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The Basics of Asphalt Paving

Asphalt Paving Summerville SC provides the foundation for safe and sustainable roadways. Routine maintenance helps mitigate deterioration and extends the pavement life.

During the construction process, asphalt layers are constructed and compacted to achieve desired smoothness and density. Obtaining adequate compaction allows the pavement to perform structurally as designed by the project engineer.

The sub-base is the most important layer of any asphalt pavement. It is the primary load-bearing layer and acts to spread the load of the paving, and any traffic on it, across the entire surface of the subgrade. Without a properly constructed sub-base, even a good quality asphalt surface can begin to deteriorate quickly.

The material used in the sub-base is often lower grade than the base course, but it must be stronger than the soil that will form the subgrade. This material is usually crushed aggregate. It must be densely graded to promote drainage, and should have a high percentage of cubically shaped particles to resist degradation from impact loading, rutting, and settlement.

Ideally, the material in the sub-base will also be free of plastic fines that may reduce the load-carrying capacity of the granular material by interlocking with adjacent aggregate particles. In addition, the grading of the sub-base should be graded to slope away from the house, garage or other buildings to prevent water from collecting and pooling on the new paving.

If the sub-grade is not properly prepared, it may have to be excavated and replaced prior to laying the base course. This is expensive and can cause a delay in the paving schedule.

A faulty sub-base can be repaired with the use of geotextiles. These fabrics are placed over the sub-grade to prevent the mixing of soils that could interfere with the structural capacity of the base course and subgrade.

In most cases, a sub-base is required for all major highways. However, it is seldom necessary for streets, secondary roads and parking lots that do not experience frequent heavy truck loadings.

If your contractor tells you that a sub-base is not needed beneath your new driveway, ask them to explain why. A strong sub-base can dramatically increase the lifespan of your paving. It will also save you money in the long run by postponing unwanted repairs. If you want to avoid the expense of a costly repair, be sure to have a quality sub-base installed by your contractor.

Binder Layer

The asphalt binder holds together the aggregate in an asphalt mix. Without it, the mix would merely be crushed stone or gravel with some sticky bituminous-like material as a non-participating component. The physical properties of the asphalt binder depend on the type and source of the raw material, its temperature, and the mixing and transport process. The asphalt binder must be sufficiently stiff to resist deformation under heavy vehicle loads and also have sufficient elasticity to allow recovery from damage or fatigue.

The asphalt binder is placed in layers and compacted with specialized equipment to achieve a specified density. This step is vital to minimizing future pavement failures (rutting and cracking).

Ideally, the new asphalt should be rolled immediately after it is laid. This not only compacts the surface, but it also oxidizes and hardens the binder. Once this happens, the asphalt should be left to cool and cure for 24 hours before traffic is allowed on it.

A geo-textile fabric is then placed over the sub-grade and runner-crush stone base to prevent the asphalt layers from mixing with one another. The geo-textile is also important in keeping the underlying sub-grade and binder layers from degrading due to the intense heat and pressure generated by the paving equipment.

The asphalt paving equipment then places the new asphalt layer. The new layer is rolled again and compacted, to ensure it is even and has the proper texture. This step is especially important in commercial and/or high-volume residential paving, where the surface of the road is expected to carry more traffic than in rural areas.

As the new asphalt dries and hardens, it is inspected for quality control and any deficiencies are addressed. Once the paving crew is satisfied that the new surface is ready to be used, the construction process is complete.

The most common type of asphalt is the “hot mix” variety, which uses a higher proportion of larger aggregate pieces for strength. In addition, the asphalt binder is usually a bituminous mixture with a low percentage of virgin oil. These mixes are designed to provide a durable, economical roadway for light-duty vehicles. They are usually designed to meet local road requirements and pass standardized engineering testing procedures. However, these asphalt mixes may not be as beneficial to long-term performance as the softer, more traditional grades.


Asphalt paving is a time-bound process. The production, laydown and compaction of hot mix asphalt (HMA) or warm mix asphalt (WMA) need to be done in a specific sequence to ensure the resulting long-life pavements. Therefore, delays must be avoided.

One of the most critical elements in achieving the target density required by a paving project is the temperature of the HMA when it’s compacted. The optimum range for the onset of compaction is between 300 and 240 degrees Fahrenheit. As the mix cools it loses its workability and becomes more difficult to compact.

Once the proof roll indicates that the sub-base layer is sufficiently strong to support the new asphalt pavement installation, the next step in the paving process involves laying the binder layer. The binder is the substance that binds the aggregate base together. It’s composed of a mixture of oil and an additive known as bitumen.

A typical bitumen mix has a high viscosity that prevents the material from flowing as easily as water. It also contains aggregates that are sized and graded to be compatible with the binder. The aggregates are mixed in a mixer at a specified rate with the binder and heated to about 300 degrees Fahrenheit before it’s loaded onto transport trucks for delivery to the job site.

Contractors know that once the asphalt arrives at the jobsite it will need to be laid and compacted as quickly as possible to ensure a long-life pavement. The size and capacity of the transport trucks is a fixed factor that can be accurately predicted, but how much HMA a truck will deliver in a specific period of time will depend on many variables. The amount of HMA delivered and the time it takes for the trucks to reach the paving site can affect the temperature of the HMA when it’s being compacted.

The first roller to compact an asphalt layer is a breakdown roller, typically a vibratory steel wheel or pneumatic tire. The breakdown roller needs to be selected in order to match the paver’s production speed and the HMA’s optimum working temperature. If a breakdown roller with a wider drum width is used, this may result in non-uniform panel density due to excessive overlap in the rolling pattern.


The final step in the paving process involves curing asphalt. This is a crucial process that ensures your new pavement has time to fully harden before it’s exposed to traffic or weather elements. It also helps to prevent premature deterioration and prolongs the lifespan of your asphalt surface.

During the curing process, volatile oils within the asphalt mix evaporate, leaving behind a harder and more durable surface. This process typically takes a couple of days to complete and requires patience. It’s important to restrict foot and vehicle traffic during this time, especially in high-traffic areas.

Many factors impact the curing process, including ambient and surface temperature, wind speed, humidity, and the type of asphalt mix used. Warm temperatures expedite moisture evaporation, hastening drying, while lower temperatures prolong it. Wind speeds likewise influence drying, with strong winds removing moisture and speeding up evaporation, while calm conditions slow it down. Humidity has a similar effect, with higher levels of moisture slowing evaporation and prolonging dry times.

Once the paving process is completed, you must allow the asphalt to dry for 48-72 hours (up to 3 days). It’s best to stay off of the surface during this time to avoid damage. This will allow the asphalt to fully cure and strengthen before being exposed to heavy traffic or damaging substances like oil.

In addition to allowing the asphalt time to properly dry, it’s important to follow proper maintenance procedures to keep your new surface looking great. Using salt to de-ice the surface will accelerate the curing process and help prevent damage during winter. Additionally, proper drainage is essential, as standing water can hinder the evaporation process and lead to weakened spots on the surface.

When it comes to preserving the quality of your asphalt, working with an experienced paving company is vital. They will be able to provide you with expert installation and guidance on how to care for your new surface. They will also be able to recommend the right asphalt mix for your specific location and climate, as different mixes have different evaporation rates.