The Balloon Density is used to determine in-place density of soil when testing compacted earth fills. The unit is a water-filled, calibrated vessel fitted with a hand-operated pump to pressurize the chamber. A thin, flexible membrane on the bottom displaces under pressure to fill a void. Using the base plate as a template, a hole is dug in the surface and the excavated soil is retained as a specimen. To determine the volume of the hole, the Balloon Density is mounted on the plate, the membrane (balloon) is pumped into the hole, and fluid displacement from the vessel is noted. In-place density is computed easily by dividing weight of the retained soil by the measured volume of the hole. A portion of the retained specimen is used to determine moisture content. This method is not suitable for very soft, easily deformed soils or in a hole which will not maintain constant volume. Water volume is read from the double-graduated scale on the high-strength clear plastic cylinder. Graduations are .00025ft³ or 7cm³.
Selection of Balloon Density model is determined by top-size of soil particles. 1/20ft³ HM-66 model is used for soils with 1/2in (13mm) maximum particle size and 1/13ft³ HM-67 model is for soils with particle size up to 1in (25mm). Each unit includes double-graduated cylinder, base plate, pressure/ vacuum pump assembly with quick-coupler, ten balloons, and an integral gauge for controlling pressure during calibration and testing. Extra Balloons are available in packs of ten. MA-26 Aqua-Check for moisture determinations and HMA-8 In-Place Density Accessory Kit are recommended optional accessories.