Using some bentonite from the different deposits, five batches of bentonite-silica sand-water mixtures, in which contains various proportion of temper water respectively were mulled continuousely by Simpson type sand mixer or an agitator type sand mixer processing in sequential series of procedures of a mulling-drying-water adding. Then the green sand properties of the mixture were studied as mulling advanced. 1) Depending on the mulling progress, the green compressive strength of the mixture enhanced considerably and approached an equilibrium value about the mixture. Maximum of green compresive strength of the mixture sifted to the sides of lower moisture content and lower compactability as the mulling further advanced. For the property changes of the mixtures mentioned above, it is considered that the occurence of green strength is primarily a result from dispersion of aggregate structure in bentonite particles. This conclusion is supported with the result that the methyleneblue adsorption capacity of the mixture increased appreciably. 2) From the methyleneblue adsorption capacity and the moisture content at 35 % compactability of the mixture, which approached to the eqilibrium green compressive strength by the continued mulling respectively, adsorption surface areas of each bentonite were calculated. Surface area were in the ranges of 600∼800cm
2 / g bentonite according to the characteristics of bentonites. It was shown that
α-cristobalite in bentonite also contributes to water adsorption and occurence of green strength of the mixture.
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