Volume 19, Issue 2 (March 1991)
Nondestructive Density Measurements of Cylindrical Specimens by Gamma-Ray Attenuation
Nondestructive density measurement of cylindrical specimens in the laboratory has several important applications. Many specimens in civil engineering laboratory testing are usually in the form of cylinders; undisturbed soil samples and field cores of concrete and asphaltic materials are primary examples. This paper describes a nondestructive laboratory technique for density measurement that can achieve a 95% confidence limit on the order of ± 0.01 g/cm3 for a useful range of density from 0.8 to 2.7 g/cm3, relevant to the above materials. The technique uses a 5 milliCurie (mCi) Cesium 137 source with a scintillation detector and counter assembly to record the radiation transmitted through the specimen. This is converted to a density value by calibration to an empirical radiation attenuation law. The principles of the method are described with consideration to the variables of the measuring system and the specimen geometry. It is shown that for solid cylindrical specimens of the materials tested, the radiation attenuation law is satisfied to a very high degree. From the law, a diameter ratio to count ratio relationship is established. Thus detailed calibration is only necessary for specimens of one diameter to determine the density of specimens of other diameters.