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Masonry

The masonry consists of a gray, hard and durable sandstone, free from admixtures of clay or iron oxide particles. It was quarried near Homewood, Pa. on the Pittsburgh and Lake Erie Railroad where it is found in large blocks of 100 to 500 cubic yards, without any stripping. The masonry is rock-faced, with drafts 1 inch wide all around the face of the stones, which are in courses of alternate headers and stretchers.

"The dimensions of the stones are 24 inches to 16 inches in thickness, 7 feet to 4 feet in length, 3 feet to 11 feet in width, with beds and joints dressed regular and true. The backing for the abutments and wing walls consisted of regular shaped stones, with dressed beds; for the heart of the piers concrete filling was used. It was applied in layers of 12 inches thick. It proved superior in every way to ordinary stone backing. Iron clamps bind the stone in the pier heads in every course.

"The use of spalls was not permitted in any part of the masonry. All spaces between stones were filled with concrete, rammed with iron rammers, making every course absolutely water-tight. Great attention was given to the bond. The stone blocks were laid in alternate header and stretcher courses, which made the coincidence of stone joints in the heart of the pier impossible. In this way each stone is bonded in every direction. The concrete backing, after setting, was very hard and tough; it adhered to the stones with great tenacity, and made the piers monolithic in fact.

"In the execution of the work care was taken to set every stone immediately before setting. When laid in position the stone was settled by repeated blows of a heavy wooden ram. Any stone breaking under this operation was removed.

"The face joints of the finished masonry were cleaned out to a depth of 1 inch, and thoroughly moistened, and caulked with Portland cement and sand mortar, mixed one to one.

"For all face masonry exposed to the weather American Portland cement was used for the mortar; for concrete backing and foundations, Rosendale cement was ordinarily used.

"All cements were required to be so finely ground that 90 percent of the whole would pass through a sieve of 50 meshes to the lineal inch. Tests as to its tensile strength were conducted on a Fairbanks testing machine with moulded briquettes of pure cement.

"Rosendale cement made of a stiff paste, having been one day in water and one day in the air, at an even average temperature of 70 degrees Fahrenheit (in a room), were tested to show the tensile strength of at least 40 pounds per square inch.

"American Portland cement briquettes, under the same conditions, were tested to show a tensile strength of at least 80 pounds per square inch.

"Similar briquettes, after having been four days in water and one day in the air, at the above average temperature, were tested for a tensile strength of 60 pound per square inch for Rosendale cements, and 150 pounds for American Portland cement.

"The concrete used throughout the work was composed of 2 parts of sound broken stone, passing through a 3 inch ring; 2 parts of clean gravel from the size of a pea to 2 inches diameter; 2 parts of washed river sand; 1 part of Rosendale cement of accepted quality.

"For concrete under water 2 parts of cement were used to allow for waste by washing in depositing it under water. With a little care in the operation the loss, however, was insignificant. The stone, gravel and sand were mixed on a board platform, then cement added, and the whole mass thoroughly rehandled in a dry state. Water was then added in barely sufficient quantity to reduce the whole mass, by lively and severe shoveling, to a stiff mortar. This was put immediately in place in layers of not over 12 inches thick, and thoroughly rammed with iron rammers about 5 inches square and weighing 36 pounds, until mass flushed uniformly over the whole surface.

"For depositing concrete under water for the pier foundations square wooden troughs were used, reaching down almost to the bottom, and the concrete dumped in and raked even with iron rakes having long handles. The running out of the concrete was prevented by sheet piling. When a change in the masonry of Pier No. 4 required the removal of a few stones they were found to form with the concrete backing one solid mass, which had to be rent asunder with steel wedges and sledge-hammer, and would sometimes break through the stone rather than through the concrete.

"Openings or slots for one car track were left in the new abutments and piers to accommodate travel on the old bridge.

"The pier posts of the channel spans on the down-stream side have their bearing near to the pier ends, and to prevent cracking of the channel piers or uneven settlement after the superstructure should be in place, riveted iron anchors were walled into the top of piers Nos. 2, 3 and 4.

"The coping on the piers, consisting of two projecting courses of cut stone, was nearly all in place for a grade 15 feet higher than the old bridge, at the time of the dispute with the river men. When the height of the piers was increased to suit a grade 20 feet higher than the old bridge, the additional masonry was built on top of the coping in the form of pedestals of cut stone.

"After the erection of the superstructure had so far progresses that travel could be turned on to one track on the new bridge, the old bridge was abandoned, and the taps and openings in the masonry of the new abutments and piers successively walled in and closed. In this way it was possible to complete the masonry work without stopping travel on the old or new bridge.

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