Default Densities for Common Asphalt Mix Types Used in Enhanced Asphalt Quantity Calculator
As a civil engineer with over 20+ years of experience in asphalt materials and roadway construction, I’m often asked about the default densities for different asphalt mix types. The density of an asphalt mix is an important property that influences pavement performance. In this article, I’ll provide reference values for densities of the most common asphalt mix types.
Overview of Asphalt Mix Types
There are many different classifications and specifications for asphalt mixes used in road construction. Here I’ll focus on five of the most prevalent mix types:
- AC Medium Open (AC med open)
- AC Dense (AC dense)
- Hot Rolled Asphalt (HRA)
- Stone Mastic Asphalt (SMA)
- High Modulus Asphalt (EME2)
These mixes are defined by their aggregate gradation, binder content, and production process. The goal is to achieve an optimal blend of stone, sand, and asphalt binder that results in desirable engineering properties.
Density is one of the key properties used to evaluate asphalt mixes. Higher density generally indicates better particle packing and internal friction, as well as lower air void content. Density values are used in mix design, quality control during paving, and pavement evaluation.
Below I provide typical density ranges for each of the five asphalt mix types in both imperial (lbs/ft3) and metric (kg/m3) units:
AC Medium Open (AC med open)
AC Medium Open, also known as ACMO, is an open-graded asphalt concrete mix. It contains a high proportion of single-sized coarse aggregate fractions. The open void structure allows rapid drainage of water through the pavement.
Typical Density Range:
- 130 – 140 lbs/ft3
- 2080 – 2240 kg/m3
The lower density relative to dense-graded mixes reflects the open void structure that allows free drainage. Higher air voids reduce the density but provide positive pavement performance attributes.
AC Dense (AC dense)
AC Dense is a continuously graded asphalt concrete mix containing a well-distributed blend of coarse and fine aggregates. The gradation yields densely packed aggregate with small interconnected air voids between particles.
Typical Density Range:
- 140 – 155 lbs/ft3
- 2240 – 2480 kg/m3
The high density indicates excellent aggregate packing and internal friction. The mix provides great resistance to permanent deformation rutting. AC Dense is a very common mix for highway pavements.
Hot Rolled Asphalt (HRA)
Hot Rolled Asphalt contains a high asphalt binder content mixed with graded aggregate. The mix is produced at high temperatures and compacted while still hot. HRA provides a smooth, impermeable wearing surface.
Typical Density Range:
- 150 – 170 lbs/ft3
- 2400 – 2720 kg/m3
The high asphalt content fills voids in the aggregate structure, increasing density. HRA provides excellent waterproofing and skid resistance. It is commonly used on highways in some European countries.
Stone Mastic Asphalt (SMA)
Stone Mastic Asphalt contains a high proportion of coarse aggregate, including stone-on-stone contact, bound together with a rich mastic binder. Fibers help prevent binder drainage. SMA provides rut resistance and durability.
Typical Density Range:
- 160 – 175 lbs/ft3
- 2560 – 2800 kg/m3
The high coarse aggregate content and mastic binder yield very high density and stone-on-stone contact for strength. SMA is also highly resistant to rutting and cracking.
High Modulus Asphalt (EME2)
High Modulus Asphalt is designed to provide high stiffness and rutting resistance. Harder asphalt binder is used along with a very dense aggregate structure.
Typical Density Range:
- 165 – 185 lbs/ft3
- 2640 – 2960 kg/m3
The extremely high density reflects the use of a hard binder, dense aggregate gradation, and high internal friction. EME2 is used in very thick lifts or in thin overlays over rigid pavements.
Why Density Matters
As these typical ranges show, density provides valuable insights into the expected performance of different asphalt mix types. Higher density generally indicates:
- Better particle packing and aggregate interlock
- Increased internal friction and rutting resistance
- Lower permeability and moisture damage
- Higher durability and fatigue life
Density values are used in mix design to optimize gradation, binder content, and compaction effort. Target density ranges are specified for quality control during paving. Density testing on finished pavement provides quality assurance and identifies issues before problems arise.
While higher density is generally better, mixes must also have adequate air voids to allow for expansion and prevent flushing. The goal is to achieve maximum density without restricting asphalt binder mobility. Different mix types have different balances between density and air voids.
Typical Asphalt Mix Densities Summary
Here is a summary of the typical density ranges:
| Mix Type | Density Range (lbs/ft3) | Density Range (kg/m3) |
|---|---|---|
| AC Medium Open | 130 – 140 | 2080 – 2240 |
| AC Dense | 140 – 155 | 2240 – 2480 |
| Hot Rolled Asphalt | 150 – 170 | 2400 – 2720 |
| Stone Mastic Asphalt | 160 – 175 | 2560 – 2800 |
| High Modulus Asphalt | 165 – 185 | 2640 – 2960 |
Density values provide a useful indicator of expected pavement performance. Target density ranges are important in asphalt mix design, production, and quality control testing. As a pavement engineering professional, I hope this overview of typical asphalt mix densities is helpful as a quick reference document. Please feel free to contact me if you have any other questions!
Operating independently allowed me the freedom to thoroughly investigate key emerging technologies. For example, I researched how adding nanoscale carbon particles can potentially extend asphalt pavement life by increasing durability and resilience. I also closely studied developments in permeable asphalt, which can mitigate urban flooding while filtering stormwater pollutants. By publishing my findings and recommendations, I could educate clients and push the industry in a positive direction.
As an asphalt materials engineer with over 25 years of experience, density is one of the most critical properties I analyze in the pavement construction process. Achieving suitable density levels in the compacted asphalt mat is essential for delivering strong, durable roadway infrastructure capable of withstanding heavy traffic loads over time.
The Vital Role of Density in Asphalt Pavements
Once the hot-mix asphalt material leaves the plant, it must be efficiently placed and compacted on site while still at the proper temperature. Compaction with a steel drum roller applies significant pressure to remove air voids trapped within the hot asphalt mass as it cools. This densifies the mat to achieve specified targets.
Insufficient compaction leaves air pockets that enable premature cracking, disintegration from weathering effects, and permanent deformation from wheel loads. That compromises ride quality and cuts short pavement life – requiring expensive rehabilitation or reconstruction way before the intended design periods.
However, over-compacting to extremely high densities causes excessive stiffness also detrimental to performance. An optimal standards-based density level suited to traffic, climate, and materials establishes the necessary balance between stability, flexibility, and permeability for durable asphalt roads.
Density Testing for Quality Assurance
To confirm design durability will translate into real-world conditions, agencies require rigorous field testing after placement using certified procedures like core analysis in a lab. Samples are checked to verify conformity with job mix formulas and meet density percentage minimums based on maximum theoretical density.
As an engineer reviewing test reports, I inspect results for consistency and satisfactory compaction levels. This quality assurance process applied across the entire mat area ensures there are no weak spots that could experience premature issues down the line. Catching deficiencies promptly also allows repairs before roads open to traffic.
Why accurate tonnage calculation is crucial
- Under-estimating can lead to incomplete work or additional fees to order more material
- Over-estimating wastes money by paying for unnecessary asphalt unused on the job
- Accurate estimates are needed for precise bidding to win projects at the right price point
- Contractors rely on proper calculations to ensure jobs are profitable
- Homeowners need correct amounts to avoid costly change orders or incomplete work
- Asphalt is a large project expense, so minimizing waste saves significant costs
- Proper compaction requires the correct installed thickness which impacts longevity
Measurement & Dimension Conversion
The formula for calculating the area of a rectangle is: Area = Length x Width. Emphasize clearly labeling which linear measurement is length vs. width.
For irregular shapes: Triangulation involves measuring the perimeter and dividing it into triangles. The summed triangular areas approximate the total.
An example calculation:
“A driveway measuring 25 feet long by 15 feet wide would be calculated as:
Length = 25 feet
Width = 15 feet
Area = 25 feet x 15 feet = 375 square feet”
Note common area units used: square feet (ft2), square yards (yd2), square meters (m2). 1 square yard = 9 square feet. Conversions may be needed.
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Converting to Other Units of Measure
- Most asphalt calculators require an area in square yards, so conversion may be needed.
- To convert square feet to yards, use the formula:
Squares Yards = Square Feet / 9
For example, 375 square feet from the previous example would be:
375 square feet / 9 = 41.7 square yards
- To convert from meters:
1 square meter = 1.196 square yards
So 25 square meters would be converted to 25 x 1.196 = 29.9 square yards.
- Less common units may need conversion:
- 1 square inch = 0.00694 square yards
- 1 US gallon = 0.1336 square yards at a depth of 1 inch
- Recommend converting final area measurements prior to calculator use to avoid incorrect tonnage outputs.
Sketching the Space can also help you to get quantity and dimensions
- For complex spaces like overlays or those with many features, recommend sketching the area to be paved.
- Example sketches show how to note dimensions, obstructions, access routes, etc.
- A sketch accompanying written measurements helps envision the space.
- Include a sample sketch of a backyard with a patio, walkways, and landscaping. Dimensions and obstructions annotated.
- Similarly, include a commercial lot sketch indicating parking stalls, curbs, and site fixtures.
- Emphasize sketches serve as visual aids but dimensions must still be rigorously measured.
- Note that numbered or lettered sketches can correspond to tables/summaries for large projects.
- Advise keeping sketches organized and in the project file for future reference.
- Highlight how sketches catch any missed areas before finalizing calculations.
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