Alternative methodology of porous media bulk density measurement in didactic physics laboratories

When the physical quality of porous media such as soil is studied one of the properties of great importance is its bulk density, ρ_s. Measurements of ρ_s have great relevance due to its influence in other porous system properties (e.g. porosity, volumetric water content, water storage, etc.). In this paper is proposed an alternative methodology of ρ_s measurement named vacuum-sealed method. Samples coating, contrary to the traditional methods such as the paraffin-coated, was carried out using a plastic packaging followed by the sample internal air evacuation through a vacuum pump device. The determination of the clod samples ρ_s by the paraffin-coated method was utilized as a reference. The obtained results showed that compared to the paraffin-coated method, the average ρ_s measured by the vacuum-sealed method presented underestimated values considering all the soils analyzed. The proposed method is faster and has greater coating reliability than the traditional method with the additional advantage of sample reuse for new measurements. The new method can also be easily implemented in teaching physics laboratories in high school grade and bachelor’s, engineering, and environmental science courses. As a method that requires minimal sample preparation, easy to implement, and fast, it becomes ideal for the study not only of ρ_s but also to the discussion of concepts involved in its measurement such as mass, volume, weight, apparent weight and buoyancy force.

Keywords
Vacuum-sealed method; Paraffin-coated clod; Porous media; Soil bulk density; Physics teaching