1. General Description and Scope
Coarse aggregate shall consist of sound, durable particles obtained from approved sources, including crushed stone, gravel, or other inert materials. The material shall be clean and free from deleterious substances such as clay lumps, organic matter, and other impurities that may affect the performance of concrete. The aggregate shall conform to the requirements of ASTM C33 or IS 383, as applicable.
2. Material Properties
The coarse aggregate shall meet the following physical property requirements:
Los Angeles Abrasion Loss: The percentage of wear shall not exceed 45% when tested in accordance with AASHTO T 96.
Soundness: The aggregate shall have a maximum loss of 12% when subjected to five cycles of the sodium sulfate soundness test, as per AASHTO T 104.
Specific Gravity: The specific gravity of the aggregate particles shall be within the range of 2.5 to 3.0.
Absorption: The water absorption of the aggregate shall not exceed 2%.
3. Grading Requirements
The coarse aggregate shall be well-graded and conform to the specified grading limits. The grading shall be determined by sieve analysis in accordance with ASTM C136. The aggregate shall comply with the grading requirements shown in Table 1.
Table 1: Grading Requirements for Coarse Aggregate
| Sieve Size (mm) | Percentage Passing (%) |
|---|---|
| 75.0 | 100 |
| 63.0 | 90–100 |
| 50.0 | 35–70 |
| 37.5 | 0–15 |
| 25.0 | 0–5 |
Note: The above table is an example; actual grading requirements may vary based on project specifications.
4. Deleterious Substances
The coarse aggregate shall be free from deleterious materials in amounts that could adversely affect the performance of the concrete. The maximum allowable limits for deleterious substances are as follows:
Clay Lumps and Friable Particles: Not more than 2.0% by weight.
Material Finer than 75 µm (No. 200) Sieve: Not more than 1.0% by weight.
Coal and Lignite: Not more than 0.5% by weight.
Chert: Not more than 0.5% by weight.
5. Particle Shape
The aggregate particles shall be predominantly cubical or spherical in shape. Flat or elongated particles, defined as those with a length-to-thickness ratio greater than 3:1, shall not exceed 15% by weight.
6. Moisture Content
The moisture content of the coarse aggregate at the time of batching shall be controlled to ensure consistent concrete workability and strength. The aggregate shall be in a saturated surface-dry (SSD) condition, or appropriate adjustments shall be made to the mix water to account for the actual moisture content.
7. Handling and Storage
Coarse aggregate shall be handled and stored in a manner that prevents contamination, segregation, and degradation. Stockpiles shall be built in layers not exceeding 1.5 meters in height to minimize segregation. Different sizes or sources of aggregate shall be stored separately to prevent intermixing.
8. Quality Control and Testing
Regular sampling and testing of the coarse aggregate shall be conducted to ensure compliance with the specified requirements. Tests shall include sieve analysis, Los Angeles abrasion, soundness, specific gravity, absorption, and determination of deleterious substances. Test results shall be documented and made available for review by the Engineer.
9. Compliance with Standards
The coarse aggregate shall conform to the requirements of ASTM C33 or IS 383, as applicable, and any additional project-specific specifications.
Post a Comment