With regard to the cross-tie the case is more difficult. Plain concrete slabs or beams cannot be used after the manner of the wooden tie because of their want of elasticity. What is called “center binding” would be disastrous to plain concrete. The rocking action of the passing load is also a factor which enters. One method of dealing with center binding is to divide the tie into two parts, connecting them with steel rods. The Corell tie is an example of this. In the Percival tie, the under part of the concrete block is given a sharpened edge. Beneath the rail itself, the cross-section is a kind of oval. There is longitudinal reinforcement in the form of four rods, three arranged at the top and one near the bottom. Three rods are bound with wire. There is a cushion block of wood which absorbs and distributes the shocks from the bottom of the rail. Screw spikes and metallic sockets are employed. Some three or more years ago a hundred such ties were put in service in a Texas railway. In June, 1909, seven only were found to have received serious injury. It is thought that this damage was scarcely chargeable to the ties themselves as when in position they were between wooden ones whose deterioration might easily have been the cause of undue disturbance being thrown on the concrete ties.
We have considered to a slight extent the use of steel as the material of concrete forms. This line of application, however, promises to become a very large one. Two notable constructions are now under way in which the steel form plays a large part. These are the great Gatun Locks of the Panama Canal and the Catskill Aqueduct. The three double locks at Gatun will require about 2,000,000 cubic yards of concrete. Each pair of locks is on a separate level and has three longitudinal walls. One separates the lock chambers. This central wall is 60 feet in width. It
is not solid as so much concrete would not be required as the water level is approached. Consequently, there is a kind of V-section which traverses it longitudinally. This is filled in except for three galleries—one for drainage, one for the electric wires and one for the men. There is a longitudinal culvert arranged below the fill in the body of the concrete wall. In the side walls of the lock chambers are other longitudinal culverts. From the central supply culvert transverse distributing culverts run off beneath the floors of the adjacent lock chambers. These have vertical outlets into the lock chambers themselves. Similarly, but for purposes of emptying the locks, the longitudinal culverts arranged along the outside are connected by transverse culverts and vertical openings with the lock chambers. The members of the two systems of transverse culverts alternate with each other. The main supply culvert has a diameter of 22 feet part of the way and of 18 feet part of the way. Now these many culverts, various in form and size, are to be molded in the mass concrete by means of steel forms. As originally announced, there would be 12 forms of open hearth boiler steel for the main supply culvert. Each of these weighs 177,000 pounds. One hundred forms were to be required. The two main outlet culverts of similar dimensions to the main supply culvert were thought to require 21 forms, each 12 feet in length and having a weight of 300,000 pounds. The transverse culverts were to require 100 forms, each having a length of 10 feet and a weight of 217,000 pounds. There were thus to be 133 forms having an aggregate weight of 15,000 tons. It is possible that there may be some modifications of this plan in minor particulars. The side walls of the lock chambers are to be mainly vertical planes having a height of, say, 81 feet. To retain the fresh concrete in place, 12 face plates, constructed of sheet steel are to be used. These are 7½ inches in thickness, having face dimensions 78 x 36 feet. Steel towers running on
suitable tracks control these face plates. It is estimated that towers and plates will have an aggregate weight of 26,000 tons. So that, quite apart from any possible reinforcement application, steel to the total of about 41,000 tons is to be used for forms and immediate accessories. But this 41,000 tons is not all. The concrete is to be cast in great monoliths and to retain the ends of these while the concrete is fresh, steel girders 6 feet high are to be employed. If these locks were to be of stone then steel would have played a rather subordinate part.
The Blaw Collapsible Steel Centering Company are engaged at Panama, but they are also applying their systems of molding concrete to the great aqueduct which is to supply New York City with water from the Catskill Mountain region on the other side of the Hudson River. A steel centering is used to give form to the interior. Steel forms are also employed to shape the upper part of the external surface. At Baltimore, more than three miles of sewer construction was carried out in accordance with the system of the same company. The centering used for one portion where the height was 11 feet and the width 12¼ feet (inside) was employed in 50-foot lengths. In 2 hours, 6 men could remove such a 50-foot section together with its falsework and have it in readiness for a repetition of its service. A typical half-round Blaw center consists of one or more steel plates bent to conform to a cross-section of a semi-circle. Turnbuckles retain this shell in position. If we are going to employ this form in sewer construction, we first dig out our trench to such dimensions and form as to furnish the mold for the outside surface of the lower part of the concrete sewer. We then lay concrete in a longitudinal strip along the bottom, giving the upper surface the form of a shallow gutter. When this is sufficiently hardened, the semi-circular center may be slid along it to suitable position. The center has its concavity opening upwards. The concrete of the invert of the sewer is now
placed. The same or a duplicate center may now be used to mold the interior of the upper part of the sewer.
Portland cement has been in use for a long time. But reinforced concrete is so modern that in some important lines of engineering application the fundamental data underlying practice are not fully determined. In what may be regarded as the first decade (1870-1880) of the considerable manufacture of Portland cement in the United States, the total amount produced was only 42,000 barrels. Fifty years and more would be required for the production of enough cement to construct the Gatun Locks. Over a decade would be necessary to yield enough cement for the operations of the Hudson Companies. The price at this period was about $3.00 per barrel. In 1908 it was 85 cents. But the production in this year was more than 1,200 times that in 1880. The value per year of the present output is about $50,000,000.
CHEMISTRY AND THE INDUSTRIES.
BY BENJAMIN BALL FREUD, B. S.