3- ASTM C29-Bulk Unit Weight and Voids in Aggregate

Summary

This experiment focuses on determining the bulk unit weight and voids in aggregates, which are crucial for concrete mix design. It covers the purpose, significance, apparatus, and the step-by-step procedure, including calibrating the measure, compacting the aggregate, and calculating the bulk unit weight and void content. The methods of compaction—rodding, jigging, and shoveling—are explained based on the size of the aggregate. Results help in concrete proportioning, mass-volume conversions, and understanding aggregate packing efficiency, ensuring optimal material usage for construction projects.

Takeaways

• 😀 The main purpose of the experiment is to determine the bulk unit weight and voids in aggregate in both compacted and loose conditions.
• 😀 Bulk density is crucial for the proportioning of Portland cement concrete mixtures and for determining mass-to-volume relationships in conversions and purchase agreements.
• 😀 The percentage of voids between aggregate particles can be determined based on the bulk density obtained in the experiment.
• 😀 The required apparatus includes a balance, tamping rod, shovel or scoop, plate glass, and a rigid metal watertight container with a known volume.
• 😀 Calibration of the measure involves filling it with water, weighing it, and calculating its volume by dividing the mass of water by its density.
• 😀 There are different methods for compacting the aggregate: rodding (for aggregates ≤ 37.5mm), jigging (for aggregates between 37.5mm to 125mm), and shoveling (for loose aggregates).
• 😀 The rodding procedure involves filling the container with three equal layers of aggregate, compacting each layer with 25 strokes of the tamping rod.
• 😀 The jigging procedure involves filling the container with three equal layers and dropping it alternately on each side 25 times.
• 😀 The shoveling procedure requires filling the container to overflowing, ensuring the aggregate is discharged from a height no higher than 50mm above the container's top.
• 😀 After compaction, the surface of the aggregate is leveled, and the net weight of the aggregate is determined to calculate the bulk unit weight and void content.
• 😀 The void percentage is calculated using the bulk unit weight and specific gravity of the aggregate, with the unit weight of water being a constant value (998 kg/m³).

Q & A

What is the main purpose of the experiment described in the script?

The main purpose of the experiment is to determine the bulk unit weight and voids in aggregates, either in a compacted or loose condition.

Why is bulk density of aggregates important?

The bulk density of aggregates is crucial for proportioning Portland cement concrete mixtures. It can also be used to determine mass or volume relationships for conversions and purchase agreements.

What are the key apparatus required for this experiment?

The key apparatus for the experiment include a balance, tamping rod, shovel or scoop, plate glass, and a rigid metal watertight container with a known volume.

What is the minimum volume of the measuring container for a 25 mm nominal maximum aggregate size?

For a 25 mm nominal maximum aggregate size, the minimum required volume of the measuring container is 0.0093 cubic meters (or 9.3 liters).

What is the first step in the test procedure for calibrating the measure?

The first step in calibrating the measure is to fill it with water at room temperature, cover it with plate glass to eliminate bubbles and excess water, and then weigh it to determine the mass of the water and the container.

What are the different compaction methods used in this experiment?

The compaction methods used are rodding, jigging, and shoveling, each suited for different aggregate sizes and conditions (compacted or loose).

What compaction method is used for aggregates with a nominal maximum size of 37.5 mm or less?

For aggregates with a nominal maximum size of 37.5 mm or less, the rodding method is used for compaction.

What is the procedure for compacting using the rodding method?

In the rodding method, the container is filled with the aggregate in three layers of approximately equal volumes. Each layer is compacted by 25 strokes of a tamping rod evenly distributed over the surface.

How is the void percentage calculated in this experiment?

The void percentage is calculated using the formula: Void Percentage = (S * W - M) / (S * W) * 100, where S is the bulk specific gravity (dry basis), W is the unit weight of water, and M is the bulk unit weight of the aggregate.

How is the bulk unit weight of the aggregate determined?

The bulk unit weight (M) is determined by the formula: M = (G - T) / V, where G is the weight of the aggregate plus the measure, T is the weight of the empty measure, and V is the volume of the measure.