Different Types of Hot Mix
In this blog we will break down the various types of hot mix asphalt used within our region and where/when they are used.
What is Asphalt anyway?
Asphalt is a mixture of bitumen with coarse and fine aggregates, used as a hard surface for driveways, roadways, and parking lots. There are two primary components of asphalt; aggregates (stone, sand, ground up recycled asphalt) and bitumen, which we call “asphalt cement” (AC). These ingredients are heated up, and mixed together to create hot mix asphalt. Like most industries, commonly used materials are given trade names, the asphalt industry is no different. For asphalt, the words “Hot Laid” are abbreviated to “HL” followed by a number which indicates its aggregate stone mixture. Within our region, the most used hot mixes are “HL8”, “HL4”, “HL3”, “HL3F”, and finally “Cold Mix.” To simplify this coding, the higher the number, the larger the aggregate used, the more stone content, the stronger the asphalt. There are several factors that contribute to the material choice which we will describe below.
HL8
The aggregate mix of HL8 is comprised of about 25% large stone, 25% medium stone, 35% sand, and 15% ground up recycled asphalt.
Uses: This is a large sized stone, binder (base) course mix. Due to the quantity of large stone, HL8 has a very stony finished look to it, which is the reason it is not used for the surface course. HL8 is used as the base layer for heavy duty applications which require 2 or more layers of asphalt, more commonly commercial parking lots or municipal roads, and then topped with HL4 or HL3.
Benefit(s): High strength.
Drawback(s): Segregated, rocky visual appearance.
HL4
The aggregate mix of HL4 is comprised of about 15% large stone, 15% medium stone, 10% small stone, 45% sand, and 15% ground up recycled asphalt.
Uses: This is a medium sized stone mix which can be used as binder (base) course and in some applications as a surface (top) course mix. Due to the large stone quantity, it is again most used as the base layer for heavy duty applications. However, thanks to the introduction of medium and small stone, it can also be used as a top course in specific applications, whether that is the surface course of a multiple layer project, or a light duty project which only requires single layer of asphalt. Most often if HL4 is used as a surface mix, it would be a commercial parking lot, or municipal road where higher strength is required, but overall visual appearance is not of high concern for the client.
Benefit(s): Medium/high strength. Long life span.
Drawback(s): Segregated, rocky visual appearance when raked.
HL3
The aggregate mix of HL3 is comprised of about 25% medium stone, 15% small stone, 45% sand, and 15% ground up recycled asphalt.
Uses: HL3 is the most versatile asphalt mix. Due to the smaller stones HL3 is again most used as the top layer applications, whether that is the surface course of a multiple layer project, or a light duty project which only requires single layer of asphalt. Due to the mixture of medium stone, small stone, and sand, HL3 provides great overall balance between strength and visual appearance. This mix is used in parking lots, roadways, and residential.
Benefit(s): Very good overall strength for many applications and finishes well visually.
Drawback(s): Still shows segregation when raked by hand. May crack when loaded heavily.
HL3F (Fine)
The aggregate mix of HL3F is comprised of about 20% medium stone, 10% very small stone, 55% sand, and 15% ground up recycled asphalt. HL3F is very similar to HL3, however has a higher quantity of sand, which is why it is called HL3 “Fine”.
Uses: This is a small to medium sized stone mix which is used as a surface (top) course mix. With the use of very small stone and additional sand, HL3F is used only in top layer applications on light duty project where visual appearance is the top priority. Due to the mixture of such small and fine material, HL3F provides lower overall strength but a nicer visual appearance. HL3F is susceptible to scuffing and scratching, so its uses are limited. This mix is used most often for light duty residential, and walkways. If a client needs high strength but is very concerned with visual appearance, HL3F can be used as a top course on a multi course application but we often recommend HL3 its durability improvements.
Benefit(s): Excellent visual appearance.
Drawback(s): Lower strength causing lower life span and susceptible to scuffing.
Cold Mix
This mix is produced by mixing emulsified bitumen with un-heated aggregates.
Uses: Cold mix is used for temporary patching in applications where hot mix is not immediately available, for example, an emergency roadway excavation which happens overnight or in the winter. Cold patch is sometimes used by owners as a solution for small pot holes due to its retail availability in hardware or building supply stores, however, it is important to remember that it is NOT intended for permanent repair, and should not be used as such.
Benefit(s): Retail availability at building supply stores. Easy to install, does not require heat.
Drawback(s): Temporary solution only. Deteriorates rapidly.
Ok, so after all that, what should I use for my project?
Every project is different but for general rule of thumb comes down to heavy duty or light duty.
Heavy Duty (Industrial or heavy duty commercial), we recommend a multiple layer approach: Most commonly 2” depth HL8 base layer topped with 1.5” or 2” depth HL4 or HL3 top layer, depending on the client’s priority. If visual appearance is top of mind, HL3, if strength is most important HL4, and the depth is often determined by project budget.
Light Duty (commercial parking lot or residential), we recommend single course, 2.5” or 3” HL4 or HL3 based again on client priority. If visual appearance is top of mind, HL3, if strength is most important HL4, and the depth is again determined by project budget.
Conclusion
Thank you for your time in reading this blog. As you have read, asphalt material selection and structure composition is very important decision to a successful long lasting project. If you happen to have any further questions regarding asphalt materials, or have a project that you may want us to quote, we’d love to hear from you!
Phone: 519-442-2281
Email: info(at)parisconstruction.ca
