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.
Concrete Reinforced by a Backbone of Steel. Joseph Monier, the Pioneer.
Concrete, as one of its minor uses, had often been molded into tubs for young trees and shrubs. In 1867, Joseph Monier, a French gardener, in using tubs of this kind found them heavy and clumsy. By way of improvement he built others in which he embedded iron rods vertically in the concrete, securing thus a strong frame-work which permitted him to use but little concrete, and make tubs comparatively light and thin. Monier was not a man to rest satisfied with a single step in a path of so much promise. Before his day builders had joined concrete and metal, but without recognizing the immense value of the alliance. He proceeded to build tanks, ponds, and floors of his united materials, at length rearing bridges of modest proportions. His work attracted attention in Germany and Austria, as well as at home in France, so that soon reinforced concrete, as it was called, became a serious rival to brick and stone. For two thousand years and more, concrete had been a familiar resource of the builder; to-day with a backbone of steel it fills an important place between masonry and skeleton steel construction, boldly invading the territory of both.
