CHAPTER XIII Tue MATERIALS Usep IN SANITARY WoRK (Part 1)

CHAPTER XIII Tue MATERIALS Usep IN SANITARY WoRK Under this heading it is proposed to give short descriptions of the composition, properties, and manufacture of the principal materials used in the various branches of sanitary work. Bricks. The principal use of bricks, from our present point of view, is for the construction of manholes and sewers, and for these items bricks should fulfil the following conditions: 1. They should be non-absorbent unless protected by a non- absorbent facing, such as cement rendering. 2. They should be well baked throughout. 3. They should be uniform in size, shape, and texture. 4, They should have sharp arrises or edges. 5. They should be free from flaws, stones and lumps of lime, the last named being liable to expand and split the brick. 6. They should ring well when two are struck together. 7. They should be strong and require repeated blows before breaking. 8. They should stand handling and cartage well without injury Brick Earth. Bricks are blocks of clayey earth, baked or burned. Their quality depends on (1) the chemical composition of the earth used; (2) the amount of preparation it has undergone; and (8) the temperature at which burned, and the care with which the burning is carried on. A good brick earth is generally composed of silica and alumina, together with a small quantity of lime or iron, or both, which act as a flux to fuse the particles together, giving silicate of alumina. Small percentages of other substances are also contained, such as magnesia, potash, soda and manganese, which give the colour to the brick. The colour is also dependent on the temperature at which burned; for example, the well-known Staffordshire blue brick owes its colour to a fairly large proportion of oxide of iron, which is, by a high temperature, converted from the red oxide to the black. A small proportion of iron, and a moderate tempera- ture, give a brick of from an orange to a deep red colour, while bricks free from iron burn white. Magnesia gives a yellow colour. , THE MATERIALS USED IN SANITARY WORK 417 Brickmaking. Brickmaking processes may be divided into four heads: (1) the preparation of the earth; (2) moulding; (3) drying; and (4) burning. In the preparation of the earth the clay is first exposed by un- soiling or removing the earth above it, then dug, freed from stones, ground in some cases, and tempered, which consists practically of kneading. Hand and Machine Moulding. The brick may be moulded by hand or by machine. Those used in sanitary work are usually machine made. Machine moulding can be carried out in three ways: 1. By forcing the clay through an opening in the form of a plastic band, cutting off the bricks by means of descending wires, which of course give a brick without a frog. The marks of the wires can always be seen on a wire-cut brick. 2. By moulding the brick from powdered clay under great pres- sure, such bricks having usually a frog; and 3. By moulding the bricks in the ordinary way and then subject- ing them to compression under a piston. Pressed bricks of the last two classes have very true surfaces and hard edges. Before the bricks are ready for burning they must be dried, which can be done either indoors or out. Burning. The burning can be accomplished in two ways, either in a clamp or in a kiln. The clamp consists of a stack of raw bricks built up over a rough system of flues formed by bricks already burned, on a properly drained floor covered with burned bricks. The quality of the bricks is often very uneven. Brick Kilns. Kilns are of two principal kinds, the intermittent and the continuous. ‘The former is known as the Scotch kiln, and consists of a low, rectangular, roofless building, with a wide doorway at each end, and fire holes along each side. Flues are formed with bricks from side to side, the kiln is loaded, and the doorways bricked up. The whole charge of bricks is then burned, allowed to cool, and then the kiln is emptied. The best-known example of the continuous kiln is the Hoffmann, of which there are many forms, differing only in detail. They are chamber kilns, circular, oval or rectangular on plan, having chambers which are separated by removable doors. In some chambers the bricks are being placed, in some they are drying, some burning, some cooling, and some being unloaded. This system is now in use in all the large brickyards, and gives a regular supply independent of weather, the kiln being roofed. 14—D.s. 418 THE MATERIALS USED IN SANITARY WORK Bricks for Sanitary Work. The best bricks for sanitary pur- poses are pressed red bricks, blue Staffordshire bricks, and hard bricks salt-glazed on the exposed faces, like the surface of a drain pipe. The salt glazing is obtained by the vaporisation of common salt in a special kiln, which covers all exposed faces with a thin film of glass. Staffordshire Blues will stand a crushing strain as high as 16,600 lb. per square inch and are almost completely impervious to water. They are therefore eminently suitable for engineering or sanitary work where these qualities are necessary, particularly in underground work in wet or waterlogged soil. Moreover, in a position where the work would be exposed to sand-laden winds or alternate wet and frost they would prove very resistant to abrasion or erosion. Pressed red engineering bricks (such as Accrington Reds) will stand up to a crushing test of 10,300 lb. per sq. inch, but are not quite so impervious to moisture. Brown salt-glazed bricks and white vitreous-glazed bricks where a smooth easily cleansed surface is required such as in sanitary conveniences, or in the case of the latter, where their light reflect- ing qualities will be useful. When the brick carrying the glaze is absorptive and the bricks are used in a position where they are exposed to moisture from the rear (as in facing a retaining wall to keep back waterlogged soil) it may be found in frosty weather that the glaze will craze or flake off, pushed off by ice forming behind the glaze. Useful data is available on the behaviour of clay engineering bricks in B.S, 1801, which specifies Class A engineering bricks to stand a minimum crushing test of 10,000 lb. per square inch and a maximum water absorption (after a 5-hour boiling test) of 4:5 per cent. of their dry weight, while Class B engineering bricks (for less stringent work) should show 7000 lb. per square inch and not exceed 7 per cent. water absorption respectively. Stone. Stone is not largely used in sanitary work, but is useful in the form of slabs for the tops of manholes and similar situations, for which York stone is the best fitted. Terra-cotta. This material is made by burning certain clays and is sometimes used for special invert blocks to egg-shaped sewers; it consists of well-burned clay—generally a mixture of clays. It has a hard vitrified outer skin, which is usually in- destructible by acids and which must not be interfered with, such as by chipping adjoining edges to make them even in surface, as this exposes the softer inside structure of the material. THE MATERIALS USED IN SANITARY WORK 419 Terra-cotta is almost always moulded hollow, with diaphragms or webs connecting the outer walls of the blocks, with a view to reducing the shrinkage, the hollows being then filled with fine concrete. Cement. Cements are of two principal varieties, the natural and the artificial. The former are burned from natural lumps of a clayey or stony nature, and the latter are burned from a mixture of materials. Further, the cements can be divided into those suitable for internal and those for external work. The principal cements for outside or underground work are Portland and Roman, and the principal for inside use are plaster of Paris, Keene’s, Parian, and similar cements. The best and strongest cement is Portland, so called from its supposed resem- blance in colour to Portland stone. It is made from a mixture of chalk and clayey materials. In some parts of the Medway, and on the Thames side, a mixture of chalk and river mud is used, the mixture being regulated so that the finished product shall have about 60 to 65 per cent. of lime, 20 per cent. silica, 10 per cent. alumina, and a small amount of other constituents. Manufacture of Portland Cement. The measured proportions of chalk and clay are thoroughly combined by passing them through a set of three wash mills, forming what is termed slurry; it is then passed through very fine screens. The slurry is then elevated, by pumping, to storage and mixing tanks, in which it is kept in motion by mechanical stirrers. Here the mixture is sampled and chemically tested to see if it is of the desired composi- tion and, if all is in order, it is conveyed or conducted to a special form of rotary kiln, to be dried and burned. The kiln is about 6 feet in diameter and 130 feet long. It is fixed with its length inclined to the horizontal. The slurry enters at the upper end, and is dried by the rising hot gases, probably in about the first sixth or seventh of the length of the kiln, and issues at the lower end in a stream of fine clinker. A temperature of about 2800° F, is kept up at the lower end of the kiln, the flames being fed by ulverised coal injected by an air or steam blast. The clinker falls into coolers, and is afterwards taken to the mill for grinding. This mill is of cylindrical form, lined with plates lapping one over the other like roof tiles, and contains a number of hard steel balls The rotation of the cylinder reduces the clinker to a fine powder, when it passes through perforations in the mill and is ready for further grinding. This is effected in another cylindrical mill con- taining specially hard pebbles, and known as a tube mill. This grinds the cement to such a degree of fineness as will allow over 90 420 THE MATERIALS USED IN SANITARY WORK per cent. of it to pass through a sieve having 28,900 holes to the square inch. To make the cement ready for immediate use, a special apparatus is attached to the end of the tube mill, which subjects the cement to a charge of super-heated steam at great pressure, this method superseding the old-fashioned method of spreading the cement over a wooden floor for a month or so to aerate it. Portland cement for sanitary work should be of the very best uality. : British Standard Portland Cement. The best way to ensure that Portland cement is satisfactory is to state, in the specification, that the Portland cement shall comply in all respects with the require- ments of the latest specification of the British Standards Institu- tion (B.S. No. 12), adding the qualification “‘normal” or “ quick- setting” as the case may require. This standard specification has been revised from time to time; it is somewhat technical in character, so that it is unnecessary to include it in a volume of this nature. Chief Qualities of B.S. Portland Cement. It will be sufficient, in this general treatise, to say that the specification prescribes tests for fineness, chemical composition, strength, setting time and soundness. It should, however, be mentioned here that the specification recognises two classes of cement, viz., “‘normal” setting and “quick” setting. The former will be cement which does not begin to set for thirty minutes after mixing with water, and in which setting is complete in something under ten hours; the latter will be cement which does not begin to set within five minutes of mixing and will complete setting in something less than thirty minutes. In any specification for sanitary or building work it should be stated which of these classes of cement is to be used; normal setting should always be specified unless there is some very special reason for requiring a quick-setting variety, as where it is difficult to keep subsoil water from the work for more than a very short period. Rapid-hardening Cement. Of late years efforts have been made to produce cements which, whilst not beginning to set any more quickly, will harden more rapidly once setting has started. To understand the action it must be realised that the setting of cement depends on the combination of the lime with the alumina and with the silica in the presence of water, and that it combines with the alumina much more rapidly than it does with the silica. Accelera- tion of the hardening can be obtained by finer grinding of the cement, so that the particles of lime may be in more intimate THE MATERIALS USED IN SANITARY WORK 421 contact with those of the other materials; also by increasing the proportion of alumina very greatly, and, of course, diminishing the proportions of lime and of silica. The rapid-hardening cements produced by fine grinding are known as “‘Ferrocretes”’ and it is claimed for them that in three days they will have the same strength that ordinary Portland cement has in twenty-eight days. High-alumina Cements. The high-alumina cements are vari- ously known as “‘Ciment Fondu’”’, “ Bauxite Cement”, and “ Alu- minous Cement’’; for them it is claimed that in one day they will have twice the strength that ordinary Portland cement has in twenty-eight days. The B.S. is 915. The cost of Ferrocrete is about 15 per cent. greater than that of Portland cement and that of Ciment Fondu 100 per cent. greater. The use of the latter is on this account likely to be confined to cases where considerable economies can be effected by the early removal of timber shuttering, the quick filling in of trenches, and diminution of a period of pumping. Blast-furnace Cement (B.S. 146). This is a comparatively new addition to the list of cements available. It utilises slag from blast furnaces in which limestone has played its part in the treatment of the iron. It may be obtained more cheaply than ordinary Port- land cement—especially in blast-furnace areas. It is also more resistant to acid attack than Portland. Use of Neat Cement versus Sand and Cement. Cement should not be used neat except as a cement wash or to make a joint required to be very smooth finish, such as the outlet of a W.C, pan to a soil-pipe or drain socket, as neat cement is more likely to expand or shrink on setting than a mortar made of 1 part of cement to 1 or 2 parts of sand. By-laws sometimes compel the use of neat cement for drain or sewer jointing, with the idea that it will make the joint stronger and more watertight. Not only is it a needless extravagance, but, should the cement contract on setting, the cement will become loose in the sockets, in which case leakage must result. An ad- mixture of at least an equal quantity of sand with the cement will revent this and will at the same time reduce the cost of the work. The B.S. Code of Practice on Building Drainage favours the ratio of equal parts sand and cement. Roman Cement. Roman cement is burned from calcareous nodules found in the London clay. It is used to a limited extent, its rapid-setting properties fitting it for work between tides or similar cases, but it has no great ultimate strength. It is said 4.22 THE MATERIALS USED IN SANITARY WORK that even before setting it resists water, and the tendency to being washed away, better than other cements. Keene’s, Parian and Similar Cements. Keene’s, Parian and similar cements are suitable only for such purposes as wall linings for inside work, since they contain a large amount of gypsum, which is soluble in water. Both are manufactured from plaster of Paris, Keene’s by the addition of alum, and the Parian by the addition of borax. They are very suitable for filling in cracks, because they expand in setting. Sand. There are three sources from which this is obtained— from sand pits, river beds and the seashore. Pit sand is often angular, sharp and gritty, and on this account has generally been preferred, for making mortar or concrete, to river sand, the grains of which are usually rounded and smoother. Of late years careful experiments seem to have shown that angular grains are not superior to round grains; whether this is the case or not, the point is of small importance compared with that of obtaining a material which is free from any admixture of clay, loam, earthy or organic matter. Sea Sand. Sea sand contains a large amount of salt, with the result that mortar and concrete containing it hold damp and effloresce. It should not, therefore, be used in mortar for brick- work above ground, or for any other purpose where dampness or efflorescence would be a disadvantage. For other purposes there appears to be no valid objection to its use. Substitutes for Sand. When sand is not available crushed stone may be substituted, or even crushed furnace ashes, or blast- furnace slag. Such materials, however, should not be crushed too small, and with some stones—notably granite—it is difficult to avoid crushing it to fine dust, which results in a weak concrete. If any furnace residue is used there must be no trace of coal dust, as unburnt coal expands when wet and, if present in mortar or concrete, will cause it to crumble. Slag is a material which varies very much in quality and should not be used on important work without expert advice. Mortar. For sanitary work, cement mortar is almost always used, composed of Portland cement and sand. It should be mixed dry, the ingredients being carefully