Tuesday, June 28, 2011

Testing Mineral Filler From Hot Plants

Usually the mineral filler of a hot plant will be relatively constant in gradation.  However, occasionally you may need to test the gradation if you make any changes to the dust collection or distribution system.  In California there is no special test method for testing the gradation of mineral filler and it is tested using CT 202.  This test method requires a sample size of 500g for typical fine aggregate samples BUT if less than 10% of the sample is retained on the #30 sieve (as most mineral fillers commonly are), a sample size of 125g can be used instead.  This reduces the amount of time needed to wash out the materials passing the #200 sieve and allows for a quick and efficient test.  The rest of the test method remains the same.


We've put together a group on Linkedin where you can ask people from all over the world your most pressing construction, plant, and/or quality related questions.  Join us today and start asking questions and sharing your knowledge!

Quality In California's Linkedin Group

Wednesday, June 22, 2011

Technician Re-Certs Change to 2 Yrs

A much anticipated and highly well received change has finally been approved in regards to technician certifications!  In the past it was required for laboratory technicians to re-certify with Caltrans annually.  As of July 1, 2011 this will no longer be the case. A new technician is required to take their initial written and practical tests and re-certify one year after the initial tests but all re-certifications after that are to be done every two years instead of one. 

The Caltrans memo can be found at: Caltrans Re-Certification Memo

Friday, June 17, 2011

CT 309-June 2011

My analysis of the June 2011 CT 309 test procedure was a quick and easy one!  There are no major changes to the test method.  It seems that Caltrans was only correcting a few typos.  The biggest change in the document is that the October 2010 version references California Test Method 304M and the June 2011 version now mentions California Test Method 304 instead.  This is most likely in conjunction to the new version of CT 304 that was released this month.

The new version of CT 309 can be found here:
CT 309-June 2011

CT 309 & CT 304 Changes

For all of you laboratory folks, Caltrans has released new versions of CT 304-Preparation for Bituminous Mixtures for Testing and CT 309-Rice Theoretical Maximum Specific Gravity of HMA.  The new versions can be found here:

I’ll summarize the changes to CT 304 in this post and in CT 309 in another post soon. 

I highly recommend reading over the new CT 304.  There are some important changes that can affect your certification procedures as well as some really helpful new sections that will be assets to your laboratory on a daily basis.  The entire format of CT 304 has been revamped to be easier to reference and understand and it is heavily focused on the mix design methods covered in Asphalt Institute’s MS-2 “Mix Design Methods for Asphalt Concrete and Other Hot-Mix Types” as well as Superpave Series No. 2 (SP-2) “Superpave Mix Design”.

The biggest change that I noticed right away is that Caltrans has finally converted this test method from metric measurements to US measurements.  I know that my laboratory will be celebrating this change.  Caltrans has set a goal to switch all of the test methods back over to US units but it is a slow process and if you look through the current test methods they are a mixed bunch with some of them referencing metric units and some referencing US units. 

The following is a list of the other mentionable changes:

  • The new format breaks out the other test methods that are referenced as well as what information should be reported. 
  • The scale used for this test method must now be accurate to 0.1 g instead of 1 g.
  • If you are hand mixing you must now use a sand bath on the surface of the hot plate to minimize localized overheating.
  • It no longer specifies the use of CT 303 to determine “K” values and now allows you to pick any starting point for determining your optimum binder content.
  • It gives equations and examples for determining the percent of asphalt by total weight of mix and how to determine the weight of asphalt required in each batch. 
  • It clearly specifies temperatures for mixing and curing divided by each different type of binder.  Some are now reliant on manufacturer specifications instead of Caltrans recommended temperatures.
  • It now specifies the temperature that the binder should be heated to prior to mixing and adds additional regulations.  The binder should not be heated above 375˚F at any time, it should not be kept at the mixing temperature for over 2 hours before using it, and it should not be reheated to mixing temperature more than 2 times.
  • There are now temperature regulations for the mixing bowl prior to mixing.  It should not be heated to over 50˚F over the mixing temperature and not over 375˚F.
  • There is now mention of buttering the bowl with a mixture that has the same binder content as the lowest batch you will be testing.
  • There is an alternate procedure for curing your specimens where instead of curing at 140˚F for 15-18 hrs you can cure your specimens at 295˚F for 2-3 hours.  This is only allowed if the combined absorption of the aggregate is less than 2%.
  • It is now regulated that the mixing bowl must be scraped to within ± 0.1% of the initial total batch weight.
  • The section on preparation of field-mixed HMA has been greatly reduced in this version of the test method.  It now only mentions the temperatures that the HMA should be heated to for testing and adds an additional note that the mix should only be reheated to test temperature 2 times and should not be held at that temperature for more than 3 hours.  This section now only mentions loose mix and no longer talks about compacted mix.
  • The specifications on molds used in this test method have been greatly expanded to not only include inside diameter and height but also specifies hardness, smoothness, and wall thickness.
  • It is now required to use a rubber specimen or handful of rags to warm up the compactor before using it on your HMA specimens.  There is also now a procedure on how to warm up the compactor.
  • Part 2, the compaction section of the test method has greatly changed to reflect a clearer step-by-step process and is no longer broken out by the type of test you will be using the specimen for.  There is no longer a mention of the Swell Test or Moisture Vapor Susceptibility Test and this section seems to focus more on compaction for stability and specific gravity tests now.
  • It is now specified that instead of only having to bring the mix to compaction temperature before starting the test that the mix must be heated for to that temperature for 2-3 hours before compacting.
  • It is now specified that the time between removing the mix from the oven and starting compaction is 1 min or less.
  • The amount of tamping blows need to form the mix into semi-compacted condition has changed from recommending 20 to recommending 25.  However, this number is still based on individual observation.  There has also been a change where the recommended range based on observation has changed from 10-50 tamps to 20-50 tamps depending on the type of HMA. 
  • It is now specified to put a paper disk on the compacted specimen before leveling off the load.
  • It is now specified that the speed on the leveling load is to be 0.25 in/min.
  • It is now specified that the specimens be returned to the oven for 15 min to 2 hours after leveling to retain temperature prior to stability testing.  In the past there was no time specified.
  • There are also now four appendices which specify the procedures for preparing HMA test specimens with up to 15% RAP, Liquid Antistrip, Dry Lime, and Lime Slurry.
Some of these changes were much anticipated, many of which are already in use by most of the industry.  Others may seem like a bit of overkill but my opinion of the June 2011 version of CT 304 is positive and I'm looking forward to the new version being a very useful tool. 

Happy reading and good luck!

*UPDATE 9/22/11: Soon after posting the new version of CT 304, Caltrans pulled it off of the website so that they could re-evaluate the reporting of binder content by total weight of mix instead of the traditional dry weight of aggregates.

Wednesday, June 15, 2011

RAP Testing

Sorry to all of my readers about being MIA the last couple of weeks.  The busy season is finally upon us and it seems to have hit like a tidal wave.  Getting back into the swing of things I wanted to talk about sampling and testing recycled asphalt pavement (RAP).

There are three types of RAP that your plant might have stockpiled on site at any given time.  The first type is plant reject.  This is the tonnage that you waste at plant start up, returned mix, or any other mix that you just didn't have use for.  This type of RAP is typically higher in oil content than the other types of RAP because it is fresh and usually hasn't had the opportunity to weather.  The second type of RAP is reclaimed asphalt.  These are the giant slabs and chunks of road that are delivered to your plant.  This type of RAP typically has higher processing costs than the other two types of RAP because it must be crushed down and screened in order to obtain a RAP product that you can use in your hot mix asphalt.  The third type of RAP is millings (or grindings).  This type of RAP is ground up from the road and processed into a much smaller and sometimes very consistent product before it even leaves the construction project to be shipped to your plant.  With a certain amount of care it is even possible for the grinder to process the millings into a product that is 3/8" minus and can be fed directly into your hot plant without additional processing.   

Both millings and grindings can be easily contaminated with other products such as base rock, metal, organics, and/or paving fabric, all of which can reek havoc on your equipment and/or finished end product.  This is why quality control starts as soon as the truck of RAP pulls into your plant.  Before allowing a truck with RAP product to dump on your stockpile, it is important to inspect the load.  If you see any of the things that I mentioned above, it would be wise of you to either reject the load or to have them dump it in another area besides your clean RAP stockpile.  If you accept contaminated loads as part of your business, I would suggest having at least two different stockpiles of RAP.  At a minimum you should have a clean RAP pile and a contaminated RAP pile.  In a perfect world, aka if you have the space, you would have a pile for your plant reject, a pile for clean grindings, a pile for clean reclaimed asphalt, and a pile for contaminated RAP of all sorts.  You could even go as far as having separate piles for materials you received from large jobs.  Material that was all removed at the same location has a high chance of originally all coming from the same plant and having a very consistent grading and/or oil content.  This could greatly help you later on in your testing and HMA production. 

Chances are that unless you had a really kindhearted contractor grinding your RAP, you will have to use additional processing to create a RAP product that you can add to your hot mix asphalt.  If you have smaller grindings or plant reject, you may only have to run the RAP over a screen to break up the chunks.  If you have larger pieces like in reclaimed asphalt you may have to crush it down first and then run it over a screen.  Whatever process you decide to use, you will eventually end up with what looks like a darker colored aggregate pile.  You can sample this pile just like you would any other aggregate pile.  However, be aware that in extremely cold, extremely hot, or wet weather your RAP pile might want to stick together.  This is normal but your loader might have to work the pile a little bit more to break the chunks apart.

As a rule of thumb it is recommended that you sample your RAP once every 1000 tons.  You should, at a minimum, run gradation and oil content tests in order to know for sure that the quality of what you're putting into your hot mix is not varying enough where you would have to make a plant change.  There are two recommended ways to test the oil content of your RAP samples.  The first is by the extraction method.  This is the most accurate for testing the oil content of RAP but is time consuming and is difficult to use as a quality control procedure during production.  What most companies do is take 3-5 samples around their RAP pile in various places and use the extraction method to determine the oil contents.  You then average these oil contents to determine a base oil content for comparing your ignition test results to.  The ignition oven is the second type of oil content test that is used for RAP.  The RAP sample is tested the same as a traditional HMA sample in the ignition oven.  However, since you cannot create a correction factor in the traditional way, you must assume one.  This is where the extraction average from before comes into play.  The test results from the ignition test are compared to the average extraction oil content to determine if the oil content is varying in production so that the asphalt plant operator can make a change to the virgin oil content if necessary. 

In regards to gradation, it is possible to run a gradation test on RAP in the same way that you would run it on a virgin aggregate.  However, know that this will leave asphalt binder residue on your equipment and may blind your smaller sieves.  More often a laboratory will use the aggregate leftover from the extraction test or ignition oven to perform a gradation. 

Caltrans test method LP-9 is a procedure for testing RAP for use in Hot Mix Asphalt and can be found at the Caltrans Lap Procedures Website

Does your plant test RAP differently?  Do you have any tips or tricks for sampling or testing RAP?