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SUPERPAVE Digest 369
Topics covered in this issue include:
1) designing above the 0.45 curve by [email protected] 2) Re: designing above the 0.45 curve by [email protected] 4) RE: designing above the 0.45 curve by "Jim Warren"
To: [email protected] Subject: designing above the 0.45 curve From: [email protected] Date: Tue, 27 Jun 2000 09:12:07 EDT
Dear Group:
I have been asked to design the 9.5mm & the 12.5mm SUPERPAVE mixes so that each respective JMF is above the 0.45 Curve. I have no experience with these finer graded SUPERPAVE mixes.
Please share with Me any knowledge the group might have for these "above 0.45 Graded" mixes. Any imput, good or bad, will be helpful.
Thanks, Mike [email protected]
To: [email protected] Subject: Re: designing above the 0.45 curve From: [email protected] Date: Tue, 27 Jun 2000 09:27:22 -0500
I'm guessing that you mean above the restricted zone and not the 0.45 curve.
Your biggest problem will be making VMA. Given that, the mixtures will be easier to compact in the field. You may have problems with Nini. Other than that, I think that you'll like those mixtures. Your permeability will be less as a general rule. You may have increased moisture sensitivity problems. You'll have to watch the dust proportion ratio. Your binder content will increase due to increased surface area of the aggregate.
We've had good success with these mixtures though I prefer that they do go below the restricted zone. This is contrary to what WesTrack told us.
Kenneth Hobson [email protected] Bituminous Branch OK DOT 405-522-4918 405-522-0552 fax
To:
Florida draws a distinction betwen coarse and fine at the higher traffic levels. Greater than 10 million ESALs are required to be coarse graded (below the restricted zone). The majority of our pavements fall in the lower traffic zones <10 million ESALs and can either be fine or coarse graded. Many lower volume pavements are not designed to take the compactive effort that coarse mixes require and you would be better off with a finer mix in these applications. I am not yet convinced that we can't make a fine mix every bit as strong as a coarse graded one - but that is a different story. FYI - we have several million tons of coarse graded Superpave down now with extremely good performance, though it takes a different attitude (and attention to detail)to be successful with these mixes.
Jim Warren ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Jim Warren Executive Director Asphalt Contractors Assoc. of Florida, Inc. 1007 E. DeSoto Park Drive, Suite 201 Tallahassee, FL 32301 tel: 850-222-7300 fax: 850-942-5632 email: [email protected] web: www.acaf.org
To: [email protected] Subject: Re: designing above the 0.45 curve From: [email protected] Date: Tue, 27 Jun 2000 13:47:21 EDT
I suspect that it would be interesting to the group if you shared with us the reasons why you have been asked to do this and whether you mean above the 0.45 curve or just above the old restricted zone. The reason I would be interested in knowing this is that if the problem is that you have a producer who wants to get rid of finer material stockpiles, it is not necessarily true that the only way to do it is by inverting the preferred direction of the curvature. You can still design below the 0.45 curve with the finer materials and still get performance if you know how to make the aggregate skeleton work for you. You may or may not be able to do it with a Superpave design, but there are published methods available that should work in terms of both ensuring long term pavement performance and optimizing the consumption of the stockpile(s) that need to be reduced in size. To: [email protected] Subject: designing above the 0.45 curve--(updated) From: [email protected] Date: Tue, 27 Jun 2000 15:52:04 EDT
Dear Group:
Yes, I mean to design a 9.5mm & a 12.5mm mix above the resricted zones. ESAL level - 3.0mill to 30.0 mill Design request was made by a federal Inspector. He wants to make 4 control strips. 2 control strips with the coarser (below restr. zone) 9.5mm & 12.5mm mixes & 2 control Strips with the finer (above restr. zone) 9.5mm & 12.5mm mixes. All 4 mixes will be using the same aggregate sources. I think the concern is the handwork using SUPERPAVE mixes in general.
The coarser (below restr. zone) 9.5mm & 12.5mm mixes are already Federal and State approved mixes. Thanks, [email protected]
To:
Designing above the caution zone is like HMA designs above the maximum density line have always been; beware the sand hump. You can see the hump easier if you plot percent individually retained versus the sieve size. If the resulting plot has two humps you may have problems with compaction and high voids. Close to 90% of our mixes in Wisconsin are designed on the fine side and are performing well.
Erv
To: [email protected] Subject: Re: designing above the 0.45 curve From: [email protected] Date: Wed, 28 Jun 2000 00:50:52 EDT
Generally speaking designing mixtures:
1.) Between the control points prescribed by Superpave, 2.) Without sand humps, 3.) Out of the restricted zone from below the maximum density line, and 4.) Within Voids, VMA and VFA criteria, will ensure high quality asphalt mixtures are producible and compactible. The most "famous" of these criterias, which requires continued evaluation is the restricted zone. Several states design excellent mixtures above the maximum density line and through the restricted zone from above this line. The important analysis required at that time is what product is taking your mixture through the restricted zone.
If the product is a fractured sand which is low on #30 material then invariably your design will pass directly through the restricted zone from above the maximum density line. The mixture produced will most likely be an asphalt mixture with low to no likelihood of segregating, good FAA measurements and compactibility as well as excellent performance capability. Fine graded mixtures which pass through the restricted zone from above should be considered acceptable when the product driving the gradation through the restricted zone is a fractured sand.
However, the criteria for staying out of the restricted zone from below the maximum density line for coarse graded designs seems valid for avoiding mixtures with sand humps. The same concept of avoiding sand humps in fine graded designs is equally valid and several states have requirements limiting the P#30 < 0.5P#4. One state I work with specifies mixtures for low ESAL applications to be designed above the maximum density line. The goal is to ensure that we don't give up all the good we have learned throughout the years regarding durability and economics for these types of roadways.
Regards,
Tim Murphy JFG Technical Center 18000 S. Williams St. Thornton, IL 60476 708-877-1801 www.jfgtechcenter.com
SUPERPAVE Digest 371
Topics covered in this issue include:
1) Re: designing above the 0.45 curve by [email protected]
To: [email protected] Subject: Re: designing above the 0.45 curve From: [email protected] Date: Thu, 29 Jun 2000 08:30:24 -0600
THe City of Albuquerque specified fine side SUPERPAVE gradations and has used them since its 1992 specification update. The gradations specification is used for both Marshall analysis and gyratory design for nominal maximum size aggregates, 1" (25 mm), 3/4" (19.0 mm), 1/2" (12.5 mm), and 3/8" (9.5 mm). The following points of consideration are offered for preparing a design.
1. Base aggregate gradations must be developed consisitent with the sieve sizes used in SUPERPAVE and AASHTO screens, particularly the no.4 screens and smaller. If the base aggregate gradations are broken on the no.10 , 40, et al, screens, you will have problems. 2. The better design and performance of mixes was found to occurr when a fine side target gradation, the combined aggregate gradation, had a characteristic shaped curve similar to the fine side gradation. This point is required in the City's specification. Thus as the coarse side gradation is a "S" shaped curve, the fine side curve becomes a series of two convex curves above the 0.45 maximum density line, with the intersection of the two curves creating a "knee" at the coarsest screen defining the "restricted zone". The design target gradation is not allowed to violate the restricted zone, but, the production limits, + tolerence, applied to the design targets may violate the zone. Only the specification control screens are considered. The intermediates are not considered in the development.
I have attached the specification for your reference.
Good luck!
(See attached file: Sec11699.wpd)
Sec11699.wpd