Monday, December 3, 2012

California Vs. Nevada Binder Specs: What's the Difference? (Guest Blog)


California vs. Nevada Polymer-Modified Asphalt Binders: 
by Chris C. Gerber and Roger Schlierkamp, Twining, Inc.

Caltrans and NDOT have each created polymer-modified asphalt binders that meet PG “plus” specifications that differ in their properties, but is there really a difference between the two? The California Department of Transportation (Caltrans) and the Nevada Department of Transportation (NDOT) use different polymer-modified asphalt binders. Since the implementation of the Superpave performance grade (PG) system, several state highway agencies, including Caltrans and NDOT, have experienced good performance with polymer-modified hot mix asphalt (HMA) mixtures and have created the PG “plus” specifications to enhance the performance of flexible pavement in harsh climates.

Caltrans uses a polymer-modified asphalt binder, PG64-28PM, in certain projects throughout the state. They use PG64-28PM polymer-modified asphalt binders with their dense-graded asphalt mixtures. The “PM” extension indicates that the binder meets the Caltrans PG “plus” specifications which include the standard Superpave PG system plus maximum phase angle on RTFO binder at the high critical performance temperature and elastic recovery on RTFO binder at 77°F. NDOT uses the polymer-modified asphalt binder PG64-28NV on all roadways in the northern part of the state. The “NV” extension indicates that the binder meets the NDOT PG “plus” specifications which include the standard Superpave PG system as well as properties such as toughness and tenacity on original binder at 77°F, ductility on original, and RTFO binder at 40°F.

In order to test their differences, the asphalt binders were supplied by two manufacturers, Paramount Petroleum Company and Valero Marketing and Supply Company. They each provided a blend of PG64-28PM and a blend of PG64-28NV asphalt binder.

The HMA mixtures were designed using the Marshall design method per the agency’s specifications.  The optimum binder content was selected at 4% air-voids and then used to determine the corresponding values for Marshall stability and flow, VMA, and VFA for the appropriate relationships. The optimum binder contents were 5.0% by total weight of mix for all evaluated mixtures. The aggregate source was consistent for all mixtures, and the same gradation was used. Laboratory tests were then performed for the following modes of pavement failure: moisture damage, fatigue cracking, permanent deformation, and thermal cracking. The tests revealed interesting results. For moisture damage, the PM and NV binders displayed excellent resistance by displaying excellent stiffness after 6 freeze-thaw cycles. For fatigue cracking, the NV binder displayed significantly better resistance under repeated flexural bending. For permanent deformation resistance, the NV binder exhibited more stability. Lastly, for thermal cracking resistance, the NV binder displayed the lowest fracture temperature and intermediate level of fracture stress, making it more resistant to thermal cracking compared to the PM binder.

The results of the laboratory tests show that the two different binders are in fact different. The PM mixture was not as stable as the NV mixture.  Although the majority of California does not experience the extreme temperatures that Nevada does, it is important to be familiar with other products and standards. We are now aware of this other binder should we come across a situation where this binder would be beneficial to use.   

Reference: Hajj, Elie Y., Sebaaly, Peter E., Schlierkamp, Roger W., Cortez, Edward. “Laboratory Evaluation of PG64-28PM Polymer-Modified Asphalt Binders.” Western Regional Superpave Center. January 2011.


About Twining: For over 100 years, Twining has been building a reputation for quality, reliability and expertise providing geotechnical, materials testing and construction inspection services.  With five state-of –the-art laboratories and over 250 inspectors across California, Twining has the resources to meet changing needs of complex construction projects from multi-building hospital campuses to interstate highways. Twining employs some of the industry’s most well known construction materials experts who perform research and consult with regulatory agencies to shape the future of construction standard practices. Find out more about Twining innovations and services at www.twininginc.com or follow us on facebook at www.facebook.com/TwiningInc.

Monday, November 19, 2012

Section 39 Updates & More!

Sorry about the lack of posts lately but I'm hoping that some of our new website features will make up for it. As you may have already noticed, we've added three more tabs to the navigation bar on the website.  "Test Method Updates" is a page that compiles all of our posts regarding changes to test methods.
"Superpave" is a page that compiles all of our posts regarding Superpave.  

"Caltrans Section 39 Updates" is the new page that we're most proud of.  We've gone through all of the Revised Standard Specification (RSS) Updates since the inception of the Caltrans 2010 Specifications and created red-lined documents to make it easier for you to see the changes for each update.  The exciting thing is that we're utilizing Google Docs which allows you to add comments to any section of the document.  This will allow you to share your opinions on changes as they come out.  Quality in California will share your comments with industry committees and/or Caltrans to ensure that your voices are heard, even if you don't have time to attend a meeting yourself.  Please take advantage of this great tool and let us know if you have any problems using the software or any suggestions on how to make the website better.

We're excited to move the website towards being a comprehensive tool for you to use to communicate with other industry and government leaders in construction quality control.  Feel free to share any ideas or suggestions by email at toni@qualityincalifornia.com.

Wednesday, November 7, 2012

"A Beginner's Guide to AASHTO Accreditation"

As part of their Fall 2012 newsletter (which I highly recommend you sign up for) AMRL recently published an article on how to get started with your AASHTO laboratory accreditation   As you must know by now, if you plan on pursuing Caltrans work in the near future you will need your labs to be AMRL accredited so this article will likely interest you.  It's short, to the point, and can be found here.  

We've also started a discussion forum to help you discuss any issues and questions you may have in regards to the AASHTO laboratory accreditation process.  The discussion forum can be found here: AASHTO Lab Accreditation Forum.  Feel free to post any questions you may have, even if you feel more comfortable posting them anonymously.  Our aim is to get you the answers you need to make this an easy transition over the next couple of years.    As always, good luck!

UPDATE 11/9/12:  Bob Lutz, AMRL Manager and Brian Johnson, Supervisor of the AASHTO Accreditation Program will be trolling our AASHTO Lab Accreditation Forum and will answer any questions that you have for our readers.

Monday, October 29, 2012

Superpave Pilot Project Changes V

This post will conclude our journey through the major upcoming changes to Section 39 that will take place with Superpave implementation.  This post will focus on the changes that your laboratories will be influenced by.  Our previous posts were as follows: The first post, Changes I, focused on changes to the paperwork and paving procedures.  The second post, Changes II, focused on changes that affect the operations group at hot mix asphalt plants.  The third post, Changes III, focused on the changes that will affect you if you produce RAP and add it to hot mix asphalt.  The fourth post, Changes IV, focused on Mix Designs & Mix Verifications.

Although the changes that affect your plants, such as lowered target ranges and possible changes to your crushing operations may seem daunting, I personally feel that the laboratories will be going through the most time consuming changes over the next two years.  Here are the major items:



LABORATORY
  • Caltrans is officially going to use AASHTO test methods with Caltrans exclusions.  When I say, "with Caltrans exclusions" I mean this: the AASHTO methods allow for things like a hand shaker in the SE test method.  Caltrans will specify that you use the AASHTO method but will exclude certain parts of it such as not being allowed to use a hand shaker in the SE test.  These changes will be noted in the Caltrans IA manual that is slated to be written (but not released) in November 2012.
  • Since Caltrans cannot legally certify a person in AASHTO test methods, they will instead be issuing a letter of proficiency to technicians for each of the AASHTO test methods which means your technicians will still need to certify one on one with the IA inspector for all of their test methods.  This also means that your technicians will be doing double certification duty because they may need to certify for the Caltrans test methods to work on non-Superpave Caltrans jobs and the AASHTO test methods to work on Superpave jobs.  The letter of proficiency will only be valid for Caltrans jobs, not for city or county jobs.
  • Letters of proficiency will be valid for 1 year.  Sometime in the future Caltrans hopes to extend this to 2 years to align with the Caltrans certifications.
  • The IA inspector will have the ability to grandfather experienced technicians into the AASHTO test methods but it will not be required for them to do so.
  • The Caltrans IA lab certification requirements will remain the same but your lab will now also be required to have your lab certified with AMRL.  For purposes of the pilot projects in 2012 & 2013, if you have submitted your paperwork to AMRL and are in the que for certification this will be enough to test on a Superpave job.  Starting in 2014, it will be required to be fully certified with AMRL so start your certification process now!  You can learn more about the AMRL Certification Program in our post: Inside AMRL's Certification Program from earlier this year.
  • IA will be cracking down on how your technicians perform test methods as we move into Superpave.  If IA find that you are doing a test wrong, no matter what test it was, they have the right to revoke ALL of that technician's certifications, not just the test they were doing wrong.  In addition, any test results that were previously obtained by that technician for that test method will no longer be valid.
  • In the AASHTO test method for fine specific gravity (T 84) you CAN wash the fines.  As of right now Caltrans will be allowing the washing of fines in Superpave.  The reasoning for this (and for the short lived change in 2011) was that Caltrans wanted to give industry the ability to recreate what may happen in the plant production environment.  For instance, if you have a mineral filler system on your plant, the fines will have been removed in production and washing your fine specific gravity sample in the mix design process may be justified.  However, in a plant that does not remove the fines during production the washing process in the lab would be unnecessary.  With Superpave you will have the ability to do one or the other but it will likely be your responsibility to ensure that the Caltrans lab is using the same method that you are.      
  • The Fine Aggregate Angularity (FAA) test is now mandatory for all mix designs, not just when you have under a certain percentage of sand.

It is recommended that you purchase the SP-2 Superpave Mix Design handbook from the Asphalt Institute here.  The asphalt institute is also working on rewriting their MS-2 Mix Design Methods for Asphalt Concrete which will now include Superpave mix designing but that will not likely be released in the next year.  

All of the changes I mentioned in these posts are for the PILOT projects and may change at full implementation in 2014.  There is a lot of industry concern about being able to obtain some of these conditions (specifically some of the variances).  When this was discussed with Joe Peterson, he encouraged industry to compile data to show that the condition may not be feasible and that he is open to changing them if he has sufficient empirical evidence.  This really goes for any of the specifications or Caltrans rules.  Be sure to voice your concerns and bring some of the issues to the table with Caltrans so they are aware that industry is struggling and why.  There are a lot of major changes coming about and there are going to be speedbumps and realities may have been overlooked in the specification design process.  I encourage you to create good working relationships with your Caltrans counterparts and get involved with the various associations that are making major headway for the industry.  The better the communication is, the more likely we are to find an appropriate solution in the long run.  One way to build a good communication base is to use our Superpave Discussion Forum.  Please feel free to post any of your questions, opinions, and concerns.  Utilize this area to discuss your findings and work with other companies to make the changes you feel are needed. 

Joe Peterson of Caltrans is currently traveling all over the state to give presentations on the upcoming Superpave specifications.  Although he will discuss many of the changes I've outlined in the last few posts I encourage you to still attend one of his presentations for a more in depth look at Superpave.  Joe is a great presenter and covers what could be very dry material in a  useful and interactive way.  In addition, these events will allow you to ask Joe any of your burning Superpave questions so look into attending one if you haven't seen it already.  He has already hit many areas but is scheduled to speak at the following events:  

Nov. 28 @ 12:15pm: CalAPA Central Coast Technical Committee Meeting-Santa Maria
Dec. 5 @ 10:00am (May be rescheduled): CalAPA Southern Technical Committee Meeting-Los Angeles
Dec. 13 @ 9:00am: Caltrans District 9-Bishop
Dec. 19 @  9:30am: CalAPA Central Valley Technical Committee Meeting-Bakersfield
January TBD: Caltrans District 4-Oakland
March TBD: Caltrans District 3-Marysville
March TBD: Caltrans District 8-SRL 

The Caltrans district presentations above will give priority to Caltrans employees but Industry professionals are also invited to participate.  If you would like to attend one of the Caltrans district presentations you can reserve a spot in advance by contacting Roseanna Rodriquez of Caltrans at (916) 227-7020, or via email at Roseanna_rodriguez@dot.ca.gov.  The CalAPA meetings do not require pre-registration.

For more information on the Caltrans Superpave movement visit the Caltrans Superpave Resource page here, where you can find general information on Superpave, a list of the new AASHTO test procedures that will be used, the most recent versions of the Caltrans Superpave specifications, and more.

Good luck!  

Monday, October 22, 2012

Superpave Pilot Project Changes IV

As the fourth post in our Superpave series, we'll be focusing on Mix Designs & Mix Verifications.  Our previous posts were as follows: The first post, Changes I, focused on changes to the paperwork and paving procedures.  The second post, Changes II, focused on changes that affect the operations group at hot mix asphalt plants.  The third post, Changes III, focused on the changes that will affect you if you produce RAP and add it to hot mix asphalt.


Verifications 
  • Caltrans is now concerned with the differences between asphalt binder suppliers and is regulating it in the Superpave specifications.  Changing binder suppliers, even if it is the same grade, will require you to submit a new jmf.  In addition, you can only change asphalt binder suppliers once per approved JMF without incurring a charge.  Additional binder supplier changes are $2000 per change.  
  • You can now only verify up to 2 JMFs per job per aggregate size and asphalt binder type.  After 2 it is $3000 each.  This includes reverifications! In addition, Caltrans does not have to turn it around to you in any specific time period.   You will go to the bottom of the priority list and they will work on your JMF when they have time.
Mix Designs
  • I hope you already know this since it is the biggest difference between Caltrans' previous mix design methods and Superpave but Superpave will no longer use the Kneading Compactor in the mix design process.  Instead, Superpave uses a gyratory compactor.  Caltrans has purchased their gyratory compactors from Pine Instrument (http://www.pineinst.com/).  If you plan on purchasing a Pine gyratory compactor there is a several month waiting period so make sure that you are aware of when you need to order to be ready for the Superpave launch. 
  • Caltrans is trying to move away from designing open graded mix designs and estimates that in approximately a year this responsibility may be turned over to the contractor just as the other mix designs are.
  • Superpave will still test for TSR for moisture susceptibility but will also use the Hamburg test to determine its susceptibility to rutting.  You will now have to meet both specifications (minimum dry strength of 120psi and minimum TSR of 70%).  Again, there is a several month waiting period on the Hamburg Wheel Tracking Device and at least one brand has a 15 month waiting list.  Take a look at your budgets now and get one ordered before its too late!
  • The crushed faces test is changing.  Currently a particle is considered crushed if 25% of the face is fractured.  The new procedure will require 50% of the face to be fractured which means that your particles must be 2x more fractured than they were before.  This may cause an an issue at natural deposits and you may have to adjust crushing operations to make sure that you're material is being fractured enough.

We've started a forum for discussing the upcoming changes here: Superpave Discussion Forum.  Please feel free to post any of your questions, opinions, and concerns.  Utilize this area to discuss your findings and work with other companies to make the changes you feel are needed. 

Our next Superpave post will focus on the changes that are coming to your laboratories.  Stay tuned!

Friday, October 19, 2012

Caltrans Update Email Lists

I know you were hoping that this post would be about Superpave but I had to pass this information on to you all as soon as I heard about it.  I'll get back to Superpave early next week :)

Caltrans now has two e-mailing lists set up to alert stakeholders of changes to its Construction Standards and Construction Manual.

You can sign up to receive notifications of changes made to the Caltrans Construction Standards, which includes the Caltrans Standards Specifications, Standard Special Provisions, and Standard Plans, at http://lists.dot.ca.gov/mailman/listinfo/construction-standards-updates-announce.

You can sign up to receive notifications of changes of Construction Manual Updates in addition to Construction Policy Bulletins and Construction Procedure Directives at http://lists.dot.ca.gov/mailman/listinfo/construction-manual-updates-announce.


Monday, October 15, 2012

Superpave Pilot Project Changes III

Welcome to our third post on the upcoming changes to the Caltrans specifications that are coming about with the instituting of Superpave.  The first post, Changes I, focused on changes to the paperwork and paving procedures.  The second post, Changes II, focused on changes that affect the operations group at hot mix asphalt plants.  This post will focus on the changes that will affect you if you produce RAP and add it to hot mix asphalt.


RAP (Recycled Asphalt Pavement)
  • Where RAP is applicable, it will now be included in mix designs at 25 ± 1%.  In many jobs 25%, not up to 25% will be required.  This is a big change from Caltrans' previous maximum of 15%.  
  • During production, you will now only be able to vary the RAP content by 3%.  This may cause a problem from those of you who use your feeder settings as a way to regulate your gradations and oil contents.  It is another specification that Caltrans is instituting to encourage producers to regulate their mix BEFORE it hits the hot plant, IE during aggregate, or in this case RAP, production.
  • For surface courses, Caltrans will allow a 25% binder replacement and the contractor has the option to bump down the virgin binder grade.  In lower courses, Caltrans will allow up to 40% binder replacement but a bump down in virgin binder grade will be required.  Since the binder in RAP is weathered and oxidized from years exposed to the elements, the binder is stiffer than a virgin binder would normally be.  When a higher content of RAP is added to a hot mix, the mix itself gets stiffer due to the recycled binder. The bump down in virgin binder allows the mixture of recycled binder and virgin binder to retain a stiffness that is still workable and long lasting.  This is one area that your operation will want to examine costs on.  Although you are saving money on using RAP in the mix, depending on the cost of the softer binder, you may end up spending more money on a higher RAP content mix than a standard 25% RAP mix.   
  • RAP must now be fractionated into + #4 and - #4 piles.  You can no longer use one size RAP if it includes sizes from both + #4 and - #4.  You will now need two separate RAP piles and two separate RAP feeders.
  • There are now tighter variances on your RAP stockpile testing.  The binder can only vary  ±2% throughout the pile and the RICE Specific Gravity variance  is now Gmm±0.0600.  
  • Despite the new variances, you can still have live RAP piles but you will need to do frequent testing to verify the variances are within specifications.
There have already been some industry complaints regarding several of these RAP specifications.  I will mention again that if you feel that your plant will NOT be able to meet some of these specifications start recording data to prove it NOW.  Caltrans is open to adjusting these specifications but industry will have to prove its case.  Step up and do so. 

We've started a forum for discussing the upcoming changes here: Superpave Discussion Forum.  Please feel free to post any of your questions, opinions, and concerns.  Utilize this area to discuss your findings and work with other companies to make the changes you feel are needed. 

Our next Superpave post will focus on the changes that are coming to Mix Designs and Verifications.  Stay tuned!

Tuesday, October 9, 2012

Superpave Pilot Project Changes II

In my last post here I addressed upcoming changes to the paperwork and changes that paving crews should look out for as we progress into Superpave with the pilot projects in 2012 and 2013.  This post will address the changes that the operations groups at hot mix asphalt plants will have to be prepared for.


Asphalt Plants

  • Caltrans will be watching and enforcing the plant's asphalt binder set points now.  Your plant's setting MUST match the optimum binder content that is shown on your JMF when you verify your mix.  If you fail the first verification you will be allowed to adjust the binder set point ± 0.2% from the optimum binder content.  During production, you can only change the set point with written consent by the RE.  This means that you will no longer be able to adjust your plant up or down with changes in your test results but will need to ensure that all of your plant components are operating correctly at all times.  Joe did mention that if you know for a fact that your plant is always set high, for example 0.3% higher than you are actually putting in, you can have this difference approved by your RE prior to starting the job. 
  • There are now tighter HMA production specifications.  For example: air voids are now ±1.5% as opposed to ±2.0% &  Binder Content is ±0.3% in HMA. and ±0.4% for RHMA as opposed as ±0.5% in previous specifications.  The change in binder content specifications is one particular area that industry is extremely worried about.  Caltrans has already heard a plethora of complaints about this change in specification and Joe made sure to mention that these specifications are currently ONLY for the pilot projects and have not been set in stone for the full implementation in 2014.  He fully anticipates changes to these specifications to occur but pointed out that he cannot make a change unless he has the data to back it up.  He encouraged all industry companies to keep careful track of their data over the next couple of years and compile a logical analysis that can prove their contention that the specification will not work.  He is completely open to making a change to the specifications if he has the data to back it up.
  • You will now be told to stop production if you have two out of specification test results in a day.  Unlike before when it would have to be two of the same test results in a row, if you have two of ANY test results out of specification in one day you will need to shut down.  AKA if your sublot 3 is out of specification in binder and sublot 6 is out of specification in SE, you will need to shut down until you can prove that you've made a change that will fix the problems. 
  • The minimum binder content in RHMA is increasing.  The new minimum will be 7.5% TWA and it will probably be moving to 8.0% soon after.  Currently the minimum binder content is 7.0% TWA. 
  • Superpave will produce even bonier mixes!  Most cities will want to move from ¾” to ½” in their design phase.  Due to the bonier nature of the new mixes you will likely be using less SAND and in some cases less dust.  You may need to adjust your aggregate and/or hot plants to account for this.

These specification changes will be the most influential on your future operations and deserve to be examined starting now.  Some plants will need to dial in their binder issues, some will need to alter their aggregate supply's shape, and others will need to hire more staff to be able to test quickly enough to catch problems as they arise.  I know I mentioned it already but I think it's worth a second shout out:

If you feel that your plant will NOT be able to meet some of these specifications start recording data to prove it NOW.  Caltrans is open to adjusting these specifications but industry will have to prove its case.  Step up and do so instead of complaining about the changes.  There are several industry associations such as CalAPA and CalCIMA that are working on these initiatives and the more information and data they have the more likely that they will be successful.

We've started a forum for discussing the upcoming changes here: Superpave Discussion Forum.  Please feel free to post any of your questions, opinions, and concerns.  Utilize this area to discuss your findings and work with other companies to make the changes you feel are needed.

Our next Superpave post will focus on the changes that are coming to RAP.  Stay tuned!

Friday, October 5, 2012

Superpave Pilot Project Changes I

I've now had the opportunity to listen to Joe Peterson of Caltrans speak twice about the changes that will be appearing with the Superpave pilot specifications and I can tell you that there are A LOT of major changes coming about, not only for laboratories but for asphalt plants and paving crews as well.  Because of the shear  volume of information I will breaking down the major changes into multiple posts over the next couple of weeks.  Stay tuned because no matter what your relationship with Superpave is going to be, you'll want to be aware of these things as you start to look at your budgets for 2013 and 2014.

 Timeline:

2012:

  • There are already approximately 6 pilot projects either completed or in the process of being built across the state.  

2013:

  • There will be 12-16 pilot projects for sure, but Joe believed that it was more like 25 at this point.

2014:

  • Full implementation.  Starting in January all new Caltrans jobs will be specified as Superpave.

Paperwork:

  • There are new JMF forms that can be found on the Caltrans website here.  They are labeled the same except that there is an SP at the end, ex: CEM-3511SP
  • Caltrans is switching from Total Weight of Aggregate (TWA) to Total Weight of Mix (TWM).  This means that your paperwork will get a little confusing since some of your jobs will be TWA and some will be TWM.  Its recommended that you document both binder contents on your paperwork to eliminate confusion.  There is a worksheet on how to convert TWA to TWM and back here.


Paving:

  • It is now required that the contractor takes a minimum of 2 cores per paving day for the contractor’s information in addition to the 1 core every 250 tons that is currently required for Caltrans. 
  • The contractor must now also take nuclear density readings on the grade (3 per 250 tons) for their own information.  This information will not need to be shared with Caltrans but the inspector will be verifying that you are using the gauge.  This is to encourage ALL contractors to utilize density information during the paving of the job so problems can be fixed early.  Currently only some contractors do this and since they have the added costs of a technician and gauge, they are at an economic disadvantage during bid time.  This will level the playing field.
  • Although Caltrans had previously stopped certifying technicians in CT 375-In Place Density and Relative Compaction of Asphalt Concrete Pavement, it will resume certifying technicians if you have a Superpave job and are interested in having the certification to prove your credibility.  A certification in CT 375 is not required though since the data is for your own use, not for Caltrans.

Our next post will address the changes that will affect the operations group at hot mix asphalt production plants.  Please feel free to comment and discuss the changes on our Superpave discussion forum here

Thursday, September 27, 2012

Contract Compliance Vs. Operating Range

One of our readers was recently looking for the difference between Contract Compliance and Operating Range.  This terminology is used for various aggregate products and in the past was used in the old section 39 of the Caltrans May 2006 standard specifications.  It no longer exists in the 2010 version of Caltrans' Standard Specifications for HMA but if you are running a job based on older specifications it can be quite confusing.

In the May 2006 Caltrans Standard Specifications for section 39-Asphalt Concrete, there were three columns of gradation ranges for each type of asphalt concrete.  The first column is "Limits of Proposed Gradation" which is for use when creating a mix design.  The combined gradation of your mix components must be within these ranges when you decide on your bin and/or feeder percentages for your mix design.

The second column is "Operating Range".  The operating range is the range that you should be producing in during the production of your asphalt concrete.

The third column is "Contract Compliance".  This column is a larger range than the Operating Range and is used to basically give you a fudge factor for not having to shut the job down or pay a deduct.  If your gradation is outside of the Operating Range but within the Contract Compliance requirements, you can continue paving for the rest of the day.  It should be noted though, that even though you're within the Contract Compliance requirements that you will still need to make changes by the next paving day to get your material back into the Operating Range or you may be forced to stop paving until you can.

If you have a test result that is outside of the Contract Compliance requirements Caltrans generally has the right to ask you to remove and replace it or charge you a payment deduction.  The same rules for Operating Range and Contract Compliance that I mentioned above apply to aggregate products such as base rocks.

I hope that answers your question anonymous user!  Feel free to post any of your questions, no matter how small, in our discussion forum to get the answers you need!

Monday, September 17, 2012

CT105 Changes-July 2012

Sorry for the hiatus from updates, its been an extremely busy month for me!  

If you hadn't heard, CT 105: Calculations Pertaining to Gradings and Specific Gravities was updated in July 2012.  Most of the update is reformatting and all of it has made this difficult to learn test method into a much more useful reference tool.  There have been no major changes to the meat of this test method but here are a list of what I noticed as actual changes:

  • There is better definition of what each adjustment is for. 
  • The calculations shown in each example are easier to follow and understand where the final value comes from because they show the calculation and what each calculation equals instead of only showing the calculation.  It also shows the answer to the hundredth decimal place so that you can see how it’s been rounded in the “as used” column.
  • Most of the adjustments’ wordings have been made broader.  Instead of referring to “a portion of the passing 4.75mm material”, it refers to “the portion of the material passing a designated sieve”.
  • The diagrams are more explanatory.
  • The adjustments are now broken down into four parts: A definition section which explains when this particular adjustment is used, Procedure which is a summary of the adjustment, Example, and Calculations/Adjustments which explains the calculations used.  This defines the adjustment better and makes each one easier to understand and refer to.
  • In Adjustment 5, the calculation for determining the total amount of material before wasting has been corrected by changing 10,000 / (100-3)=10,309 g  to  10,000 / [(100-3)/100]=10,309 g.  This same type of correction was made in adjustment #10.
  • The equation in Adjustment 5 for determining the amount of material passing No. 4 sieve that will be needed before screening out the passing No. 200 material now uses 54% in the example instead of 55%.
  • When moving from section to section, the adjustment numbering system does not restart.  There are now a total of 11 adjustments covered over 3 sections.

The July 2012 version of CT 105 can be found on the Caltrans website and here.



Wednesday, August 22, 2012

Self Healing Asphalt (Guest Blog)

About a year ago I started following a research project that has got me pretty excited about the possibilities for the future of pavements.   The project is examining an approach to what is lovingly being called "self-healing" pavements.  In other words, pavement, that when cracks start to form...heals itself!  How cool is that!?

California is extremely lucky to have so many great pavement research programs but every once in a while venturing outside of California for the world's view on pavements proves extremely interesting.  I contacted the professor in charge of this project, Erik Schlangen of Delft University of Technology in the Netherlands, and he generously put together the synopsis below for the Quality in California readers. Lucky you!  I'd also encourage you to visit their blog to learn more about the project and keep up to date on their progress and updates.  The blog's link can be found at the end of the post.  Happy Reading!



Induction heating and healing of porous asphalt concrete

An induction heating/healing approach was developed at Delft university of Technology in the Netherlands to enhance the durability of porous asphalt pavement. Steel fibers are added to the porous asphalt mixture and induction heating is used to heat the porous asphalt pavement when micro cracks are expected to occur in the asphalt mastic of the pavement.  In such a way, porous asphalt concrete can repair itself and close the cracks through the healing of the binder (diffusion and flow) at the high temperatures. The closure of micro cracks will prevent the formation of macro cracks. In the end, raveling and cracking can be avoided or delayed .

To prove that induction healing works in porous asphalt concrete, the electrical conductivity, induction heating speed, mechanical properties and healing capacity of porous asphalt concrete with steel fibers were studied in this research.  The following aspects can be outlined from this research:

1.      Adding steel fibers to porous asphalt concrete makes it electrically conductive.

2.      Porous asphalt concrete with steel fibers can be heated with induction energy. It is proven that induction heating doesn’t cause extra aging to the binder.

3.      Addition of a moderate amount of steel fibers reinforces porous asphalt concrete by increasing its the ravelling resistance, indirect tensile strength, fatigue resistance and water damage resistance.

4.      The healing capacity of porous asphalt concrete with steel fibers is greatly increased by induction heating. The completely fractured porous asphalt concrete beams with steel fiber can be healed many times due to induction heating. The stiffness of fatigue damaged porous asphalt concrete samples recovers more and faster when induction heating is applied on them. The fatigue life of porous asphalt concrete samples with steel fiber is significantly extended after induction heating.

5.      The optimal heating temperature is 85 ÂșC. Overheating, causing swelling and drainage problems,  decreases the healing rate of porous asphalt concrete.

6.      Induction heating can be repeated when cracks return. Through multiple times induction heating, the fatigue life of a porous asphalt beam can be strongly increased.

7.      The durability of porous asphalt concrete pavement will be improved with induction heating because of the improvements in the healing capacity and in the fatigue resistance.

8.      A porous asphalt trial section with the concept of induction healing was paved on Dutch motorway A58 in December 2010. The trial section was fully intact after the two winters of 2010-2011 and 2011-2012. The trial section can be heated with induction energy and cores form the trial section show better particle loss resistance than the reference section. It is expected that the durability of the trial section will be enhanced by induction heating.

9.      An induction generator for field heating is being developed.

In further research, the efforts will be focused on the following issues:

1.      Optimization of steel fibers
Steel fibers will be optimized to obtain the highest induction heating speed without affecting the mechanical properties of porous asphalt concrete negatively.

2.      Optimization of the mixing technology
To shorten mixing time and save energy consumed in dispersing steel fiber into porous asphalt concrete, the mixing technology needs to be optimized.

3.      Optimization of induction generator
To enhance the induction speed, the induction generator should be optimized by changing its frequency and the shape/size of the coil.

4.      Modeling of induction healing in porous asphalt concrete
The capillary flow of the Newtonian binder in cracks under surface tension force will be simulated in further research to fully understand the mechanisms involved in induction healing.

More information about this research can be found in the self healing asphalt blog: http://selfhealingasphalt.blogspot.nl/

The work described above forms also the basis for a PhD-thesis by Quantao Liu at Delft University. He will defend his thesis on October 2nd 2012. After that date it will be possible to download the thesis from the self healing asphalt blog.

 

Monday, July 9, 2012

Low Asphalt Content Solutions


A couple of weeks ago I ran through some of the lab and plant issues that may cause varying asphalt contents and high asphalt contents.  The following is the last article in the trilogy and will explain some possible causes for consistently low asphalt contents.  You'll probably notice that most of these are the exact opposite of what you'd see with consistently high asphalt contents but I encourage you to read all the way through because there are still a couple here that are unique to low results.    


Again, for the purposes of this post I am assuming that you are using an ignition oven to test for asphalt contents.


For verifying the lab, try these sources:
Incomplete Burn Off from Ignition Oven
  1. Is the technician calculating the results correctly? (technician error) 
  2. Are you using the correct correction factor? (technician error) 
  3. Is the correction factor current? Has the rock source changed in such a way that the correction factor should be adjusted? 
  4. Did the correction factor contain the correct amount of additives?  Many people don't realize that 0.5% Liquid Antistrip means 0.5% of the weight of the binder, NOT the weight of the aggregate.  This could give you a 0.45% higher correction factor than you should have and your test results will look consistently low by the same amount.  
  5. Is there still a residual film of black asphalt on the aggregates following your burn?  Your oven may not be burning off all of the oil that it should be.  This could be due to a variety of reasons but most involve dirty and/or clogged air tubes.  Perform a lift test to verify this and if it fails refer to your user manual for what needs to be cleaned and how.  
One way to double check your AC content results in the laboratory is to run additional tests in the lab.  The Rice test, bulk specific gravity of compacted HMA, AC content by Nuclear Oven, AC content by extraction, stabilometer, and calculating the sample's volumetrics can all verify your varying oil contents on their own or when compared to the charts in the mix design.

If you can't find an issue in your lab move on to the plant. 
Here are some sources of problems at a drum plant:
  1. Are you using the correct mix formula?  (plant operator error)
  2. Does the aggregate moisture in your computer match the actual aggregate moisture?  If the plant is set higher than the actual moisture the computer will think that you are putting in less rock than you actual are and add less asphalt than you need per your mix formula.   One way to check this is testing the feed aggregates for their moistures and comparing the combined moisture content to what is entered in the computer.  You can also typically mitigate this in the laboratory by running a CT 370 test on every oil content you run.  However, I caution you with depending too much on CT 370 when running rubber mixes as CT 370 may not be effective with crumb rubber in the mix.
  3. Are your aggregate belt scales weighing correctly?  If your scale(s) are reading low then you will have lower asphalt contents because the computer thinks that you are putting in less rock so it puts in less oil per your mix formula.
  4. Is your belt scale binding?  You can see the same problems as in #3.
  5. Is your asphalt meter calibrated correctly?  If it is reading low you will have the same issues as in #3.
  6. Are you sampling early in the production range (0-50 tons)?  Drum plants take some time to get the materials mixed well and if you are sampling too early you may be getting material that has not gotten enough oil yet.  Some plants even waste their first 50 tons out of the drum for this reason.
Here are some sources of problems at a batch plant:
  1. Is your weigh pot emptying completely with each batch?  If it is not, you may have some rich batches and some dry batches.  You should check your scales to make sure that they are weighing correctly.  Batch plants are typically very accurate in how much oil you are putting into the mix. This is because there is not as much risk as in a drum plant in how it is mixed because each batch is mixed on a much smaller scale.  One benefit to a batch plant is that most automated systems can give you a readout of the exact weight of each bin of material and asphalt that was added to the batch.  These reports can be extremely useful in seeing trends in your asphalt weights.
  2. Is your weight pot calibrated correctly?  If it is reading high you will have a lower oil content.   
  3. Is the aggregate fully coated with asphalt?  If not, it may be due to the oil injectors not operating properly.  There could be an electrical issue or leak.  Your technician may be consistently sampling from the dry side of batches, showing a consistently low asphalt content.  
  4. Is the mix gradation cohesive or are some parts fine and some parts rocky?  Take a look at a truck of hot mix and be sure to dig into the bed a little bit.  If the pugmill is not mixing fully, the top half of the batch (the part you can see) could still look cohesive even though the bottom half may not look like the top.  Coarse samples have less asphalt than fine samples because the fines will absorb and hold onto more asphalt.  Improper mixing could be due to missing pugmill tips, poor paddle alignment, or you may just need to increase your mixing time. 
  5. Is there and automation error?  Many batch plant automation systems have complicated equations that are used to determine how much aggregate and/or asphalt is added to a batch.  One of these equations is "free-fall compensation" which calculates gravity into the weight of the aggregates and/or asphalt in an effort to reduce the amount of time it takes to make a batch.  Instead of waiting until the scale meets its actual target value it will calculate the free fall compensation and drop the material into the pugmill a little bit early.  It is rare but possible that your computer is not calculating this correctly and if you run out of options you can always call the manufacturer and find out if it may be the cause of your high asphalt contents. 
  6. Do you have a mineral filler injection system?  Check to ensure that it is operating properly.  If it is injecting too much mineral filler into your mix you could see a lower oil content and a dryer mix.  
  7. Are there any holes in your bins that could be leaking aggregates into your pugmill when it shouldn't be?  The additional aggregates may not show up in your weights of aggregate and you will end up with more aggregate than you need, and as a result a low asphalt content.  
There are sure to be several other reasons that you may be showing a consistently low asphalt content at your plant.  The key is to have an open mind and make sure that you keep the finger pointing to a minimum so that your employees feel comfortable letting you know what is wrong when they see it.  



If you have any additional solutions post them on our discussion forum!  Trouble-Shooting 

CT 106-June 2012 Changes

Caltrans has released a new version of CT 106: Definitions of Terms Relating to Specific Gravity.  The changes are minimal and are as follows:

  • Changed the definition of Specific Gravity from a ratio of mass to a ratio of weight.
  • Changed the reference materials for "absolute specific gravity" from ASTM E12 and AASHTO M132 to ASTM E1547 and AASHTO T84
  • For each specific gravity term mentioned, it now notes what California Test Method(s) you will see it in.
The June 2012 version can be found on the Caltrans website and here.  Happy Reading!

Thursday, June 21, 2012

CT 227 Changes-June 2012

Caltrans has come out with another version of CT 227 (last updated in March 2012).  The June version only had a few changes and a couple changes that look like they were only correcting a mistake made in the March version.  Below are what I noted as the important changes:

  • In the apparatus section it now specifies the type of graduated plastic cylinder as Assembly B, in Transportation Laboratory drawing No. C 218 as opposed to referencing CT 217.  (This drawing is not shown in CT 227 but is shown in CT 217)
  • Changed the name of “Stock Calcium Chloride Solution” to simply “Calcium Chloride Solution” in the materials section.
  • Now references which catalog numbers are applicable for “Sand Equivalent Stock Solution” in the materials section.
  • Tap water is once again allowed to be used in lieu of distilled or deionized water when proven to not affect the test results.  In addition, if during testing with tap water, a clearly defined line of demarcation does not form between the sediment and the liquid above it or if the cylinder is still darkly clouded after 20 minutes you will need to retest an untested portion of the same material using distilled or deionized water.
  • Temperature correction factors are no longer allowed.  Although the sentence is confusing, it seems that only test results that are achieved when the testing water is at 72˚F±5˚F are valid.

Happy Reading!


Monday, June 18, 2012

Caltrans Earth

I was floating around the Caltrans website today and noticed this: Caltrans Earth

Its a version of Google Earth geared completely towards Caltrans.  The map is divided by the twelve Caltrans districts and show all sorts of things like scenic highways, HOV lanes, live traffic, lane closures, earthquakes, and more.  It's worth a peak if you work with Caltrans or even if you just travel throughout California.

Happy Mapping!

High Asphalt Content Solutions

Last week I told you about what might be going on if you have asphalt contents that go back and forth from high to low and back again. This time I'm going to go over some reasons your asphalt contents might be consistently higher than they should be.

Again, for the purposes of this post I am assuming that you are using an ignition oven to test for asphalt content.


For verifying the lab, try these sources:
  1. Is the technician calculating the results correctly? (technician error) 
  2. Are you using the correct correction factor? (technician error) 
  3. Is the correction factor current? Has the rock source changed in such a way that the correction factor should be adjusted? 
One way to double check your AC content results in the laboratory is to run additional tests in the lab.  The Rice test, bulk specific gravity of compacted HMA, AC content by Nuclear Oven, AC content by extraction, stabilometer, and calculating the sample's volumetrics can all verify your varying oil contents on their own or when compared to the charts in the mix design.


If you can't find an issue in your lab move on to the plant. 
Here are some sources of problems at a drum plant:

  1. Are you using the correct mix formula?  (plant operator error)
  2. Does you the aggregate moisture in your computer match the actual aggregate moisture?  If the plant is set lower than the actual moisture the computer will think that you are putting in more rock than you actual are and add more asphalt than you need per your mix formula.   One way to check this is testing the feed aggregates for their moistures and comparing the combined moisture content to what is entered in the computer.  You can also typically mitigate this in the laboratory by running a CT 370 test on every oil content you run.  However, I caution you with depending too much on CT 370 when running rubber mixes as CT 370 may not be effective with crumb rubber in the mix.
  3. Are your aggregate belt scales weighing correctly?  If your scale(s) are reading high then you will have higher asphalt contents because the computer thinks that you are putting in more rock so it puts in more oil per your mix formula.
  4. Is your belt scale binding?  You can see the same problems as in #3.
  5. Is your asphalt meter calibrated correctly?  If it is reading high you will have the same issues as in #3.

Here are some sources of problems at a batch plant:
  1. Is your weigh pot emptying completely with each batch?  If it is not, you may have some rich batches and some dry batches.  You should check your scales to make sure that they are weighing correctly.  Batch plants are typically very accurate in how much oil you are putting into the mix. This is because there is not as much risk as in a drum plant in how it is mixed because each batch is mixed on a much smaller scale.  One benefit to a batch plant is that most automated systems can give you a readout of the exact weight of each bin of material and asphalt that was added to the batch.  These reports can be extremely useful in seeing trends in your asphalt weights.
  2. Is your weight pot calibrated correctly?  If it is reading low you will have a higher oil content.   
  3. Is the aggregate fully coated with asphalt?  If not, it may be due to the oil injectors not operating properly.  There could be an electrical issue or leak.  Your technician may be consistently sampling from the rich side of batches, showing a consistently high asphalt content.  
  4. Is the mix gradation cohesive or are some parts fine and some parts rocky?  Take a look at a truck of hot mix and be sure to dig into the bed a little bit.  If the pugmill is not mixing fully, the top half of the batch (the part you can see) could still look cohesive even though the bottom half may not look like the top.  Fine samples have more asphalt than coarse samples because the fines will absorb and hold onto more asphalt.  Improper mixing could be due to missing pugmill tips, poor paddle alignment, or you may just need to increase your mixing time. 
  5. Is there and automation error?  Many batch plant automation systems have complicated equations that are used to determine how much aggregate and/or asphalt is added to a batch.  One of these equations is "free-fall compensation" which calculates gravity into the weight of the aggregates and/or asphalt in an effort to reduce the amount of time it takes to make a batch.  Instead of waiting until the scale meets its actual target value it will calculate the free fall compensation and drop the material into the pugmill a little bit early.  It is rare but possible that your computer is not calculating this correctly and if you run out of options you can always call the manufacturer and find out if it may be the cause of your high asphalt contents. 
There are sure to be several other reasons that you may be showing a consistently high asphalt content at your plant.  The key is to have an open mind and make sure that you keep the finger pointing to a minimum so that your employees feel comfortable letting you know what is wrong when they see it.  


Keep your eyes peeled for our next post on consistently low asphalt contents.


If you have any additional solutions post them on our discussion forum!  Trouble-Shooting 

Wednesday, June 13, 2012

Varying Oil Content Solutions

Pay factors.  In these tough economic times, contractors are bidding with smaller and smaller margins and the pay factor can make or break a job.  For materials suppliers one of the most complicated pay factors relies on the asphalt content.  Keep a steady, in specification, asphalt content and you're swimming in money but let it jump around and even if you're in spec you could be paying out of your pocket.  So what if your plant's asphalt contents are bouncing around: going from high to low from sample to sample?  What could be going on?

This is a loaded question and one that materials suppliers struggle with constantly.  Unless you have unlimited money and time, your plant personnel is probably going to first ask your laboratory if you ran the test correctly.  It typically takes less effort and costs less for your technician to rerun the sample than to stop the plant's production to check out what is going on at the plant so usually your first step in a situation where you have varying oil contents is to ensure that there was not an issue with your technique or equipment in the laboratory.  For this reason, you should always pull extra hot mix just in case you need to run another test or two.  The following suggestions assume that you are using an ignition oven to test asphalt contents.

For verifying the lab, try these sources:
1. Is the technician calculating the results correctly? (technician error)
2. Are you using the correct correction factor? (technician error)
3. Is the correction factor current?  Has the rock source changed in such a way that the correction factor should be adjusted?
4. Is your equipment clean from previous asphalt residue and cleaning solutions?  If something like your splitter has asphalt residue on it, you may get a higher oil content on your next sample.  On the flip side, if you use certain cleaning products and leave enough of it on the equipment it may eat away at the asphalt in the next sample and give you a lower oil content.
5. Is your ignition oven's exhaust pipe clean?  Does it pass a lift test?
6. After a burn, is there still black residue on the sample?  If so, your oven is not burning all of the oil off.  This could be due to a variety of problems including low air flow, high air flow, the door not sealing, the elements not working correctly, or the scale needing calibration.  See your manufacturer's manual for more information.
7. Is each sample a similar size?  Is the technician spreading the sample across the basket in the same way each time? This can also leave black residue on the sample from inadequate burning.  (technician error)

One way to double check your AC content results in the laboratory is to run additional tests in the lab.  The Rice test, bulk specific gravity of compacted HMA, AC content by Nuclear Oven, AC content by extraction, stabilometer, and calculating the sample's volumetrics can all verify your varying oil contents on their own or when compared to the charts in the mix design.

If you can't find an issue in your lab move on to the plant.
Here are some sources of problems at a drum plant:

1. Is there variance in how wet the aggregates are?  The plant is probably set for one moisture so with greatly varying moistures (ex: adding washed material instead of dry material) you could see varying asphalt contents as well.  One way to check this is testing the feed aggregates for their moistures and comparing the combined moisture content to what is entered in the computer.  You can also typically mitigate this in the laboratory by running a CT 370 test on every oil content you run.  However, I caution you with depending too much on CT 370 when running rubber mixes as CT 370 may not be effective with crumb rubber in the mix.
2. Is the mix gradation cohesive or are some parts fine and some parts rocky?  Take a look at a truck of hot mix and be sure that the aggregates and oil are being fully mixed together.  If you see an inconsistent mix the plant may need to slow down the plant or, in extreme circumstances, change the flighting in the drum.
3. Another sources of inconsistent coating may be due to the oil injectors not operating properly.  There may be an electrical issue or it could even be as simple as a clog.

Here are some sources of problems at a batch plant:
1. Is your weigh pot emptying completely with each batch?  If it is not, you may have some rich batches and some dry batches.  You should check your scales to make sure that they are weighing correctly.
2. Is the aggregate fully coated with oil?  If not, it may be due to the oil injectors not operating properly.  There could be an electrical issue or clog.
3. Is the mix gradation cohesive or are some parts fine and some parts rocky?  Take a look at a truck of hot mix and be sure to dig into the bed a little bit.  If the pugmill is not mixing fully, the top half of the batch (the part you can see) could still look cohesive even though the bottom half may not look like the top.  Improper mixing could be due to missing pugmill tips, poor paddle alignment, or you may just need to increase your mixing time.

In addition, I'd like to point out that many of us have upgraded to automation at our hot plants.  Along with the upgrade, many of us have learned to trust and rely on the programming blindly.  Remember that although most automation is tested at great length, it is still designed by people and has the potential to be wrong sometimes.  If you have a software at your hot plant don't be afraid to call them and ask if anyone has seen this problem before.  You'd be surprised how quickly they can fix a problem with the software or even give you other ideas on how to investigate your plant.

Have more suggestions or questions?  
Try our discussion forum: Trouble-Shooting

Tuesday, May 15, 2012

CT 207 RSP Warning

If your lab is performing the CT 207 RSP sample for Caltrans this month be sure to notice that the form that Caltrans has given you to fill out is NOT the same as the form referenced in the test method.  The table and calculations are different than in the March 2012 version.  I've contacted Caltrans about the discrepancy and have been assured that you should use the form provided by Caltrans for your RSP sample.  You might want to make sure your techs are aware of the difference and that they aren't pencil whipping the form.

Good luck!

Wednesday, May 2, 2012

May 2012 RSP Samples Being Distributed

May's RSP samples will be shipped this week.  They will include samples for CT 207 and CT 234.  If you do not receive your sample by the end of the week you should contact Caltrans at caltrans_reference_sample_program@dot.ca.gov.

Monday, April 23, 2012

Change to May 2012 RSP Samples

It has been announced that Caltrans will no longer be sending a sample for CT235-Flat, Elongated Particles in Coarse aggregates with the May 2012 RSP set.  Instead they will be sending samples for CT 207-Specific Gravity and Absorption of Fine Aggregates.  A sample for CT 234-Method of Test for Uncompacted Void Content of Fine Aggregates will still be sent along with the CT 207 sample.

If you did not receive an email from Caltrans alerting you of this change or are now eligible to test the materials for this RSP sample set now that CT 207 is being offered make sure you contact Ms. Frances Banda at caltrans_reference_sample_program@dot.ca.gov.
 

Wednesday, April 11, 2012

Shell Martinez Plant Closing the Doors to Construction

You may have heard rumors flying around that Shell has decided to get out of the asphalt bitumen market.  As of May 2012 Shell's refinery in Martinez, California will no longer be producing asphalt bitumen as one if its products.  This is largely due to the larger demand for other petroleum products going forward. In recent correspondence, Mark Bouldin, Regional General Manager Americas Specialties of Shell, states: "As you are probably well aware of, this is a very difficult time for the refining industry, both internationally and nationally, and in California specifically.  Hence we have had to focus our initiatives.  Regrettably, given the urgency to streamline and optimize our operations it is impossible to further delay our consolidation beyond the previously announced date without experiencing additional impairments."

Shell's Martinez plant has the capability to produce several types of products from crude oil.  It is capable of converting up to 165,000 barrels of crude a day into products such as automotive gasoline, jet fuel, diesel, petroleum coke, industrial fuel oils, liquefied petroleum gas, asphalt, and sulfur.  With California's economic recession in full swing, Shell has been constantly evaluating the construction market's forecasts for asphalt bitumen.

It's not surprising to hear that with 2013 and 2014 showing little construction funding coming in, Shell has decided to streamline their production facility in Martinez and focus on its other products.  This will undoubtedly leave a gaping hole in the supply of asphalt bitumen to the California markets.  Shell's Martinez Refinery has an estimated capacity of 3,000 tons of asphalt bitumen production capacity per day and is the 4th largest refinery in California.  With the loss of such a big player...the looming question remains whether our asphalt prices will raise yet again in the coming months.            

Friday, March 30, 2012

Changes to CT 231-March 2012

Caltrans has released a March 2012 version of CT 231: Method of Test for Relative Compaction of Untreated Soils and Aggregates Using Nuclear Gauges.  In general they have formatted and re-worded the majority of the test method to make it clearer but the following is a list of the major changes:

  • It now defines the nuclear gauge and standardizing block.
  • It no longer defines the exact dimensions of the guide plate but specifies that it should be at least as big as the footprint of the nuclear gauge.  It also now specifies a tolerance for how flat it must be (1/16in).
  • It no longer defines the exact dimension of the pin but specifies that it should meet manufacturer’s specifications.
  • To standardize your nuclear gage for wet density and moisture the test method now tells you to take 1 four minute count instead of 4 one minute counts.  I think this is a mistake but that’s how the method reads.  It refers you to record the counts on the form in the back of the test method and there is still room for multiple counts so I believe you should still take 4 one minute counts. 
  • When preparing the site, it is no longer specified that you should remove loose surface material to a depth of not less than 50 mm below the deepest penetration by the roller.  It is now more general and only requires that you remove the material until you are blow the deepest penetration.
  • It now tells you what position the gage should be in for each test: Direct transmission for wet density and backscatter for moisture content.
  • It now expands on what the direct transmission depth of the rod should be in the field test for wet density.
  • It now allows for gauges with direct readout capability to be used to determine density.
  • It is now noted that when testing for relative compaction, the tests should be conducted in areas free of debris, standing water, loose materials, and pumping conditions.
  • Under determination of wet test maximum density, it is no longer specified that “If the impact test result is to be used in a “common” composite control density, nuclear moisture, as well as a nuclear density must be taken for each test site in an area and be averaged”.
  • It now specifies and explains how to plot the correction for oversize material on the graph of the TL 2148.
  • The test method itself no longer explicitly points out that there are different calculations for relative compaction if there is 10% or more material retained on the ¾” Sieve (oversized material).  However, this calculation is still present on the example computations worksheet and TL-2148 and you still need to use different input variables in your equation if you have oversize material.
  • The directions for choosing a random sample plan are much more concise.  It no longer specifies how to choose a random sample plan, just that you should do it randomly. 
  • The appendices have been updated and moved around.  

If you use this method often you might want to read through it before your next venture out into the field.  The new version of this test method can be found on the Caltrans website and here.

Good luck!