Planning an asphalt paving project in the near future? Then it’s a good idea to familiarize yourself with the various types of asphalt mixes so you know what to expect. Understanding how each asphalt mix performs and where it’s typically used can help you plan for asphalt repairs and long-term maintenance.
Here are five types of asphalt mixes you should know about.
Hot mix asphalt, commonly referred to as HMA, bitumen, or blacktop, is the most widely used type of asphalt in major paving projects. There are a few different types of HMA, each of which has unique performance properties and ideal usage applications. They include:
Properly designed and constructed dense-graded mixes are, for the most part, impermeable, which makes them suitable for all traffic conditions and pavement layers.
There are two types of dense-graded mixes: fine-graded and coarse-graded, each of which is characterized by the size of the majority of the aggregate particles in the mix. These mixes can be used for surfaces, as well as asphalt repairs, and are the most commonly used and well-understood type of HMA in the U.S.
Also known as SMA or stone mastic asphalt, this type of mix is a gap-graded HMA designed to increase rutting resistance and durability. Because aggregates do not deform under load to the degree that asphalt binder does, SMA consists of a higher ratio of course stone aggregates to achieve stone-on-stone contact within the mix.
That contact, combined with a higher asphalt content than HMA, allows SMA to resist deformation, making it suitable for high-volume roadways. This type of mix also helps reduce tire noise and reflective cracking. Because SMA consists of highly durable aggregates, it’s generally about 20%-25% more expensive than its other HMA counterparts.
This type of asphalt mix has a greater purpose, stormwater management. Porous asphalt is made to allow water to drain through the asphalt into a layer of aggregate, designed to naturally filter the water and reduce the amount of pollutants carried to a waterway. Filtration of runoff volume can reach nearly 80% with proper installation and maintenance. Porous asphalt consists of standard bituminous asphalt, but the void spaces are approximately 16% as opposed to two to three percent for conventional asphalt mixes. Developers for residential, commercial, and industrial sites might find this asphalt mix helpful to decrease the amount of stormwater runoff, especially when there is increased velocity and volume.
Like HMA, warm mix asphalt (WMA) is heated during the production process. But, unlike HMA, WMA contains either water or organic/chemical additives that reduce its required production temperature. Notably, WMA production requires less oil/fuel consumption and produces fewer emissions than HMA production, making it more cost effective and environmentally friendly.
WMA’s lower production temperature allows it to remain more workable as it cools as there’s ultimately a smaller difference between the temperature of the mix and the surrounding air. Asphalt transport trucks can also haul warm mix farther distances from the plant to the project site given its lower temperature. And, since WMA has a lower viscosity than HMA, it can be compacted at a lower temperature than HMA.
Presently, WMA is relatively new in pavement application in the U.S., so long-term performance data is currently limited. However, WMA has experienced rapid adoption and it’s growing in popularity due to its versatility, durability, and usability outside normal asphalt paving weather conditions. Warm mix asphalt is durable enough to withstand heavy traffic load and can be used in virtually all pavement applications.
As its name indicates, cold mix asphalt (CMA) is not heated at all during production, which allows it to be transported and laid while cold. But CMA isn’t nearly as durable as HMA or WMA, so it’s really only suitable for patching and other asphalt repairs. Ideally, CMA should serve as a temporary fix in low-traffic areas and should generally be replaced with a warm or hot mix when weather conditions allow.
Ready to discuss your asphalt paving needs? Get in touch with our team at Bituminous Roadways to schedule a consultation! For more than 75 years, we’ve proudly served commercial clients throughout the Twin Cities, and we operate four local asphalt plants to ensure the quality and consistency of our raw materials.
To learn more or get started, feel free to call our Mendota Heights office today at 651-686-7001 or request a consultation online, and we’ll be in touch.
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