If you have recently had an asphalt paving job completed, but the surface isn’t smooth, why is that? What’s the problem? To understand why the surface of your asphalt isn’t as smooth as you’d like it to be, you need to have an understating of what asphalt is composed of as well as the properties of asphalt.

Asphalt road in sunset close upWhat exactly is Asphalt?

Asphalt is a natural substance that has some amazing physical properties. It’s sticky and elastic and able to stretch, bend and flex without breaking. At air temperatures, asphalt cement is a very thick liquid. When heated, it becomes thinner and easier to use. Asphalt has been used since before Roman times as a glue and for waterproofing. In a few places in the world, it’s naturally occurring, such as in a lake on the island of Trinidad and in the La Brea “tar pits” in downtown Los Angeles. Almost all of the asphalt used today for paving comes from petroleum crude oil. Liquid asphalt is the heaviest part of the crude, what’s left over after all of the volatile, light fractions are distilled off for products such as gasoline, kerosene, jet fuel, diesel fuel, or fuel oil. In Europe and Canada, it is commonly called bitumen.

Asphalt is supplied in several different grades. Softer asphalts are used in colder temperatures and harder asphalts in hotter climates. The US government sponsored a multi-million dollar research project (Strategic Highway Research Program, SHRP) in the 1990’s which developed new standards for asphalt binders called performance grade (PG) binders. Premium grades usually have polymers or other modifiers for use in heavy duty applications such as intersections on city streets or airports or in extreme climates.

Like any good recipe, the ingredients should be high quality, they should be carefully measured, and they should be cooked at exactly the right temperatures.  At the asphalt plant, the aggregates are precisely blended and then dried and heated to the right temperature.  The mixture is then completely coated with liquid asphalt cement.  There are two types of asphalt plants, batch and drum.  Drum mix plants dry the aggregate and blend it with asphalt in a continuous process in the same piece of equipment.  With batch plants, the rocks are first dried and heated, then added to the pugmill and blended with the asphalt one batch at a time.

Once mixed, the asphalt is loaded into trucks and transported to the job sites.  The asphalt is then placed on the asphalt paving project using a paver. Once the paver lays the asphalt mix, it is compacted with rollers until it has just the right number of air voids. Temperature is a very important factor.  The best temperatures for mixing, transporting, laying and compacting asphalt are based on how stiff or viscous the asphalt is, how far and for how long it must be transported, and when it will be compacted.  If it is compacted too hot, the air voids will be too low.  If it is too cold, it will be difficult to compact, and the air voids will be too high.

All that to say, an asphalt paving job can be complicated, and if the finished product isn’t as smooth as it could be, you could be looking at a substandard job.  Is the problem merely aesthetic, or is having a smooth surface important?

If you asphalt surface is rough or uneven, you could slip or fall on it. It can cause poor drainage where rain can seep down into small gaps in the surface and cause crack or chip. A smooth surface is safer to drive on than a rough and uneven one. A smooth asphalt surface doesn’t have cracks, potholes, or bumps, which are all safety concerns. The most common reasons your asphalt surface may not be smooth are:

  • Using the wrong aggregate mix
  • Not enough asphalt to bind the aggregate together
  • Inadequate compaction

Using the wrong aggregate mix

The aggregate mix you choose can significantly affect the smoothness of your asphalt surface. Aggregate is the material that makes up sand, gravel, and crushed stone. The shape and size of the aggregates determine their ability to adhere to the asphalt to create a smooth surface. An aggregate with a small sand or gravel content may leave little air pockets or voids when you pour in the hot asphalt. These voids may allow water to seep through your asphalt surface, causing it to crack or create uneven areas.

An aggregate with round-edged stones or particles also does not bind well with asphalt compared to sharp-pointed crushed aggregates. You could also consider using a medium-sized aggregate mix. A fine aggregate mix may result in a slippery surface, while large-sized aggregates may result in an uneven surface. If you are unsure of the best aggregate mix for your asphalt surface, you can contact a paving company near you. An asphalt paving professional will advise you on the best mixture for your area and where you can get it at a reasonable price. They’ll have the knowledge and equipment to heat the asphalt to the right temperature and consistency. A soupy consistency asphalt is easy to evenly distribute on your surface for a smooth and wear-resistant surface.

Not Enough Asphalt to Bind the Aggregate

Using the right amount of asphalt is essential when paving your driveway or any other surface. The asphalt has to be hot so it can penetrate between the particles of the aggregate mix base to create a smooth surface. To create a smooth asphalt surface, you will need enough asphalt to penetrate all of the aggregates and bind them tightly. If the asphalt is inadequate, parts of the aggregate mix will be left loose, creating holes and cracks on your surface.

The amount of asphalt used on your surface will vary depending on the weather in your home area, but a good rule of thumb is to keep it at least two inches thick. This amount ensures your asphalt covers all the aggregate base and dries with adequate adhesion quality for more extended service.

By looking at the side edges of your pavement, you can know if you have used enough asphalt for a smooth surface. You can add more asphalt if you see dry patches or a rough texture. You can also check for uneven surface sections and add asphalt as it may not have penetrated well to create a flat and smooth surface.

Inadequate Compaction

Compaction is the last and critical stage in paving with asphalt. Compaction helps bind the asphalt and aggregate mix by removing spaces or air pockets between the two to create a smooth surface. Compaction is essential because it prevents potholes and cracks from forming on the surface of the asphalt. Compaction creates a uniform surface that quickly drains, reducing the chances of cracking and chipping. This process gives the asphalt surface a smooth, consistent look. The more compaction pressure, the more uniform the surface will be, and the less likely it will be to crack or chip.

You can know that your asphalt and aggregates are not well compacted if you see loose rocks or uneven sections on the surface. The surface may also have cracks that make it appear to be crumbling. Bumpy or rounded areas on an asphalt surface indicate inadequate compaction pressure. Compaction should be done soon after pouring hot asphalt on your aggregate mix base. A professional paving company will have the right equipment and experience to ensure timely and adequate compaction on large and small sections of your asphalt surface.

Rough and uneven asphalt surfaces can potentially cause freak accidents such as slips or falls. Rough asphalt is also more susceptible to cracks and chips, negatively impacting the durability and aesthetic value of the surface. An experienced professional paving company can diagnose your problem and work toward a timely solution. If you have any problems involving asphalt, or if you have a paving project in your future, you need to contact the pros at Cactus Asphalt. We are a Phoenix, AZ-based asphalt paving company well-known for our ability to quickly and efficiently perform both residential and commercial services. For over 39 years, we have provided paving for new construction, seal coating, crack sealing, and more, making us Arizona’s number one name in asphalt paving.

We have the experience and resources to ensure that you will make an impression on all who visit your property. We promise to keep our customers happy, which is one reason they keep coming back for additional services. For additional information about our company or the services we offer, visit our website, or contact us at 923-207-8391.