good polish. Coach or carriage ways are laid, or pitched with blue lias, which wears very well, though it will not bear the frost." 1859. A very useful hydraulic mortar for executing sea-walling, consists of 1 part of chalk lime, or of Halkin lime, with one part of puzzuolana from Civita Vecchia, and 1} parts of sand; but the value of this mixture depends upon the influence exercised by the puzzuolana on the setting of the lime. A mixture of the natural calcareous cements, or of Portland cement with sand, is another good mortar. The presence of sulphate of lime in any composition intended to resist the action of sea water would be fatal, as it crystallises at a different rate of rapidity, and it is more easily soluble than the carbonate of lime. French authorities lay particular stress on the following qualities for the formation of good hydraulic mortar: I. It is essential that the materials should be perfectly pulverised before mixing, so that the combination may be as perfect as possible. II. Sufficient free lime must be present to allow the carbonic acid in the water to combine with it, and form a protective coating of carbonate. III. Long soaking of the materials is advisable, in order that the chemical combinations necessary for the ultimate stability of the mortar may take place before it is actually used. 1859k. Mr. Smeaton discovered, by a course of experiments, that the scales (grey oxide of iron) that fly off under the forge hammer from red hot iron, pulverised, sifted, and mixed with lime, form an admirable cement, equal to puzzuolana. He found, in pursuing his experiments, that roasted iron ore produced an effective water cement, by using a greater proportion of it than either terras or puzzuolana. Equal quantities of iron scales and argillaceous lime, with half the quantity of each of these of sand, produced a cement in every respect equal to terras mortar. If pure carbonate of lime be used, equal parts of cach of the ingredients ought to be incorporated. We do not think it necessary here to give any account either of Loriot's cement, or that proposed by Semple: neither are to be depended on: indeed the first, as a water cement, is of inferior utility, and very little better than common mortar dried before the admission of water upon it. 1860. Grout, or liquid mortar, is nothing more than common mortar mixed with a sufficient quantity of water to make it fluid enough to penetrate the interstices and irregularities of the interior of brick walls, which common mortar will not reach. The mortar whereof it is made will bear 4 of sand to 1 of lime, but it should be thoroughly beaten. It may be kept a little longer, whereby its quick setting will be facilitated. 1861. CONCRETE is a compound of ballast, or stone chippings, and lime mixed together. It is so called from the speedy concretion that takes place between these particles. If, however, gallots or small stone chippings are used, sand in a large proportion to the lime must be used. The use of concrete was well known at an early period; it is mentioned by De Lorme in his work published in 1568; and it is by no means, therefore, a discovery of modern days. Wherever the soil is soft, and unequal for the reception of the foundations of a building, the introduction of concrete under them is an almost infallible remedy against settlement. The Thames ballast, commonly used for concrete, is a mixture of sand and small stones. With this, and lime in the proportion of never less than 4 to 1, and never properly exceeding 9 to 1, of stone lime, or such as is known to set hard in water, a mixture is made. The lime is generally used in powder, and the whole being shovelled together, it is wheeled in barrows to a stage over the spot where it is to be used, and let fall into the trench dug out for the reception of the foundation. The greater the height the concrete is made to fall, the sounder and stronger it becomes. It must always be recollected that no more lime is necessary than with the thinnest coat to surround the particles of the ballast, and that therefore the size of the pebbles or stones should influence the quantity of the lime. As the ground is more or less to be trusted, the thickness of the concrete must be regulated; when used on the best ground, a foot in thickness will be sufficient; while on the worst, as many as four feet or more may be required. The upper surface being levelled, it is usual to lay on it a tier of Yorkshire stone landings, for the reception of the brick-work or mason's work in some cases, after carrying the wall a certain height, a second tier of landings has been introduced. When the soil is watery, no water should be put to the concrete, but the ballast and lime merely mixed and tumbled in. The usual practice of making concrete as above stated, is objected to by many practitioners, who recommend that the French method of making béton should be followed in lieu of it. 1862. In forming concrete, the stones or pebbles used should never exceed the size of a hen's egg, of which 2 parts may be combined with part of the smaller substances used; this makes it about equal to Thames ballast. It has been calculated, that as the lime absorbs the water, and with the sand fills up the interstices of the larger material, if the proportion of the lime be about one eighth of the ballast, then 33 cubic feet of ground lime, and 30 cubic feet of ballast, with a sufficient quantity of water to effect the admixture (and this is generally rather less than a gallon to a cubic foot of ballast, or than equal measures of water and lime), will be required to make 27 cubic feet of concrete; that is, there is a loss of bulk equal to all the lime, and of about 10 per cent. of the ballast. But some experi ments made in 1857-8, in which the present editor assisted, showed that the same measure olue lias, which wears lling, consists of 1 part : les for the formation of gox sand, produced a cemet 2 rutility, and very little less in mortar mixed with a si uld be thoroughly besta. › to the gs, and lime mixed taget on. omes. It must always be st coat to surround the p ire stone landings for the n the soil is watery, no y mixed and tumbleda. ed to by many practi uld be followed in liew uld never exceed the size s been calculated, that s which gave a cubic yard of ballast, held precisely the same ballast with the addition of one sixth in bulk of ground stone lime made with it into concrete, besides about fourteen pails of water; and likewise tended to disprove the assertion that concrete swells in setting. This cubic yard of concrete weighed 27 cwt. In estimating, allowance must be made for the loss of material. 1862a. Expansion taking place in concrete made of unground lime, during its slaking, has been taken advantage of by G. L. Taylor in the underpinning of some walls at Chatham, as detailed in the Transactions of the Institute of British Architects, 1835. This expansion has been found to average about of an inch for each foot in height, and the size thus gained the concrete never loses. Care must be taken when using it for floors and for the spandril of arches, to allow sufficient space, and to lay it in such a way that this increase may take place without thrusting out the walls, as has occasionally happened. In old malt houses in the West of England, with concrete floors 5 to 6 inches thick, stone walls 2 feet 6 inches to 3 feet thick have bulged out 3 or 4 inches on each side by the expansion of the concrete, as also noticed in the Transactions of the above named society, 1854, p. 74. When ground lime is used the assertion that concrete swells is very questionable, as stated in the previous paragraph. 18626. For water works required to set rapidly, an excellent concrete may be made by a mixture, the proportions of which were found by Treussart as follows:-30 parts of hydraulic lime, very energetic, measured in bulk, and before being slaked; 30 parts of terras of Andernach; 30 parts of sand; 20 parts of gravel; and 40 parts of broken stone, a hard limestone. These proportions diminish one fifth in volume after manipulation; the mortar is made first. When the Italian puzzuolana is used, the proportions should be 33 parts of lime, as before; 45 parts of puzzuolana; 22 parts of sand; and 60 parts of broken stone and gravel. The first of these concretes should be employed immediately it is made; the second requires to be exposed about twelve hours before it is put in place. When burnt clay or pounded bricks are used, 30 parts will suffice, but this mortar must not be used in sea water. If only rich, instead of hydraulic, limes be used, the quantity of the natural or artificial puzzuolanas must be increased, and that of the stones and gravel be decreased. (Burnell, Limes, &c.) 1862c. After many experiments M. Kuhlmann recommends a cement composed of 30 parts of rich lime, 50 of sand, 15 of uncalcined clay, and 5 of powdered silicate of potash, as having all the requisite hydraulic properties, especially for cisterns intended for spring water. In marine constructions care should be taken to add an excess of silicate to those portions of cement which are exposed to the immediate contact of the sea. 1862d. The object to be aimed at in making hydraulic concrete, is to give such a sufficiency of mortar as will produce the aggregation of the whole mass of rough rubble materials. In Portland cement concrete for instance, the proportions for the mortar may be 1 of cement to 3 of sand, and this mortar may then be mixed with 6 parts of ballast or shingle. In blue lias lime concrete, the proportions may be 1 of unground lime to 2 or 2 of sand, and this mortar may be mixed with 3 or 4 parts of ballast; and it must be understood in all cases that the mortar must be made first, and that it then should be thoroughly incorporated with the ballast or shingle. This concrete as used at the recent extension of the London Docks by Mr. Rendel, consisted of 1 part of blue lias lime with 6 parts of gravel and sand. The proportions for the blocks of the mole at Marseilles, were 3 parts of Theil lime to 5 parts of sand mixed up into mortar, and then added to 2 parts of broken stone. 1862e. Béton, or concrete, as made in France, is invariably composed as follows:-I. The mixture of lime and sand, either by hand or by a pug-mill, as for ordinary mortar. Great importance is attached to the choice of the lime and to the mode of slaking it; and if a sufficiently good one cannot be obtained, artificial puzzuolanas are introduced. The mode of slaking is prescribed in the specification according to the nature of the lime, instead of being left to the choice of the workmen. II. The mortar so prepared is then well mixed by rakes with broken stones or ballast in such proportions as shall ensure its filling up the intervals between them; the volume having been ascertained by immersing the stones in a known quantity of water. These spaces are equal to about 0:38 to 0.46 of the cubical contents of the vessel; but in practice, about one fourth more mortar is added than necessary to ensure solidification of the mass, especially when the béton is intended to resist water pressure. III. The material is then wheeled to its situation and rammed down carefully until the mortar begins to work up to the surface. 1862f. In an English patent, 1859, No. 2757, M. Coignet, of Paris, argues that the tenacity of mortar is not produced as hitherto supposed by the formation of silicate of lime and alumina, but by the crystallisation of lime. His concrete, called Béton Aggloméré, consists of about 180 parts of sand, 44 of lime produced by slaking, 33 of Portland cement, and 20 of water, combined by a process of two main operations: I. A complete consolidation of the materials with little water; and II., the steady but not violent compression of the consolidation in moulds. The cement is mixed with the sand and lime, and sprinkled whilst mixing with a little water. This mixture is thrown into a machine, formed like an endless screw enclosed in a cylinder, at the rate of two shovelfuls followed by about a quart of water, until the cylinder is full. The screw, turned by two men, delivers the mixture through a series of holes in the bottom of the cylinder; but on a large scale, a machine is used of 10 to 15 horse power. This mixture, after its delivery from the machine, is put by degrees into moulds, and each layer is rammed in by workmen. In reply to questions put to the inventor by the Committee of the Institute already mentioned, he stated that chalk lime was not sufficiently hydraulic for the purpose: that ground lime as delivered had always core in it, and therefore had to be slaked with one fifth of its bulk of water for forty-eight hours before employment; such mixture was equal in effect to two of common ground lime: that when very hard mortar was required it was necessary to use less water and more sand than usually adopted that water evaporated from mortar as usually made, leaves it full of minute holes, and that the more water, the less is the crystallisation that in the proportions above given, if cement be used as a twentieth part, it requires to be twice passed through the large machine, but if used as a thirtieth part, only once that he found by experience that the purer the lime the quicker was the crystallisation; and that, although pure hydrate of lime will take carbonic acid, silicate of lime and alumina will not take it, because silicic acid took the place which carbonic acid did with the pure lime; and frankly admitted that his first experiments in 1855, in marine works, had not entirely succeeded, but claimed perfect success for those at Marseilles since 1859, and for those now (1864) executing in Paris and elsewhere. 1862g. The resistance of béton and concrete should never be regarded as being superior to those given for limes, if the superstructure be commenced upon them immediately. In both cases the resistances are found to increase with comparative rapidity during the first six or seven months. That 1863. Among the CEMENTS used in England, Parker's, also called Roman cement (1796), is manufactured principally from stone found in the Isle of Sheppey, and at Harwich, being septaria from the London clay, and properly classed among the limestones indigenous to this country. It consists of ovate or flattish masses of argillaceous limestone arranged in nearly horizontal layers, chiefly found imbedded in the clay. The substance being coated with a calcareous spar or sulphate of barytes, forms the basis of the cement. now in use we do not think at all equal to the material originally employed. About 1810-15 it was possible to use it in the depth of winter; which, we apprehend, would be a hazardous thing to do with the cement at present made. Whether the inferiority arises from adulteration, bad manufacture, or the material being worse, we cannot pretend to say; we, however, do not believe that it arises from the badness of the raw material. If this cement be of extremely good quality, 2 parts of sand to 1 of the cement may be used. The cement itself is a fine impalpable powder; yet when wetted it becomes coarse, and, unless mixed with great care, it will not take a good surface. When mixed with the sand and water, it sets very rapidly; it is necessary, therefore, to avoid mixing much at a time, or a portion will be lost. The colour of this cement, when finished, is an unpleasant dark brown, and the surface requires frequent colouring. The great value of Parker's cement is its being impervious to water almost the moment it is used; hence it becomes highly serviceable on the backs of arches under streets, for the lining of cisterns, and for carrying up in it, or coating with it, damp walls on basement stories. It will not resist fire so well; and it should therefore never be employed for setting grates, ovens, coppers, or furnaces. 1864. Atkinson's cement is a good material, preferable in colour to the last named, but, as we think, inferior in quality. It takes a much longer time to set than Parker's cement, than which it absorbs more moisture. It answers well enough in dry situations. Vicat formed a factitious Roman cement; but its efficacy was doubtful, though it had, for want of a better substitute, been much employed at Paris. 1864a. Portland cement, the latest (about 1843) of all these cements, is made from lime. stone and clay. The mud of the river Medway, corresponding to the argillo-calcareous stone of Roman cement, is mixed with chalk and ashes from former makings, and calcined at a heat amounting almost to that of vitrification. A larger quantity of sand may be mixed with it than with Roman cement, to which it is superior in colour and hardness of setting. The heaviest, considered the best in quality, weighs 110lbs. per striked bushel. 18646. The distinguishing peculiarities which should render Portland cement a permanent substitute for Roman cement, have been explained by a London manufacturer of both materials (Builder, 1863, p. 761). It may be condensed into the statement:-That the stone from which Roman cement is made, though composed of lime and the silicate of alumina, yet the proportion of the latter preponderates to such an extent as to prevent a perfect amalgamation of the ingredients in burning. The result is a cement loose in its texture, because containing inert foreign matter, which is retentive of moisture, and consequently attackable by frost and vegetable growth. In Portland cement the case is otherwise. The dose of lime to clay is in the ascertained correct proportion of two to one, and with this condition there is the power thoroughly to combine the ingredients by burning, and thus to give a density and compactness to the product, which in enabling it to resist water, frost, and other decomposing agencies, are the elements of its durability and of its superiority to the natural cements. Carelessness, or want of proper knowledge in its manufacture; an improper mixture of the ingredients; an imperfect calcination; its bad manipulation; and unfair handling when used as a cement, are all likely to result in disastrous effects on being used. When employed as a mortar or as a concrete, it has seldom been known to fail. 1864c. It is usual for the manufacturer to grind the cement after burning it. It is then placed in well-closed casks which should not exceed 6 cwt. each, when the cement may be preserved for some time; but contact with the atmosphere rapidly deteriorates its quality, as it absorbs humidity and carbonic acid from it, and thus becomes useless. It should be ground very fine. For the sieve in sifting it, the French engineers require 185 meshes to the square of 4 inches on a side. One-third of the volume of the cement for the quantity of water is the best proportion, and the more that the cement is beaten up, the harder it becomes. The best cement will harden in about five or six minutes, and under water in about an hour: when mixed with sand it takes a little longer. When mixed with seawater, and used in sea-water with a large quantity of sand, it may take even twenty-four hours before setting. 1864d. The resistance to rupture of pure cement after 20 days' exposure to the air, is about 54 lbs. per inch square; if sand be added in the proportion of to 1 of cement, it falls to 37 lbs.; and if it be in equal proportions, it falls to 27 lbs. The permanent load in any large works should never be inore than one-sixth of that required to produce rupture: and if small materials be employed, only one-fifteenth should be calculated upon. The strength of Portland cement has been tested for drainage works by John Grant, as described at the Institution of Civil Engineers, December 1863, giving it as 500 lbs. upon an area of 14 inches square, equal to 24 square inches. 1865. Hamelin's mastic cement, though patented of late years, is an invention of P. Loriot, a century old; the medium for mixing the pounded brick-dust, limestone and sand, is oil instead of water. It is much more difficult to use than the other cements, and requires great experience and care. A coat of it should never exceed one quarter of an inch in thickness; hence it is totally unfit for working mouldings in the solid. In the metropolis it is generally used in a very thin coat over a rough coat of Roman cement, in which case it is rarely more than an eighth of an inch thick. Thus used, it not only presents a beautiful surface, but is extremely durable, but it requires to be constantly painted to resupply the oil that has evaporated, or been taken up by the atmosphere. 1866. Keene's cement is obtained by soaking plaster in alum water after a first calcination: it is then kiln-burnt a second time and ground. It is in reality only a plaster, and is capable of being worked to a very hard and beautiful surface. Martin's patent fireproof and ornamental cement is a plaster of somewhat similar make, and equally goodlooking. It is manufactured in three qualities, coarse, fine, and superfine. It is said to be used with greater facility by workmen than any other cement yet produced, requiring only about an hour to set, which is less by one-half the time of other cements. It appears to be chiefly prepared at Derby. Parian cement (Keating's patent) is also composed of gypsum, but mixed with borax (borate of soda) in powder, and the mixture calcined and ground. A fine quality produces a hard scagliola imitation of marble. When applied to old brick or plastered work, as in repairs, these cements may be papered, or painted upon, in about 18 to 24 hours after execution. But on new work time must be given for any efflorescence to disengage itself. 1866a. John's patent permanent stucco wash, stucco cement, and stucco paint, were introduced about 1843. As a paint it is cheap, durable, agreeable in colour, and finishes without a gloss. It gives out no deleterious exhalations or odour in drying, and it is stated that as the oil cannot evaporate (?), but is held in intimate and indissoluble union with the other materials, there can be no decay, an objection to which oil mastic is so liable. It requires no driers or turpentine, and is applicable both for outside and inside work. The cement, which is stated not to deteriorate with age, is packed in casks, and requires to be mixed with 3 parts of good, sharp, clean sand to make a stucco, its application for which is the same as for any other stucco. It adheres well to glass, iron, slate and tiles in roofing, wood, old plaster, or Roman cement. When set it is hard, and impervious to wet and damp. One coat of its own paint, which it will take after twenty-four hours, is sufficient. Mouldings may be run in it, and castings made. 18666. A cement which will withstand a moist climate, is stated to be composed of one bushel of lime with 15 gallons of water and half a bushel of fine gravel sand, mixed with 3 lbs. of copperas dissolved in hot water, and kept stirred while being incorporated and in use. Sufficient should be made for the day during which it is to be used, as the colour is not easily matched. 1866c. GYPSUM, better known as Plaster of Paris, is a sulphate of lime. It is found at Alston, in Cumberland; at Shotover Hill, Oxfordshire; at Orston, near Grantham; in Nottinghamshire, in Derbyshire, and in Cheshire; in France, in the neighbourhood of Paris, chiefly at Montmartre; and in the departments of the Saone, Loire, of the Rhone, and of many others; and in Tuscany, Savoy, Spain and Switzerland; in some parts of the British Colonies of North America, wherefrom it is exported principally to the United States. The stone is broken into small blocks, and burnt in a walled space with openings in the tiled roof to let out the steam. After its water of crystallization is driven off, it becomes pulverulent and like flour. On fresh water being added, it combines with the normal quantity of water, and reassumes the form of a hydrate, recovering its original density and strength to a very great degree. A heat of about 200° centigrade is sufficient. The London manufacturers adopt a kind of oven for burning the stone, which prevents the smoke from injuring the plaster. In France it has been proposed to throw a jet of steam heated above 400° Fahr. over the stone, which is broken very much smaller than usual: this jet takes up all the water present, and leaves the plaster in the state of a pure anhydrous sulphate of lime. The plaster obtained from Paris is considered the best of all in quality, probably arising from the fact that the stone is the hardest. Gypsum swells in setting in contradistinction to the cements, which generally shrink. The specific gravity of pure gypsum may be taken at 2-322; and its constituent parts to be sulphuric acid 46, lime 32, and water 21. (See GLOSSARY, S. v.) 1867. The best bituminous cements are obtained from the natural asphalte, which is found in large quantities on the shores of the Dead Sea; in Albania; in Trinidad; at Lobsann, and Bekelbronn, in the department of the Bas Rhin; in the department of the Puy de Dome; at Gaugeac in that of the Landes, &c. The asphalte which is found in inexhaustible quantities at Pyrimont Seyssel, in the Jura Mountains, in the department of the Aire in France, was introduced into England about 1838, under Claridge's patent. The principal ingredient in its composition is a bituminous limestone, of a rich brown colour. After it has been reduced to a fine powder, a certain portion of grit is mixed with it; it is then placed in cauldrons heated by strong fires with a sufficient quantity of mineral tar to prevent the asphalte from calcining. The whole mass is thoroughly incorporated and reduced to a mnastic, in which state it is run into moulds to form blocks, each 1 foot 6 inches square, 6 inches in depth, and weighing 125 lbs. 1867a. The mastic is of three qualities, fine, gritted, and coarse gritted. The first, being without any admixture of grit, is used for magazine floors, and as a cement for making, in special cases, very close joints in brickwork. II. The fine gritted is used for covering terraces, roofs and arches, lining of tanks, and as a cement for brickwork, and for running the joints of stones. III. The coarse gritted is used for paving and flooring, and where great strength of work is desirable, such as gun-shed floors, tun-room floors, and margins of stable floors; while in gateways for heavy carriage traffic, small pieces of granite chippings are introduced. These mastics, and more particularly the first two, being ductile and readily yielding to any change that may take place on the surfaces upon which they are laid, require a proper foundation to be prepared. 18676. When required for use, an iron cauldron having been prepared, 2 lbs. of mineral tar are put in, and then 56 lbs. of asphalte broken into pieces of not more than 1 lb, in weight. These are mixed together until the asphalte becomes soft. After a quarter of an hour the stirring is repeated, and another 56 lbs. of asphalte added, and so on until a proportion of 112 lbs. of asphalte to each 1 lb. of tar, under ordinary circumstances, fills the cauldron and the whole is thoroughly melted. When fit for use the asphalte will emit jets of light smoke, and freely drop from the stirrer. 1867c. It will be well to note that it is stated asphalte never flames, but merely passes into a state of fusion. At the fire at Hamburg in 1842, it was remarked that when asphalted roofs fell in, "the asphalte, in which a sort of rubble is mixed up, was found to have resisted the effects of the heat, and, like a mass of dirt, served rather to smother the flames than to give them increased vitality." A like result is recorded of a fire that took place at the Bazaar Bordelais, at Bordeaux, in 1835; of another in Stangate, London, in 1855; and experiments were made by order of the authorities of the British Museum before this material was allowed to be applied to the snow gutters of the dome of the new Reading Room and other roofs, with a satisfactory result. Notice is not generally taken of the fact that if in works, asphalte or tar be used in places where it may be affected by heat, a smell arises which is very prejudicial to the comfort of the occupiers of the building. 1867d. The term asphalte has also been given to several compositions formed by the admixture of chalk, lime, gas tar, and other substances for cheapness. The coal tars, and vegetable pitch, although not so good as the bitumens, are fairly good substitutes in many cases, as in coating vaults, or walls exposed to the dampness of earth. The proportions in which to mix powdered calcareous stone must be regulated by practice, as also the heat, that the stone be not converted into quicklime, perhaps from 6 to 7 of the pitch in volume to 1 of limestone will suffice; and it is recommended to use these in greater thickness than the asphalte, being about half an inch for the latter material. |