AIR GAP PROCEDURE FOR THE MEASUREMENT OF SURFACE DENSITY BY GAMMA RAY BACKSCATTER TECHNIQUE
THERE HAS BEEN INCREASING INTEREST IN THE APPLICATION OF NUCLEAR MOISTURE-DENSITY SURFACE GAGES FOR THE CONTROL OF COMPACTION IN HIGHWAY CONSTRUCTION. ALTHOUGH THE BACKSCATTER TEST PROCEDURE CONVENTIONALLY USED WITH THIS NUCLEAR DENSITY EQUIPMENT IS RAPID AND NON-DESTRUCTIVE, IT HAS BEEN SHOWN THAT THE ACCURACY OF THESE GAGES IS QUESTIONABLE UNDER CERTAIN CONDITIONS. BECAUSE OF CALIBRATION DIFFICULTIES, IT SEEMED APPROPRIATE TO EXPLORE SOME SOLUTION TO THE PROBLEM. THE AIR GAP OR MAXIMUM COUNT RATIO METHOD SUGGESTED BY KUHN SEEMED TO HOLD GREATEST PROMISE IN OVERCOMING THE DIFFICULTY OF CALIBRATION FOR DIFFERENT MATERIALS. THE AIR GAP REQUIRED TO YIELD THE MAXIMUM COUNT WAS DETERMINED FROM A SERIES OF COUNTS MADE ON VARIOUS SAMPLES OF TYPICAL MATERIAL USED IN CONSTRUCTION. IT WAS DETERMINED THAT AN AIR GAP OF 1 5/8 INCHES WAS THE BEST COMPROMISE TO BE USED IN THE CALIBRATION MEASUREMENTS. CONCLUSIONS WERE THAT' /1/ AIR GAP CALIBRATION PROCEDURES WERE SUCCESSFULLY APPLIED TO A NUCLEAR CHICAGO, MODEL P22A, SURFACE DENSITY GAGE, /2/ THE ACCURACY OF THE NUCLEAR GAGE WAS IMPROVED FROM A STANDARD ERROR OF ESTIMATE OF PLUS OR MINUS 10 PCF FOR THE STANDARD COUNT RATIO METHOD TO PLUS OR MINUS 1.9 PCF FOR THE AIR GAP METHOD WHEN CALIBRATING ON A SERIES OF DENSITY STANDARDS WITH WIDELY VARYING CHEMICAL COMPOSITION, AND /3/ THE STANDARD ERROR OF ESTIMATE BETWEEN GRAVIMETRIC SOIL DENSITIES AND NUCLEAR GAGE MEASUREMENTS WAS REDUCED FROM PLUS OR MINUS 4.2 PCF FOR THE STANDARD COUNT RATIO METHOD TO PLUS OR MINUS 2.1 BY THE USE OF THE AIR GAP METHOD.
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Supplemental Notes:
- No 44, pp 1-36, 18 FIG, 4 TAB, 5 REF. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
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Authors:
- Rostron, J P
- Schwartz, A E
- BROWN, F B
- Publication Date: 1966-8
Media Info
- Media Type: Digital/other
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Serial:
- Highway Research Circular
- Issue Number: 44
- Publisher: Highway Research Board (HRB)
Subject/Index Terms
- TRT Terms: Accuracy; Backscattering; Calibration; Compaction; Density; Measurement; Methodology; Nondestructive tests; Nuclear density gages; Nuclear density gauges; Nuclear tests; Road construction; Test procedures; Texture
- Old TRIS Terms: Air gaps; Density measurement; Nuclear moisture-density determinations
- Subject Areas: Construction; Geotechnology; Highways; Materials;
Filing Info
- Accession Number: 00215815
- Record Type: Publication
- Files: TRIS, TRB
- Created Date: Dec 22 1994 12:00AM