ASTM C127 Relative Density and Absorption of Coarse Aggregates

Scope ASTM C127:

The ASTM C127 standard is the “Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Coarse Aggregate.” It offers a thorough approach to assessing the physical characteristics of coarse aggregate. This standard can ascertain the bulk density of aggregates determined by Test Method C29/C29M, relative density, and water absorption properties of aggregates. 

The ASTM C127 standard helps to guarantee that aggregates used in building projects are suitable for the intended application by offering exact measurement and preparation processes. It helps maintain consistency and structural integrity in the built environment. The process involves preparing a sample of coarse aggregate and saturating it with water to fill its pores. Then its weight is measured in both dry and saturated conditions. These measurements are important for calculating the material’s specific gravity and absorption rate. They directly influence the quality and durability of concrete. Adherence to this standard ensures that the aggregates are tested under consistent conditions. It provides reliable data for construction professionals to use in making informed decisions about materials.

Procedure:

The testing procedure under ASTM C127 involves several key steps:

1. Sample Preparation: Aggregates are cleaned, dried, and sieved. This is done to remove fine particles.
2. Saturating Aggregates: The prepared samples are soaked in water. This ensures complete saturation and fills any voids within the aggregates.
3. Surface Drying: After saturation, the aggregate surface is dried, usually using a cloth, to remove any excess water.
4. Weighing: The aggregate is weighed in three states: dry (after oven-drying), saturated surface-dry (SSD), and submerged in water.

The test uses a pycnometer to measure the relative density. It is a flask used to determine the sample volume by the water displacement. The specific gravity at SSD condition is determined by dividing the weight of the oven-dried aggregate by the weight of the displaced water. This ratio gives the SSD specific gravity, which is dimensionless and typically ranges from 2.5 to 3.0 for most aggregates. For oven-dry specific gravity, the dry weight of the aggregate is used instead of the SSD weight.

Data:

The collected data are important for calculating the specific gravity and absorption:

1. Relative Density (OD) – Oven-Dry Specific Gravity

This is calculated using the formula:

Relative density (OD) = A/(B-C)

A = Mass of Oven-Dry Aggregate in Air

B = Mass of Saturated Surface-Dry Aggregate in Air

C = apparent mass of saturated sample in water

where:

Relative density(SSD) = B/(B-C),

Apparent relative density (apparent specific gravity) = A/(A-C),

Absorption (%) = ((B-A)/A) x 100.

This calculation is straightforward and uses the mass and volume of the oven-dry aggregate as determined by the displacement of water.

2. Relative Density (SSD) – Saturated Surface-Dry Specific Gravity

This is calculated using the formula:

Specific Gravity (SSD)=Mass of Saturated Surface-Dry Aggregate in AirVolume of Aggregate (displaced water mass)Specific Gravity (SSD)=Volume of Aggregate (displaced water mass)Mass of Saturated Surface-Dry Aggregate in Air​

For SSD, the aggregate’s mass is used when all pores are saturated with water but without any water on the surface.

3. Apparent Relative Density – Apparent Specific Gravity

This calculation is slightly different and less commonly discussed under ASTM C127 specifically, but it is relevant in other contexts, such as lightweight aggregate testing (ASTM C128). The formula is:

Apparent Specific Gravity=Mass of Oven-Dry Aggregate in Air (A)A−CApparent Specific Gravity=A−CMass of Oven-Dry Aggregate in Air (A)​

Here, “C” represents the buoyant force or the apparent mass of the saturated aggregate submerged in water. This value is crucial as it accounts for only the volume of the solid particles themselves, excluding the pores that get filled with water.

Specimen Size:

The specimen size for ASTM C127 testing is carefully selected to represent the aggregate supply. It is essential to ensure that the aggregate sample has a significant range of particle sizes. For the test, aggregates that pass through a 3-inch sieve and are retained on a 3/8-inch sieve are often required. 

This size range ensures that the sample includes significant characteristics of the aggregate batch, allowing for reliable testing and results. The correct specimen size is vital for obtaining accurate bulk density, relative density, and absorption measurements. They are essential parameters for evaluating the suitability of aggregates in construction projects. Properly sizing the specimen guarantees the precision and relevance of the test outcomes.

Further Analysis:

Further analysis includes:

• Particle Shape and Surface Texture: These attributes affect the aggregate’s water absorption and its performance in concrete.
• Porosity and Pore Structure Analysis: Helps understand the aggregate’s durability and frost resistance.

Different Tests Used for ASTM C127:

1. ASTM C136: Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates: This test method is similar to ASTM C127 but specifically determines the particle size distribution of fine and coarse aggregates separately.
2. ASTM C29: Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate: This test method determines the bulk density or unit weight and the voids in aggregates, which are important properties for concrete mix design.
3. ASTM C39: Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens: This test method determines the compressive strength of cylindrical concrete specimens, which is crucial for assessing the strength of concrete mixes.
4. ASTM C78: Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading): This test method determines the flexural strength of concrete beams, which is another important property for assessing the performance of concrete mixes.
5. ASTM C109: Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens): This test method determines the compressive strength of hydraulic cement mortars, which is important for evaluating the quality of mortar mixes used in construction.

These tests complement the data obtained from ASTM C127 by comprehensively analysing the aggregate’s properties, thereby ensuring optimal selection for specific applications.

Infinita Lab for ASTM C127

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Specific Gravity & Water Absorption of Coarse Aggregate