Concrete on the Farm

New Zealand Journal of Agriculture, Volume 62, Issue 2, 15 February 1941, Page 85

Concrete on the Farm

=■■■ 1■ 11■ 11111 By

J. A. S. MILLER,

= Instructor in Agriculture, 1 = Wellington. i 71111111111 iiiiiiiiii min in in iiiiini m ii ii unit nun mi mi laim i*.

Full Description Of

How To Use Concrete

For Varied Purposes

concrete has been used A for hundreds of years as a building material, its application to farming is of comparatively .recent origin, and each day we find a new use for this very durable and efficient substance. Its use in the construction of 'floors, tanks, silos, troughs, fence-posts, paths, buildings, pipes, field drains, etc., is well recognised and there are few farmers who have not at some time laid down a path or constructed a trough from concrete. The advantages of concrete lie in the fact that it is relatively cheap to use, easy to prepare, and, once placed, is there for years. Types of Concrete There are two main types of concrete, namely, plain concrete and reinforced or ferro-concrete. Although plain concrete will resist a considerable crushing forcethat is, 600 to 750 lb. per square inch safe load —it will not withstand a bending force of any great dimensions. For instance, unreinforced concrete beams would break because of their own weight with no loading. To overcome this difficulty, concrete requires to be reinforced, and steel, having a tensile strength of about 18,000 lb. per square inch, is ideal for this purpose. A combination of the two, concrete and steel, results in a body of considerable strength, but the steel must be placed in a position where it will take the appropriate strain. Indiscriminate reinforcing is useless. Main Ingredients Concrete consists of three main ingredients, namely:— (1) Cement. (2) Aggregate. (3) Water. CEMENT. There are three varieties of portland cement used in New Zealand, and all

three are put up in bags of 124| lb. net, that is, 18 bags to the ton. (a) Normal Portland Cement. — This is the usual type and is familiar to all. (b) Rapid Hardening Portland Cement, “Rapid hardening” must be taken literally, not to mean “rapid setting.” It takes as long to set as the ordinary variety but, once set, hardens much more rapidly. In a similar mix it is as strong in one week as normal cement would be in four weeks. (c) Water-Proofed Portland Cement. —This cement contains a waterproofing agent which renders it invaluable for cellars, damp-proof walls, etc. Its mixing proportions are the same as for ordinary cement, but it requires slightly longer to set. It has

also the property of being little affected by “air setting” while in storage. All three of the above cements can be mixed at random, that, is, they will blend without any disturbing chemical reaction. Kinds of Aggregate Aggregate. This forms the bulk of the concrete, and is divided into the two main heads:' (a) Coarse Aggregate. . - ■ (b) Fine Aggregate. Coarse aggregate generally consists of gravel ranging in size from | in. to 3 in. or more, depending on the nature of the work. For walls and similar structures, the ratio of the size of the stones to the thickness of the material can be considered as 1 to 5, that is, for a 5 in. wall the maximum diameter of the stones should not excede 1 in. In plain concrete work such as floors and yards the ratio may be 1 to 3, that is, a 6 in. floor may contain stones up to 2 in. diameter. In mass concrete work it is not generally economical to try to mix in stones of a greater diameter than 3 in. because of the difficulty of working with shovel or mixer. Sometimes in bulky work where it is desired to save concrete, massive stones or “plums” are

inserted in newly laid concrete, but these must not be closer together than 2 in., otherwise the strength of the material may be impaired. Fine aggregate consists of fine, clean sand, and this is required to fill up the spaces between the stones of the coarse aggregate. Water.— Water used in mixing concrete should be of a standard such as that required for livestock. Where fresh water is unavailable, sea water may be used, . but the resulting concrete often shows an efflorescence, and has a “mouldy” appearance. ■ ■ ■ • ■V. Amount of Water Proportions. lt has been shown that the amount of water used to a given quantity of cement has a direct bearing on the strength of the resulting material, provided, of course, that the consistency of the mix is the same in both cases, that is to say, 1 bag of cement mixed with 6 gallons of water would produce a mix which would be twice as strong as one prepared from 1 bag of cement to 10 gallons of water. It will be understood, of course, that the 6 gallon mixture will not produce as much concrete as the 10 gallon mixture. For ordinary good concrete such as that required in the construction of paths, : cow-yards, floors, and walls, satisfactory results may be obtained by using about 8 gallons of mixing water to each bag of portland cement (124| lb. net) and then mixing in as much of the aggregate as is required for good consistency. With average f in. aggregate, . the above will generally yield about 7 cubic feet of set concrete for each bag of cement used. Extra Strong Concrete - For extra strong concrete, such as that required for hard-wearing floors, tanks, troughs, etc., or resistance to milk acid attack, a mix of not more than 6 gallons of water to each bag of cement should be used. In this case only about 5 cubic feet of set concrete will be obtained by using f inch aggregate. These proportions are the limits to which it will be found necessary to go in constructing any type of article such as is likely to be used in farming practices. Fence posts are satisfactorily made from a mix containing 7 gallons of water to each bag of cement.

The size of the aggregate used will depend on the concrete work on hand, or on the size available. This table holds good only in cases where “pure” materials are used. The gravel, for instance, is considered to be free from sand. However, in most cases the gravel will be found to contain a certain amount of sand, and the table will have to be adjusted accordingly. This is done by trying out a sample of the proposed mix.

Suppose we have an aggregate of f in. average size which we ...require to make into ordinary good concrete, a glance at the table shows that we require 7| cubic feet of gravel and 4 cubic feet of sand to each bag of cement. On mixing together (without the cement) they should give a total volume of 8 cubic feet. If the result gives a return of more or less than 8 cubic feet, the amount of sand must be adjusted accordingly.

Means of Measurement Of course it is not necessary to use the cubic foot as a measurement of volume. A tin of, say, one gallon capacity, would be satisfactory, that is, we, could mix 7| tins of gravel with 4 of sand and we should get 8 tins of mixture. The materials used must be moist and ■ should not be compressed into the tins, but put in loosely. . If, on mixing, it is found that the concrete is too stiff to work after the addition of all the water, the amount of water must not be increased —rather the amount of aggregate be reduced, and vice versa, if the concrete is too sloppy, increase the amount of aggregate. Mixing A good firm surface such as that obtained by using a wooden platform or a concrete floor is required for hand mixing. Tongued and grooved Oregon is generally used, and a size of about 8 ft. by 6 ft. is required for a one bag mix.

The coarse aggregate should be spread over the platform or floor to a depth of about six inches, the sand spread evenly over this and the cement over the whole surface. The heap should be turned over twice dry, and three times while wetting. The measured quantity of water is usually applied through an ordinary watering can fitted with a rose. There should be no patches of dry material left after the mixing. When a mixer is used, the water should be poured into the drum to be followed by half the aggregate, the cement, and then the remainder of the aggregate—all this while the drum is revolving. About two minutes are required to complete the process, but this is the minimum, and more time should be given, if possible, as the longer the concrete is kept mixing the finer will be the resulting material. For larger mixers filled with a hoist, the aggregate is generally placed at the bottom of the hopper to be followed by the cement and then the sand, the whole

being deposited in the drum which already contains the mixing water. Placing In placing concrete for floors and yards, all that is necessary is to ensure that the material is well compacted. It is generally beaten down with a heavy wooden straight edge, and then smoothed off with a wooden float. The final touch is given when the concrete is losing its glossy appearance (about two hours after placing). For a smooth surface, a steel float is used, and for a rough surface a wooden float, or even a stiff broom is used where a really rough surface is required, as in the case of sloping paths, etc. Concrete in moulds, as for example those used in the construction of walls, requires compacting in the same manner. As reinforcing will be used in practically every case, a large faced tool or rammer is useless, and a steel rod of 3-8 in. diameter is used. This tool should have a rounded end. Another means of attaining a compacting

of the material is that derived from tapping the outside of the boxing with a hammer, but this should be supplementary to the actual' ramming. Curing Although concrete may appear hard and “set” after a day or so, in actual fact it may take some months to become properly matured.’ Drying-out of the concrete in an effort to hasten the process is quite a mistake, as concrete actually requires moisture in order to complete the chemical reaction necessary to produce the final substance. This is why it is necessary to protect newly placed concrete from excessive drying-out. Paths and floors should be covered with damp bags for at least seven days with ordinary cement—the longer the period, the better for the concrete. / In walls, the boxing has the effect of protecting the concrete from excessive drying, and should be left on as long as practicable. Warmth also is necessary in the curing of concrete, and the best concrete may be prepared when the temperature of all the ingredients approximates 70 degrees Fahrenheit. Under winter conditions, concrete may take twice as long to mature, and actual freezing of the material in its early stages will entirely ruin it. As most farmers find time to do their concreting work only during the winter months, they frequently run the risk of having their efforts rendered useless as a result of adverse weather conditions, such as a series of frosts. This difficulty may be overcome to a certain extent by ’ heating the mixing water and using it hot — boiling. Even moderate warming would be of great assistance, as concrete develops a slight temperature rise after placing which will be maintained provided the material is protected from excessive cold. Straw can be used to considerable advantage in this connection. There is one useful substance which is of considerable value in hastening the setting of concrete in providing a certain amount of warmth. This is a chemical compound known as calcium

chloride, and is not unlike washing soda in appearance. It is comparatively cheap, and not more than 2,1-3 lb. are required for each bag of cement, also it does not injure either the concrete or the steel. To use it, a stock solution consisting of 4 2-3 lb. to the gallon of water is made, and half a gallon of this is used as part of the mixing water for every bag of cement used. In very cold weather it may be warmed. It is also used in warm weather to hasten the setting of such articles as fence posts, the moulds of which may be required urgently for other work. However, once out of the moulds, the posts should be given the same treatment as regards retaining the moisture as pertains in cases where calcium chloride is not used as an accellerant. Vibrating Vibrating the mould in which concrete is being placed is a new development in the science of manufacture. The idea is that vibration at a fairly high frequency results in a much more even packing of the material. It' also enables a mix of stiffer consistency to be used. . The method involved is that of coupling the mould— example, a gang post mouldto a vibrating medium, such as a stationary oil engine, or to an eccentric of small-throw attached, to a shaft revolving at high speed. While this system is highly desirable, it may not always be practicable

on a small scale where only a few fence posts are being prepared. However, on farms where there is some live machinery, such as a tractor, there are means ■ by which the vibration of such a machine may be directed towards the. reciprocation of the mould, which must be mounted in such a way as to allow free movement.. Several examples of concrete work as applied to the farm are now given. While most farmers have their own ideas of going about the work, the details set out are the result of the experience of men who have specialised in concrete construction. Hence, they arrived at the most economical means of doing the work. Concrete Paths Concrete paths are about the simplest of all concrete works, and are usually the first concreting job to be done by amateurs. There are no, special tools required in this worka good eye is the main thing. Cord lines are used to indicate the direction and to maintain the correct width of the path. Turf and soil are dug out between the lines until a firm foundation is reached. This should be even in depth for its full length, and any necessary levelling should be accomplished by the judicious use of sand or fine gravel, which is also necessary to prevent the concrete from binding to the soil.. Side forms constructed from battens and nailed to pegs driven into the side of the track are necessary to confine the material. At this stage shrinkage definers are introduced at approximately 6 ft. intervals to localise the shrinkage cracks which appear when the concrete has matured. These usually consist of 2j in. by 3-8 in. laths secured transversely to the side forms at a depth of j in. below their surface. The concreting is carried right over them.

The concrete mix used should be stiff enough to be beaten flush of the side forms with a timber straight edge of. 4 in. by 3 in. This beating should be sufficient to knock down any protruding stones and to work up a fine surface. When the water glaze is disappearing from the surface the straight edge is again applied to give a rough finish, after which the edges should be bevelled along the side forms. Later on, cover with wet bags, wet straw, or other suitable material and leave covered for about a week. The mix for this work should consist of 4 cubic feet of sand measured wet and loose, cubic feet of 1 in. graded gravel or crushed rock, 1 bag of cement and 8 gallons of water. This will cover approximately 30 square feet. . The cost, exclusive of timber and labour, works out at about 3s a square yard for 3 in. concrete. Concrete Floors Concrete floors are constructed in the same way as paths. If small, they may be put down in one piece, but for larger areas, shrinkage definers at 6 ft. intervals (both ways) should be provided. In cow yards or stables the concrete should be given a slope of J in. to the foot to facilitate drainage. The most desirable way in which to lay large areas of concrete, as in floors, is to do so in strips 6 ft. wide defined laterally by side forms and transversely by shrinkage definers. The scheme is to fill in alternate strips between the side forms and then to fill in the remaining areas when the first portion has set

sufficiently to allow tramping. The side forms are, of course, removed before the work is started.

The following table gives an indication of the strength of the concrete required for typical paths and floors:

An estimate of the area covered by a cubic yard of concrete when the proposed) thickness is known is given below: Thickness of concrete in inches 2 | 3 | 4 | 6 | 8 | 9 |l2 Area covered in sq. feet 162|108|81|54|40||36!|27 I A final point in laying paths and floors— finish off the section on which work is being done—that is, fill up to the nearest shrinkage definer if it is impossible to finish the whole job at one time. New concrete does not bond well with older mixes. If there is any prepared concrete left over, use it for foundations or for filling in a depression rather than append it to the finished section, and then continue laying from it the next day. (To be continued)

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Quantities to mix with one bag cement and 8 gallons water. OR If material Sand and Gravel graded in if already mixed, to loose f used is size up Quantities to mix with one bag cement and 8 gallons water. OB Sand and Gravel if already mixed, loose measurement. Amount of concrete to be expected (approximately) graded in to Sand, moist, size up Sand, moist, loose measurement. Gravel (or metal), loose measurement. Sand only . 1 4 cubic feet I; — : . . 31 cubic feet gin. 21 cubic feet 4 cubic feet 41 cubic feet 41 cubic . feet Bin. 21 cubic feet . 41 cubic feet 43 cubic feet 43 cubic feet 3in. 21 cubic feet 41 cubic feet 5 cubic feet 5 cubic feet lin. , 21 cubic feet 51 cubic feet 51 cubic feet 51 cubic feet Ilin. 2J cubic feet 5 J cubic feet 53 cubic feet 51 cubic feet 2in. 21 cubic feet 53 cubic feet 5§ cubic feet 53 cubic feet 3in..: . 21 cubic feet 53 cubic feet 6 cubic feet 6 cubic feet

The following tables give the average quantities of sand and gravel to mix with one bag (124 J lb.) of cement for extra strong and ordinary concrete: — EXTRA STRONG AND WATERTIGHT CONCRETE.

Quantities to mix with one bag cement and 6 gallons water. OR If material used isSand and Gravel graded in size upif already mixed, to: loose Quantities to mix with one bag cement and 6 gallons water. OR Sand and Gravel if already mixed, loose . measurement. Amount of concrete to be expected (approximately) graded in to Sand, moist, size up Sand, moist, loose measurement. ' Gravel (or metal), loose measurement. Sand only . . 61 cubic feet “ - «■ ' 42 cubic feet ■■■ . 4f cubic feet gin. .. 4 cubic feet 6 cubic feet . 71 cubic feet 61 cubic feet Jin. 4 cubic feet 6 J cubic feet 7-J cubic feet 6 J . cubic feet tin. . . 4 cubic feet 71 cubic feet 8 cubic feet 7 ’ cubic feet Iin. . . : . .' 4 cubic feet 73 cubic feet 81 cubic feet 71 cubic feet IJin. 4 cubic feet 81 cubic feet 84 cubic feet 72 cubic feet 2in. .... 4 cubic feet 81 cubic feet 82 cubic feet 8 cubic feet 3in. .:. 4 cubic feet 81 cubic feet 9 cubic feet 81 cubic feet

Class of Work. Thickness in inches. Quality of Concrete. Size of gravel in inches. Light footpaths, dairy and light shed floors 3-4 Ordinary good concrete (see table) 1 or less Cow yards, heavy shed floors, garage floors 4-6 Ordinary good concrete 11= or Jess > ■ 'p-';', IS or less Floors, drives, etc., for heavy duty 4-6 Extra strong concrete 1 J or less