. The elements of railroad engineering . even at twice the costper barrel. 1474. Pointing of Joints.—Arch culverts for water-ways are invariably rubble masonry, but of the best of itskind. Sometimes the corner stones of the abutments, as wellas the arch stones of the faces, are of cut stone. The jointsof these should be left open at the faces until the work iswell advanced or completed, when they should be pointed RAILROAD CONSTRUCTION. 893 with mortar made of the best cement in the proportions of1 part of cement to 1 part of sand, and neatly dressed witha pointing tool. The joints of the rubb
. The elements of railroad engineering . even at twice the costper barrel. 1474. Pointing of Joints.—Arch culverts for water-ways are invariably rubble masonry, but of the best of itskind. Sometimes the corner stones of the abutments, as wellas the arch stones of the faces, are of cut stone. The jointsof these should be left open at the faces until the work iswell advanced or completed, when they should be pointed RAILROAD CONSTRUCTION. 893 with mortar made of the best cement in the proportions of1 part of cement to 1 part of sand, and neatly dressed witha pointing tool. The joints of the rubble masonry aresimply struck^ i. e., the trowel is pressed against the mortarand drawn the full length of the joint, forming a water-shed for each joint. The joints are struck as the stonesare laid, the same mortar being used at the faces as in theinterior of the walls. There are two principal methods used in pointing cutstone, as shown in Figs. 301 and 392. Fig. 391 shows theform in most o^eneral usre. It is not so ornamental as that. Fig. 391. Fig. ■6di shown in Fig. 392, but it is less exposed to the weather, and,hence, is more enduring and a more certain protection tothe joints. Mortar intended for pointing must be usedimmediately after mixing, and the pointing tool repeatedlyrun over the joint or bead, under considerable pressure, inorder to compress the mortar and give it a smooth surfaceand uniform groove or projection. 1475. Centers for Arches.—A center is a temporarywooden structure for supporting an arch while it is beingbuilt. Centers are built lying flat on a fixed platform, to afull-sized drawing, and vary widely in design, according tothe type and dimensions of the arch. The different parts ofa center are given in Fig. 393, which is a standard type ofcentering for all arches of moderate span, say from 6 to 16 feet. 894 RAILROAD CONSTRUCTION. The frames A, A are made of ribs of H-inch plank andunited as shown in the figure, breaking joints and fastenedtogether
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
