NCAT invites your comments and questions, which may be submitted to Christine Hall. Questions and responses are published with editing for consistency and space limitations.
Jerry Geib, John Garrity; Minnesota DOT
Do you use the spray paver with a 4.75 dense-graded mix? Do you have concerns with the water in the emulsion being trapped between the two lifts? Do you use the spray paver with larger NMAS mixes?
Oak Metcalfe, Montana DOT
I am curious to know how other states have been affected by the changes to AASHTO T 324 Standard Method of Test for Hamburg Wheel-Track Testing of Compacted Asphalt Mixtures. Research conducted for the purpose of better standardizing equipment requirements resulted in changes to the method that caused one widely used manufacturer's legacy equipment to be out of compliance. However, there is a long history of performance using that particular device. The changes to T 324 allow an agency to deviate from certain requirements and I'm curious if any have done so. We are trying to develop a comparative database to show that the legacy machine is still accurate, but are currently using another manufacturer for contract quality assurance (QA) and payment.
Tony Collins, North Carolina DOT
How many revisions do you allow on a job mix formula (JMF) before the mix needs to be redesigned?
Kevin Suitor, Oklahoma DOT
What states require the use of liquid antistrip agents in all mixes and what are the required dosage rates?
The following responses have been received to questions shared in the previous issue.
For those that use liquid antistrip agents, what method(s) do you allow to introduce them for asphalt mix during production (i.e. in-line at the mix plant, terminal blended, etc.)? What is the preferred method by contractors that use them and why? -Eric Biehl, Ohio DOT
Zane Hartzog, Alabama DOT
ALDOT allows blending of antistrip agents at the refinery or inline at the plant. I am told that contractors prefer inline blending for controlling cost of mixes that do not require antistrip agents. The ALDOT Standard Specification is Section 410.02 (c).
Michael C. Benson, Arkansas DOT
Blending is in-line at the mix plant or terminal blended. Our preferred method is terminal blended (producers do not have to modify plant).
Michael Stanford, Colorado DOT
CDOT does not allow liquid antistrips at this time.
David Howley, Connecticut DOT
ConnDOT has two producers that use WMA technology that doubles as an antistrip. One has it blended by the binder supplier, the other has purchased equipment to line feed at the mix plant.
Greg Sholar, Florida DOT
FDOT only allows terminal blending for liquid antistrip agents.
Mark Brum, Massachusetts DOT
We do not specify how antistrips are introduced. The majority of our producers choose to have antistrip terminally blended when it is required.
Jerry Geib, John Garrity; Minnesota DOT
MnDOT rarely uses an antistrip. If used, it would be liquid, terminal blend.
Tony Collins, North Carolina DOT
We have a few contractors that introduce the antistrip during production but most prefer terminal blended. I am not exactly sure why some prefer to introduce it during production.
Kevin Suitor, Oklahoma DOT
Either inline or terminal blended.
Seyed Tabib, Ontario MOT
In Ontario, the liquid antistripping additive is added in the asphalt cement terminal by the asphalt supplier (although we do not prohibit the in-line method at the plant).
Cliff Selkinghaus, South Carolina DOT
We only allow the antistrip to be terminally blended to ensure the dosage is correct, and we put this responsibility on the binder terminals to be sure they are compatible. Our LASA specification is SC-M-406, and our QPP and QPL is No. 104 on our website.
Matthew Chandler, Tennessee DOT
We allow in-line blended, terminal blended, or contractor tank dosing. I think the contractors prefer the in-line system if they have the equipment, as it gives the freedom to not have to use antistrips for private work if the client doesn't want it.
Enad Mahmoud, Texas DOT
Our TxDOT Standard Specification is Item 301: https://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/specs/2014/standard/s301.pdf
With the increased use of RAP and growing RAP piles, consistency of these piles is important in good quality control and pavement uniformity. What are other DOTs requiring for quality control measures by contractors for testing the RAP piles? What tests are required and at what frequency? -Eric Biehl, Ohio DOT
Zane Hartzog, Alabama DOT
From ALDOT Testing Manual Section 372: gradation and AC% are checked using 10 samples in the first 10,000 tons then once for every 5,000 tons of RAP added to a stockpile.
Michael C. Benson, Arkansas DOT
RAP stockpiles are tested by the contractor for quality control (QC) purposes.
Michael Stanford, Colorado DOT
We test RAP at the same frequency that we do other aggregates. An AC extraction is performed by the contractor during the mix design, then we check the AC through burn offs throughout the project.
David Howley, Connecticut DOT
ConnDOT requires two moisture content tests per day. We adopted percent within limits (PWL) to determine pay factors on binder content in 2017. At that time, we removed the requirement of determining binder content of RAP daily. Producers seem to be determining binder content daily in order to maintain acceptable PWL results.
Greg Sholar, Florida DOT
FDOT requires that gradation and AC content be measured every 1000 tons and Gmm measured every 5000 tons. We have allowable tolerances for these properties. If results consistently fall outside of tolerance, then a mix design revision may need to be made.
Nathan Awwad, Indiana DOT
INDOT requires RAP to be processed so 100% passes the 2" sieve. For surface mixtures, we require the RAP to be a fine RAP with 100% passing the 3/8" sieve and 95 to 100% passing the No.4 sieve. We require producers to document their testing frequency in their QC plans. Tests shall include binder content, gradation, moisture content, CAA, and Gsb of the aggregate.
Mark Brum, Massachusetts DOT
Producers are required to test their RAP for binder content and gradation at a frequency spelled out in their QC plan. For mixes that use >25% RAP, the producer is required to perform full binder grade testing at least every 24,000 tons of mix produced in accordance with AASHTO M 323 Appendices X1 to X3 and show that the combined binder meets the specified binder grade for that mix type. We have an ongoing RAP research project looking at RAP pile consistency at different times and from plant to plant across the state. We expect that specification changes will be made once the project is completed.
Jerry Geib, John Garrity; Minnesota DOT
MnDOT does not test RAP piles.
Oak Metcalfe, Montana DOT
We recommend fractionating but have stopped short of requiring it.
Tony Collins, North Carolina DOT
NCDOT Standard Specification 7.5.8 QC Quartering (RAP or RAS Samples): the 25 lbs. RAP or RAS sample shall be quartered by the Contractor to obtain the appropriate size sample for binder content and gradation tests. Split portions of RAP or RAS samples will be retained for a period of seven calendar days, commencing the day the sample(s) is tested, or until disposal permission from QA personnel is given, whichever occurs first. QA personnel will also take verification RAP or RAS samples directly from the cold feed or stockpile. Calculations of the percent moisture in the aggregate, RAP, and RAS samples will be to the nearest 0.1 percent. To determine moisture content, it is necessary to secure a representative sample of the aggregate. The size of the sample taken is determined by the nominal maximum aggregate size of the material. Regardless of the size of the aggregate, the procedure for making a moisture determination is basically the same. Note: It is easier to obtain a representative sample from the production stream, such as from the conveyor belt, than from storage bins or stockpiles. When the sample is taken from the conveyor belt, it should be removed from the entire cross-section of the belt for a minimum of two (2) feet. NCDOT Standard Specification 7.9.1 General A.: washed gradations will be performed on the recovered aggregate from the mix and individual RAP samples.
Kevin Suitor, Oklahoma DOT
ODOT will soon be requiring isolated piles, extraction, gradation and PG grading of the RAP material.
Seyed Tabib, Ontario MOT
We do not currently allow RAP in surface mixes on Provincial highways. For binder mixes that include RAP, we test the extracted aggregate for acceptance. We are letting trial contracts where RAP is allowed in the surface course but then the recovered asphalt binder will be tested for acceptance. We may require mix performance testing on the production mix in the years to come. We are currently in the process of developing acceptance criteria for performance tests (i.e., SCB, Hamburg, DCT).
Cliff Selkinghaus, South Carolina DOT
We allow the contractors to replenish when they choose to fractionate their RAP. We require the contractors test for binder content and gradation at a minimum of 1 test per 1000 tons of processed-fractionated RAP.
Matthew Chandler, Tennessee DOT
We require gradation and AC content to be verified once per 1000 Tons of RAP utilized.
Enad Mahmoud, Texas DOT
To help mitigate this, we require fractionated RAP (over 3/8” or ½” sieve) at plant. Also, we have reduced the amount of RAP in surface mixtures since these layers are the most cracking susceptible.
How are other DOTs handling approval for mix designs using a specific RAP pile and then switching to another RAP pile? Is a new mix design submittal required? Is verification required to ensure that the RAP used is similar to the original pile? -Eric Biehl, Ohio DOT
Zane Hartzog, Alabama DOT
We do not approve mixes using specific RAP stockpiles.
Michael C. Benson, Arkansas DOT
We require initial approval of the mix design only.
Michael Stanford, Colorado DOT
A new RAP pile would require a new mix design. We test RAP throughout the project to ensure consistent gradation and AC content.
David Howley, Connecticut DOT
We do not monitor RAP piles.
Greg Sholar, Florida DOT
FDOT does not allow contractors to switch RAP piles for a mix design. It would require a different mix design.
Nathan Awwad, Indiana DOT
INDOT assigns RAP a Gsb of 2.640 by default on all designs. We have provisions for stockpile specific testing if the producer believes it is more than 2.660 or less than 2.620. Actual binder content is reported by the producer. INDOT does not determine unless we feel there is an issue.
Mark Brum, Massachusetts DOT
We currently do not approve mixes based on a specific RAP pile.
Jerry Geib, John Garrity; Minnesota DOT
Acceptance is based off of the mix design. No verification of RAP is required.
Oak Metcalfe, Montana DOT
We use what we refer to as volumetric "targets" in our QA program. A contractor normally gets a quantity of "start up" mix to work with to establish these targets at the beginning of a job. This mix is not subject to our full QA penalties/incentives. Once those targets are established, we measure deviation for QA. If the situation you describe takes place (we refer to it as an 'aggregate source change after verification'), there is no "start up" mix and targets must be set immediately, eliminating the contractor’s ability to "dial in" their plant without suffering the full QA penalties.
Tony Collins, North Carolina DOT
Switching of RAP piles or verification of RAP is not being policed. We hardly ever require a new mix design when RAP piles change.
Seyed Tabib, Ontario MOT
We do not track the RAP piles; therefore no procedure is in place. The end product should meet specifications at all times.
Cliff Selkinghaus, South Carolina DOT
We make sure the contractors are keeping up with the requirements for binder content and gradation testing when submitting new designs. Most contractors do not have the space to place caps of individual stockpiles, so management is a nightmare unless you fractionate and you do not allow them to replenish. Also, we do not require the contractor to perform blending charts when running higher aged binder mixtures-no binder grade changes are required.
Matthew Chandler, Tennessee DOT
We consider RAP to be mix plant specific stockpile. If they fractionate, then they would become separate stockpiles. If they were to switch between a coarse and fine stockpile that would require a change to the JMF.
Enad Mahmoud, Texas DOT
If they change RAP piles, then they should be performing another trial batch since gradations, aggregate, and binder is most likely different. We also have operational tolerances during production. So, if their densities, gradations, AC%, etc., fall outside tolerances, they will be penalized. It is in the contractor’s best interest to disclose a change up front and ensure they can still meet the specification. I don’t know if all contractors are being held accountable for this, however, we have large RAP stockpiles in Texas, so I’m not sure how often they run out during production.
If you require prime coat, what material/type of emulsion do you allow to be used for prime coats?-Matthew Chandler, Tennessee DOT
Zane Hartzog, Alabama DOT
ALDOT Standard Specifications for Highway Construction Section 401: emulsified asphalt: AE-P, CRS-1h, CMS-1hp, or NTSS-1HM; cutback asphalt: MC 30 or MC 70 for tight bases; MC 250, RC 70, or RC 250 for open bases. Emulsified Petroleum Resin: EPR.
Michael Stanford, Colorado DOT
CSS-1h & SS-1h. We have a specific requirement for our Asphalt Emulsion for Prime Coat (AEP). Saybolt: 20-150 seconds at 50°C, per AASHTO T 59. % Residue: 65% minimum, per AASHTO T 59. Oil distillate by volume, %: 7% maximum, per AASHTO T 59. Test on residue from distillation: solubility in Trichloroethylene, %: 97.5 minimum, per AASHTO T 44.
Greg Sholar, Florida DOT
FDOT has traditionally used AASHTO specified prime materials but lately several trackless tack suppliers have gone through the process of building test sections to get their trackless tack products approved as prime.
Mark Brum, Massachusetts DOT
We do not use prime coat.
Jerry Geib, John Garrity; Minnesota DOT
MnDOT does not prime.
Oak Metcalfe, Montana DOT
We have been allowing Magnesium Chloride as an "aggregate treatment" with varying results. We still allow a cutback emulsion (MC-70) but no one in our state uses or produces it.
Tony Collins, North Carolina DOT
NCDOT uses EA-P, CMS-PX, and CSS-1RP.
Eric Biehl, Ohio DOT
OH DOT requires medium cure cutbacks (usually MC-30 or MC-70) for prime coats, but we haven't done many in a while. For soil stabilization, rapid set emulsions (typically CRS-2) have been used and have appeared to work well.
Kevin Suitor, Oklahoma DOT
Several companies are producing a product specifically for asphalt prime coat.
Cliff Selkinghaus, South Carolina DOT
We have an emulsion called an EAP Special (Section 407.2.4 of the SCDOT standard) that is commonly used in SC.
Enad Mahmoud, Texas DOT
TxDOT uses MC-30, AE-P, EAP&T, and PCE.