A study of porosity and grain relationships in experimental sands

Fourteen samples, each of 50 grams, of well-sorted, moderately rounded, medium-grained St. Peter sand were artificially packed and cemented with Lakeside 70 cement. Thin and polished sections of the samples were prepared and studied to determine the original or pre-induration condition of such a sand with respect to (1) porosity, (2) average number of contacts per grain, (3) percentages of grains with given numbers of contacts, and (4) percentage of contact types. These data will serve as a basis for determining the presence and extent of pore-space reduction in natural sandstones due to induration. The investigation showed that natural sands similar in texture to those used in this study should have (1) a porosity of about 37 per cent; (2) 0.85 contacts per grain; (3) 46 per cent floating grains, 31 per cent grains with one contact, 16 per cent grains with two contacts, 6 per cent grains with three contacts, and 1 per cent grains with four contacts; and (4) 77 per cent tangential contacts, 17 per cent long contacts, and 6 per cent concavo-convex contacts. The investigation further suggests that the factors of porosity, average number of contacts per grain, and percentage of grains with given numbers of contacts are controlled primarily by sorting and packing while the percentage of contact types is a function of grain shape. The difficulties encountered in measuring the properties of porosity and grain relationships in this study were due chiefly to the Lakeside 70 cement. Future experimental work of this kind will yield more satisfactory results if a bonding agent can be found that nearly equals the grains in hardness and will not flow or melt during the preparation of thin sections.