HMA aggregate size and gradation design
HMA aggregate size and gradation design
(OP)
GRADATION: I don't understand the differences between the "coarse" and "medium" gradations used by Caltrans (neither of which is "open").
SIZE: When would you use a 3/4" as opposed to a 1/2", what are the benefits and drawbacks? When would you specify a 1/2" course as opposed to a 1/2" medium?
None of this affects the equivalent gravel thickness of the AC?
SIZE: When would you use a 3/4" as opposed to a 1/2", what are the benefits and drawbacks? When would you specify a 1/2" course as opposed to a 1/2" medium?
None of this affects the equivalent gravel thickness of the AC?





RE: HMA aggregate size and gradation design
Conversely, decreasing the coarse aggregate nominal size increases the AC content required and makes the void parameters more difficult to control.
RE: HMA aggregate size and gradation design
There are two questions (about HMA characteristics):
1) Differences between max size 1/2" vs 3/4"
2) Differences between "coarse" and "medium" gradation.
What are the characteristics which make one worth specifying over the other, relative to the pavements in service life and its constructability.
From what I read of Ron's response, he is saying that using 3/4" instead of 1/2" uses less binder and therefore 3/4" is easier to compact. It would seem that the gradation would have more to do with the binder required than the max size of the aggregate?
This response is a start, but...Are there any pavement experts there...a true-blue civil?
RE: HMA aggregate size and gradation design
Each state DOT tends to define their own based on what has worked in that state. Some states use viscosity grading for their asphalt cement, some use penetration grading (in my experience, more popular). It depends on the leanings of the state materials engineering group and the requirements of traffic, durability, material sourcing, etc.
In general, mixes with a 3/4" top size aggregate would be consider "coarse" mixes, with 1/2"-3/8" being in the "medium" gradation range, and smaller coarse aggregate being in the "fine" gradation range...below that would be sand-asphalt hot mixes.
The mix structural properties do not change significantly for dense graded mixes between "coarse" and "medium" gradations. Both can achieve significant stability and durability with proper design.
RE: HMA aggregate size and gradation design
Anyone able to discuss pavement aggregate size and gradation, an abstract and conceptual or pragmatic perspective...Anything?
"Coarse", "medium", or "open", means gradation. I am specifically asking about aggregate variations--not cement, and am also not asking about open graded friction courses, I know what "open" gradation is used for.
It appears from Ron's post above I did not explain what I'm asking well enough since that post is off-topic.
The question is what attributes and drawbacks do aggregate variations lend to the pavement. What types of service and observed distress make one preferable over the other. There wouldn't be these multiple gradations unless they were suitable for differing circumstance. Anyways, I give up...either I can't explain the question well enough or there are no AC pavement experts participating in this form.
RE: HMA aggregate size and gradation design
RE: HMA aggregate size and gradation design
Variation -size-
Sorry USCU, no expert here but I will give it a shot.
The HMAC Mix Designs we specify in our pavt.s are mainly B, C, and D.
The B mix has the larger aggr. and is used for thicker "base course" type applications (6"-12" in multiple lifts)
The "C" mix aggr. is smaller than the "B" and is generally used for thin base (4"-6") courses, but mostly surface courses.
The "D" is used exclusively for thin applications where we only need a thin overlay (2" or less)
This is one small attribute/drawback of aggr.s -size- or Master Gradation Band.
The big question is will the HMAC compact to a density specified in our spec.s (which correlates to % air voids) and to longevity out on the roadway.
Speak to a lab tech that designs and tests HMAC. Call a local hot mix plant and speak to the QC person.
RE: HMA aggregate size and gradation design
"There are no AC pavement experts participating in this forum."
Having dealt with ACP for a number of years, the one thing I have learned: THERE ARE NO EXPERTS.
RE: HMA aggregate size and gradation design
RE: HMA aggregate size and gradation design
If you know an ACP expert, I would greatly appreciate the name and number. I have unanswered questions of my own. The experts I have met...well I guess it's best unsaid.
RE: HMA aggregate size and gradation design
RE: HMA aggregate size and gradation design