CT 375 Changes-February 2012

This month Caltrans released a new version of CT 375-Determining the in-place density and relative compaction of hot mix asphalt pavement using nuclear gauges.  The new test method can be found on the Caltrans website and here.  Most of the changes were relatively minor sans the one I bolded below.  The following is a list of the changes worth noting:

• Changed from metric to English units.
• The apparatus requirements have been reduced and are now more general.  The gauge now only needs to contain radioactive sources, detectors, electronics, and battery packs and be calibrated with CT 111.
• It now specifies that you must have a reference standard block to check the instrument operation and establish standard counts to compare to.
• To establish the standard count for a traditional lift, you now only need to take one 4-minute density reading whereas in the past you needed to take 3 and average them.
• It is no longer specified that each nuclear density device should be calibrated annually, not to exceed 15 months.  There is no longer reference to a specific time period as long as it is in accordance with CT 111. The calibration section has also been removed.
• To establish the standard count for a thin lift, you are now to follow the manufacturer’s recommendation.  It used to be noted that you can take up to five 4-min counts to pass the internal statistical test. 
• If is now specified that if cores are damaged and additional cores cannot be obtained from within the outlined position of the nuclear gauge, an alternate site shall be selected and outlined for TWO replacement nuclear readings and a replacement set of TWO core samples.  In the past it did not specify how many replacement readings and samples should be obtained. 
• It is no longer specified that when using Table 2 for random test site selection, you should arrange the test sites sequentially in order of stationing when transferring them to the test form.
• The directions for how to use the random test site location tables have been moved from the main body of the test method to below the actual tables in the appendix.
• Line K of the TL-3112 form is no longer rounded to the 0.1m but is rounded up to the next whole number due to the change from metric to English units. 
• It is now specified that if your combination gauge has an asphalt mode and a thin lift mode, you should only use the asphalt mode for lifts of 2.4 inches or greater.
• It is now specified that if your combination gauge has an asphalt mode and a thin lift mode, you should only use the thin lift mode for lifts of 1.2-2.4 inches.
• The term “monographs” in section 4A.1b has been corrected to read nomographs.
• It is now specified that when sampling for maximum density the covered metal bucket should be half full, previously the volume was not specified.  The option of using cardboard boxes is also available now.
• LTMD is now to be retested if there is a change in the job mix formula, not just the HMA itself.
• If the 1% average test fails, you are to perform an additional test using the untested portion of that same sample.  In the past, this was specified to use “untested daily samples following the last valid LTMD” 
• When using Method C to determine the density of each test specimen, the correction factor must now be verified every three months.  Previously it only specified that it should be verified periodically.
• 
  

     There is also a minor mistake in the new test method where there is no section 2A.2.  This may be confusing for you since section 2B.5b refers to section 2A.2.  You should refer to section 2A.3 instead.

      Happy Reading!

First Water Injection WMA Method Approved by Caltrans

The long awaited news of a water injection warm mix asphalt method being approved is finally here.  Caltrans has now added Astec Inc.'s Double Barrel Green technology to its list of approved methods for WMA jobs.  This is a much anticipated approval by such companies as Granite Construction who have invested a considerable amount of capital in Astec Double Barrel Green asphalt plants all over the state.  Information on the Astec Double Barrel Green technology can be found on their website here.

Astec's Double Barrel Green System
Source: www.astecinc.com 

The technology, which Astec rolled out in June of 2007, is an apparatus that can be added easily to any of Astec's double barrel drum plants and can also be retrofitted onto several other types of hot plants.  What makes the Astec system desirable to many producers is that it does not require an expensive additive to produce warm mix asphalt.  All you need is the physical system and water.  As the virgin asphalt bitumen passes through the apparatus, water is injected at a metered rate.  The water and bitumen mix to form microscopic steam bubbles, in other words, a foamed product which causes the liquid asphalt to expand in volume and become less viscous.

Viscosity is a measure of the resistance of the fluid, or in other words how freely it flows.  An example of a highly viscous liquid is honey whereas a lower viscous liquid is water.  Cold asphalt bitumen is typically a highly viscous liquid until it is heated.  Once it starts to cool back down it becomes highly viscous again which is why hot mix asphalt becomes harder to lay down as it cools.  The foaming technology of the Astec system allows the bitumen to have a lower viscosity without as high of a temperature.  This makes it possible to produce the material at a lower temperature and/or have workability of the asphalt mix for longer.  After a time period the steam bubbles in the asphalt mix begin to evaporate, leaving only the asphalt bitumen behind.  This is typically as you compact the pavement and the temperature of your mix drops below 212 degrees F., leaving you with what looks like a traditional hot mix asphalt pavement.

Just like with other WMA mixes, the paving crew will likely have to change some of their rolling patterns to account for the differences in the mix viscosity.  Typically rollers can be used immediately instead of having to wait until the mat has cooled down.

Caltrans's approval of the Astec Double Barrel Green technology means that on Caltrans jobs where warm mix is either an option or a requirement, contractors are able to use this product without a lengthy approval process through Caltrans.  For more information on the approval process see my previous post here.  The list of Caltrans approved products can be found at: Approved Products.

This is a big win for producers across the state.  One of the benefits of WMA that has been proposed to producers is that producing WMA will reduce fuel consumption at the plant and lower operating costs.  With chemical additive WMA, this cost savings can be eaten up by the additional cost of the additive.  With a water injection system, once you've paid for your capital expenditure for the system, the cost of the added water is negligible.

It has been rumored that water injection WMA may not be as effective as chemical additive WMA but with a water injection technology finally added to Caltrans's approved products list you have to assume that there is not enough of a difference to warrant fear in investing in such a technology.

Inside AMRL's Certification Program

I recently spoke with Bob Lutz, the manager of the AASHTO Materials Reference Laboratory (AMRL) and got some insight into the AASHTO Accreditation Program for materials testing laboratories.

The AASHTO Accreditation Program (AAP) was founded in 1988 and is the largest program of its kind.  State DOTs from all over the country use it for their central laboratory accreditation. 

The process is as follows:

• The lab receives an on-site assessment by an AMRL assessor.  The assessor performs a detailed review of the lab's quality management system and their testing equipment.  The assessor will also observe your technicians performing the test methods.  Most labs will have an assessor on site for 1-2 days.  A big change from the weeks of time with assessors in the Caltrans program.  
•  The quality management system review includes reviewing the lab's documented policies, procedures, and records.  Your quality management system must meet the requirements of AASHTO R-18 which is for sale for $55 at the online AASHTO Bookstore here.
• The assessors will check to see that you have the most current versions of the AASHTO and/or ASTM test methods that you have requested to be evaluated on. AASHTO standards are updated once a year in late summer or early fall.   ASTM standards are updated more frequently, and ASTM International offers a free service that allows you to receive email notifications each time one of the standards that you use is updated.  You can sign up for this service by clicking here.   
• The assessors will physically check some of the lab's testing equipment to determine whether it conforms to the requirements/tolerances stated in the test methods.  This exercise also lets the assessor know whether a lab's quality management system is being effectively followed.
• The testing procedure review involves the assessor observing technician(s) running the tests with real material.  This gives the assessor an indication of how well they follow the standard methods and their proficiency to perform the tests.  Unlike Caltrans's IA program, each technician does not have to prove that they can run each test.  The assessor will watch one person per test method although they do like to observe a good cross-section of the technicians throughout the time that they are on site to assure that all of them are competent.  
• The assessor will provide a preliminary report to the laboratory on the last day of the assessment and a more formal report will be provided to the laboratory a few weeks after the assessment.       
• Any findings in the final report labeled as "Nonconformities" must be addressed by the laboratory and the solution communicated to AMRL through their website within 90 days from the day the report was issued.  Some of the nonconformities may have to be addressed with a root-cause analysis to prevent recurrence.
• Labs must enroll in the proficiency sample testing program (PSP).  This is equivalent to the Caltrans RSP sample program.  Most samples in the AMRL program are sent out once per year, although a few, such as asphalt binder, are sent twice a year.  The proficiency sample testing program is how AMRL gauges a lab's performance between assessments.
• Once accredited, labs will continue to receive on-site assessments approximately every 24 months and will need to complete these assessments regularly along with the PSP samples in order to maintain their accreditation.  Laboratories will also be required to submit some basic information on an annual basis.    

Fees for the AASHTO accreditation will vary depending on the tests that you do at your lab.  A basic laboratory that runs gradation, SE, asphalt binder content, and moisture can be accredited for around $3500 every two years.  This includes an on-site assessment, annual fees for proficiency samples, and annual fees for accreditation maintenance.  You can find a full break down of the fees on the AMRL website here.

Bob and I also spoke about a concern that Caltrans has with the California test methods that do not have AASHTO or ASTM equivalents.  Caltrans had mentioned that they would probably keep part of their IA program open to certify labs in these test methods.  However, Bob let me know that AMRL is very open to adding Caltrans test methods to their accreditation program but only if there is no AASHTO or ASTM equivalent, so as to promote the use of national standards.  This is great news and hopefully will help to lean Caltrans towards this type of accreditation instead of their own IA program.  

If you're interested in learning more about the AASHTO Accreditation Program you can visit the AMRL website at www.amrl.net.  AMRL also has a great newsletter that they publish twice a year, in the spring and fall.  If you're interested in keeping up with AMRL updates you can email subscribe@amrl.net to have them add you to their subscription list and the newsletter can also be found on their website.  

In addition, Bob would be happy to answer any of your questions and can be reached at rlutz@amrl.net or 240-436-4801.  Good luck!

Another Warm Mix Additive Approved by Caltrans

Caltrans has just announced that the product Readiset LQ by AkzoNobel Surface Chemistry LLC is now an approved technology for Caltrans warm mix jobs.  This means that on Caltrans jobs where warm mix is either an option or a requirement, contractors are able to use this product without a lengthy approval process through Caltrans.  I spoke about this approval process here.  Unlike AkzoNobel's Rediset WMX additive, which was approved by Caltrans in March 2011, the Readiset LQ product is a liquid chemical additive and can be metered into the asphalt line at the plant with an injection system, much like a liquid anti strip additive would be.   AkzoNobel also boasts that the Readiset LQ product will eliminate the need for additional anti strip additives to be added to the mix in order to meet moisture resistance requirements.

Still no approval on water injection warm mix technologies but maybe someday in the future.

*Special thanks to Russell Snyder of California Asphalt Paving Association for this insiders tip.