How Asphalt Pavement Is Made

Asphalt pavement is found on roads, parking lots, airport runways, and other pavement structures. It consists of aggregates such as gravel, sand, and crushed stone mixed with bitumen, an oil-based substance. Best way to find Asphalt companies in Lancaster.

Surface asphalt mixes serve as a “roof,” protecting and dispersing vehicle loads over a specified area. Different mix designs may be utilized to achieve various performance characteristics.

Predose

Recycled asphalt pavement (RAP) is a valuable nonrenewable resource made up of two components: aggregates and bituminous binder. When utilized in HMA production, RAP can help save significant quantities of new aggregates and bituminous materials that would otherwise be downcycled for unbound pavement layers or low-value applications.

RAP stockpiles typically feature high water contents due to milling existing pavement layers and crushing processes of aggregates [14]. This moisture may restrict how much RAP material can be added into new asphalt concrete formulations produced at traditional batch plants, as final mix gradation requirements might not be fulfilled if the material soaks with too much moisture before heating in a drum mixer.

RAP’s hydration is an integral factor in its ability to adhere to asphalt binder during mixing and compaction. Open pores tend to absorb too much asphalt binder for it to form an effective film between aggregate particles (see Figure 4). Pretreating RAP with lime can replace negative ions on its aggregate surface with positive calcium ions that provide stronger adhesion between asphalt binder-aggregate adhesion and aggregate particles.

Drying

Drying asphalt is an integral step in turning the hot mix into a complex and durable surface, and it depends on several environmental factors like humidity and climate as well as factors specific to each asphalt layer’s thickness and whether or not it was laid as a hot mix or warm mix.

Once the asphalt has dried, it can withstand vehicle traffic and be considered “cured.” However, it may still be damaged by hazardous spills like antifreeze or gasoline, hefty traffic loads (like semi-trucks), or sharp objects like power steering wheels.

Atmospheric factors that contribute to drying include temperature and sun exposure; warmer weather with more direct sunlight will expedite drying time, while humidity has an impactful influence, too, as higher moisture levels slow evaporation rates. A light breeze can also help draw away excess moisture from asphalt surfaces and expedite their evaporation processes.

Mixing

Air voids in an aggregate-asphalt mix are crucial for its stability and resistance to deformation (rutting). Most practitioners agree that an effective compact cannot be reached without sufficient air voids.

Air voids may become inadequate due to multiple factors, including aggregate degradation during handling and mixing. This often happens during transport from stockpiles to aggregate bins, batching from bins onto an aggregate belt conveyor system, heating in drum or hot bins, heating from mixing, etc. A common reason for plant production adjustments during aggregate degradation-related air void reduction is reduced stiffness, typically corrected by decreasing asphalt binder content, but this decreases the durability of HMA durability over time.

Stiffness in HMAs is essential to reduce rutting by spreading traffic and environmental loads over a wider area. Achieving adequate stiffness requires sufficient stone-on-stone contact and stiff or modified biners. High stiffness also offers superior fatigue resistance.

Compaction

Compaction refers to the process of compacting asphalt mix material to reduce air voids and enhance pavement surface performance. Most practitioners consider proper compaction a critical aspect of quality paving work.

Air void content directly impacts how much permanent deformation or rutting develops in an HMA, so compacted HMA can significantly decrease rutting and other forms of distortion.

Many factors influence compaction, such as the temperature and environmental conditions at a construction site. Mix temperature is particularly significant because it determines how long is available for compaction; the cooling rate also plays an integral part in shaping compaction outcomes.

Weather conditions will dictate whether the cooling rate of the mixture will be fast or slow, making compacting it harder due to insufficient time for aggregate particles to reorient themselves and pack tightly together. Conversely, slower-cooling mixes tend to be more accessible as heat from mixing plants will remain in place longer, giving more time for compaction.

Repair

Asphalt is a highly durable material with many advantages, including cost-effectiveness and ease of repair. Regular inspections should be conducted to spot minor issues like cracks, potholes, and uneven surfaces before they escalate into larger problems. A well-kept parking lot can increase the curb appeal of your property and make a strong selling point to potential tenants.

Localized damage can be repaired using spot repair services, which are more cost-effective than full-depth repair or overlay. This approach is particularly advantageous for commercial properties which experience higher traffic volumes and pressures on their pavements.

Edge cracking occurs due to inadequate support at the edges of pavement, typically as a result of poor drainage, heavy traffic, or settlement of the underlying materials. Untreated, these cracks will expand and lengthen over time unless repaired; alligator cracks resemble small wavy skin-like strips across all layers from surface up through stabilizing sublayers; alligator skin cracks require full-depth patching as well as moisture sealant application to stop further moisture penetration and future cracking.