Leavened Flooring

Aerocrete, a light concrete building material which rises like leavened bread, has passed the fire, load and water tests required of flooring materials in New York, it was announced last week. A Swedish discovery, aerocrete has been used in Europe for a decade to construct building parts which are not subjected to much weight (floor filling, roof blocks). Two years ago, Aerocrete Corp. of America introduced it into U. S., worked with Columbia University's Civil Engineers to improve the material, make it strong enough to be used as a structural flooring.

Aerocrete is made of Portland cement, sand and small quantities of lime, aluminum powder, soda. When poured out in thick liquid form, the presence of the aluminum powder in an alkaline solution causes a chemical reaction, liberates hydrogen, forms a cellular structure. Within a half-hour after pouring, aerocrete begins to puff up. At the end of an hour, expansion reaches its limit, the material hardens. By varying the amount of ingredients, expansion can be controlled, may vary from 50% to 150% of original volume.

At Columbia University's fire testing station at Green Point, L. I. the upper surface of a floor of aerocrete 4 1/2 in. thick kept a temperature of 139DEG to 207DEG F. during the last hour of a four-hour fire of 1,825DEG F. blazing underneath. (The maximum temperature of a burning fire proof building averages 1,700DEG F.) The same floor when cooled resisted a load of 450 lb. per sq. in. with deflections ranging from .06 in. to 2 in.

Advantages of aerocrete as a structural floor lie in its high heat-insulating value, its sound-deadening properties, its light weight. According to the use for which it is needed, it can be made from 20% to 75% of weight of ordinary concrete. Authorities expect it to reduce by almost one-fourth the weight of steel necessary to support a building. Aerocrete floors have been put in a new addition to Bethlehem Steel Corp. at Bethlehem, Pa. and in the Golden Hill Building, Manhattan.

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