TAKING SHAPE

Evening Post, Volume CXVI, Issue 80, 2 October 1933, Page 3

TAKING SHAPE

GIANT AMERICAN DAM

ELABORATE TESTS

Behind the announcement that tho Boulder Dam Concreto Engineering Council has met and that actual pouring of the world's largest block of concrete is. partially under way, lies one of the most romantic tales of modern natural science, says the '' Christian Science Monitor." Engineers, and especially those at tho Reclamation Bureau in Denver, are not usually given to regard their business with romance. "Oh, you haven't, seen anything yet," they will say when you question them about Boulder .Dam. "Come back in ii few years and we ■will show you a dam ten times larger than that." But in-the mat-tor of the concreto for Boulder Dam, it is a. different story, for if ever anything in this world was really tested, from an engineering viewpoint, it has been the concrete which is to go into that dam. When completed, Boulder Dam will be a solid block of concrete 750 feet high, 650 feet thick at the base, and composed of some 4,400,000 cubic yards of concrete —enough to pave a standardwidth highway from Chicago to San Francisco. But this concrete must be more than concrete has ever been before. First, it must withstand the- enormous pressure of 30 tons a square foot. Second, it mnst be able to withstand the wear of water rushing over its Surface—in flood time a quantity oi: water about equal to the Mississippi . fit St. Louis. Third, it must cool slowly—engineers ■fistimatc that if artificial cooling is not installed, it would take Boulder Dam ;i full hundred years to "cool." In Wyoming, and in south-western Colorado, tests were eonclnccted on small jnountain streams, with velocity conditions similar to those in Black Canyon, upon many samples of cement to test water .wear. Miniature' dams were built and spillways, so now the engineers know just what to- expect from concrete at the giant dam. 1 SPECTACULAR TEST. But the most spectacular tests were conducted in the basement of the new United States Customs House in Denver, *trhero the Reclamation Bureau is quartered, and where the Boulder Dam •was largely planned. A powerful testing machine, made for the Bureau by the Baldwin Locomotive Worko, was erected. In this machine concrete cylinders 36 inches in diametcr,*ix feet high, and weighing somo 6000 pounds apiece, wcro tested for diametrical expansion and compression strain. • Then the concrete columns were- set in the testing machine. The pressure "was exerted, slowly at first, then in ;jumps—it was just about the nearest :imaginable approach to the ancient physicists' dream of an immovable object struck by an irresistable force. Upward went tho pressure until the maximum compression of 4,000,000 pounds had almost been reached, and then with acrack and shock that, jarred the block-long building, the big, solid ■concrete column crnmbled. Day after day, month after month, for two years'the tests went on, and then the Concrete Council met, heard the . evidence "■ of rushing mountain streams, of almost inconceivable pressures, and judged. . Actual pouring followed. , ■• '' ■ In the matter of cooling, it was decided to embed more than 160 miles of steel" "piping in the concrete mass. Cold water will be pumped through this two-inch piping, and the "cooling" of the concrete effected in a relatively Bhort time. ' ~