ASTM C128 Relative Density (Specific Gravity) and Absorption of Fine Aggregate

Get Certified ASTM C128 Fine Aggregate Testing

ASTM C128 testing offers consistent measurements of the relative density and absorption of the fine aggregate for concrete and other mixtures that use fine aggregate. A qualified technician can perform the test using calibrated weighing, water-saturation, and volume-measurement equipment while following the applicable ASTM requirements.

• Relative Density: Determines the dimensionless ratio between aggregate particle density and water density. 
• OD Condition: Measures relative density after drying the aggregate. 
• SSD Condition: Measures relative density after the prescribed water-soaking and surface-drying procedure. 
• Absorption: Determines the percentage increase in aggregate mass caused by absorbed water. 
• Apparent Relative Density: Represents the solid material excluding pore space accessible to water. 

What are the uses of ASTM C128 testing?

ASTM C128 results help engineers determine the volume occupied by fine aggregate in mixtures proportioned on an absolute-volume basis. The results also support calculations involving aggregate voids, surface moisture, and mixture proportions. This method helps in:

• Concrete Mixture Design: Provides aggregate data for proportioning hydraulic cement concrete. 
• Bituminous Mixtures: Supports absolute-volume calculations for asphalt mixtures. 
• Void Calculations: Provides relative-density data used with aggregate void calculations. 
• Moisture Evaluation: SSD relative density and absorption support assessment of aggregate moisture conditions. 
• Quality Control: Helps technicians characterize fine aggregate properties before use. 

Which Materials Can Be Tested According to ASTM C128?

ASTM C128 applies to fine aggregate materials for which relative density and water absorption need to be determined. The method represents the average properties of the essentially solid portion of the aggregate particles rather than the bulk volume between particles. 

• Natural Fine Aggregates: Sand and naturally occurring fine aggregate. 
• Manufactured Fine Aggregates: Processed aggregates used in concrete and related mixtures. 
• Mineral Fine Aggregate: Suitable fine aggregate materials used in proportioned mixtures. 
• Excluded Materials: Lightweight aggregates covered by Specification C332 Group I are outside the intended scope. 

Why is ASTM C128 Testing Important?

Fine aggregate relative density and absorption directly affect mixture proportioning and moisture calculations. Accurate ASTM C128 testing helps engineers account for aggregate volume and water absorption when developing consistent concrete and bituminous mixtures. 

ASTM C128 Testing Process and Data Collection

The technician first prepares and dries the fine aggregate, then determines its required mass. The specimen undergoes water saturation for the prescribed conditioning period before the technician establishes the SSD condition. The technician records the relevant masses and measurements and uses them to calculate relative density and absorption. ASTM C128 distinguishes between OD relative density, SSD relative density, apparent relative density, and absorption. Relative density is dimensionless, while absorption is reported as a percentage. 

Common Challenges and Troubleshooting

Excess surface water or insufficient surface drying can affect the measured mass. Technicians should carefully establish the saturated-surface-dry condition. Insufficient conditioning can produce an inaccurate absorption value. The prescribed conditioning procedure should be followed consistently. Small mass errors can affect calculated relative density and absorption. Use calibrated weighing equipment and verify measurements. Poorly representative samples can produce results that do not reflect the aggregate supply. Proper sampling and preparation are essential.

• The report should identify the tested fine aggregate and provide the measured and calculated values for oven-dry relative density, saturated-surface-dry relative density, apparent relative density, and absorption.
• Relative density is reported as a dimensionless value, while absorption is reported as %.
• The technician records the specimen identification, measured masses, and relevant test conditions used during the determination.
• The analyst documents the calculated relative density and absorption values and verifies that the reported results follow the applicable ASTM C128 requirements.
• The final report includes the test results, specimen information, measurement data, calculation results, and other required reporting details to support consistent interpretation of the fine aggregate properties.

Link to ASTM C128