A Test Shows How Concrete May be Cheaply Strengthened.

Measurements may be conducted in the strict spirit of scientific research, not immediately directed to industrial ends. Methods thus perfected are more and more being adopted for large questions of industry. Let an example be presented from the field, briefly touched upon in this book, of concrete as a material for the builder. Says Mr. C. H. Umstead of Washington, Pennsylvania:—

“Many thousands of tons of the finer grades of stones from the crushers all over the country are rejected by engineers for use in concrete foundations and walls, sand being preferred at greatly increased cost. I prepared seventy-two three-inch cubes with quartz sand and with varying proportions of crushed stone which was going to the dump as unfit for foundation work, and submitted them to crushing tests at periods of fourteen and twenty-eight days. The proportion of Portland cement was constant.”

From Mr. Umstead’s table of results the following figures are chosen; on comparing those for the first and third cubes they show that a gain in strength of forty-three per cent, followed upon using six pounds of crusher refuse instead of five and one half pounds of sand.

Sand			Portland Cement		Water			Crushed Refuse		Compressive Strain
Sand			Portland Cement		Water			Crushed Refuse		14 Days				28 Days
8	.5	lbs.	4.5	lbs.	1		lb.	none		2850	lbs.	per	sq. in.	3670
6		„	4.5	„	1		lb.	3	lbs.	3120	„	„	„	5050
3		„	4.5	„	1	.125	lbs.	6	„	3620	„	„	„	5250

So much for the value of a test in the improvement of an important manufacture.

Mr. Umstead’s full report appeared in 1903, in the third volume of bulletins published by the American Society for Testing Materials. This Society, whose secretary is Professor Edgar Marburg of the University of Pennsylvania, Philadelphia, is affiliated with the International Association for Testing Materials, one of the most important agencies in existence for providing the engineer with trustworthy data.