Page:The American Cyclopædia (1879) Volume V.djvu/214

 210 CONCRETE in the water in the place they were intended to occupy, and the second on shore, to be after- ward thrown into the sea. The first were made by immersing be"ton in caissons which were constructed of timber and plank, and lined on the inside with tarred cloth, the four sides being connected by hinged angle irons so as to be readily unshipped. The second kind of blocks were prepared on shore in moulds of timber and plank, resting upon an inclined plane, ending at the point where the block was to be sunk. After the b6ton had properly set, the sides were removed and the block launched into the sea. In making the mortar for the first description of blocks, one part of rich lime was slaked and made into a paste and then mixed with two parts of Italian poz- zuolana, while for the blocks made on shore pozzuolana was mixed with an equal quantity of sand. The lime employed was from a hard, granular limestone, weighing about 156 Ibs. per cubic foot. . Slaked and reduced to the consistence of a thick pulp, it was found to absorb once and a half its weight of water and to increase in bulk 75 per cent. One volume of this with two volumes of pozzuo- lana made two volumes of mortar. To form the concrete, one part of mortar was incor- porated with two parts of broken stone of about 1 cubic feet. The entire work was performed in five years at a cost of less than $420,000, notwithstanding that the mole at the time of the occupation of Algiers by the French army in 1830 was in a state of complete dilap- idation, in spite of the extensive repairs which had been annually made by the Moors for two centuries. The success met with in this work established two important facts : 1, that blocks of be"ton can be made sufficiently strong to resist the action of the heaviest waves, and form indestructible masses; 2, that these blocks are immovable by the waves when constructed above a certain size, determined by experiment to be about 353 cubic feet. One great advan- tage in the use of blocks of concrete over those of stone is in the diminished cost of handling and transportation, because the concrete blocks can be made at the place where they are used. The b6ton used by Vicat for the bridge of Souillac, upon the Dordogne, was composed of 26 parts of hydraulic lime in paste, 39 of granitic sand, and 66 of gravel. It was found to diminish in volume in the proportion of 1*81 to 1. The immense masses of concrete which form the foundations of the East Eiver bridge between New York and Brooklyn are composed of one part of Rosendale cement, two of sand, and four of coarse beach gravel from an inch to 2 inches in diameter. The cement and sand were first mixed with water in a mill, and afterward incorporated with the gravel by means of shovels used by hand, the latter operation being performed for the most in the caissons, which were 172 ft. in length by 102 ft. in width. As this concrete lies below the bed of the river, and is therefore confined, there is little doubt that it will endure for centuries. The concrete blocks which form the foundation of the piers that are now (June, 1873) under construction at the Battery in New York harbor, are composed of one part of Portland cement, two of sand, and five of broken trap rock from the Palisades on the Hudson. The matrix of cement and sand was first formed by hand, and afterward incor- porated with the broken stone by the same process. It was then shovelled into forms and compressed by ramming. After the be~ton had set, the forms were removed, and the blocks were exposed to the weather for two months. The concrete with which the natural stone masonry above the water floor is filled in is mixed in the same way, and rammed down in the spaces left by the walls and arches. Concrete is used as a foundation for roads and for cement walks in parks. A good article for this purpose may be made by using equal parts of Rosendale and Portland cements with sand and broken stone. The artificial stone of Mr. Frederick Ransome, patented in 1856, made by the patent concrete stone company at East Greenwich, near London, England, is one of the remarkable productions of the day, not only furnishing an excellent building stone, but also a material for making a superior quality of grindstones. This concrete is composed of sand held together by silicate of lime, and is formed by an indirect process in which silicate of soda is decomposed by chloride of calcium. The silicate of soda is made by digesting flints with a solution of caustic soda of about 1*2 sp. gr. in boilers, under a pressure of 70 or 80 Ibs. to the square inch. The solution of silicate of soda which results should have a specific gravity of about 1*7. Clean sharp sand, which has been dried in a current of hot air, is then mingled with a little finely ground chalk or marble, and the silicate of soda is added in the proportion of a gallon to the bushel of mix- ture, and the whole is thoroughly triturated in a mill. It becomes pasty during the operation, and susceptible of being moulded into any de- sired form. The mould blocks, formed by ram- ming, are then nearly saturated with a solu- tion of chloride of calcium of about 1 "4 sp. gr. Double decomposition immediately takes place, whereby silicate of lime and chloride of sodium, or common salt, are produced ; and in a few minutes the blocks become hard enough to be handled. They are then immersed in vats containing the solution of chloride of calcium at a temperature of about 212 F., in order that a thorough decomposition of the silicate of soda and formation of silicate of lime may be effected. The latter substance, being in- soluble and firmly enveloping the grains of sand, forms a firm and it is believed durable block of stone. The chloride of sodium, being soluble, is then discharged by displacement with water. It might be supposed that the stone would be left in a very porous condition, but experiment has proved that this is not the