In construction, determining the bulk density and void percentage of aggregates is crucial. This information is often required for concrete mixture proportions. Various codes, such as ASTM C 29/C29M-17a, IS: 2386 (Part 3) – 1963, or BS 812-2:1995, provide standardized methods for these evaluations. This article focuses on the ASTM standard (ASTM C 29/C29M-17a) and aims to explain the process in simple terms.
Bulk density, or unit weight, signifies the weight per unit volume of an aggregate. It is essentially the mass per unit volume or density of the material. Meanwhile, voids in the unit volume refer to the spaces between particles in an aggregate mass that are not filled with solid minerals.
To conduct the bulk density and void percentage test, specific equipment is necessary. These include a sensitive balance, a tamping rod, a cylindrical metal measure of various sizes, a shovel or scoop, and equipment for measuring volume. The volume measurement equipment involves plate glass, grease, and a thermometer.
Preparing the sample involves drying it to a constant mass in an oven at a specified temperature. The size of the test sample should range from 125% to 200% of the amount required to fill the measure.
The volume of the measure is determined by evaluating the mass of water, plate glass, and measure. This involves specific steps such as applying a layer of grease on the measure’s rim to prevent water leakage and measuring the temperature of the water.
The test procedure includes taking the weight of the empty measure, filling it in three layers, and compacting the aggregate based on its size. Methods such as rodding, jigging, or shoveling are employed, depending on the aggregate size.
Finally, the mass of the measure plus its contents is determined and recorded.
Calculations involve determining the compacted bulk density of the aggregate and void content.
These calculations provide valuable insights into the characteristics of aggregates, aiding in construction material selection and concrete mixture design.