Fine Aggregate Angularity Test

AIM

The fine aggregate angularity test determines the loose uncompacted void content of a fine aggregate material.

APPARATUS

Cylindrical Measure, Funnel (Pycnometer Top), Funnel Stand, Square Glass Plate, Pan, Metal Spatula, Balance

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PROCEDURE  (METHOD A)

  1. Obtain an aggregate sample by separating individual sizes from the No. 8 (2.36 mm) sieve to the No. 100 (150 mm) sieve.
    Note : The tolerance for each of these increments is ± 0.2 grams.
  2. Thoroughly mix the individual sieve increments with a spatula until it appears to be a homogeneous 190-gram sample.
  3. Position the jar and funnel section in the stand and center the cylindrical measure.
  4. Using a finger, block the opening of the funnel.
  5. Pour the test sample into the funnel and level with a spatula.
  6. Remove your finger and allow the material to fall freely in the cylindrical measure.
  7. After the funnel empties and the cylindrical measure is full, strike-off the excess fine aggregate with a single pass of the spatula using the straight edge of the blade vertically and in light contact with the top of the measure.
    Note 4: Until this operation is completed avoid any vibration or disturbance that could cause the material to compact.
  8. After strike-off, lightly tap the cylinder to compact the material so none will be lost when transferring the cylinder to the scale and brush the adhering material from the outside of the cylinder.
  9. Determine the mass of the cylinder and material to the nearest 0.1g and record.
  10. Do Sections 1206.5B through 1206.5H twice and determine the average of the two readings minus the weight of the cylinder.
  11. Calculate the Uncompacted Voids as follows:
    U = {V – (F/G)}/V x 100
    Where:
    U = Uncompacted Voids
    V = Volume of Measure
    F = Net mass of fine aggregate in the measure
    (Average mass determined in step #10 above)
    G = Bulk Dry Specific Gravity of the Blend of fine aggregate
  12. Report the Uncompacted Voids to the 0.1 percent.

DISCUSSION

Fine aggregate angularity (FAA) test is an indirect method of accessing the angularity of the fine aggregates. Fine aggregate angularity important because excess of rounded fine aggregate can lead to rutting.

FAA measures the angularity of Fine aggregate by measuring the loose uncompact void content of the fine aggregate sample. The higher the void content, higher the assumed angularity and rougher the surface.

This test is to ensure that the bend of the fine aggregates has sufficient angularity and texture to resist permanent deformation (rutting) for given traffic level.

Note:- Complete test procedure can be found in:- AASHTO T 304 or ASTM C 1252: Uncompacted Void Content of Fine Aggregate

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