Page:Architectural Review and American Builders' Journal, Volume 1, 1869.djvu/864

 696 The Architectural Review and American Builders' Journal. [May, CONCRETE AND BETON. "TTT^HEN it was first introduced as a V V mode of construction, Concrete created a sensation, and drew forth various essays on its merits. For a sound sub-stratum on which to lay foun- dations, nothing could be better. It was not alone worthy of notice for its cheapness, ease of formation and economy of time, but also for its entire reliability as a material in underground construction ; and we may add that its utility and excellence in the formation of sea walls has been most thoroughly tested both in this country and in Eng- land. Certainly in the latter it has been found that although it becomes intensely hard as a backing, it is more or less affected by the action of the sea- water on its exposed side. This, how- ever, is by no means a fatal objection, as a facing of blocks made of cement-con- crete is sufficient protection from such action. The specific gravity of concrete, as compared with that of other materials, is as follows : ^ Concrete weighs to the cubic foot about 1 40 lbs. Brickwork, 110 " Granite, 160 to 170 " Limestone, 145 to 150 " Concrete, as made of quick-lime, is composed of the following proportions: Broken Stone 7 or 8 ounces (, I 80 parts. 40 parts. 10 " in weight each, Sharp river sand, Quick-lime, The Lime is to be mixed with water to the consistency of thin cream and grouted into the other ingredients. The mass is to be then worked up thoroughly and used at once. Some prefer mixing the lime, ground fine, through the other materials, and then throwing on suf- ficient water. It should then be turned over briskly with shovels, put into barrows, and wheeled away for instant use. It is advisable to employ two sets of men to perform this operation, with three men in each set, one man fetching the water, &c, while the other two turn over the mixture to the second set, and they repeating the process, turn over the concrete thus mixed to the barrow-men. It should be wheeled up inclined planks to a height of some yards, and dumped down into the tren- ches. This fall is most desirable, as it forces the mass together, and drives the moisture to the surface. Soon after being thrown in, the mixture shows con- siderable commotion, and vapor arises, as is usually seen after the slaking of lime. The concrete should be thrown on in layers, the first being allowed to set before a second is thrown on. A bar- row load, spreading over the ground in its fall, will form generally from seven to nine inches thick, and a cubical }*ard of concrete will take about thirty feet cube of material and three and a half feet of ground lime, with a sufficient quantity of water. Of the latter no more should be used than is absolutely necessary to effect a perfect mixture of the ingre- dients. Hot-water accelerates the indu- ration. In answer to correspondents who re- quest information on the subject of con- crete as a material for construction above ground, we would say that if properly manipulated, there is strength and durability in this composition; and although a recent failure of a pub- lic building, constructed of a certain de- scription of small blocks called by the name of concrete, has brought down upon it the marked displeasure of some, the public have too many standing testi- monies of its strength to condemn it on this account. The fact is, the " concrete blocks ", as they are called, have weak-