A RADIOISOTOPE BACKSCATTER GAUGE FOR MEASURING THE CEMENT CONTENT OF PLASTIC CONCRETE

A GAMMA-RAY BACKSCATTER GAUGE FOR MEASURING THE CEMENT CONTENT OF PLASTIC (FRESH) PORTLAND CEMENT CONCRETE HAS BEEN EVALUATED AND MODIFIED TO ACHIEVE THE DESIRED ACCURACY AND FIELD APPLICABILITY. THE GAUGE WAS INITIALLY DEVELOPED FOR FHWA UNDER AN ADMINISTRATIVE RESEARCH CONTRACT. AN AMERICIUM-241 SOURCE IS USED WITH A 1-INCH X 1-INCH NAI(TI) SCINTILLATION CRYSTAL IN A PROBE WHICH IS PLACED WITHIN A CU. FT. CONCRETE SAMPLE BY MEANS OF AN ACCESS TUBE. ACCURACY OBTAINABLE VARIES FROM STANDARD ERRORS OF 22 PC/CYC (1BS. CEMENT/CU.YD. CONCRETE) WITH SILICEOUS AGGREGATE MIXES TO 31 PC/CYC WITH CALCAREOUS AGGREGATE MIXES. ACCURACY MAY BE IMPROVED BY AVERAGING CEMENT CONTENT DETERMINATIONS FROM TWO OR MORE SAMPLES. GAUGE RESPONSE IS VERY DEPENDENT ON THE CHEMICAL COMPOSITION OF THE AGGREGATE MATRIX, BUT THE CEMENT CONTENT DETERMINATIONS ARE NOT DEPENDENT ON BULK DENSITY, WATER CONTENT, OR AIR CONTENT. INDIVIDUAL CALIBRATION CURVES MUST BE ESTABLISHED FOR MIXES WITH CHEMICALLY DISTINCT AGGREGATES AND FOR MIXES WITH DIFFERENT RATIOS OF COARSE TO FINE AGGREGATE WHEN THE TWO SIZES ARE DISTINCTLY DIFFERENT CHEMICALLY. ACCURACY AND SENSITIVITY TO VARIATIONS IN CEMENT CONTENT GENERALLY ARE WORST FOR MIXES WITH CALCAREOUS AGGREGATES AND WITH OTHER AGGREGATES WHICH CONTAIN SIGNIFICANT QUANTITIES OF ELEMENTS WITH HIGH ATOMIC NUMBERS SUCH AS IRON, TITANIUM, CALCIUM, AND BARIUM. TEMPERATURE AND ELECTRONIC STABILITY EFFECTS ARE MINIMIZED BY USING A COUNT-RATIO PROCEDURE WITH POLYMER IMPREGNATED CONCRETE STANDARDS. DENSITY MEASUREMENTS EMPLOYING A CESIUM-137 SOURCE IN THE SAME SAMPLE GEOMETRY AND WITH THE SAME DETECTOR SYSTEM ARE REPORTED.

  • Corporate Authors:

    Federal Highway Administration

    Office of Research and Development, 1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Mitchell, T M
  • Publication Date: 1973-4

Media Info

  • Pagination: 54 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00212144
  • Record Type: Publication
  • Source Agency: Federal Highway Administration
  • Report/Paper Numbers: FHWA-RD-73- 48 Intrm Rpt., FCP 24F3-014
  • Files: TRIS, USDOT
  • Created Date: May 7 1976 12:00AM