08 Uses and Standard Requirements

Pumice Deposits of the Klamath Indian Reservation, Klamath County, Oregon

Uses and Standard Requirements

The principal use of pumice is as a lightweight aggregate in concrete and acoustic plaster. Large quantities are also used as an abrasive in cleansing and scouring compounds, in finishing furniture and other wood products, and in finishing metal surfaces prior to silver-plating. Locally, large quantities of a select type of pumice also have been used as pozzuolana in the manufacture of pozzuolanic cement. Although pumice is also used in manufacturing insecticides, insulating material, filters, solvents, and plastics, and as paint filler, absorbent material, and chicken grits (U. S. Bur. Mines, 1948), the total amount so used is small. The only uses that have been considered in this report are as aggregate, pozzuolana, or abrasive, because in central Oregon the main markets available to pumice producers are for these three uses.

Pumice for Aggregate

Ideally, pumice that is to be used for lightweight aggregates, should have adequate structural strength though light in weight, (U. S. Bur. Reclamation, 1949; Am. Soc. for Testing Materials, 1944). Void spaces should be fairly uniform in size and shape and should not be interconnected. The aggregate should be relatively inert and free from contaminating substances such as silt, clay, mica, coal, humus, and other organic matter, and chemical salts, and it should also have a low opal content. The best aggregate has a fairly even distribution in the size of particles which range from very fine sand to about one-fourth inch.

Pumice for Pozzuolana

Pumice that is to be used as pozzuolana, in contrast to pumice for aggregate, should in the presence of water react with the lime in cement to form compounds that have low solubilities and possess cementing properties. Materials with a high opal content are reactive and are, therefore, usually best suited for this purpose. Substances that occur naturally usually are too coarse to be used directly as pozzuolana without fine grinding to meet specifications.

Pumice for Abrasive Material

High quality abrasives (Hatmaker, 1932; Am. Inst. Min. Met. Eng., 1949) derived from pumice requires material that is hard, sharp, and uniform in texture and particle size. The size and shape of the vesicles in the individual particles should also be uniform. The best abrasive material is in lumps 3 inches or more in diameter. Grains or crystals of feldspar, quartz, or other foreign minerals in pumice prohibit its use where high-grade material is needed. Lower quality abrasives may contain small amounts of deleterious, gritty, and noncellular material, and the texture and size of vesicles do not have to be uniform.

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