AASHTO T 27 Sieve Analysis of Coarse and Fine Aggregates

Summary

This video provides a comprehensive guide to performing sieve analysis of fine and coarse aggregates, a vital procedure in construction for determining particle size distribution. It covers the preparation of samples, sieving through progressively smaller sieves, and calculating the results, including the percentage of material retained or passing each sieve. The video also explains how to calculate the fineness modulus, an essential index for evaluating fine aggregates. The detailed step-by-step instructions ensure accurate testing and reporting, helping technicians comply with industry specifications for aggregate grading in concrete production.

Takeaways

• 😀 Sieve analysis determines the particle size distribution of fine and coarse aggregates by sieving.
• 😀 The procedure involves separating aggregates through progressively smaller sieve openings to evaluate size distribution.
• 😀 Sample size and preparation are critical: fine aggregates need at least 300 grams, and the sample must be dry and weighed accurately.
• 😀 A mechanical sieve shaker is recommended to ensure efficient separation, especially for larger sample sizes.
• 😀 The sieves should be clean and arranged in order of decreasing size from top to bottom to prevent contamination and ensure accurate results.
• 😀 After agitation, weigh the material retained on each sieve and record the data carefully to check for sieve blinding.
• 😀 To calculate the percentage of material retained on each sieve, divide the weight on each sieve by the initial dry sample mass, then multiply by 100.
• 😀 The percentage passing through each sieve is simply 100 minus the percentage retained on that sieve.
• 😀 The fineness modulus is calculated by adding the cumulative percentages retained on specific sieves and dividing by 100.
• 😀 For accurate testing, it is common practice to run both T 11 and T 27 tests to determine material passing the number 200 sieve, with detailed calculations for fine aggregates.
• 😀 Reporting should include percentages for material passing specific sieves, the fineness modulus, and any material finer than the number 200 sieve, with careful rounding based on the specifications.

Q & A

What is the primary purpose of the sieve analysis procedure described in the script?

The primary purpose of the sieve analysis procedure is to determine the particle size distribution of fine and coarse aggregates by sieving, ensuring compliance with specifications and controlling the production of various aggregate products and mixtures.

What are the essential pieces of equipment required for performing sieve analysis?

The essential equipment required includes an oven (capable of maintaining 230°F ± 9°F), a balance accurate to 0.1% of the sample mass, a nest of sieves conforming to ASTM standards, and a sieve shaker for efficient agitation.

How should the aggregate sample be prepared before the sieve analysis begins?

The aggregate sample must be dried in an oven at 230°F ± 9°F to a constant mass, then weighed to the nearest 0.1% of its original dry mass before starting the sieve analysis process.

What is the correct procedure for setting up the sieves for testing?

The sieves should be nested in decreasing size order, from top to bottom, with the sample placed in the top sieve. A cover should be placed on the top sieve before agitating the sample.

What role does the mechanical sieve shaker play in the process?

The mechanical sieve shaker is used to agitate the sieves in a manner that ensures efficient separation of the aggregate particles, helping to achieve accurate and consistent results.

What should be done if the sieves are overloaded during testing?

If sieves are overloaded, the material should be carefully checked for blinding, and any particles lodged in the sieve should be removed using a rigid instrument for coarse sieves or a brush for finer sieves.

How are the results of the sieve analysis calculated?

The results are calculated by dividing the accumulated weight of material retained on each sieve by the original dry sample mass, then multiplying by 100 to get the percentage retained. The percentage passing each sieve is calculated by subtracting the percentage retained from 100.

What is the significance of the fineness modulus in sieve analysis?

The fineness modulus is a value used to describe the particle size distribution of fine aggregates. It is calculated by adding the cumulative percentages of material retained on specified sieves and dividing the sum by 100, providing insight into the suitability of the aggregate for applications like concrete mix design.

What is the difference between T11 and T27 in the sieve analysis process?

T11 is used to determine the amount of material finer than the number 200 sieve, while T27 is the standard sieve analysis procedure. Both methods may be used in conjunction to accurately assess the -200 material in aggregates.

How should results be reported if the percentage passing the number 200 sieve is greater than 10%?

If the percentage passing the number 200 sieve is greater than 10%, it should be reported to the nearest whole number. If it is less than 10%, it should be reported to the nearest 0.1%.