and sometimes waste materials. Additional liquid antistripping additives and polymer modifiers may be added to the asphalt. Lime or cement can also be used in some asphalt applications. The materials are heated and combined at asphalt plants.
