Cementation

“ Improvements in the manufacture of hydraulic cements have given an impetus to the use of concrete, but its use is by no means of recent date. It is no uncommon thing in the taking down of heavy walls several centuries old to find that the method of building was to carry up face and back with rubble and stiff mortar, and to fill the interior with bowlders and gravel, the interstices of which were filled by grouting—the whole mass becoming virtually a monolith. Modern quick-setting cement accomplishes this object within a time consistent with the requirements of modern engineering works ”

“ There are various minor external causes for the failure and ultimate destruction of cement mortar and concrete, but their discussion is a matter for the specialist. Failure from inherent vice in the cement has been already touched on; it can always be traced to want of skill and care in manufacture.
Calcium Sulphate Cements.—Under this term are comprehended all cements whose setting properties primarily depend on the hydration of calcium sulphate. They include plaster of Paris, Keene’s cement and many variants of these two types. The raw material is gypsum (q.v.) ”

“ It should be used on the surface only and not for the entire tile or pottery. If used without any sand or gravel, it is termed “too fat,” and has the fault of cracking sooner or later. Therefore neat cement is always backed up with a concrete mixture.
CONCRETE is a mixture of sand and cement, gravel and cement, or rock and cement. In all instances where such a mixture is made, the two parts should be mixed dry before any water is added. Only enough should be mixed to meet immediate needs as it is not best to use cement that has stood so long that it has commenced to harden. ”

“ Soft, spongy foundations of natural cement or Portland cement of inferior quality are not only an inadequate support for the yielding surface, but they are easily penetrated by water from below and act as conveyors of water, while a sound and firm foundation of the best Portland cement concrete not only presents an unyielding support to the surface, but also, when properly set and dried before the surface is laid, keeps the surface as free as is possible under the circumstances from ground water, and thus contributes to the longevity of the surface. ”

“ We find various mixtures and preparations of mortar used in the station:—
(1) A brownish sort, rather coarse and more friable and earthy and inferior, used in the lower courses of the foundation walls, mixed with mould and humus and gravel and sand.
(2) A whitish cement, mixed with small-sized clean river gravel, poured between the blocks of red sandstone and the facings, as seen in the walls of the prætorial building.
(3) A fine cement, made of broken bricks and lime, used for the floorings of the hypocaust. ”

“ The common cement used in building, which is called mortar, is made of sand and quicklime mixed with water. Roman and Portland cements consist of certain kinds of clay burnt and ground. Plaster of Paris forms a useful cement, it is to be mixed with water to the consistence of cream, and it hardens in a few minutes. Glue is an invaluable cement for wood and many other purposes, it also joins any kind of broken glass or china that will not have to be subjected to much wetting. Shellac dissolved in spirit is a useful cement ”

“ Cement is more expensive than brick. The surface to be covered should, first, be levelled, then saturated with water; after which is laid a three-inch bed of cement concrete, made of gravel, sand, and cement in proper proportions. Upon this is placed a three-fourth-inch layer of cement mortar. Ordinary American, hydraulic cement may be used for concrete, but for the three-fourth-inch layer nothing but best Portland cement should be considered. Sometimes the cement work in the cellar is done by the plasterer. Outside cement work for walks requires special skill. ”

“ With us the least depth is 2 feet 9 inches under the surface of the street, and I am confident, could our mains remain in the ground as we put them down, our loss from leakage by them would be very small indeed. While, as I stated in the beginning, I have no doubt that a cement joint can be made tight, I can see no benefit in using cement for the purpose, as I consider lead far superior in accommodating itself to any upheaval or settling of the earth where the mains are laid down. ”

“ The cement is made from the slag-sand, common lime, and iron oxides. It is little inferior to Portland cement in strength, while it does not cost one-fourth as much. The concrete made from this cement, mixed with the "shingle," is an excellent conglomerate for use in monolithic structures. It is stated by Mr. Charles Wood, in a paper read before the British Iron and Steel Institute, that "it took two good men, with steel bars and sledge-hammers, as much as four days to cut through a wall of this concrete about twenty-six inches thick." ”

“ In the manufacture of natural cement the raw material generally used is some stone in which the carbonate of lime, silica, and alumina are present in more or less correct proportions, while in the manufacture of the artificial cement the raw material used consists of the essential ingredients, each in a comparatively pure state, thoroughly mixed in theoretically the correct proportions. It is due to this fact that artificial or Portland cement is not only much superior to natural cements, but that it is much more uniform in its quality. ”

“ Concrete (opus caementicium, Vitr. ii. 4, 6, 8) , the most important of all the materials used, is made of rough pieces of stone, or of fragments of marble, brick, &c., averaging from about the size of a man's fist and embedded in cement made of lime and pozzolana-forming one solid mass of enormous strength and coherence. Stucco, cement and mortar (tectorium, opus albarium and other names) are of many kinds; the ancient Romans especially excelled in their manufacture. ”

“ This clinker is ground until it is reduced to a powder, and this is the Portland cement. Portland cement is generally mixed with an aggregate to produce strength and this aggregate is usually stone, gravel or sand. The third material needed to complete the combination is water.
SUCCESS IN THE USE OF CEMENT depends largely upon cement that is fresh. Cement is very sensitive to moisture and if kept where fogs, dew or moisture of any nature is absorbed into it, the first set or “hydration” takes place and destroys its use for fine handicraft. ”

“ Good results cannot be obtained unless you use a good cement, nor will the work be at its best unless care is taken in the selection of clean sand and clean stone.
Among the uninitiated, there is an all too prevalent idea that anything is good enough for the making of concrete. Some will tell you that sawdust, shavings, mud, clay, etc., will do to complete the mixture, but the absurdity of this notion will very soon become evident to anyone who neglects the precautions which have been above pointed out. ”

“ Slag and cinder concretes are for this reason given minor consideration in this volume.
BROKEN STONE.—Stone produced by crushing any of the harder and tougher varieties of rock is suitable for concrete. Perhaps the best stone is produced by crushing trap rock. Crushed trap besides being hard and tough is angular and has an excellent fracture surface for holding cement; it also withstands heat better than most stone. Next to [Pg 14] trap the hard, tough, crystalline limestones make perhaps the best all around concrete material; cement adheres to limestone better than to any other rock. ”

“ The amount required to combine chemically with the cement is about 16% by weight, but in practice much more than this is used, because of loss by evaporation, and the difficulty of ensuring that the water shall be uniformly distributed. If the situation is cool, the stone hard, and the concrete carefully rammed directly it is laid down and kept moist with damp cloths, only just sufficient to moisten the whole mass is required. On the other hand, water should be given generously in hot weather, also when absorbent stone is used or when the concrete is not rammed. ”

“ A similar cement is a mixture of dried fresh curd with 1/10th of its weight of quicklime and a little camphor; it is made into a paste with water when employed. A cement for Derbyshire spar and china, &c., is composed of 7 parts of rosin and 1 of wax, with a little plaster of Paris; a small quantity only should be applied to the surfaces to be united, for, as a general rule, the thinner the stratum of a cement, the more powerful its action. ”

“ The ladle containing the concrete is passed down behind the tubbing by means of a windlass at the surface, and when it reaches the [112] lowest point, the piston is pushed down and the cement allowed to escape from the chamber. The weight of the cement and the ladle is sufficient with a little ballast to enable it to descend easily.
A number of experiments have been made to discover a cement which will not harden too quickly, and which, when hardened, will form a perfectly compact and solid mass. ”

“ Concrete produces strength and the neat cement produces a smooth texture and surface. When concrete is used the cement and water will rise to the top and if the surface is worked{14} and pressed with a trowel the cement is “flowed” to the top, producing a smooth surface.
MOLDS ARE USED FOR FORMING CEMENT AND CONCRETE, and are made from wood, metal or plaster-of-Paris. The forms in all instances should be tied or braced together to prevent the moisture of the mixture from running out, as the water is essential to the successful hardening of the cement. ”

“ If the ingredients of the cement are chosen so that when hard the cement has about the same coefficient of compressibility as the stone or brick, the pressure will be nearly uniformly distributed. The cement also adheres to the surfaces of the stone or brick, and allows a certain amount of tension to be borne by the joint. It likewise prevents the stones from slipping one on the other, i.e. it gives the joint very considerable shearing strength. The composition of the cement is chosen according as it has to “set” in air or water. ”

“ It should be stirred quite often. A pound of unslaked lime, finely pulverized in a mortar, is then added, and the whole is thoroughly mixed by beating. This done, the whites of 25 eggs are incorporated with the rest, and the whole is ready for use. There is another cement for the same purpose which is used hot. It is made of resin, beeswax, brick-dust, and chalk boiled together. The substances to be cemented must be heated, and when the surfaces are coated with cement, they must be rubbed hard upon each other, as in making a glue-joint with wood. ”

“ Indeed, it is more easily done than sand, as the water flows through the larger voids in the gravel more readily than through the voids in the sand. Dust may be left in the crushed stone without fear of its interfering with the strength of the cement, but care should be taken to see that such dust is distributed evenly through the whole mass, and when dust is found in stone, slightly less sand should be used than ordinarily. ”

“ The materials of concrete as used at present are cement, sand, gravel, broken stone, and, of course, water. It is, perhaps, unnecessary to say that one of the primary requirements in materials is that they should be clean. Stone should be angular, gravel well washed, sand coarse and sharp, cement fine and possessing a fair proportion of the requirements laid down in the orthodox specification. ”

“ Boil the linseed oil and litharge half an hour, then stir the lime into the hot mass, and use the mixture hot. This cement is excellent for filling in joints between stones, for flat roofs, water reservoirs, etc. For a better adhesion of the cement, apply a coat of linseed oil varnish to the surfaces to be cemented. Porous stones are made water-proof by heating the cement in a boiler and adding sufficient linseed oil to form a mass which can be readily worked with a smoothing board. Apply as hot as possible. ”

“ Portland cement is the best matrix known, since it is the most powerful and the most durable. It is used for mortar wherever great strength, hard-wearing properties, and resistance to damp are required. It should weigh 112 ℔ per striked bushel and be ground fine enough to pass through a sieve having 2500 meshes to the square inch and leave not more than 10% residue. Test briquettes after setting under water for seven days should stand a tensile strain of 350 ℔ on a square inch. It is used in the proportions of one part of cement to from one to five parts of sand. ”

“ When people first make concrete, they often expect too much of their materials. A good rule for the strongest sort of cement, strong enough for floors on which heavy machines are to stand, is one fourth of a barrel of cement, half a barrel of sand, and one barrel of gravel or broken stone. ”

“ Safety in this respect calls for a much greater degree of hardness than would be needed to bear the weight of the building. Again, strength and hardness, with a given proportion of cement, depend greatly on the character of the other materials used; blocks made of cement and sand, 1 to 3, will not be so strong or so impermeable to water as those made from a good mixed sand and gravel, 1 to 5. On the whole, it is doubtful whether blocks of satisfactory quality can be made, by hand mixing and tamping, under ordinary factory conditions, from a poorer mixture than 1 to 5. ”

“ If a long nail or rod or strong stick is placed in the center of this mass, it can serve the purpose as an axis to a templet which will form the contour of the jardinière when moved around in a circular direction. The metal must be good and heavy and sometimes it is necessary to reinforce the templet with wood.
After the clay form is built, cases are made in several sections from the plaster the same as for small forms; and cement and concrete used in large quantities after the same method as for small forms. ”