The determination of bulk density and void percentage of aggregates is crucial for evaluating their properties, and this can be achieved by following standard test methods provided in applicable codes such as ASTM C 29/C29M-17a, IS: 2386 (Part 3) – 1963, or BS 812-2:1995. In this article, we will focus on the ASTM C 29/C29M-17a standard, which specifies the procedure for determining the bulk density or unit weight of aggregates. The bulk density refers to the weight per unit volume or density, while the voids in unit volume represent the space between particles in an aggregate mass not occupied by solid minerals.
The bulk density values obtained from this test are useful in many ways, including selecting concrete mixture proportions. Additionally, the percentage of voids between particles in aggregates, whether fine, coarse, or mixed, depends on the bulk density. It is important to note that stockpile aggregates often contain absorbed and surface moisture, with the latter affecting bulking, while the test method determines bulk density on a dry basis.
Apparatus
1. Balance
The instrument used for weighing is a type of balance that has a high sensitivity to even small changes in weight. Specifically, this balance is capable of detecting weight differences as small as 0.5% of the weight of the sample being weighed. This level of sensitivity is crucial for accurate and precise measurements, particularly in scientific and industrial applications where even small errors can have significant consequences. The balance is likely calibrated regularly to ensure that it maintains its high level of sensitivity and accuracy. Overall, the use of such a balance is an important aspect of ensuring reliable and trustworthy measurements.
2. Tamping Rod
The given context describes a metal tamping rod that is cylindrical in shape and has a diameter of 16 mm. The rod is 75 cm long and has one end that is rounded. The rod is straight and made entirely of metal. The cylindrical shape of the rod has a uniform diameter of 16 mm throughout its length. The rod’s length is 75 cm, making it a relatively long object. The rounded end of the rod is likely designed to make it easier to use, as it can be pressed against a surface without damaging it. The rod’s material composition is not specified, but it is known to be made entirely of metal. Overall, the given context provides a detailed description of a straight metal tamping rod of cylindrical cross-section that has a diameter of 16 mm, is 75 cm long, and has a rounded end.
3. Cylindrical Metal Measure
Table 1 contains the specifications that the capacity of a cylindrical metal measure should conform to.
Table 1 Capacity of Measures
| Nominal Maximum Size of Aggregate, mm | Capacity of Measure, m^3 (L) |
| 12.5 | 0.0028 (2.8) |
| 25 | 0.0093 (9.3) |
| 37.5 | 0.014 (14) |
| 75 | 0.028 (28) |
| 100 | 0.070 (70) |
| 125 | 0.100 [100] |
4. Shovel or Scoop
To fill a measure with aggregate, you will need a shovel or scoop that is of a convenient size. This will ensure that the process of filling the measure is efficient and effective. The size of the shovel or scoop should be appropriate for the amount of aggregate that you intend to fill in the measure.
A shovel that is too small will require you to make more trips to fill the measure, which will waste time and effort. On the other hand, a shovel that is too large may make it difficult to accurately fill the measure and may cause spillage, which could result in inaccurate measurements.
Therefore, it is important to select a shovel or scoop of the right size to make the task of filling the measure with aggregate easy and precise. By doing so, you can ensure that the measurements are accurate and that the process of filling the measure is completed efficiently.
5. Equipment for Measuring Volume of Measure
The items on the list are plate glass, grease, thermometer, and balance. These are all objects that can be used in various scientific and laboratory settings. Plate glass, for example, is a type of glass that is often used for windows and other applications where clarity and transparency are important. Grease, on the other hand, is a lubricant that can be used to reduce friction between two surfaces. A thermometer is a device used to measure temperature, while a balance is a tool used to measure the mass of an object. Each of these items has its own specific use and purpose, and together they represent some of the most common tools and equipment found in scientific and laboratory settings.
Sample Preparation
The given context provides instructions for testing the size of a sample. The sample should have a size range of 125% to 200% of the amount needed to fill the measuring device.
To prepare the sample for testing, it must be dried in an oven. The drying process requires a temperature of 110±5°C to be maintained in the oven. The sample must be dried until it reaches a constant mass, indicating that all moisture has been removed.
Overall, the instructions indicate the necessary steps to prepare and test a sample, including the appropriate sample size and drying process. Following these instructions accurately will ensure accurate and reliable test results.
Determination of Volume of Measure
To evaluate the mass of a plate glass, a method is described as follows:
- Place a thin layer of grease on the rim of the measuring device to prevent water leakage.
- Fill the measuring device with water and cover it with the plate glass, ensuring that there are no bubbles or excess water.
- Determine the mass of the water, plate glass, and measuring device to the nearest 0.05 kg.
- Measure the temperature of the water to the nearest 0.5°C and obtain its density from Table 2.
- Calculate the volume of the measuring device, V, using Equation 1: V=(W-M)/D.
- Calculate the factor for the measuring device, F, using Equation 2: F=D/(W-M).
In Equation 1, V represents the volume of the measuring device in cubic meters, W represents the mass of the water, plate glass, and measuring device in kilograms, M represents the mass of the plate glass and measuring device in kilograms, and D represents the density of the water for the measured temperature in kilograms per cubic meter.
In Equation 2, F represents the factor for the measuring device in cubic meters per cubic meter, D represents the density of the water for the measured temperature in kilograms per cubic meter, and W and M have the same meanings as in Equation 1.
Table 2 Density of Water
| Temperature, C | kg/m^3 |
| 15.6 | 999.01 |
| 18.3 | 998.54 |
| 21.1 | 997.97 |
| 23.0 | 997.54 |
| 23.9 | 997.32 |
| 26.7 | 996.59 |
| 29.4 | 995.83 |
Test Procedure
To determine the weight of the empty measure, follow the provided procedure and round the result to the nearest 0.05kg. Once you have obtained the weight of the empty measure, fill it with aggregate in three layers and compact each layer using one of three methods. The method you use will depend on the maximum size of the aggregate. For aggregates with a maximum size of 37.5mm or less, use Method A, which involves rodding. For aggregates with a maximum size greater than 37.5mm but not exceeding 125mm, use Method B, which involves jigging. Finally, if you want to determine the loose bulk density of the aggregate, use Method C, which involves shoveling. By using the appropriate method for your aggregate size, you can obtain accurate and reliable measurements of its density.
Method A: Rodding
The task at hand is to fill a measure with aggregate in three nearly equal layers. To ensure the consistency of the layers, 25 evenly distributed strokes of a tapping rod must be applied to the surface of each layer. However, it’s crucial to make sure that the rod doesn’t hit the bottom of the measure during the rodding process.
During the rodding of the second and third layers, it’s important to prevent the rod from penetrating into the first and second layers. By doing so, we can ensure that the layers remain separate and consistent. Overall, this process will help to ensure that the measure is filled with aggregate in a precise and uniform manner.
Method B: Jigging
To fill the measure with aggregate in nearly equal three layers, you should first place the measure on a firm base. After that, raise the opposite sides of the measure alternately to a height of approximately 50mm, and then allow the measure to drop. The impact should be sharp and forceful to ensure that the aggregate is properly compacted.
The next step is to repeat the process of compacting the layers by dropping the measure 50 times, 25 times on each side. This ensures that each layer is evenly compacted and will result in a solid foundation.
Once you have compacted all three layers, the final step is to level the surface of the aggregate. This will provide a smooth and even surface that is ready for use. By following these steps, you can ensure that your aggregate is properly compacted and ready for any project.
Method C: Shoveling
To determine the mass of a sample of aggregate, the first step is to fill a measure to overflowing using a shovel or scoop. It is important to discharge the aggregate from a height no greater than 50 mm above the top of the measure to avoid any potential errors in measurement. Additionally, it is important to prevent segregation of the particle sizes within the sample during this process.
Once the measure is filled, the surface of the aggregate should be leveled to ensure accuracy in measurement. This involves removing any excess aggregate from the top of the measure to create a flat, even surface.
The final step is to determine and record the mass of the measure and its contents. This should be done to the nearest 0.05 kg to ensure precision in measurement. By following these steps, a reliable and accurate mass of the aggregate sample can be obtained.
Calculations
1. Calculation of Compacted Bulk Density of aggregate
This passage describes equations for determining the bulk density of an aggregate in an oven-dry condition. The bulk density is a measure of the mass of the aggregate per unit volume. Two equations are given, Equation 3 and Equation 4, which both include the mass of the measure (T) and the volume of the measure (V or F). Equation 4 also includes a factor for measure (F) that is computed from Equation 2.
The passage notes that the bulk density determined by this test method is for aggregate in an oven-dry condition. However, if the bulk density in terms of saturated-surface-dry (SSD) condition is required, Equation 5 can be used. Equation 5 includes the bulk density in SSD condition (MSSD) and the percent absorption (A).
2. Void Content
To calculate the void content in an aggregate, one can use Equation 6. This equation requires the bulk density of the aggregate, which can be determined through the rodding, jigging, or shoveling procedure. The bulk specific gravity (S) of the aggregate should also be known.
Once the bulk density and bulk specific gravity have been determined, Equation 6 can be used to calculate the void content in the aggregate. The equation involves subtracting the bulk density (M) of the aggregate from the product of the bulk specific gravity (S) and the density of water (W), which is 998 kg/m^3. The result is then divided by the product of the bulk specific gravity (S) and the density of water (W). The resulting value is then multiplied by 100 to obtain the percentage of voids in the aggregate.
In summary, to calculate the void content in an aggregate, one needs to know the bulk density and bulk specific gravity of the aggregate. These values can be determined using the rodding, jigging, or shoveling procedure. Once the values are known, they can be used in Equation 6 to calculate the percentage of voids in the aggregate.