Laboratory tests

Sample reduction

Recommended procedures always call for a minimum of three (3) samples or a composite sample to be taken, therefore reduction will always be necessary to produce a representative sub-sample for analysis.

The sample(s) should be thoroughly mixed and then reduced in size by one of the two following methods appropriate to moist or dry sand.

2.1 Moist/Damp Sand

The sample size is reduced by cone and quartering. This is carried out by placing the sample on a clean surface and mixing it horizontally and vertically to form a cone. The sand cone is then divided into four equal parts using a straight edge. Each quarter produced is then recombined diagonally to produce two equal halves, one half being discarded (or retained for further work). The other half is reused and the operation repeated until the required sample size is obtained.

2.2 Dry Sand

Dry sand samples are reduced using a standard riffle box (two way splitter) of suitable size to accommodate the whole sample weight. A spinning riffle or rotary sampling device may be used for a more representative sample. The samples presented to the riffle box to be sub- divided need to be evenly introduced to the top of the riffle vanes which separate the sample into two halves. For further reduction in size the sample is repeatedly riffled until the required weight is obtained.

Riffle boxes (sample dividers) are available in a range of sizes and materials. Commonly stainless steel is used. A suitable size depends on the initial sample size for reduction.

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