Laboratory tests

Grain shape

This test seeks to relate the shape of the grains to factors such as compaction and flow during use.

Apparatus

Microscope capable of up to 25 times magnification and appropriate lighting unit. A binocular stereoscopic microscope is most effective.

Method

The sand is placed under the microscope and examined at a magnification appropriate to the grain size of the test sand. At least 50 grains chosen at random are examined for sphericity and degree of angularity using the standard shapes shown in the table below.

Note 1

The evaluation is strictly qualitative and does not provide an index value to link grain shape to any physical characteristic of the sand.

Note 2

Almost all natural sands display a significant range in sphericity and angularity of the grains. This is due to the different geographical sources providing granular material to the area where the sand accumulated originally. For this reason the range in sphericity and angularity should be estimated and reported with the mean value.

Note 3

The evaluation of the shape factors is very subjective . Experienced microscopists can produce significantly different estimates for the same test sand.

Typically Rounded

Typically Round to Sub Angular

Typically Sub Angular

Typically Angular

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