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Today we’re going to demonstrate reducing bulk samples of fine aggregate to testing size using the Gilson SP-33 Universal Mini-Splitter, the smallest of Gilson’s exclusive design Universal Splitters, a great choice for powders and granular materials with top sizes less than 1/4in (6.4mm).

According to ASTM C702 there are three methods for the reduction of large bulk samples of aggregate to the appropriate size for testing to minimize variations in material characteristics between the reduced test samples and the original bulk sample. Method A is using a mechanical splitter, Method B is a procedure called Quartering, and C, the miniature stockpile sampling method for damp fine aggregate only.

(ASTM Referenced Documents: C702 Standard Practice for Reducing Samples of Aggregate to Testing Size; C125 Terminology Relating to Concrete and Concrete Aggregates; C128 Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate; D75 Practice for Sampling Aggregates; and E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves.)

According to ASTM C702 Method A, using a mechanical splitter is the preferred method, and provides a proven process for reducing the large bulk sample obtained in the field or in the laboratory to a convenient testing size to define material characteristics in a manner that the reduced test sample portion is most likely to represent the larger bulk sample.

Failure to carefully follow this process could result in a non-representative sample being used in subsequent testing.

Fine Particles with Surface Moisture
Since we are demonstrating splitting fine aggregates, it is important to note that if the sample has free moisture on the particle surfaces, then you must dry the entire sample using temperatures that do not exceed those specified for any contemplated tests. The sample today has been dried using the BO-350 Quincy Lab Oven supplied by Gilson.

If the moist bulk sample is very large, make a preliminary split using a mechanical splitter like the Gilson SP-52 1/16th Sample Reducer with its adjustable 45° or 60° flow table. Then dry the reduced sample, and ready it to be further reduced using Method A to create a sample amount suitable for testing.

The Mechanical Splitter Apparatus
Sample splitters for fine aggregate should have an even number, but not-less-than-twelve, equal-width chutes, which discharge sample material alternately to each side of the splitter. With the minimum width of the individual chutes being be at least 50 % larger than the largest particles in the sample being reduced. As an example, for dry aggregate that will pass a 9.5-mm (3⁄8-in.) sieve, a sample splitter having chutes 12.5 to 20 mm [1⁄2 to 3⁄4 in.] wide should be used.

The Gilson SP-33 Universal Mini-Splitter has a 48 chute bars, each with a width of 1/8in (3mm), and at a 60° chute angle. The SP-33 has two pans to hold the two halves of the sample following splitting, and a 0.06ft³ (1.7L) hopper by which the sample may be fed at a controlled rate to the chutes.

Sample Reducing Procedure
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.
Using the SP-33’s spring-loaded hopper release gate, 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.

Now that you have reduced a large bulk sample of fine aggregate to the appropriate testing size, minimizing variations in material characteristics between the reduced test sample and the large bulk sample, you can continue with your fine aggregate testing.

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