Wednesday, February 22, 2012

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!

1 comment:

  1. Toni,
    Think it's awesome that you broke down the changes made to this test method. Very helpful to see what Caltrans changed in one place.
    Thanks for taking the time to do this.