In the past and until very recently the chief uses of volcanic ash have been based on its physical properties of fine size and angularity of particles, friability, and light color, as illustrated in its use as an abrasive and as topping for bituminous matt roads. In the past few years increasing attention has been given to the chemical or pyrochemical properties of volcanic ash as an alkaline aluminum silicate flux in ceramics and as a pozzolanic additive to cement in concrete mixtures. In the United States in 1934 the quantity employed for use in abrasives was eight times as great as that used as a cement aggregate and pozzolanic admixture. In 1945 the quantities employed in these two major uses were nearly equal. In 1947 the quantity used with cement was four and one-half times as great as that used for abrasive purposes (Barr, 1949). The most extensive use of pumicite or volcanic ash in concrete has been on the west coast. Only small amounts have been used in Kansas for this purpose, and the tonnage does not appear in the statistics on Kansas production. Inasmuch as commercial production in Kansas is largely for abrasive uses, the quantity used for these purposes is clearly shown in published statistics. The earliest figures available on Kansas production are for the year 1916 when 23,804 tons was produced. Peak production was reached in 1923 with a total of 51,907 tons and from 1923 to 1940 was fairly steady. Reported output ranged from 35,385 tons in 1925 to 49,760 tons in 1929, and the average production for the 17-year period was 41,953 tons. Following a near-average year of 39,215 tons in 1940, the 1941 production declined to 23,659 tons, but by 1945 had recovered to 47,484 tons--exceeding the previous 17-year average. Since 1945 production has declined sharply. As previously stated, these production statistics are available only on commercial production and it is probable that the tonnage used by the State Highway Department substantially exceeds that mined by commercial producers. In one deposit alone we estimate that at least 25,000 tons have been removed by the Highway Department for use on black-top roads.
Volcanic ash has been used as an abrasive in the United States for about 50 years. In 1903 the entire production of 885 tons in this country was from Nebraska. By 1911 volcanic ash was reported by the U.S. Geological Survey as being mined in Kansas, but production figures were concealed under the heading of miscellaneous items. In 1916 a figure of 23,804 tons was given for Kansas. Doubtless most of this tonnage was used in abrasives.
As an abrasive volcanic ash is adapted for use as a polishing, scouring, and cleansing agent because of its fineness, angularity, and moderate hardness (5.5 to 6.0 on Mohs scale). A large proportion of volcanic ash used as an abrasive has gone into scouring compounds such as Old Dutch Cleanser. Formerly these compounds were composed largely of volcanic ash mixed with small quantities of soap powder or other detergents. Volcanic ash is also used as an abrasive in mechanics paste soap, abrasive hand soaps, and rubber erasers. Very fine ash is used in some toothpaste and powder, and minus-200-mesh ash has been used for polishing plate glass. Volcanic ash could be used instead of powdered pumice whenever the latter material is suitable. These uses include polishing metals, wood, and varnished wood finishes. Other abrasive uses include polishing powders for bone, celluloid, and hard rubber, and in dentists tape.
Processing of volcanic ash for abrasive uses commonly includes only drying and the screening out of coarse particles, aggregates of particles, and incidental contaminants. This practice is possible because of the natural fineness of the material. Screen analyses on 96 samples (Table 4) show that an average of 93.6 percent passes a 100-mesh screen and that an average of 76.3 percent passes a 200-mesh screen. Minus-200-mesh material constitutes more than 80 percent in 34 of the 96 samples. Subsieve analyses on 12 samples (Table 3) indicate that the median diameter of the particles averages 34 microns, which is equivalent to smaller than 400-mesh. Air classification is used in some cases, particularly where grades of 200 mesh or finer are required. Although volcanic ash is seldom subjected to grinding in order to reduce the particle size, it is readily susceptible to dry grinding in a ball or pebble mill.
Volcanic ash, or pumicite, is composed of minute shards of volcanic glass corresponding roughly to a frit composed of feldspar and quartz. It is surprising that a material with this composition has received so little attention from workers in the field of ceramics. The ceramics laboratory of the State Geological Survey ran a number of tests during 1937 and 1938 using volcanic ash in ceramic glazes and bodies, and the work was summarized briefly by Plummer (1939). Prior to this time the only work done on ceramic uses of volcanic ash in the United States was reported by Preston (1935) on the use of volcanic ash in glass batches. After publication of the 1939 report by Plummer our attention was called to the fact that similar work had been published in the Journal of the Canadian Ceramic Society by Worcester (1934). Worcester used Canadian volcanic ash in ceramic bodies and glazes with results somewhat similar to those obtained with Kansas ash in the Survey laboratory. Additional experiments with Kansas volcanic ash glazes were reported briefly by Carey (1948). During the past three years a number of tests have been run on volcanic ash glazes and ceramic bodies. The results will be published in a Geological Survey bulletin at a later date.
Kansas volcanic ash fuses at a lower temperature than feldspar. The pyrometric cone equivalent of feldspars ranges from cone 4 to cone 10, with a general average of cone 8 to 9 (2240° to 2280° F.). Kansas volcanic ash samples tested have a pyrometric cone equivalent ranging from cone 06 to cone 4, with a general average in the neighborhood of cone 03 to 01 (1975° to 2030° F.). This difference in fusion temperature gives volcanic ash a distinct economic advantage, and in the field of ceramic art permits the use of the lower temperatures considered desirable.
The chemical composition of Kansas volcanic ash from the various deposits is remarkably uniform, as can be observed from the analyses of 54 samples given in Table 2. It is probable that the variations found are due largely to contaminants such as quartz, calcite, and clay.
Volcanic ash from a deposit in Lincoln County (LV-1) has been used extensively in glaze and ceramic body tests because it is easily available and has a chemical composition that is approximately an average of the Kansas ash deposits. The composition of this ash is given below.
|Chemical composition of LV-1 volcanic ash|
|Silica (SiO2)||72.51 percent|
|Alumina (Al2O3)||11.55 percent|
|Iron oxide (Fe2O3)||1.21 percent|
|Titanium oxide (TiO2)||0.54 percent|
|Calcium oxide (CaO)||0.68 percent|
|Magnesium oxide (MgO)||0.07 percent|
|Potassium oxide (K2O)||7.84 percent|
The molecular formula, or ratio of the molecular weights of the various groups of oxides in this volcanic ash, is as follows.
The formula weight of the above is 794.30. Feldspar from Keystone, South Dakota, has the following molecular formula.
The formula weight of this feldspar is 577.72. Owing to the fact that the volcanic ash has a higher ratio of silica to alumina and the RO group, a substitution of an equal weight of volcanic ash for feldspar is not possible. Roughly 100 parts by weight of volcanic ash may be substituted for 70 parts feldspar and 30 parts potters flint. A more exact method of substitution is given in Table 5. This table is based on molecular ratios of oxides in both materials, and necessitates taking out feldspar, flint, and whiting, and adding volcanic ash and ball clay.
Table 5.--Volcanic ash and clay required for an exact replacement of feldspar, flint, and whiting in glazes or ceramic bodies. Parts per hundred in total glaze batch, by weight.
|Feldspar||Flint||Whiting||Volcanic ash||O-38-4 clay|
The calculations were made for Keystone feldspar, Lincoln County volcanic ash (LV-1), and a Kansas ball clay (O-38-4) containing 64.67 percent silica, 22.38 percent alumina, 1.58 percent iron oxide, 1.32 percent titanium oxide, 0.27 percent calcium oxide, 0.66 percent magnesium oxide, 1.11 percent potassium oxide, and 0.55 percent sodium oxide. Any similar ball clay could be used. It will be noted that if a total of 100 percent feldspar, flint, and whiting were taken out of a glaze or body a total of 103.38 percent volcanic ash and clay would be added as a replacement. This is due to the fact that the ash and clay contain a higher percentage of inactive ingredients. Although such high percentages of feldspar or volcanic ash are not used in glazes and ceramic bodies, we have prepared a usable glaze containing 95 percent volcanic ash. Ordinarily, however, the percentage of ash included in a glaze batch will not exceed 75 percent, and in most cases ceramic bodies are not improved by additions of more than 25 percent volcanic ash.
A few volcanic ash glazes of proven worth are given below as an illustration of the range of compositions possible. The following glaze matures within the range of cone 02-1.
|Eagle-Picher lead silicate||31.4 percent|
|LV-1 volcanic ash||25.0|
|Keystone (S.D.) feldspar||2.8|
|Zircopax (zirconium silicate)||12.1|
The glaze above was used with 5 percent commercial yellow stain to produce a good shade of yellow. Without the stain an opaque glaze is produced.
A very simple glaze within the range of cone 04 to cone 10 has the following composition.
|Volcanic ash||70 parts by weight|
|Colemanite||30 parts by weight|
|Bentonite||5 parts by weight|
This glaze has a rather muddy color due to the iron oxide content of the volcanic ash. The addition of 5 percent whiting will improve the transparency of the glaze. If the glaze is to be used as a base for colored glazes the addition of 5 percent of an opacifier such as zirconium silicate will produce a warm white suitable for this purpose.
A raw lead glaze that has been used very successfully on a number of types of body within the temperature range of cone 07 to cone 04 is given below. It is probable that the glaze could be used over a much longer range.
|Red lead||35.2 percent|
A high-temperature glaze that has produced excellent results on a siliceous body is given below. This glaze was used at cone 7 and cone 9, but should be usable from cone 6 to 10. Colored glazes can be made by adding the correct oxides or stains.
|Volcanic ash||39.9 percent|
|Ball clay (O-38-4)||28.5|
Volcanic ash glazes are used in at least three potteries in the State and by a number of schools. The chief advantage in the use of volcanic ash is the low cost, although there are the added advantages of an unusually long firing range and the fact that the colors in volcanic ash glazes are somewhat softer than those obtained with the conventional materials. Kansas potteries also find that advertising the use of volcanic ash glazes attracts customers.
The substitution of volcanic ash in ceramic glazes for equivalent amounts of other materials produces very little difference in the final glaze, although the firing temperature may be slightly lower due to the surprisingly low fusion temperature of the ash. In ceramic bodies, however, the results are not so predictable. Generally the results are more beneficial than would be expected. A number of test bodies with different types of clays and shale and with varying amounts of volcanic ash indicate that from 7 to 15 percent volcanic ash additions to a shale or red-firing clay body lowers the vitrification temperature, increasing the firing range for a matured body, and producing a greater rigidity in the ware at the maximum temperature. These qualities produced by the volcanic ash additions permit economy in use of fuel, and reduce losses in the kiln due to the less critical temperature range requirements and the ability of the ware to stand up under its own weight at the maximum temperatures attained in the kiln. Not all clays and shales react with equally favorable results. Some materials are benefited only in that the firing temperature is reduced. The benefits of volcanic ash additions to sewer pipe bodies have received considerable attention. A group of clay plant operators sponsored a project at the Engineering Experiment Station at Ohio State University to test the value of additions of volcanic ash to sewer pipe bodies. J. O. Everhart, research professor in charge of this project, reported to us that definite benefits were obtained by the use of volcanic ash. In a letter accompanying the report Everhart summarizes the effects of volcanic ash as follows: "It seems to have a somewhat stabilizing influence on the mix to which we added it, and might be of considerable value for use in local clay and shale mixes having a short firing range. We attribute this influence to the fact that it forms a very viscous glass which remains so over a long range of temperatures." F. K. Pence (personal communication) of the University of Texas reports that very beneficial results are realized from the use of volcanic ash in a sewer pipe body in a Texas plant.
Somewhat similar results are obtained with additions of volcanic ash to pottery or whiteware bodies, although in this case the fired color of the body is darkened slightly by the iron content of the ash. The use of volcanic ash in amounts ranging from 10 to 25 percent lowers the firing temperature required, or to look at the matter from another angle, it makes it possible for the art potter whose maximum temperature is limited to produce hard-fired ware that does not leak or craze. In general the casting properties of pottery bodies are improved with the addition of volcanic ash. This is due largely to the size and shape of the particles. At least one pottery in Kansas is using volcanic ash with Kansas clay in the casting body and produces a vitrified ware at cone 4.
Glass and Vitreous Enamels
Volcanic ash performs the same function in glass and in vitreous enamels as it does in ceramic glazes. Due to the iron oxide of about 1.5 percent the use of volcanic ash in these products is limited. Volcanic ash has been seriously considered as an ingredient in fiber glass batches and in foam glass where the slight darkening of color is of minor importance. If used in the production of fiber glass the problem of preventing the disintegration of the platinum dies by the iron present in the ash would have to be solved.
Laboratory trials with volcanic ash as an ingredient in vitreous enamel were made by one of the major manufacturers of sanitary ware. The laboratory reported that the cream-colored and ivory-colored enamels produced with additions of volcanic ash were slightly superior to those produced with feldspars, but that due to the distance the ash would have to be shipped to their plants no saving in cost would be realized.
Lightweight Aggregates and Cellular Blocks
The Oklahoma Geological Survey has investigated the possibility of producing cellular products similar to Foamglas and an extremely lightweight aggregate consisting of bloated individual particles of volcanic ash (Burwell, 1949). The cellular product was produced by heating volcanic ash to a high temperature in refractory molds. The resulting product, which was named "pumicell" by the Oklahoma Survey, is a glass containing small disconnected cells of air. It has high insulating value, and can be sawed or nailed. The bulk density of the product ranges from 45 to 90 pounds per cubic foot as compared to a true specific gravity of 2.34 to 2.48, corresponding to a density of 146 to 155 pounds per cubic foot. The volume of closed cells in the product was as much as 56.8 percent of the total.
Experimental bloating of Kansas volcanic ash in the laboratory of the State Geological Survey of Kansas indicates that the Kansas ash has the same bloating characteristics as the Oklahoma material.
The lightweight aggregate produced in the laboratory of the Oklahoma Geological Survey is similar to expanded perlite, although the method used to "pop" the volcanic ash was not the same as that used to expand perlite. The volcanic ash was expanded by introducing a stream of volcanic ash into the air intake of an inspirator-type gas burner. The product consists of glassy beads containing one or more bubbles. The bulk specific gravity of the "popped" volcanic ash ranges from 0.22 to 0.088, corresponding to a bulk density ranging from 5.5 to 13.7 pounds per cubic foot. Products made from this material insulate against the transmission of heat, sound, and electricity. It can be used in acoustical and insulating plasters, wall board, lightweight blocks, and slabs.
The State Geological Survey of Kansas has been able to produce a similar expanded or "popped" product from Kansas volcanic ash of Pleistocene age. Attempts to produce a similar product from Pliocene ash were not successful. Additional testing is planned, and the results will be published in a Survey bulletin in 1952.
An expanded volcanic ash product similar to perlite is being produced at Hutchinson, Kansas, under the trade name Mira-Colite. The method used for production of this material is not known in detail.
About 1,800 years ago the Romans made a cement composed of two parts by volume volcanic ash and one part slaked lime. Seaworks constructed with this pozzolanic cement are in use today. The Roman or pozzolanic cement is extremely slow-setting if made with slaked lime. To avoid this objectionable feature modern pozzolanic cements are made with Portland cement. Cements of this type are of special interest because they resist disintegration by sea water and in some cases minimize the reaction of some types of siliceous aggregates with the alkalies present in Portland cement. Volcanic ash, in addition to its natural cementing properties, serves the purpose of a fine aggregate that fills the voids between the fine sand aggregate and the cement. In concrete made with volcanic ash as much as 50 percent of the cement may be replaced by the ash, although a smaller proportion commonly is used.
According to Barr (1949, p. 752) the principal use of volcanic ash (pumicite) is for concrete aggregate and its use as an admixture in cement for concrete is attaining increasing importance. In 1945 nearly equal amounts of volcanic ash and pumice were produced for use in abrasives and in concrete. In 1947, 4.5 times as much of these same materials was used in concrete as was employed for abrasive purposes.
Volcanic ash is used as the chief ingredient in some sweeping compounds, as an insulation in packing water and steam pipes, lagging boilers, and as a loose fill insulation in walls and ceilings. It is also used as a filler or diluent in paint and as a carrier for insecticides. Volcanic ash has been used for the purification and clarification of oils by filtration. It is probable that partially altered volcanic ash is used for the latter purpose.
Within the past few years the State Highway Department has produced large quantities of volcanic ash from at least eight pits in Kansas. This is used largely for top dressing on "black top" or bituminous matt roads. It is probable that in Kansas more ash is used for this purpose than in any other state.
Kansas Geological Survey, Kansas Volcanic Ash Resources
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Web version Jan. 2005. Original publication date Feb. 15, 1952.