ELECTRIC POWER FROM THE MISSISSIPPI RIVER CLARK. 207 



In mixing the concrete three parts of a standard grade of quartz 

 sand, taken from the natural deposits of the Des Moines Kiver, 

 2 miles south of Keokuk, is placed with one part of a standard 

 grade of American Portland cement, and tempered with water. 

 The stone to place with this mortar, available a few hundred 

 feet from the end of the dam, is the run of crusher where the 

 crusher jaws are set for standard 2^-inch broken stone. The quan- 

 tities of mortar and stone are such as to produce the maximum 

 density and specific gravity. Mass rock is used in the body of the 

 concrete work where any minimum dimension of the finished con- 

 crete is 3 feet or over. The cubiture of such mass rock may vary from 

 one-half cubic foot to 60 cubic feet, but all such rock deposited is 

 thoroughly embedded in the concrete so as to form a complete union 

 with the surrounding concrete, and stones are separated from one 

 another in dimension by at least 12 inches. No mass rock is placed 

 within 12 inches of any finished surface. 



POWER-HOUSE STRUCTURE. 



At the Iowa end of the dam, slanting downstream toward the lock, 

 is being built the power house, 1,616 feet long and about 123 feet wide, 

 the location of which is charted opposite page 200. The substructure 

 is being built of massive concrete, in which are molded the water 

 passage and water-wheel chambers. On top of this is planned the 

 superstructure, a house of concrete brick and steel. The super- 

 structure will contain the electric generators, transformers, and 

 switchboards. The height of the power house from foundation to 

 roof will be about 133 feet. 



In building the power house the method is to construct a cofferdam 

 around the entire area in which the power house is built, inclosing 

 approximately 37 acres. The water is pumped out of this inclosure, 

 and the work of building proceeds in the space so unwatered. In 

 connection with the power-house construction it is necessary to 

 excavate a large amount of rock for the foundations. The rock is 

 blasted out with dynamite and loaded on cars by steam shovels. It 

 is then hauled to the crushing plant and after being crushed is 

 mixed into concrete. The concrete is hauled to the point of use in 

 buckets and deposited in the substructure of the power house by 

 movable steel cranes. The molds or forms for this portion of the 

 work, involving the water passages and wheel chambers, are com- 

 plicated. 



The concrete used in the power-house construction complies with 

 the specifications mentioned above in connection with the dam. 

 Further than this, where partitions in the superstructure are less than 



