The New York Rapid-transit Subway

40 PARSONS ON NEW YORK RAPID-TRANSIT SUBWAY. [Minutes of tests such as bending and drifting; annealing for testing was for- bidden. Cast iron was required to withstand a tensile stress of at least 21,000 lbs., and a transverse stress of 750 lbs., per square inch. In order to ensure a proper quality of cement, the specifications provided that it should be subjected not only to the usual short-time tests of 1 and 7 days, but also to a test of 28 days; and, as cement was being used at the rate of 2,000 barrels per day, special provisions had to be made by the manufacturer to furnish the necessary facilities for this inspection. This was done by erecting, at the mill, bins holding 1,500 barrels each, from which samples were taken and tests made until the cement was accepted, when it was shipped to the work in bags fastened by a metal seal. In addition to the usual requirements in respect of fineness and checks for sound- ness by boiling and the making of thin pats on glass, the specifications required that this cement, when tested neat, should exceed in strength 150 lbs. per square inch at the end of 1 day, 400 lbs. at the end of 7 days, 6 days being in water, and 500 lbs. at the end of 28 days, 27 days being in water. Briquettes composed of 2 parts of cement and 1 part of sharp coarse sand were to have a strength of not less than 200 lbs. per square inch at the end of 7 days, and 300 lbs. at the end of 28 days. To ensure a. continual increase in strength, it was also required that neat briquettes must show a minimum increase in strength of 15 per cent., and sand briquettes of 25 per cent, between the tests at the end of 7 days and 28 days. An average of tests on upwards of 1,000,000 barrels of Portland cement showed for neat Portland cement a strength of 300 lbs. at the end of 1 day, 700 lbs. at the end of 7 days, and 800 lbs. at the end of 28 days; and for the same cement with sand in the ratio of 2 to 1, 400 lbs. at the end of 7 days, and upwards of 500 lbs. at the end of 28 days. As explained already, the greater part of the cement was used in concrete, which was of varying proportions according to its position in the work. For the concrete in the thin walls and roof, where a very tight and compact mixture was necessary, it was composed of 1 part cement, 2 parts coarse sand, and 4 parts broken stone or gravel, the last being limited in size to what would pass through a 2-inch ring. In the less important parts of the work mixtures of 1:3:4, 1:3:5, and 1:3:6, were employed. In all cases the concrete was laid exceedingly wet, so that the usual ramming with rammers was avoided, the concrete being cut with spades in order to ensure a compact mixture. In addition to the tests of cement in briquette form, further tests