Miscellaneous Uses of Reinforced Concrete

Roofing the 10-acre Ivanhoe reservoir cost approxi mately $27,000, and required 1,000,000 feet of lumber and 2,000 barrels of cement for the 630 reinforced con crete pillars that support the roof; 200 kegs of nails were required to fasten the timbers together. The roof is of truss construction, and 1,280 trusses are used. From either end of the reservoir the appearance is that of a row of 19 house roofs of great length, the base of each truss frame being 40 feet.

Concrete Conduits and Sewers. In regard to the use of reinforced concrete in the construc tion of conduits and sewers, the Corrugated Bar Company of St. Louis makes the following statement: "Concrete has been extensively used in the construc tion of conduits and sewers, and its use is becoming more general. No one questions its suitability for the con struction of aqueducts, conduits, and storm sewers; but doubt is sometimes expressed as to the ability of con crete sewers to withstand the possible action of acid sewage. This is a question that has been investigated by sewage experts; and the adoption of concrete for the construction of sewers in many large cities, in some cases after exhaustive tests to determine its value as com pared with brick construction, shows the confidence that engineers place in this material.

"The following extract from an article on 'Cement Sewer Pipe,' by Rudolph Hering, may be of interest in this connection.

" 'It should be added that the acid question must be viewed in a reasonable light. When the dilution by sewage is sufficient, the discharge of a small amount of even strong acid will not cause objectionable effects, as evidenced in European cities by the use of concrete sewers almost exclusively in some cities, as Paris and Vienna. In England, concrete sewers are also very common.' "Many American cities have adopted concrete or reinforced concrete for the construction of large and important sewers, and the following list refers only to the more important works: New York, Jersey City, Harrisburg, Wilmington, Cleveland, Duluth, New Orleans, Louisville, and St. Louis.

"Concrete inverts have proved in practice to be equal, if not superior, in durability to the best hard-burned brick.

" 'The hardness and smoothness of surface obtainable with concrete reduce the friction to a minimum, and render it less liable to erosion than are other materials.

Concrete sewers built in Duluth, Minnesota, furnish a practical example of the ability of Portland cement mortar to resist erosion. After twenty years of wear, they show no appreciable deterioration or enlargement in diameter, while brick sewers laid at the same time required rebuilding after six or seven years. A section of the Duluth drains, about 2,000 feet long and 4 feet in diameter, was built on a 13 per cent grade where the velocity of the water was 42 feet per second, with an invert of flat granite flags laid with 1:1 Portland cement joints. The flow of water during heavy storms was tre mendous, carrying down with it quantities of sand and boulders ; but after two years of wear the invert showed ridges of mortar between the granite flags, indicating that the Portland cement mortar was more durable than the granite.'* "In connection with the subject of acid sewage and the durability of concrete inverts, it should be borne in mind that strong acids may affect the brickwork as well as the mortar in the joints. The smooth surface and true lines that are easily possible with concrete con struction, cannot be attained in brickwork. As a result, *From "Concrete, Plain and Reinforced," by Taylor and Thompson.

the concrete surface offers less obstruction to the flow, and is less liable to erosion.

"One striking advantage of reinforced concrete con struction is the possibility of successfully constructing sewers in poor ground without the heavy foundation that would be required for a brick or masonry sewer. By the use of longitudinal reinforcement, the sewer section itself may be transformed into a stiff beam capable of span ning soft spots or even openings in the supporting soil.

"Some of the advantages of reinforced concrete con struction will be given: "Concrete is not affected by ordinary sewage. A concrete sewer is durable—the surface is smooth and strong, with minimum opportunity for erosion.

"A concrete sewer has a smaller friction coefficient than one of brick or masonry, resulting in larger capacity for a given section.