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DENSITY MEASUREMENTS ON EMULSION TREATED BASES USING NUCLEAR DENSITY GAUGES

by Gerhard du Toit. DENSITY MEASUREMENTS ON EMULSION TREATED BASES USING NUCLEAR DENSITY GAUGES. Presentation to the RPF 07 November 2006. TYPICAL “AS-BUILD” PAVEMENT STRUCTURE. TYPICAL MATERIAL PROPERTIES. Untreated material. Bearing capacity. (CBR @ 98% ModAASHTO) 106.

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DENSITY MEASUREMENTS ON EMULSION TREATED BASES USING NUCLEAR DENSITY GAUGES

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  1. by Gerhard du Toit DENSITY MEASUREMENTS ON EMULSION TREATED BASES USING NUCLEAR DENSITY GAUGES Presentation to the RPF 07 November 2006

  2. TYPICAL “AS-BUILD” PAVEMENT STRUCTURE

  3. TYPICAL MATERIAL PROPERTIES Untreated material • Bearing capacity (CBR @ 98% ModAASHTO) 106 (CBR @ 95% ModAASHTO) 76 • Grading Modulus 2.08 • Plasticity Index 8.63 • Max Dry Density 2300 kg/m3 • OMC 8.1

  4. Calibration Factors: Troxler = 1.026 CPN = 1.023 Average Troxler = 2113.6 Kg/m3 Average SR = 2060.4 Kg/m3 Average CPN = 2107.6 Kg/m3

  5. Note: Trend line indicate deviation from line of equality and hence, lack of deriving a constant calibration factor between devices

  6. Note: Trend line indicate deviation from line of equality and hence, lack of deriving a constant calibration factor between devices

  7. NOTED VARIATIONS IN RELATIVE DENSITIES Average Max Min • CPN vs. Troxler -1.2% +2.7% -7.6% • CPN vs. SR +1.7% +5.6% -1.1% • Troxler vs. SR +2.6% +8.3% -4.2%

  8. Moisture measurements needs to be corrected – gravimetric method • Do not measure mass, nor volume - relate loss in α, β and γ rays (based on standard calibration values) to density • Readings affected by material properties : • Mineralogy of dolerites – bound crystal water NUCLEAR DEVICES • Carbon hydrates (free H+) in emulsions and/or “chunks” of milled-in old bituminous surfacing • Calcium present in cement additive • Ferro / ferro oxides in materials

  9. Susceptible to “errors” during testing operations : • Calibration of instrument • Device to be level and “flush” with surface NUCLEAR DEVICES(continued) • Disturbances when making hole for probe • Probe to be positioned “flush” with side of hole • etc.

  10. Direct measure of mass and volume – less susceptible to material influences • Susceptible to “errors” during testing operations : • Sand to be calibrated • Loss of density sand when determining volume of density hole SAND REPLACEMENT METHOD • Disturbances when hammering density rings to surface • Inexperienced testing staff • etc. • Major draw-back – test is tedious and time-consuming

  11. Nuclear density devices are valuable and useful instruments, provided : • Applied correctly SUMMARY AND CONCLUSSIONS • Readings are not influenced by material properties – albeit mineralogical, or due to addition of stabilising agents, or other • Density readings are calibrated against that of sand replacement

  12. “Error” in nuclear gauge density readings : • “Overestimate” density by as much as 8% - 9% • “Underestimate” density by as much as 4% - 5% SUMMARY AND CONCLUSSIONS (continued) • Could therefore have significant (detrimental) consequence when considering acceptance and/or rejection of a particular layer

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