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.