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