NON-DESTRUCTIVE MEASUREMENT OF DENSITY AND MOISTURE CONTENT BY MEANS OF A NUCLEAR METER

PREVIOUS EXPERIENCE IN THE DETERMINATION OF THE DENSITY OF COMPLETED BITUMINOUS SURFACINGS USING NUCLEAR METERS HAS SHOWN THAT THE DEVIATIONS FROM CONVENTIONALLY MEASURED DENSITY CAN HAVE VARIOUS CAUSES. THEY CAN ORIGINATE AS MUCH FROM FAULTS IN THE MEASURING PROCESS (E.G. UNSATISFACTORY SUPPORT OF THE METER, FAULTY CALIBRATION) AS FROM THE COMPOSITION AND LAYING OF THE MIX (E.G. VARYING COURSE DEPTHS, STRONGLY DIVERGING DENSITIES IN ADJOINING LAYERS, OPEN WEARING COURSE). THEREFORE THE INTRODUCTION OF THE METER FOR USE IN ACCEPTANCE TESTS, AS HAS ALREADY HAPPENED IN CERTAIN AUSTRIAN PROVINCES, APPEARS PREMATURE. FURTHERMORE MEASUREMENTS AND EVALUATION MUST FOLLOW STRICT STATISTICAL METHODS AND THE ESTABLISHMENT OF ALLOWABLE MARGINS OF ERROR NEEDS TO BE CONSIDERED. ON THE OTHER HAND THE DETERMINATION OF DENSITIES BY USE OF BACK-SCATTERING INSTRUMENTS CAN HELP TO OPTIMISE MIX DESIGN IN REGARD TO THE DEGREE OF COMPACTION AND LEAD TO THE OPTIMISATION OF THE COMPACTION PROCESS FROM THE ROLLING ASPECT INCLUDING THE NUMBER OF PASSES AND THE TEMPERATURE OF THE MIX.