Changes to CT 231-March 2012

Caltrans has released a March 2012 version of CT 231: Method of Test for Relative Compaction of Untreated Soils and Aggregates Using Nuclear Gauges.  In general they have formatted and re-worded the majority of the test method to make it clearer but the following is a list of the major changes:

• It now defines the nuclear gauge and standardizing block.
• It no longer defines the exact dimensions of the guide plate but specifies that it should be at least as big as the footprint of the nuclear gauge.  It also now specifies a tolerance for how flat it must be (1/16in).
• It no longer defines the exact dimension of the pin but specifies that it should meet manufacturer’s specifications.
• To standardize your nuclear gage for wet density and moisture the test method now tells you to take 1 four minute count instead of 4 one minute counts.  I think this is a mistake but that’s how the method reads.  It refers you to record the counts on the form in the back of the test method and there is still room for multiple counts so I believe you should still take 4 one minute counts. 
• When preparing the site, it is no longer specified that you should remove loose surface material to a depth of not less than 50 mm below the deepest penetration by the roller.  It is now more general and only requires that you remove the material until you are blow the deepest penetration.
• It now tells you what position the gage should be in for each test: Direct transmission for wet density and backscatter for moisture content.
• It now expands on what the direct transmission depth of the rod should be in the field test for wet density.
• It now allows for gauges with direct readout capability to be used to determine density.
• It is now noted that when testing for relative compaction, the tests should be conducted in areas free of debris, standing water, loose materials, and pumping conditions.
• Under determination of wet test maximum density, it is no longer specified that “If the impact test result is to be used in a “common” composite control density, nuclear moisture, as well as a nuclear density must be taken for each test site in an area and be averaged”.
• It now specifies and explains how to plot the correction for oversize material on the graph of the TL 2148.
• The test method itself no longer explicitly points out that there are different calculations for relative compaction if there is 10% or more material retained on the ¾” Sieve (oversized material).  However, this calculation is still present on the example computations worksheet and TL-2148 and you still need to use different input variables in your equation if you have oversize material.
• The directions for choosing a random sample plan are much more concise.  It no longer specifies how to choose a random sample plan, just that you should do it randomly. 
• The appendices have been updated and moved around.  

If you use this method often you might want to read through it before your next venture out into the field.  The new version of this test method can be found on the Caltrans website and here.

Good luck!