LIGHTWEIGHT AGGREGATES 



345 



minimal. On the basis of these assumptions the 

 total resource is between 150 and 300 million tons, 

 exclusive of the volcanic ash of the Great Plains. 



Pumicite deposits on the Great Plains are numer- 

 ous and vary greatly in size; Ham (1949) reported 

 one in Oklahoma to contain about 10 million cubic 

 yards (perhaps 7-8 million tons). He estimated a 

 total of about 20 million cubic yards in known de- 

 posits ; by our definitions this 20 million cubic yards 

 would be considered an identified resource of about 

 17-18 million tons. Carey, Frye, Plummer, and 

 Swineford (1952) estimated about 20 million tons 

 for known deposits in Kansas, which we would also 

 class as identified resources. Data are lacking for 

 Nebraska, but on the basis of past production and 

 the distribution of the deposits, a tonnage on the 

 same order of magnitude as Kansas and Oklahoma 

 is reasonable. A conservative estimate for all the 

 Great Plains States may be taken as 50-60 million 

 tons of identified resources, and perhaps the same 

 amount for hypothetical and speculative resources 

 combined; the total resource may be thought of as 

 about 100-150 million tons. 



DIATOMITE 



Although diatomite has been and is used as a 

 lightweight aggregate, the usage seldom exceeds a 

 few tens of thousands of tons per year and is not 

 a significant factor in the reserve and resource posi- 

 tion of the United States. In general, its value for 

 other uses, such as filter aids, is far too great to 

 justify its utilization as a low-cost aggregate. Only 

 in a very few special cases can diatomite be used 

 economically, and then it is generally as a byproduct 

 from the treatment of the material for its more 

 speciaHzed roles. Information on distribution, geo- 

 logic habit, and resources are in the chapter 

 "Diatomite." 



OTHER MATERIALS 



Expanded blast-furnace slag and fly ash are a 

 significant part of the supply of structural light- 

 weight aggregates in the heavily industrialized 

 Great Lakes and Pennsylvania areas and in Ala- 

 bama, Colorado, California, and North Carolina. 

 Expanded slag production ranged from about 21/2 

 million tons per year during the period 1960-70 

 (fig. 40). Expanded slag is only a fraction of the 

 slag produced annually; it is likely to be ample to 

 meet any demand for many years. Fly ash produc- 

 tion (which includes bottom ash) in 1970 was more 

 than 35 million tons and was widely distributed 

 throughout the country with only about 4 million 

 tons being utilized in any way. Lightweight aggre- 

 gate production of sintered fly ash totaled about 



260,000 tons and was confined to the Detroit, Mich., 

 Pittsburgh, Pa., and Charlotte, N.C., areas. 



There appears to be an obvious market potential 

 for both expanded slag and fly ash — perhaps a little 

 more favorable for the ash — because the coal- 

 burning power-generating stations are widely dis- 

 tributed and the country's increasing demands for 

 energy probably entail the construction of more 

 plants. 



ULTRALIGHTWEIGHT AGGREGATES 

 INTRODUCTION 



The natural ultralightweight aggregates are per- 

 lite, pumicite, and vermiculite; the first two are 

 products of dominantly silicic volcanism (see sec- 

 tion on "Pumice and Pumicite"), whereas vermicu- 

 lite is a low-temperature alteration product of ultra- 

 mafic igneous and metamorphic rocks. High-tem- 

 perature heating is required of all three crude ores 

 to cause expansion and to develop the vesicularity 

 that gives the materials their desirable attributes. 

 Properly treated, all three materials develop high 

 porosity but low permeability and have very thin 

 cell walls. Thus, they make excellent thermal and 

 acoustic insulators, but their compressive strength 

 is low. Concretes and plasters using them as aggre- 

 gates have strengths from 100 psi to about 2,200 

 psi ; the more cement used, the greater the strength 

 and the greater the weight. The materials are very 

 well employed in fireproof plasters, in concrete cur- 

 tain walls, floor fills, and roof decks, in concrete 

 refractory and insulating walls in bake ovens, and 

 in decorative, non-load-bearing blocks and facings 

 (Schroeder, 1970a, b). In loose fill or bulk form they 

 are primarily used for insulation, both thermal and 

 acoustic, but significant amounts are used as inert 

 carriers and extenders in horticultural products and 

 in manufacturing processes. 



As with the structural lightweight aggregates, 

 the ultralightweights are not indispensable ; syn- 

 thetic materials (polystyrene beads, polyurethane 

 foams, foamed phenolic resins) can be substituted 

 in some applications; lightweight concretes and 

 plasters can be made by air entrapment through the 

 use of aluminous foaming compounds ; foamed glass 

 can be used for some special requirements. In gen- 

 eral, however, the use of expanded natural materials 

 is more economic and less complicated in prepara- 

 tion and use. 



The United States produces all the perlite and 

 pumicite that it consumes and has ample material 

 to export, but, because of the low unit value of 

 crude perlite, only a few thousand tons is exported 

 annually — all of it to expanders in Canada. No 



