MEASURING THE DENSITY OF THIN ASPHALT OR CONCRETE LAYERS WITH A GAMMA-RAY BACK-SCATTER APPARATUS

ONE DRAWBACK OF RADIOACTIVE BACK-SCATTER APPARATUS FOR MEASURING DENSITY IS THE DIFFICULTY OF DEFINING ADEQUATELY THE DEPTH-SAMPLING CHARACTERISTIC. THE CONCEPT OF THE MEAN DEPTH TO WHICH USEFUL GAMMAS PENETRATE IS INTRODUCED. PROVIDED THE INSTRUMENT HAS BEEN DESIGNED TO MEASURE THE ABSORPTION OF BACK-SCATTERED GAMMA RADIATION, THE DENSITY DETERMINED IN THE PRESENCE OF SMALL DENSITY GRADIENTS WILL BE THE AVERAGE DENSITY OF THE LAYER LYING ABOVE THE MEAN DEPTH. THE DERIVED DENSITY OF THIS SHALLOW LAYER MAY BE SLIGHTLY ERRATIC DUE TO THE PRESENCE OF LAYERS WITH A DIFFERENT DENSITY AT DEPTHS BETWEEN ONE AND THREE TIMES THE MEAN DEPTH TO WHICH THE GAMMA RAYS PENETRATE. ALLOWANCES ARE CALCULATED FOR SUCH ERRORS FOR A PARTICULAR INSTRUMENT USED IN THE EXPERIMENTS DESCRIBED. FOR THIS PARTICULAR APPARATUS WITH A RADIUM 226 SOURCE, THE MEAN DEPTH OF PENETRATION OF THE USEFUL GAMMA RADIATION WAS FOUND TO BE BETWEEN 1.2 AND 1.8 IN FOR MATERIALS WITH DENSITIES RANGING FROM 150 TO 100 LB/FT TO THE THIRD POWER. THIS APPARATUS WAS FOUND USEFUL FOR MEASURING THE INCREASE OF DENSITY DURING COMPACTION OF A 2 1/2-IN ASPHALT BASE COURSE, AND FOR MEASURING THE DENSITY VARIATION NEAR THE SURFACE ACROSS LAYERS OF BITUMINOUS-BOUND MATERIALS. /RRL/A/

• Supplemental Notes:
  • Vol 3, No 3, PP 467-475, 7 FIG, 6 TAB, 8 REF
• Corporate Authors:

  Nuclear Engineering & Design /Neth

  ,    
• Authors:
  • HARLAND, D G
• Publication Date: 1966-4

Subject/Index Terms

• TRT Terms: Absorption; Asphalt; Backscattering; Bituminous aggregates; Concrete; Density; Gamma rays; Measurement; Measuring instruments; Pendulum tests; Thinness
• Old TRIS Terms: Density measurement
• Subject Areas: Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00216496
• Record Type: Publication
• Source Agency: Road Research Laboratory /UK
• Files: TRIS
• Created Date: Jan 30 1994 12:00AM