Скачать или смотреть Standard Practice for Reducing Samples of Aggregate to Testing Size (ASTM C702, AASHTO R 76)

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There are three methods for the reduction of large bulk samples of aggregate to an appropriate size for testing where variations in measured characteristics between the test sample and the large bulk sample are minimized.

Method A is using a riffle-type mechanical splitter or universal splitter. Method B is process called quartering. And Method C is a procedure called miniature stockpile sampling.

Method A

The Mechanical Splitter Apparatus
Sample splitters for aggregate should have an even number of alternating equal-width chutes, with a minimum of 8 chutes for coarse aggregates and 12 chutes for fine aggregates, which discharge sample material alternately to each side of the splitter. With the minimum width of the individual chutes being at least 2 to 3 times larger than the largest particles in the sample being reduced.

Sample Reducing Procedure for Method A
Place the original sample in the hopper and uniformly distribute it from edge to edge, so that when it is introduced into the chutes, approximately equal amounts will flow through each chute.

Release material over chutes. Be sure to introduce the sample at a rate to allow the sample to flow freely through the chutes and into the pans below.

If you require a test sample that is less in quantity, reintroduce the sample from only one of the pans into the sample splitter in as many times necessary to reduce the sample for the intended test.

Save the remaining sample material collected in the other pan, not meant for the current test.

Method B
The quartering method is generally used in situations where an adequate mechanical splitter is unavailable or when there is free moisture on the particle surfaces of the bulk samples.

The quartering apparatus should consist of a scoop, shovel, or trowel with a straight edge, a broom or brush, and a six by eight foot canvas blanket.

The Quartering Apparatus

Sample Reducing Procedure for Method B
To divide a sample you first place the sample on the canvas blanket. Now mix the sample by turning the entire sample over three times with the shovel. Shovel the sample into a conical pile by depositing each shovelful on top of the previous one.

Flatten the conical pile to a uniform thickness and diameter by pressing down with the shovel until the diameter is approximately four to eight times the thickness of the pile.
Now divide the flattened sample into four equal quarters with a shovel or trowel. Next remove two diagonally opposite quarters making sure to remove all the fine material. Successively mix and quarter the remaining material in the same fashion as the original sample until the desired sample quantity is obtained.

Save the unused portion of the original sample until all testing is completed.

Method C
The miniature stockpile sampling method is only for sampling damp fine aggregate and is not permitted for sampling of coarse aggregates or mixtures of coarse and fine aggregates.

The Miniature Stockpile Sampling Method Apparatus
The apparatus for the miniature stockpile sampling method shall consist of a straight-edged scoop, shovel, or trowel for mixing the aggregate, and either small scoop, or spoon for sampling.

Sample Reducing Procedure for Method C
Place the original sample of damp fine aggregate on a hard clean, level surface where the potential for material loss or the accidental addition of foreign material is minimized.

Mix the material thoroughly by turning the entire sample over three times turning the entire sample into a conical pile.

Flatten the conical pile to a uniform thickness and diameter by pressing down the apex of the pile with the scoop, shovel, or trowel.

Obtain a test sample by selecting at least five increments of material at random locations from the miniature stockpile using the small scoop or spoon.

By following the sample dividing procedures as required by ASTM and AASHTO standards, an aggregate bulk sample reduced to a laboratory test sample will have minimal variations in the aggregate characteristics.

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