Abstract The invention relates to a process of preparing a lightweight granular aggregate for use in concrete objects and structures, by an intimately mixing a clayey material with materials that help to reduce the weight, granulating this mixture and then heating the granules at least to the temperature at which their mass expands. Use is made of a combination of two known auxiliary materials, the first being a porous inorganic material with open pores, added in an amount of 10-20 percent by volume with respect to the clayey material, and substantially having a grain size below 2 mm., and the second consisting of one or more substances that, upon heating, yield gaseous components at a temperature over 800* C. Use is made of a porous inorganic material having a softening temperature equal to or lower than that of the clayed material.
Process for preparing a granular aggregate for use in light-weight construction elements, comprising substantially uniformly mixing: A. a non-expanding clayey material, chosen from the group consisting of clay, weakly expanding clay, weathered slate, ground slate, weathered shale, ground shale and coal washery shale having a relatively high softening point of at least about 1,350*C and a melting point of at least about 1,600*C; B. an open pored, porous, inorganic, silicious material consisting essentially of white pumice having a particle size measuring up to 2 mm. in width and present in an amount equalling 10-20 percent by volume of said clayey material; and C. at least one material consisting essentially of gypsum which, when heated to over 800*C yields gaseous components, present in an amount equalling up to 5 percent by weight of said clayey material; granulating said mixture to produce granules having a range of sizes up to about 15 mm. across; heating the granules up to the softening temperature of said clayey material and over the temperature at which said one material gives off gas, expanding the gas from uniformly distributed quanta of said open pored porous, inorganic matErial as nuclei; cooling the resultingly expanded granules to provide expanded granular aggregate having white or grey color on the walls of the expansion cavities formed by expanding said gas within said granules.