Westinghouse Air Brakes and Signals.
By all odds the most important use of compressed air is that developed by Mr. George Westinghouse, of Pittsburg, in his automatic brakes for railroads. For each locomotive he provides an air compressor which fills in the engine itself, and beneath each car, a reservoir of compressed air. Every reservoir aboard a long train in rapid motion may at the same instant, by a touch from the engine-runner, actuate the brakes so as to stop the train in the shortest possible time. This invention has accomplished more for the safety of quick railroad travel than any other device; no wonder, then, that Westinghouse brakes are in all but universal use. They are now being adopted for trolley-cars which often require to be stopped in the briefest possible period. The Westinghouse Company builds and installs elaborate signal systems worked by compressed air and electricity. All these are described and pictured in the “Air Brake Catechism,” by Robert H. Blackall, published by N. W. Henley & Co., New York. This book is constantly appearing in new editions, of which the reader should procure the latest.
CHAPTER XXIX
CONCRETE AND ITS REINFORCEMENT
Pouring and ramming are easier and cheaper than cutting and carving . . . Concrete for dwellings ensures comfort and safety from fire . . . Strengthened with steel it builds warehouses, factories and bridges of new excellence.
Stone and wood in the builder’s hands require skill and severe labor for their shaping; vastly simpler and easier is the task of molding a wall from wet clay, or other semi-plastic material. It was long ago discovered that certain mixtures of clay and sand, duly mingled and burned, became as hard as stone. To this discovery we owe, among other arts, that of brick-making. In joining brick to brick, or stone to stone, a mortar of uncommon strength was used by the Romans. All by itself, when laid a little at a time, it formed a strong and lasting structure. Then it occurred to some inventive builder, Why not save mortar by throwing into it gravel and bits of broken stone? He accordingly reared a wall of what we should now call rude concrete, whose lineal descendant to-day is a semi-plastic mass of Portland cement, sand, and gravel or broken stone, together with the necessary water. Its use allows the ease and freedom of pouring, while affording structures with all the strength of stone or brick.
For much of the early work lime and sand were mixed to make a mortar of the usual kind, in which stone or gravel was embedded. Afterward it was found that volcanic ashes, such as those of Puzzuoli near Naples, formed with lime a compound which resisted water and was therefore suitable for structures exposed to damp or wet. In the middle ages concrete was employed throughout Europe, after the Roman fashion, for both foundations and walls. In walls it was usually laid as a core faced with stone masonry, large stones often being embedded in the mass. About 1750, while building the third Eddystone Lighthouse, John Smeaton discovered that a limestone which contained clay, when duly burnt, cooled, ground, and wetted, hardened under water, was indeed a natural cement, by which name it is still known. Deposits suitable for the direct manufacture of natural cement were in 1818 discovered in Madison and Onondaga Counties, New York, by Canvass White, an engineer who used this cement largely in building the Erie Canal. Natural cement has a powerful rival in Portland cement, due to Joseph Aspdin, of Leeds, who in 1824 mixed slaked lime and clay, highly calcined. The resulting clinker when ground, and only when ground, unites with water, the strength of the union increasing with the fineness of the grinding. Because this product looks like Portland stone, much used in England, it was given the name of Portland cement. The raw materials suitable for making it are widely distributed throughout North America, much more widely than those from which natural cement may be had. This is the principal reason why Portland cement is now produced in the United States in about six-fold the quantity of natural cement.
So rapidly has concrete grown in public favor with American builders that in 1905 they used seven-fold as much as in 1890. It has been widely adopted for pavements, as at Bellefontaine, Ohio; for breakwaters, as at Galveston and Chicago; for tunnels, as in more than four miles of the New York Subway. The foundations beneath the power-house of the Interborough Rapid Transit Company, New York, required 80,000 cubic yards; for the new station of the Pennsylvania Railroad Company, New York, a much greater quantity is being employed; in their turn these figures will be far exceeded by the needs of the new Croton Dam for the water supply of New York, and the Wachusett Dam for the water supply of Boston.
Concrete silo foundation, Bricelyn, Minn.
Concrete silo, Gedney Farms, White Plains, N. Y.
Concrete has long been adopted for a variety of less ambitious purposes. At St. Denis, near Paris, it was many years ago molded into a bridge of modest span. It has formed thousands of dwellings in factory and mining villages and towns, as well as many villas of handsome design. It is particularly well adapted for silos, as here [illustrated].[36] All this expansion of an old art has been stimulated by a steady reduction in the price of Portland cement, and by constant improvement in its quality. As the manufacture has expanded, its standards have risen, its machinery has become more economical and trustworthy in results. While the cost of concrete has thus been lowered by a fall in the price of cement, the wages of bricklayers and stone-masons have advanced, adding a new reason for building in concrete, since it requires in execution but little skilled labor. The good points of concrete are manifold; it forms a strong, fire-resisting, and damp-proof structure. For mills and factories another item of gain is that it forms a unit such as might be hewn out of a single huge rock, vibrating machinery therefore affects it much less than it does an ordinary building. At the same time its walls and floors obstruct sound, conducing to quiet. Concrete must be honestly made and used, otherwise, just as in the case of rubbishy bricks, ill laid, it may tumble down from its own weight. And furthermore it is necessary to recognize how widely concretes of diverse composition vary in strength and durability. There should be a careful adaptation in each case of quality to requirement. Concrete walls, as first produced, had a forbidding ugliness; this is being remedied by surfacings of pleasant neutral tones. A well designed residence executed in concrete at Fort Thomas, Kentucky, is shown opposite this page.
[36] The illustration of a [silo] and its [foundation] are taken by permission from “Concrete Construction about the Home and on the Farm,” copyright 1905 by the Atlas Portland Cement Co., 30 Broad St., New York. This book of 127 pages, fully illustrated, with instructions and specifications, is sent gratis on request.
In Mr. Edison’s judgment a vast field awaits the concrete industry in building small, cheap dwellings. He once said to me, as he spoke of his cement mill,—“What I want to see is an architect of the stamp of Mr. Stanford White of New York take up this material. Let him design half a dozen good dwellings for working people, all different. Each set of molds, executed in metal, would cost perhaps $20,000. Such dwellings could be poured in three hours, and be dry enough for occupancy in ten days. A decent house of six rooms, as far as the shell would go, might cost only three hundred dollars or so. It would be stereotypy over again and the expense for the models would disappear in the duplications repeated all over the country.”
MANSION IN CONCRETE, FORT THOMAS, KENTUCKY.
Ferro-Construction Co., Cincinnati.
Concrete is now supplied to builders in blocks, usually hollow and much larger than bricks. When cast in sand they look like stone. Of course, subjected as they are to more than ordinary stresses, their production demands special care. The methods, therefore, which are adopted in manufacturing these blocks may be taken as the best practice in the industry broadly considered. Says Mr. H. H. Rice, of Denver:—“The sand employed should be sharp, silicious and clean. The gravel used should contain a fair proportion of as large sizes as can be advantageously employed in the particular machine used. Where gravel is not available, crushed stone takes its place. Care should be exercised to obtain stone as strong as the mortar. What proportions of sand, gravel and broken stone should be mixed together is a question determined by the extent of their voids: these may vary from one third to one half the whole volume. Assuming that we have to deal with the larger fraction, a mixture of 1 cement, 2 sand, 4 gravel, should be employed; this is classified as the lowest grade of fat mixture. At times a lean mixture, 1 cement, 3 sand, 5 gravel, might be advantageously adopted. Where gravel or broken stone is not used, the proportion of cement to sand should be as 1 to 4. A fat mixture has greater tensile strength than a lean mixture, but resistance to compression depends upon a thorough filling of voids. A lean mixture thoroughly worked, proves more satisfactory than a fat mixture with hasty and indifferent handling. With any mixture success is attained only by completely coating every grain of sand with cement, and every piece of stone or gravel with the sand-cement mortar. (See Mr. Umstead’s results, [page 240].)
Wall of two-piece concrete blocks.
American Hydraulic Stone Co., Denver.
In producing concrete blocks there are three different methods, tamping, pressing, and pouring, each adapted to a particular mixture for a special kind of work. Two-piece walls, devised in 1902, deserve a word of description. The pressed blocks of which they are built show the new freedom conferred by concrete as a building material. Each block has a long right-angle arm extending inward from the middle, and a short arm extending from each end. In laying the blocks in a wall no portion of a block extends through the wall. By leaving the exterior vertical joints open to afford a free circulation of air, no part of a block on one side of the wall touches any block from the opposite side; this prevents the passage of moisture and produces in effect two walls, tied by the overlapping arms or webs in alternate courses, and affording in its bond a great resistance to lateral stresses. Blocks in other forms equally useful are steadily gaining popularity.[37]
[37] Mr. H. H. Rice’s first-prize paper on the manufacture of concrete blocks and their use in building construction appeared in the Cement Age, New York, October, 1905. Permission to use his paper and the [illustration] here presented, both copyrighted, has been courteously extended by the publishers.
Concrete, although widely available to the builder, is in many cases a material he cannot employ. For a store-house, thickness of wall, ensuring an equable temperature, is an advantage; for an office-building, reared on costly ground, this thickness is out of the question. Beams, too, cannot have much length in a material which is only one tenth as strong in tensile as in compressive resistance. Clearly the scope for concrete by itself was to be limited unless it could find a partner able to confer strength while adding but slight bulk. An experiment of the simplest was to be the turning point in a great industry.