The New York Rapid-transit Subway

42 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of with steel rods | inch and J inch square embedded in the blocks to a deptli of 9 inches. At the age of 1 month one set of rods was pulled, and at the age of 3 months another set. In each set the rods were in the following different conditions: rusted, cleaned by removing the rust, or painted with red-lead, linseed-oil and graphite. The tests gave the following interesting figures, demonstrating the very injurious effect of any preservative coating if adhesion between the metal and the concrete is intended to be relied on, as is the case in reinforced concrete. For convenience the total load has been reduced to the corresponding adhesion per square inch of surface of rod in contact witli the concrete. Table VI. Size and Condition of Rod. 1 Month Old. 3 Months Old. Total Load. Adhesion per Sq. In. Total Load. Adhesion per Sq. In. J-inch, rusted Lbs. 11,800 Lbs. 437 Lbs. 17,350 Lbs. 642 Z-inch, clean 9,260 294 13,590 431 f-inch, red lead 1,700 63 3,460 128 3-inch, linseed oil .... 900 33 1,700 63 4-inch, graphite 460 17 The injurious effect of a hard-coated paint, and still more of a slippery surface of oil or graphite, is very apparent. As the result of these tests and other experience, the Author inclines strongly to the belief that the best method of preserving steel when embedded in concrete, even when no reliance is to be placed on the combined strength of the steel and concrete, is to omit any paint or other coating. The union of the metal and the cement is so complete that the former is not capable of rusting. To ensure, however, a complete covering of the metal with cement, the concrete should be quite fluid. The rods referred to in Table VI were plain and square in section. In order to determine the effect of section and the value of a mechanical bond between the concrete and the rod in addition to surface adhesion, tests were made on 3-inch twisted rods and 3-inch rods rolled with enlargements in section alternating at right angles. At the age of I month the adhesion per square inch of the twisted rods averaged 509 lbs., and of the enlarged rods 637 lbs., but in all cases the concrete block was split, indicating a wedge-like action of