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The use of recycled concrete aggregate in a dense graded aggregate base course.
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2008-03-01
[PDF-791.08 KB]
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Edition:Final report; 1/2007-3/2008.
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Abstract:The research project was broken up into 2 different parts. The first part involved evaluating the potential use of the Time
Domain Reflectometry, TDR (ASTM D6780), as a non-nuclear means for determining the dry density and moisture content of
granular base and subbase aggregates during quality control. Just prior to the study, Humboldt Equipment Company provided
a device called the Electrical Density Gauge (EDG) that also claimed to be a non-nuclear means of determining dry density and
moisture content. Both units were used on five separate field trials (5 sections for the TDR and 3 sections for the EDG) and
compared against the NJDOT’s nuclear density gauge. The field trials indicated that the TDR test method, as it currently
stands according to ASTM D6780, does not compare well with the nuclear density gauge readings. This was mainly attributed
to the TDR’s soil constant calibration procedure. There also appeared to be a lack of sensitivity with the TDR method when
compared to the nuclear gauge. The EDG showed a better correlation to the nuclear gauge, although this was expected since
at the time of the study, the EDG device required field calibration. A newer version of the EDG now incorporates a laboratory
calibration procedure that would eliminate the need for field calibration with a nuclear gauge.
The second part of the research study was to evaluate potential methods of increasing the permeability of recycled concrete
aggregate (RCA), while attempting to maintain its structural integrity (i.e. – California Bearing Ratio, CBR). Before laboratory
testing began, a survey was developed, sent to various state agencies, and tabulated to determine if other state agencies
currently utilized RCA, and if so, what experience did they have regarding the drainage characteristics of the material. After the
survey results were tabulated, laboratory testing was conducted on RCA blended with different aggregates; dense-graded
aggregate (DGA), NJDOT I-3, and poorly graded sand. Work was also conducted on RCA material which was processed over
a coarser sieve size (2 inches), as opposed to the finer 1.5 inches currently specified by NJDOT, in an attempt to include a
larger, coarser fraction that could open up the internal structure of the RCA. This was in an attempt to meet some of the state
agency specifications of the various states who responded to the survey saying they did not have any current issues with the
permeability/drainage of their RCA materials. The results of the laboratory testing showed that the best performing
modification to the RCA was when blended with 50% DGA. This increased the permeability to levels considered average,
while still providing excellent bearing strength. The attempts of using the NJDOT I-3 and poorly graded sand did not
dramatically increase the permeability, while a decrease in bearing strength was still reported. Increasing the top size of the
processed/screened RCA from 1.5 inches to 2.0 inches helped to increase the permeability, while achieving the same bearing
strength properties (CBR).
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