What is asphalt stabilization?
To begin with, we need to know what it is. Base stabilization is often performed on new road, or when full-depth repairs are being performed on an older road. Stabilization is the process of preparing a base for proper asphalt stabilization.
Why is it needed?
Asphalt stabilization may be required when the earth beneath asphalt-to-be-laid is not strong enough to support the new asphalt paving. For example: sandy soil, soil high in clay, soil prone to erosion, and weak, soft, non-compacted soil often need asphalt stabilization measures.
The stabilization process is performed when the bottom layers of asphalt and the soil beneath it are pulverized. The pulverization process is something familiar to anyone in the asphalt paving business- it’s the process of grounding big rocks and pebbles into smaller ones. The tools used in this step are typically jackhammers, steamrollers, pavement shredders, tampers and more. Don’t be surprised if a few good old-fashioned shovels and sledgehammers make it into the mix.
After the pulverization is complete, the tools mentioned above will be used to shake and compress the base into settling. This stage is known as compaction. In cases where the soil beneath the asphalt isn’t too terrible, this may be all that’s required to set up a stabilizing base.
Sometimes, after pulverization, additives are added to improve cohesiveness and stability. Depending on the soil type beneath the asphalt, different additives will be used. Cement is often used in sandy locations (as an additive to the stabilized asphalt). High-clay content soils will require lime as an additive because it reduces plasticity. Cement, fly ash, asphalt emulsion, and foamed bitumen can increase weight-bearing capacity. Additionally, more than one type of additive may be used. Lime may first be added to reduce clay-heavy soil’s plasticity, followed by foamed bitumen to improve its load-carrying capacity. There may be different stabilizing additives used in different locations on the same project as well. This happens when the soil varies in composition beneath a construction. The percent composition of stabilizer is usually in the 2-4% rage, based on requirements, authorities, and/or project owners.
After the additive or additives are used and thoroughly mixed with the asphalt, the process of compaction can begin.
Soil vs Asphalt base stabilization
Sometimes, the only thing (or primary thing) being stabilized is the earth the asphalt will rest on. Sometimes it’s a combination of existing asphalt (that must be repaired) and soil. Other times it’s a combination of soil and a special material used as asphalt subgrade/base that is brought in by the paving contractor. Depending on the material being pulverized, the type of stabilization changes.
This is primarily earth beneath the asphalt. There may be some other stuff, such as an added subgrade or preexisting asphalt, but the majority is earth beneath asphalt.
Asphalt base stabilization
This is when more of the material being stabilized is the subgrade material/preexisting asphalt. Of course, some soil will no doubt be part of this process, but the majority is base/soil.
Regardless of which type of stabilization you are doing, there are a series of steps you must follow. Ensuring that your asphalt is stable requires careful planning, engineering, and know-how, doing things wrong, forgetting steps, or going out of order will result in big problems.
- Step 1: Testing and planning. First you will check out the soil you will be building on. Make sure it can support asphalt. If it can’t, analyze it to figure out what needs to be added.
- Step 2: Pulverize that asphalt.
- Step 3: Additives (if necessary)
- Step 4: Compaction.
- Step 5: Further testing. Once all of the tests are passed and the base is deemed stable enough, we are ready to lay some asphalt. This is an extremely important part of the process, it must be ensured that too much moisture isn’t trapped in the soil. Also, it must be determined that there are no irregularities that can damage the asphalt later.
- Step 6: Surface treatment. A thin seal may be applied, it will protect the surface while letting out any residual trapped moisture. Common surface treatments include chip seals, slurry seals, micro surfacing, cold and hot mix overlays, and cape seals.
Check out Asphalt Pro Magazine’s in-depth how-to on asphalt stabilization.
Why should you stabilize asphalt?
Another way of asking this question is as follows: what happens if you don’t stabilize asphalt? Well, no doubt you’ve seen damaged asphalt before. That’s what will happen. The majority of major asphalt damage, such as potholes, heaving, major cracking, etc, comes from the asphalt not being stable below the surface. Even asphalt that is laid well and surfaced/sealed will have those problems, while avoiding smaller issues.
If you don’t stabilize your asphalt pavement, you can expect the following:
- Surface unevenness/sunken asphalt. If not stabilized, entire slabs of asphalt/concrete can sink.
- Potholes. Smaller areas of uncompacted base can lead to potholes.
- Cracking. Moisture in the base can expand when the weather changes and make it so that it comes out of surface, leading to cracking. The moisture can also seep into the paving from the base, leading to expansion and cracking.
- Pavement drift/moving. An unstable base will lead to unstable pavement on top of it.
- Chipping edges. Pavement that is laid without a solid base or wider than its base will see its edges weaken and chip off.
Ensure your paving is done right
If reading this has scared you a little, we understand. Not doing something – especially paving – right is a huge mistake. Not only will it cost you money in repairs/replacements in the future, but your clients and visitors will have a bad impression before they even go into your business. If you want to ensure that your pavement is high-quality, and stands the test of time, then go with Reliable Paving. Reliable has been in this business for over 35 years, and knows how to get the job done right the first time. Contact us today for high-quality paving in the Dallas Fort-Worth area.