Asphalt is a bit of a catchall term. While it may all look pretty much the same to a layman, there's actually a wide variety of asphalt mixes that are used in different situations. The success or failure of a paving project depends heavily on the choice of asphalt mix. Here are the different types of asphalt mixes and the best situations for them:
Hot mix asphalt is the general term for asphalt mixes that have to be heated to high temperatures (300-350°F) for use. This is the most commonly used type of asphalt for major paving projects, and has several subtypes with their own unique strengths:
Water is the enemy of pavement -- when it slips into cracks and gaps, it can freeze and cause asphalt to break up. Porous asphalt, on the other hand, is a hot mix asphalt designed for water infiltration. It allows water to drain through, so it can eventually infiltrate the soil. This is because porous asphalt's void spaces are about 15-16%, as opposed to the tiny 2-3% void spaces of other types.
This can be a huge boon when it comes to stormwater management. Rather than harbor standing puddles, it lets water filter through a special aggregate bed. This cuts down on standing water, and the aggregate helps reduce waterborne pollutants. Stormwater enters the soil more easily and is cleaner when it does so.
Use this asphalt in areas that experience seasons of heavy rainfall. It can be a big help when it comes to stormwater management.
Stone matrix asphalt, or SMA, is a hot mix asphalt designed to resist deformation. Asphalt binder is slightly flexible, even when completely cool. Aggregates aren't. Stone matrix asphalt has a higher ratio of coarse aggregates, so there's more stone-on-stone contact to provide a higher rutting resistance.
This mix is best for applications where noise reduction and rutting resistance are important. That said, it's also more expensive than other hot mix asphalts, so it may not be a cost-effective choice for very large projects.
Dense-graded mixes are good general-purpose hot asphalt mixes. They're generally impermeable and useful for paving and patching alike. This asphalt mix is assigned a grade based on the particle size of the component aggregates, and comes in two types:
Coarse-Graded Mix. Coarse-graded mix contains larger aggregate particles than fine-graded mix. These particles may be crushed, uncrushed, or partially crushed gravel and stone.
Fine-Graded Mix. Fine-graded mix contains aggregate particles that are very small. These are usually various types of sand, either from natural sources or produced as a byproduct of crushing gravel and stone.
These mixes are the ones most commonly used for driveways and other paving projects in the United States. They're resistant to rain and cracking, so they hold up well under high-traffic applications.
Warm mix asphalt is fairly new. It's heated, unlike cold mix asphalt, but doesn't get nearly as hot as hot mix -- only about 120°F at maximum. Otherwise, it's very similar to hot mix asphalt, albeit more versatile. Its low temperature means that it loses heat to the atmosphere more slowly, so it has a larger working window than hot mix asphalt. It can even be used during seasons where hot mix asphalt wouldn't be appropriate, which makes it ideal for emergency paving repairs. It can also be transported for longer distances than hot mix without suffering a loss of quality.
Interestingly, it's also a somewhat "greener" choice than hot mix asphalt. Since less energy is required to heat it, its production doesn't release the same amount of greenhouse gases as a conventional hot mix. Since it takes a temperature of 118°F to cause first-degree burns on human skin, warm mix asphalt is also much safer for pavers to work with.
Cold mix asphalt isn't heated. Since it doesn't need to be kept hot in order to be usable, you can transport it long distances without a decrease in quality. It's also even more environmentally friendly than warm mix asphalt. All of this aside, it isn't nearly as strong as hot asphalt mixes generally are. It also takes a lot longer to set, so it's not a good choice for high-traffic areas that can't be blocked off for an extended period of time to let the asphalt harden.
As a result, cold mix asphalt is usually only used for temporary patch jobs. If a hole needs to be repaired in winter, for example, cold mix asphalt can cover it until a more permanent solution is appropriate.
Your paving project depends heavily on several factors. Traffic, climate, and season are just a few of them. The right paving mix will hold up to whatever traffic you throw at it, handle rainfall with ease, and result in a durable finish that's the perfect compromise between smoothness and traction. Choose the best paving mix for your application, and you'll save on future repairs.
POSTED: July 7, 2022
TAGS: Asphalt Paving