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diff --git a/59379-0.txt b/59379-0.txt new file mode 100644 index 0000000..af42074 --- /dev/null +++ b/59379-0.txt @@ -0,0 +1,1311 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 59379 *** + + + + + + + + + + + + +Transcriber Notes + +Text emphasis is denoted as _Italics_ and =Bold=. Whole numbers and +fractional parts denoted as: 33-3/4. + + + + U. S. DEPARTMENT OF + AGRICULTURE + + FARMERS' BULLETIN No. 1279 + + + + PLAIN + + CONCRETE + + for + + FARM USE + + +The successful and economical use of concrete involves the selection +of suitable materials, the correct proportioning of mixtures in the +development of qualities to meet specific requirements, the proper +placing and the care of the green concrete. + +A concrete of great strength is uneconomical if a weaker mixture will +serve and a cheap or weak concrete is costly if it does not fulfill all +requirements. The cost of concrete depends not only upon the price of the +materials and labor but also upon the judicious use of the two. Lack of +foresight in locating the mixing plant, in the design of forms, and in +planning the successive operations may cause unnecessary expense, while +neglect of any one of the precautions which should be observed is likely +to result in unsatisfactory work. + +The bulletin discusses the requirements of good concrete and describes +the making and placing of plain concrete according to the best practice. + + +Washington, D. C. + + +Issued October, 1922 + + + + +PLAIN CONCRETE FOR FARM USE. + + +T. A. H. Miller, _Agricultural Engineer, Division of Agricultural +Engineering, Bureau of Public Roads_. + + + + +CONTENTS. + + + Page. + + Introduction 1 + Materials 1 + Proportioning the materials 6 + Quantities of materials required 7 + Consistency 8 + Estimating 9 + Forms 10 + Mixing 13 + Placing 18 + Care of concrete 21 + Protection from freezing weather 21 + Contraction and expansion joints 23 + Lintels 23 + Surface finish 24 + Concrete exposed to fire 25 + Water-tight concrete 26 + + + + +INTRODUCTION. + + +Portland cement concrete is the mass formed by mixing Portland cement, +sand, gravel (or particles of other suitable materials), and water. + +The quality of concrete may be made to conform to certain requirements +which vary with the purpose of the structure in which the material is +to be used; economy, strength, water-tightness, fire resistance, or +resistance to wear and shock may be the chief requisite. The character +of the constituent materials, the proportions in which they are used, +the consistency, the method of mixing, and the placing and curing of the +concrete are important factors in securing the desired qualities of the +finished product. + +Total failure or a product which does not give the service expected +is often the result of the nonobservance of practices recognized as +necessary in the preparation and use of concrete. This bulletin is +intended to assist the inexperienced in making and using concrete +suitable for general farm construction and is confined to a discussion of +the rudiments of plain (not reinforced) concrete work. + + + + +MATERIALS. + + +CEMENT. + +Portland cement is used because it is the only kind adapted to general +construction. Other cements are manufactured but they possess individual +characteristics that restrict their use. The word Portland is not a trade +name, but signifies the kind and distinguishes it from the slag, natural, +and other cements. + +A number of brands of Portland cement are manufactured, most of which +are made to meet the requirements of a fixed standard adopted by the +United States Government and the American Society for Testing Materials. +Cement always should be tested for use in important work, but this is +impractical for the user of small amounts and it is generally safe +practice to omit the test if a reliable brand of Portland cement +of American manufacture is selected, especially if the dealer's or +manufacturer's guaranty that it meets the standard is secured. + +The following simple test for soundness is easily made and is on the side +of caution. Make a ball, about 1-1/2 inches in diameter, if neat cement +and water; place it under a wet cloth and keep it moist for 24 hours, +then put the ball in a vessel of water; allow the water to come to the +boiling point slowly and to boil for 3 hours. A good cement will not be +affected, but an inferior one will check, crack, or go to pieces entirely. + +Portland cement is shipped in paper bags, cloth sacks, and wooden barrels +(sometimes in bulk). For the average user the cloth sack is the best +container, as it is easier to handle; and while the manufacturers charge +more for this kind of package, they allow a rebate for the return of the +sacks in good condition. A sack of Portland cement weighs 94 pounds and a +barrel contains the equivalent of four sacks. + + +STORING. + +As cement readily absorbs moisture from the atmosphere, it should be +stored in a dry place; if exposed to dampness it soon becomes lumpy, or +even a solid mass, and in this condition it is useless and should be +thrown away. The lumps caused by pressure in piling the sacks are not +injurious. They can be pulverized easily, thus distinguishing them from +those due to dampness. + +Cement never should be stored on the ground. Build a raised platform for +it and keep it away from the sides of the shelter. As it is heavy, care +should be taken not to overload the supporting floor. + + +FINE AGGREGATE (SAND). + +All grains, small pebbles, or particles of broken stone are considered as +sand if they will pass through a wire screen with one-fourth inch meshes. +The particles or grains should be hard and well graded and should vary in +size, as a stronger concrete is thus obtained than when the size of the +grains is nearly uniform. If a large proportion of the sand is very fine +an extra quantity of cement should be used and if exceptionally fine it +is advisable to use 25 per cent more cement. + +The sand should be clean; that is, free from vegetable matter, loam, or +any considerable amount of clay. If the hands are soiled when a small +quantity of sand is rubbed between them the following test should be +made: Put 4 inches of sand into a pint preserving jar, fill with clear +water to within an inch of the top, fasten the lid, and shake the jar +vigorously until the whole is thoroughly mixed. Set the jar aside and +allow the contents to settle. The sand will settle to the bottom with the +clay and loam on top of it. If more than three-eighths of an inch of clay +or loam shows, the sand should be rejected or washed. The difference in +fineness and color shows clearly the line of division between the clay or +loam and the sand. + +[Illustration: Fig. 1.--Sand and gravel washing trough.] + +Should sand require washing the simplest way for small quantities is to +build a loose board platform from 10 to 15 feet long, with one end higher +than the other. On the lower end and sides nail 2 by 6 inch boards. +Spread the sand over the platform in a layer 3 or 4 inches thick and +wash with water. The water may be supplied by any means which will cause +agitation of the sand and allow the lighter material to run off with the +water. When pressure or a head is obtainable the water is most easily +applied by means of a garden hose. The washing should be started at the +higher end and the water allowed to run through the sand and over the 2 +by 6 inch piece at the bottom. Figure 1 illustrates a convenient trough +for washing larger quantities. + +A small amount of clay, provided it is not in lumps, does not injure +sand, but amounts over 10 per cent should be washed out. + + +COARSE AGGREGATE (STONE, GRAVEL, ETC.). + +The larger particles used in concrete may be gravel, broken stone, +air-cooled blast-furnace slag, or other suitable materials. The coarse +aggregate should be sound and clean, that is, free from disintegrated or +soft particles, loam, clay, or vegetable matter. Air-cooled blast-furnace +slag should weigh at least 70 pounds per cubic foot. The best results +are obtained from a mixture of sizes graded from those retained on +a one-fourth inch screen to those passing a three-fourths to 2 inch +ring, depending upon the work. Ordinarily the greatest dimension of any +particle should not be over one-fourth of the thickness of the concrete +work. + + +GRAVEL. + +Gravel which is too dirty for use usually can be detected by observation. +It may be washed in the same manner as sand. Lumps of clay should be +eliminated and care should be taken to see that the gravel is not coated +with a film of clay or loam which will prevent the bonding of the cement. + + +BROKEN STONE. + +Broken stone should be clean, hard, and of a size suited to the character +of the work, and the same care in grading should be exercised as in the +case of gravel. Trap, granite, hard limestone, and hard sandstone are +commonly used. The composition and physical character of the stones +should be considered, as some possess qualities that limit their use +under certain conditions (see Substitutes for gravel). + +Field stones are common in many localities and their use, when crushed, +may be economical. The finer particles, after the dust is removed, can be +used as sand. Small stone crushers, operated by three or four horsepower +gasoline engines, can be purchased at a relatively low price and may +prove profitable if a large quantity of stone is needed. + + +BANK-RUN GRAVEL. + +Bank or creek gravel, which will answer the purpose of sand and gravel +combined, sometimes can be obtained, and frequently it is used in small +jobs of concrete work just as it comes from the pit or creek. Although +such gravel occasionally contains nearly the right proportions of sand +and gravel, in the majority of sand pits and gravel banks there is a +great variation in the sizes of the grains and pebbles or gravel and +in the relative quantity of each. It is advisable to screen the sand +and gravel and to remix them in the correct proportions, as well-graded +aggregates make stronger concrete and, ordinarily, enough cement will be +saved to pay for the cost of screening. + +Experience has shown that it is advisable to screen bank gravel twice; +first over a screen with large meshes to eliminate particles too large +for use. The size of the mesh will depend upon the nature of the work +involved (see Coarse aggregate); then the material which has passed +through this screen should be sifted again over a screen with one-fourth +inch meshes. All material which passes the latter screen may be +considered sand and should conform to the characteristics discussed under +"Fine aggregate." + + +SUBSTITUTES FOR GRAVEL OR STONE. + +For general work gravel or broken stone always is preferred to other +coarse aggregate. Other materials at times are easier to obtain and, when +used with discretion, will provide a satisfactory concrete. + +Broken terra cotta, brick, and old concrete, if hard and strong, may +be used for unimportant work where no great strength is required, but +special care should be taken that the particles do not show on the +finished surface. + +The maxim that a chain is only as strong as its weakest link applies +to concrete. If the coarse aggregate is weaker than the cement mortar, +as in the case of some sandstones, it should be used with caution. +The aggregate may have properties that render it unsuitable for use +under certain conditions; for instance, cinders should not be used +if water-tightness or strength is expected, but they are useful for +fireproofing. Material that disintegrates or flakes when heated is +undesirable in places exposed to high temperature; thus marble and some +limestones should not be used in fireplaces. Some aggregates when exposed +at the surface of concrete are apt to cause discolorations, and when this +would be objectionable aggregates of this type should be avoided. Flat +or elongated slab-like fragments should be avoided, as particles of this +shape do not bond well; slate and shale are examples. + + +CINDERS. + +Cinders should be composed of hard, clean, vitreous clinkers, free from +sulphides, soot, and unburned coal or ashes. As a precaution against the +presence of small amounts of detrimental substances, cinders should be +soaked thoroughly with water 24 hours before being used. If clean they +will not discolor the hands when a small quantity is rubbed between the +palms. + +Cinder concrete, on account of its light weight, commonly is used for +filling between sleepers of floors and grading roofs, and frequently for +fireproofing, for which it is very effective. Cinders should never be +used when the concrete is to be subjected to heavy loads or abrasion. + + +LAVA ROCK. + +Lava rock varies widely in chemical composition and physical qualities. +In some instances lavas are so light and frothy or contain so large a +proportion of easily oxidizable material that they are wholly unsuited +for concrete work. In general, the lava rock found in the Northwestern +States is a suitable substitute for gravel. Rhyolite, a light colored +volcanic rock, and many of the darker colored basaltic lavas can well be +used for concrete for building purposes. + + +WATER. + +Water should be clean and free from strong acid and alkali. Sea or +brackish water should not be used if fresh water can be obtained. + + +PROPORTIONING THE MATERIALS. + +In mixing concrete various proportions of cement, sand, gravel, and water +are employed, depending upon the purpose for which the concrete is to be +used. The ideal mixture is one in which all the spaces or voids between +the grains of sand are filled with the cement and all the voids in the +gravel are filled with the cement-sand mortar. This perfection is seldom +attained, because the voids in each lot of gravel and sand vary slightly, +and in order to be absolutely safe a little more sand and cement than +will just fill the voids are used. + +The strongest concrete is not required in every structure, and, in +many instances, the cost of it would be unwarranted. For important +work involving large quantities of materials of unknown qualities, +tests should be made to determine the best proportions. Such tests, +being rather complicated, are made usually in a laboratory, and are +not practical for the user of small quantities of concrete. Various +proportions have been tested by experienced engineers to determine which, +under average conditions, will develop the greatest strength, best +resist wear, and assure greatest impermeability or water-tightness. The +mixtures given below have been found to meet the requirements indicated, +and having been adopted as arbitrary standards, are recommended for use +in farm concrete work. The amount of water required is discussed under +"Consistency." + + +ARBITRARY MIXTURES. + +=Rich mixture.=--Used for concrete subject to high stresses or where +exceptional water-tightness and resistance to abrasion are desired: +1:1-1/2:3; i. e., 1 part cement, 1-1/2 parts sand, and 3 parts gravel. + +=Standard mixture.=--Used generally for reinforced concrete and +water-tight work: 1:2:4; i. e., 1 part cement, 2 parts sand, and 4 parts +gravel. + +=Medium mixture.=--Used for plain concrete of moderate strength: 1:3:5; +i. e., 1 part cement, 3 parts sand, and 5 parts gravel. + +Leaner mixtures are sometimes used after a test has proved them to be +suitable for the work at hand. + +It will be noticed that always in indicating the proportions the first +number refers to the cement, the second to the sand, and the third to the +gravel. The three materials must be measured by volume, using the same +unit. The cubic foot is a convenient measure, because a sack of cement, +weighing 94 pounds, is considered to contain 1 cubic foot. + +When the coarse aggregate (gravel, etc.) is omitted the mixture is +generally spoken of as mortar and the proportions are indicated thus, +1:2, meaning 1 part cement and 2 parts sand. Mortar is used for +plastering, stucco, top coats of floors, and for laying masonry. + + + + +QUANTITIES OF MATERIALS REQUIRED. + + +More concrete can be made from given volumes of aggregates if the gravel +used is graded from fine to coarse than if the particles are too nearly +of one size, because the small stones help to fill the voids between the +larger ones and less sand-cement mortar is required. The extra mortar +thus adds to the volume of the concrete. + +A common mistake to be guarded against is to assume that the volume +of concrete produced is equal to the quantity of sand plus the gravel +as indicated in the proportion. For instance a 1:2:4 mixture will not +produce 6 cubic yards of concrete, if 2 yards of sand and 4 yards of +gravel are used, because the sand will lodge in the voids between the +pebbles. If 6 cubic yards of concrete are desired it will be necessary to +use 2.7 cubic yards of sand and 5.34 cubic yards of gravel. + +Table 1 shows the quantity of cement, sand, and gravel required under +average conditions for the indicated proportions. + +Table 1.--_Materials for 1 cubic yard of rammed concrete._ + + Proportions. | | | + | | | + Cement.| Sand. | Gravel.| Cement. | Sand. | Gravel. + -------+-------+--------+----------+----------+----------- + | | | _Sacks._ |_Cu. yds._| _Cu. yds._ + 1 | 1 | --- | 19.20 | 0.74 | --- + 1 | 2 | --- | 13.48 | 1.00 | --- + 1 | 2-1/2| --- | 11.00 | 1.01 | --- + 1 | 3 | --- | 10.40 | 1.16 | --- + 1 | 1 | 2 | 10.52 | .39 | 0.78 + 1 | 1-1/2| 3 | 7.64 | .42 | .85 + 1 | 2 | 4 | 6.04 | .45 | .89 + 1 | 2-1/2| 5 | 4.96 | .46 | .92 + 1 | 3 | 5 | 4.64 | .52 | .86 + 1 | 3 | 6 | 4.24 | .47 | .94 + -------+-------+--------+----------+----------+---------- + + + + +CONSISTENCY. + + +The quantity of water used in mixing has a very great influence on the +strength of the concrete. An excess of water weakens the concrete, while +an insufficient amount prevents thorough mixing. + +[Illustration: Fig. 2.--The result of using too dry a mixture, lack +of spading and careless placing; note irregularity of layers and poor +bonding.] + +Therefore, only sufficient water should be used to produce a workable or +plastic mixture. + +Recent tests have proved that to secure the greatest strength the +concrete should be mixed considerably drier than has heretofore +been customary. Of course, for thin walls containing closely placed +reinforcement, or for water-tightness, a fairly wet mix is necessary. A +little experience will show the proper amount of water to use. + +A very rough estimate of the quantity of water required in mixing for +general work is 4 to 5 gallons to each sack of cement. + +Three degrees of consistency (corresponding to different proportions +of water) are used in general practice, namely, wet, medium, and dry. +In the light of recent investigations it is thought the wet mixture of +present-day practice contains too much water. The following definitions +are therefore recommended: + +=Wet mixture.= One that does not flow readily and yet can not be piled +up. It is recommended for thin sections when reinforcement is closely +placed. + +=Medium mixture.= One that is between the wet and dry mixture. This +consistency is recommended for general work. + +=Dry mixture.= One about like damp earth. If a handful is squeezed it +will retain its shape. This consistency requires thorough ramming to +eliminate voids and is used when forms are to be removed immediately, +but should not be used where a water-tight job is expected. The porous +structure of the concrete in Figure 2 is due to the fact that it was +placed as a dry mixture. + + + + +ESTIMATING. + + +ESTIMATING CONCRETE. + +In estimating the amount of concrete in a given piece of work and the +quantities of materials required, the unit of measurement is usually the +cubic yard (27 cubic feet). The following examples will explain best the +method of determining the quantities required: + + =Example 1.=--A wall 9 inches thick, 12 feet high, and 30 feet long + has a door opening 3 feet wide and 6 feet high, also a footing 18 + inches wide and 9 inches deep. The concrete is to be mixed in the + proportions of 1:2:4. + + The volume of the footing is found by multiplying together the + dimensions expressed in feet, thus, 1-1/2 × 3/4 × 30 = 33-3/4 cubic + feet. Similarly, the volume in the wall is 3/4 × 12 × 30, less the + door opening 3/4 × 3 × 6 = 256-1/2 cubic feet. + + The total volume in footing and wall is 290-1/4 cubic feet = 10-3/4 + cubic yards. + + To find the quantity of cement, sand, and gravel, multiply the + amounts for 1 cubic yard, indicated in line 7 of Table 1, by + 10-3/4, and it will be found that 65 sacks of cement, 4.83 cubic + yards of sand, and 9.56 cubic yards of gravel are necessary to + build the wall. + + =Example 2.=--A pavement 27 feet long, 4 feet wide, and 6 inches + thick has a 5-inch base mixed in the proportions of 1:3:5 and a + 1-inch surface mixed in the proportions of 1:2. + + The volume in the base is 27 × 4 × 5/12 = 45 cubic feet = 1-2/3 + cubic yards. + + The volume in the top is 27 × 4 × 1/12 = 9 cubic feet = 1/3 cubic + yard. + + Multiplying the quantities in line 9 of Table 1 by 1-2/3 and those + in line 2 by it is found that the base requires 7.74 sacks cement; + 0.86 cubic yard sand; 1.43 cubic yards gravel; and the top requires + 4.49 sacks cement; 0.33 cubic yard sand. + + =Example 3.=[1]--A tank 9 feet inside diameter has walls 6 inches + thick and 4 feet high (above the floor). The floor is 6 inches + thick, the concrete is to be 1:2:4. + + The volume in the floor is 10/2 × 10/2 × 22/7 × 1/2 = 39-2/7 Cubic + feet. + + The area of the larger circle is 5 × 5 × 22/7 = 78-4/7 cubic feet. + + The area of the smaller circle is 4-1/2 × 4-1/2 × 22/7 = 63-4/7 + cubic feet. + + The area of the wall, therefore, is 15 cubic feet and the volume is + 15 × 4 = 60 cubic feet. + + The total volume in the structure is 99-2/7 cubic feet or 3-2/3 + cubic yards. Multiplying the quantities in line 7 of Table 1 by + 3-2/3, it is found that the following material is needed: 22.14 + sacks of cement; 1.65 cubic yards of sand; 3.27 cubic yards of + gravel. + + +[1] A practical rule in finding the area of a circle is to multiply +one-half the diameter (radius) by itself and the product by 22/7. In +finding the volume in the wall of a circular structure, such as a silo +or tank, the area of the circle formed by the inside circumference +is deducted from the area of the circle formed by the outside +circumference and the remainder is multiplied by the height. + + +FORMS. + +Forms are required to hold the concrete in place until it has attained +sufficient strength to sustain itself and the initial loads to which it +may be subjected. Concrete is plastic and will assume the shape of the +form, thus any imperfection or impression on the face of the forms will +be reproduced. + +Wood is commonly used for forms, as it can be easily worked into +different shapes, though various other materials sometimes are better +adapted to special conditions. Cast iron, for instance, is suitable for +casting small objects that are to be reproduced in quantities, such +as concrete block or tile; plaster of Paris, glue, or moist sand are +employed for casting ornaments or to produce a fine, smooth surface; +sheet metal is suitable when the forms can be used repeatedly or for such +circular structures as silos. When the sides of an excavation are not +likely to cave in the earth may serve as a form. + + +WOOD FORMS. + +Wood for forms must be of a kind that is easily worked and that will +retain its shape when exposed to the weather. White pine is the best +wood, but is seldom used because of its cost. Spruce, yellow pine, and +fir are satisfactory woods for forms and are best, used partially green +or unseasoned. + +The edges of boards should be surfaced, tongued and, grooved, or beveled +in order to obtain a tight form, so that the soft mortar will not ooze +out. A better surface* is secured if the boards are dressed on one side +and are free of loose knots or other imperfections. + +As forms must be removed, they should be so planned that they can be +taken down without destroying the lumber, especially if the boards are +used for sheathing or again for forms. Therefore the nailing of the +boards to the support should be only sufficient to keep them in place +until the concrete has hardened. Greasing the surface next to the +concrete with crude oil, soap solution, or linseed oil will prevent the +concrete from adhering and facilitate removal. + + +METAL FORMS. + +Metal forms can be used to advantage when the work involved is to be +repeated many times. If it is known or if it is probable that the forms +may have to be altered, the relative costs of wood and metal forms should +be carefully determined. + +Metal forms of various types and designs may be purchased. Although the +first cost may be high, yet their use may lower the total cost when the +work is such as to warrant it. + +Circular forms may be built as shown in Figure 3. The sheathing is +generally of wood 4 to 6 inches wide, or sheet metal, and, if of wood, +is laid perpendicular to the battens. In forms of small diameter, sheet +metal sheathing is necessary if a smooth surface is desired, as the +4-inch boards can not be made to conform to a true circle. The radius +used for cutting the battens of the inner circle should be the thickness +of the sheathing less than the inside radius of the structure and the +same amount greater than the outer radius for the outside battens. + + +REMOVAL OF FORMS. + +The period of time after which forms may be removed varies according to +conditions. Rich and dry mixtures set quickly, and warm weather tends to +hasten the setting of concrete. The character of the structural member +and the loadings also must be considered. + +Thus, an unloaded wall 12 inches or more thick may be stripped of forms +in from 1 to 3 days, while the forms of thinner walls should remain in +place from 2 to 5 days. Slab forms and the sides of beam and girder forms +may be removed in from 6 to 14 days if the span is not over 7 feet. The +bottoms of beam and girder forms, even though of a span less than 7 feet, +should remain in place and braced form 10 to 14 days and even longer. +Experience is the best guide to the time of removal, but if there is any +doubt ample time should be allowed, especially in cold weather. + +[Illustration: Fig. 3.--Suggestion for circular form.] + + +BUILDING AND SETTING FORMS. + +Concrete, while plastic, exerts a great pressure on the confining +walls, necessitating rigid tying and bracing of the forms to keep them +from bulging out of alignment. The effect of the bulging of a form is +corrected only at a considerable expense; hence it is advisable to pour +the concrete to a depth of not more than 2-1/2 or 3 feet, allowing it to set +or harden before pouring more. + +The form most used in concrete construction is that for a straight wall. +The methods of building such a form apply in general to the forms for +most structural work, though modifications may be necessary to meet +particular conditions. + +[Illustration: Fig. 4.--Form for basement or cellar wall. The earth may +be used as an outside form if it is sufficiently firm.] + +The straight wall form may be built continuous (Figs. 4 and 5), or in +panels of a size convenient to handle, and from stock lengths of lumber +(Fig. 6). Generally the face boards are placed horizontally and secured +to studs or posts. The face boards may be 1 or 2 inches thick and from 6 +to 10 inches wide, preference being given to the narrower widths, which +are less liable to cup or warp. The thickness depends upon the spacing +of the studs, the number of times the forms are to be used, and the +depth of pouring. Ordinary sheathing, if the joints are made tight, is +satisfactory for foundations of dwellings, etc., and the studs, if 2 by +4 inches, should be spaced 18 inches on centers. The studs for a long, +high form had best be 4 by 4 inches or 2 by 6 inches, spaced from 2 to 3 +feet center to center. The studs of the inside and outside forms must be +tied together to prevent spreading; this is conveniently done with No. 10 +wire, as shown in Figure 4, or with one-half or three-quarter inch bolts, +which is the more expensive method. Bolts should be greased to facilitate +removal. Temporary spacers of wood, 1 by 2 inches, of a length equal to +the thickness of the wall, should be used to prevent drawing the forms +together when the wire or bolt is tightened. They should be spaced at the +ties, but need not be at every wire, and are knocked out and removed as +the concreting progresses. + +[Illustration: Fig. 5.--Straight wall form for level ground.] + +The ties should be spaced on each stud about 2-1/2 feet vertically. If +more than 3 feet of concrete is poured at one time the ties should be +closer together, vertically, at the bottom of each pouring. The thickness +of the wall does not affect the number of ties. On removing the forms the +wires should be clipped close to the face of the concrete and punched +back, unless the surface is to be stuccoed. If a pit hole is caused by +punching back the wire it should be pointed up with mortar, which then +should be rubbed to make it blend with the general surface. + + + + +MIXING. + + +PREPARATION OF PLANT. + +Before starting to mix, annoyance and money may be saved by planning the +location of the mixing plant with regard to convenience in depositing +the concrete in the forms and ease of access to the materials. Often the +board can be located so that by moving it once or twice the bulk of the +concrete may be shoveled directly into the forms. It is more economical +to wheel material a distance of from 10 to 25 feet than to carry it in +shovels. Eight feet is about as far as it is profitable to shovel. + +When material is to be wheeled, runways of planks should be provided, +because more material can be handled in a given time, and the wear and +tear on men and equipment is not so great. The planks used in the runways +should be thick enough to sustain the weight passing over them and should +be 10 to 12 inches wide to permit foot room. They should be anchored +securely and made rigid, as springy or loose boards retard progress +of the work. Smooth joints in the planking will prevent bumping and +stumbling. + +[Illustration: Fig. 6.--Sectional forms.] + + +NUMBER OF MEN. + +The number of men required is determined by the amount of concrete to be +placed in a given time, the method of mixing, and the size of the batch; +that is, the number of bags of cement mixed at one time. The amount of +concrete one man can mix by hand in a day depends upon the experience of +the man, the layout of the work, and other duties required of him. One +man should average 1-1/2 to 1-3/4 cubic yards of concrete in eight hours, +including mixing and wheeling not more than 50 feet. + +The gang for a one-bag batch may consist of 3 men, but a larger number +make a more efficient force, for when the concrete is mixed by hand the +men can take turns at the various tasks and will not tire so easily. The +assigning of tasks so that each man's time fits into that of the others +requires considerable study and is one of the chief factors making for +loss or profit. + + +MACHINE MIXING. + +Good concrete can be mixed by hand or machine. The quantity of concrete +work in prospect is the factor that determines the more economical +method. A small amount (say 100 to 200 cubic yards) does not warrant the +purchase of a machine, but it is often feasible and economical to hire a +machine from a neighbor or contractor if the quantity of concrete to be +placed is more than 15 cubic yards. + +A mixer should be purchased only after careful consideration of the +amount and character of the work to be done and the conditions affecting +its use. + +The two types of mixers most used are the batch mixer, which mixes +and dumps a definite quantity, and the continuous, which discharges a +constant stream of concrete. The continuous type is not adapted to farm +work unless the concrete can be handled as fast as it is mixed, thus +permitting the machine to work continuously. + +[Illustration: Fig. 7.--Home made concrete mixer.] + +There are numerous types and various sizes of batch mixers. A one-bag +batch machine is most suitable for general work, though there are smaller +mixers that may prove handy. Some of the smallest sizes are operated by +hand, but the medium and large sizes are power operated. Mixers can be +had with or without the power plant attached and may be stationary or +on wheels, which facilitate moving to different sites. Engines used for +sawing wood, the larger ones used for pumping water, and tractors furnish +sufficient power to operate an average mixer. Figure 7 shows a homemade +mixer built of discarded farm implement parts and operated by the farm +engine. + +Directions for operating a mixer are generally furnished with the +machine. The tendency is to use too much water in mixing concrete in a +machine. The consistency of the mixture should be as described under the +heading "Consistency" on page 8. The mixing should be continued for at +least a minute after the drum has been charged, but a better mixture is +secured if two minutes are allowed. At the end of each day's work the +machine should be thoroughly washed, and when not in use it should be +well greased and covered. + + +HAND MIXING. + +Hand mixing is the more economical on the farm unless a large amount +of work is to be done at one time. Few tools need be purchased, and, +as a rule, only farm help need be employed. The following tools will +be needed in mixing and placing plain concrete: Two or more square-end +short-handled shovels, 1 heavy garden rake, 1 sprinkling can or bucket +(if a hose is not available), 1 52-gallon barrel, 2 wheelbarrows with +metal trays, 1 sand screen (Fig. 8), 1 tamper (Fig. 9), 1 wood float or +trowel (Fig. 10), measuring boxes (Fig. 11), mixing board (Fig. 12), 1 +spader (Fig. 13). The number of shovels and wheelbarrows needed will +depend upon the size of the batch, number of men mixing, and the layout +of the work. Long-handled pointed shovels will be found more convenient +at the sand and gravel piles. + +A bottomless box is necessary for convenient and accurate measurement +of the sand and gravel. Where wheelbarrow measurement of materials is +practiced, as in charging a mixer, the capacity of the wheelbarrow +should be determined by use of a measuring box. The box may be made as +illustrated in Figure 11, from boards 12 inches wide. The dimensions in +Table 2 are of boxes for use in measuring quantities for mixtures of +various proportions, assuming that one bag of cement is used in a batch. +If two bags are used in a batch the boxes should be filled twice. + +[Illustration: Fig. 8.--Sand screen.] + +[Illustration: Fig. 9.--Tampers.] + +[Illustration: Fig. 10.--Wooden float.] + +[Illustration: Fig. 11.--Measuring box.] + +[Illustration: Fig. 12.--Mixing Board.] + +[Illustration: Fig. 13.--Spading tool.] + + +Table 2.--_Inside dimensions of measuring boxes for various proportions._ + + [1-bag batch, box 12 inches deep.] + + Proportion. Box for sand. Box for gravel. + ----------- --------------- ---------------- + _Feet._ _Feet._ + 1:1:2 1 by 1 1 by 2 + 1:1-1/2:3 1 by 1-1/2 1 by 3 + 1:2:4 1 by 2 2 by 2 + 1:2-1/2:5 1-1/4 by 2 2 by 2-1/2 + 1:3:5 1-1/2 by 2 2 by 2-1/2 + 1:3:6 1-1/2 by 2 2 by 3 + +A tight platform should be provided similar to that illustrated in Figure +12 upon which to mix the concrete. For mixing 1 or 2 bag batches a +platform 9 by 10 feet will serve. + + +DIRECTIONS FOR HAND MIXING. + +The mixing board should be located in convenient relation to the supply +of materials and the work and should be level. The sand box is placed +on the board, about 2 feet from one of the longer sides, and filled +level with sand; the box is then lifted away and the sand spread in a 3 +or 4 inch layer. The cement is spread as evenly as possible on' top of +the sand. Two men with shovels, standing on opposite sides of the pile, +turn the sand and cement in such a way that the materials axe thoroughly +mixed. In turning the material it should not be simply dumped off the +shovel, but should be shaken off the ends and sides, so that the two +constituents will be mixed as they fall. The mass should be turned two +or three times, or until it is of uniform color and there are no streaks +of either sand or cement. A man with a hoe or rake may assist by raking +the top over as the two men turn. When the sand-cement mixture is of a +uniform color it should be spread out carefully in a layer and the gravel +box placed on top. The box is filled with gravel and then removed, the +gravel being spread over the sand-cement mixture. The mass is soaked with +about one-half the quantity of water to be used, care being taken not to +wash away any of the cement. The materials then should be turned over +in much the same manner as was the sand-cement, except that instead of +shaking them off the end of the shovel the whole load should be dumped +and dragged back toward the mixer with the square end of the shovel. +The wet gravel picks up the sand and cement as it rolls over when +dragged back. The mixing should be continued until the mass is uniform, +water being added to the dry spots during the mixing until the desired +consistency is obtained. + +Experience counts considerably in mixing concrete with the least amount +of labor; ordinarily three or four turnings are required to mix the +materials thoroughly. After the final turning the concrete should be +shoveled into a compact pile and then is ready for placing in the forms. + + + + +PLACING. + + +PLACING CONCRETE. + +The mixed concrete should be deposited in the forms within from 20 to 30 +minutes from the time the water is added to the cement, as it begins to +set or harden after this time. To disturb the concrete after the set has +begun is risky, as it will lose some of its strength, the extent of the +injury depending upon the seriousness of the disturbance. + +Concrete which has set before it can be placed in the forms should not be +tempered or softened with water, but should be discarded. + +To prevent delay in placing, all forms should be examined before the +mixing is begun to see that they are properly braced, that all chips or +loose particles are removed, that the surface of concrete which has set +has been properly roughened and wetted to assure a bond, as described on +page 20, and that all reinforcement, bolts, inserts, etc., are properly +located and secured. + +At the lunch' period, or at the end of a day's work, the mixing board +and equipment should be thoroughly washed, for if this is not done many +pounds of heavy concrete are needlessly carried around by the men and the +addition of a pound in the weight of tools will lower the efficiency of +the workers. Moreover, it will save time and wear and tear of equipment +incident to cutting the surplus concrete away with a cold chisel. + +[Illustration: Fig. 14.--1592 Showing result of leaky forms and poor +placing. The soft cement mortar ran out, leaving areas of honeycombed +surface not necessarily harmful but unsightly.] + +In depositing concrete in the forms care should be taken that the +materials do not separate. + +If the mixing is done close to the place of depositing, the concrete +may be shoveled into the forms directly or through a chute. If it is +necessary to lift or transport the concrete, buckets and wheelbarrows are +convenient containers. The concrete should be deposited in horizontal +layers, preferably not over 6 inches thick, and a spade or paddle should +be worked up and down against the forms to push the coarse material +away from the surface, as illustrated in Figure 13. The object of the +spading is to eliminate impounded air that may form pockets in the mass +and to insure a smoother and more impervious surface. In addition to +being spaded, stiff concrete should be rammed until water flushes to +the surface. Tapping the forms with a hammer is a very effective way of +securing a smooth surface. Figure 14 shows the result of improper spading. + +Fresh concrete will riot bond readily to concrete that has hardened and +a seam may be formed that will permit water to trickle through. When +bonding fresh concrete to that which has been in place for a short time +it is usually sufficient to roughen the hardened surface with a pick or +by other means so as to expose the gravel or stone, and to clean off +all loose particles. The hardened concrete should be soaked with water, +the excess water removed, and the surface then given a coat of grout (a +mixture of cement and water) of the consistency of cream just before the +new concrete is deposited. + +When pouring of a wall is to be discontinued for some time, provision for +the bonding of future work should be made. This may be done by placing +short steel dowels in the concrete when it is poured, or a rebated joint +or groove may be made, as shown in Figure 15. In bonding a new wall to +old concrete, holes should be drilled for the dowels, which should be +grouted in, and the old surface should be roughened, cleaned, and wetted; +or a groove may be cut in the old wall to receive the new concrete. + +[Illustration: Fig. 15.--Method of forming horizontal rebate.] + + +PLACING UNDER WATER. + +Concrete can be placed under still water if proper precautions are taken. +It should never be placed, while soft, in running water unless a form or +cofferdam is used, as the cement will be washed out. When concrete is to +be placed under water a form of tube or chute, known as a tremie (Fig. +16), may be used advantageously. The tube should be of sheet metal, about +8 inches in diameter, with a hopper on top, and means should be provided +for quickly raising and lowering it without jolts, so that the concrete +will feed out at the bottom without breaking the seal. The lower end of +the tube should rest on the bottom or on the concrete as it is built up +and a continuous flow of concrete, mixed somewhat soft so that it will +flow easily, should be maintained. + +Scum or laitance is likely to form on concrete when placed under water, +and unless all of the concrete is! poured in one operation and brought to +a little above the water surface, seams or planes of weakness will occur. + + + + +CARE OF CONCRETE. + + +After the concrete has been poured, care should be taken that it does not +dry out too quickly, and in hot weather it must be protected from the +sun. Exposed surfaces and objects made of dry concrete should be sprayed +thoroughly with water twice or oftener each day for a week or 10 days. +Sometimes surfaces are shielded with canvas, paper, boards, or layers of +moist sand. + +[Illustration: Fig. 16.--Tremie for use in placing concrete under water.] + + + + +PROTECTION FROM FREEZING WEATHER. + + +CONCRETING IN FREEZING WEATHER. + +If suitable methods are used, good concrete work can be done in cold +weather, but with more difficulty and at somewhat greater cost than when +the weather is warm. Ordinarily it is best not to attempt to do concrete +work during freezing weather. However, the extra cost at times may be +warranted by urgent need of the structure or the fact that other farm +work is not so pressing during the winter and the concrete work may be +carried on without seriously interfering with regular farm operations. + +Concrete must be protected from alternate freezing and thawing until it +has set. Cold retards the setting and hardening of concrete; therefore, +even though the temperature is not at the freezing point, the concrete +should be protected and special care taken not to subject it to loads. +The forms should be kept in place until there is no doubt that the +concrete has properly hardened. Hot water should be poured on the +concrete to make sure that apparent hardness is real and not due to a +frozen condition. Just before the concrete is placed all ice and frost +should be removed from the forms and reinforcement, if used, by warming +the surfaces with steam or by other means. + +Concrete that has been frozen once may, with proper care, attain its +ultimate strength, but should it freeze a second time the chances of +saving the work are very slight. Exposed surfaces are apt to scale or pit +if the concrete is allowed to freeze before it is thoroughly hardened. + +Pleating the materials, protecting the green concrete, and the use of +salt are precautions generally taken to prevent freezing. + + +THE USE OF SALT. + +The use of salt is objectionable, as it forms a white efflorescence +on exterior surfaces and is liable to corrode the steel in reinforced +concrete work. The quantity of salt required varies with the temperature, +but it should not exceed 10 per cent of the weight of the water used +in mixing. A 10 per cent solution is eight-tenths (approximately 13 +ounces) of a pound of salt per gallon of water and will prevent freezing +at a temperature of 22° F. Lower temperatures would require a greater +proportion of salt, which would impair the strength of the concrete, and +hence is not practicable. + +A rule, frequently advocated, for varying the percentage of salt is +to use 1-1/3 ounces per gallon of water for each degree Fahrenheit +below freezing. Since it is impossible to foretell the exact drop in +temperature, the exact quantity of salt can not be predetermined, so that +provision should be made for several degrees lower than anticipated. +The salt should be dissolved in the mixing water, and in order that the +proportion be correct the amount of water required for each batch should +be determined by trial and this quantity used throughout the work. + + +THE USE OF HEAT. + +Perhaps the most satisfactory method of preventing freezing of concrete +is to heat the materials and to inclose or cover the completed work for +a few days or until most of the water has disappeared and sufficient +strength has developed. In extreme weather protection may be needed for +five or six days. When the weather is cold but not freezing, heating the +materials will be sufficient. If a freeze is expected the concrete work +should be protected by wood inclosures, paper, or canvas, over which, if +the surface is horizontal, may be spread a 6 or 8 inch layer of straw. +Manure should not be used to protect fresh concrete, since the acids in +it are destructive and cause unsightly stains. Splits or other openings +in coverings may admit cold, which may freeze parts of the work. As the +temperature drops (to about 20° F.) it will be necessary to arrange the +covering so that live steam can be turned in between it and the concrete +or that heat may be supplied from stoves or salamanders. + +Mass work, except in very cold weather, will not require as careful +protection as thin sections and, as a rule, the forms are sufficient if +the exposed parts are covered. + + +HEATING MATERIALS. + +The water can be heated sufficiently for use in concrete (approximately +150° F.) in kettles on stoves or by steam from a boiler. + +A metal smokestack placed horizontally with a fire in one end makes an +efficient heater for the sand and gravel. The materials are piled over +the stack, but not so high that their weight will crush the pipe. Small +quantities of sand and gravel may be heated on top of metal plate with +a fire under it. If a small boiler is available it may be economical to +use steam for heating the sand and gravel. Steam is effective when forced +from nozzles into the piles or circulated through perforated pipes placed +under the material. Covering the piles with canvas or other material will +retain much of the heat. + + + + +CONTRACTION AND EXPANSION JOINTS. + + +Concrete expands and contracts with changes in temperature, causing +cracks to appear. Contraction cracks occur in thin sections exposed to +wide variations in temperature and are common in sidewalks; therefore, +large stretches of concrete should not be laid without breaks or spaces +to allow for the changes in size. The spaces should be filled with tar or +some similar material that will yield or give when the concrete expands. +A joint like that shown in Figure 17 is frequently used for thick walls. +A section of the wall is poured and before the next is poured the +abutting end is covered with tar and paper, the thickness of the covering +depending upon the length of the section and the exposure. Sidewalks and +similar work, when not cast in alternate blocks, should have a one-fourth +inch space left at intervals of 40 feet. The joint may be filled with tar +paper or tar. Steel is used to take care of contraction in long or high +walls and water-tight work. Important structures in which temperature +reinforcement is necessary should be designed by one experienced in +concrete design. + +[Illustration: Fig. 17.--Expansion joint showing rebate form removed and +filler in place.] + + + + +LINTELS. + + +The subject of reinforced concrete is not within the province of this +bulletin, but as openings of various widths are required in the walls of +most farm structures, a general explanation is given of the reinforcement +of lintels or that portion of concrete immediately above an opening, such +as a floor or window. + +A lintel is a beam, and when a beam bends the lower part is stretched or +pulled while the upper portion is compressed. Good concrete will stand +great pressure but is not capable of resisting any great pulling or +tensile stress. For this reason steel is used in the lower portion to +take care of the tensile or pulling force. + +It will be found generally satisfactory, where no heavy or concentrated +load occurs over an opening and the span is not more than 4 feet, to +place two rods three-eighths of an inch in diameter in the bottom of the +lintel, so that there will be 1 inch of concrete below them. Two diagonal +rods should be placed at each top corner of a window or door, as shown +in Figure 18. When the opening is between 4 and 8 feet the rods should +be bent up as shown in Figure 19 and when between 8 and 12 feet, three +one-half inch rods should be used, two of them being bent. + +Barbed wire, old fencing, and scrap or rusty iron is not suitable for +reinforcement. Loose rust should be cleaned off the rods and they should +be free of grease and oil. + +[Illustration: Fig. 18.--Reinforcement of openings less than 4 feet wide.] + +[Illustration: Fig. 19.--Reinforcement of openings more than 4 feet wide.] + + + + +SURFACE FINISH. + + +Joints and imperfections in the forms are reproduced on the concrete +surfaces. Patches of honeycomb and rough places are left where the mortar +has run out of the forms or where the concrete has not been properly +placed. Such imperfections do not necessarily affect the strength of the +concrete, but they do detract from the appearance (see Fig. 14). Too of +ten the finishing of the concrete work in even the more important farm +buildings is neglected. With little extra trouble exposed surfaces can +be given a finish which will add to the attractiveness and hence the +value of the completed work. Rubbing off the form marks and pointing up +depressions or holes greatly improves the appearance of the work. The +rubbing may be done with a wooden float or hard-burned brick, using a +little sand and water as an abrasive and a 1:2 mortar for pointing up. +The surface can be worked best if the forms are removed within 24 hours +or before the concrete has set too hard. After the concrete has hardened +it may be necessary to use a carborundum block for rubbing. + +A pleasing finish can be secured by scrubbing the surface with a stiff +fiber or wire brush, using plenty of water to wash off the loosened +particles. The work must be done while the surface is workable for if the +concrete is too green or soft the aggregate will break out and if too +hard the work can not be done effectively. + +Artistic effects can be secured by picking or tooling the surface with +a bush hammer, toothed chisel, or pick. For such treatment the concrete +should be two or three weeks old to prevent breaking out the aggregate. +Other finishes may be obtained by etching with acid to expose selected +colored aggregates and by the application of stucco. The limitations +of the bulletin do not permit of a discussion of these more elaborate +treatments. + + + + +CONCRETE EXPOSED TO FIRE. + + +Concrete is practically fireproof in that it can not be consumed by fire, +but unless properly made and of the right materials it will disintegrate, +at least on the surface. + +To resist fire concrete should be mixed fairly rich, say, 1:1-1/2:3, or +1:2:4 and special care should be taken to grade the sand and gravel to +secure a dense mixture. + +The aggregates should be selected with a view to their fire-resisting +properties. The sand should be siliceous and the larger aggregate +should not disintegrate when heated; hence, marble, granite, limestone, +materials containing quartz, and some gravels are unsuitable. Cinders are +specially valuable, due to their non-conductivity, but can not be used +where strength is required. Trap rock will resist destruction by heat +and produce a strong concrete. Blast furnace slag is very good for this +purpose. + +Fireplaces and chimneys of dwellings[2] may be constructed of ordinary +concrete but the back, jambs, and inner hearth, which are directly +exposed to the heat of the fire, should be made of specially prepared +concrete as described above or should be lined with firebrick, although +concrete made with broken hard-burned brick or terra cotta has been +used successfully. If suitable large-sized aggregate is not available a +mixture of one part cement and three parts sand may be used. + +[2] See Farmers' Bulletin No. 1230, Chimneys and Fireplaces, U. S. +Department of Agriculture. + + + + +WATER-TIGHT CONCRETE. + + +Practical water-tightness in concrete may be secured by using a fairly +rich mixture properly proportioned. Foreign ingredients, membrane and +surface coatings, or other means need not be used, except where poor +workmanship is likely or where considerable damage and inconvenience +may result in case of leakage. Under such circumstances the membrane +treatment used in addition to a properly proportioned concrete, while +the most expensive method of waterproofing, probably will give the most +reliable results. This treatment consists of layers of burlap or tar +paper cemented to the surface and together with tar or asphalt. Where the +membrane is subject to injury it is sometimes protected by a coating of +cement mortar or brick backing. + +First-class workmanship and special attention to details are required +to secure water-tightness. The essential requisite is that the voids be +filled. A lean mixture may be made more impervious by using hydrated +lime which tends to fill the voids and makes the concrete flow easily. A +little more cement in the mixture would serve the same purpose. The lime +should not be in excess of 10 per cent of the weight of the cement and +under no circumstances should unslaked lime be used. + +The materials for water-tight concrete must be well graded, so as to +obtain a maximum density; that is, enough sand must be used to fill the +spaces between the gravel or stone and enough cement to fill the spaces +between the grains of sand. A 1:2:4 concrete will prove practically +impermeable in ordinary construction, but if a head or pressure of +water is to be resisted a 1:2:3 or richer mixture may be necessary. The +consistency is very important. A sluggishly flowing consistency is best, +for if the concrete is too wet the mortar may flow away from the stone, +leaving leaky places and, if too dry, the mass may prove porous. The +proportions and consistency must be accurately maintained for each batch +and the concrete must be exceptionally well mixed. + +It is necessary to exercise great care in the placing of the concrete. +Where practicable, the structure or object should be poured in one +operation to avoid leaky joints, but when this is not possible +precautions should be taken to secure a tight joint between concrete of +different ages. The surface of concrete which has set must be cleaned of +dirt and scum down to the true concrete. This surface then should be well +whetted and painted immediately with a creamy mixture of cement and water +before placing the new concrete. A good plan, when discontinuing work on +structures intended to hold liquids, is to embed a 6 or 8 inch strip of +tin or thin sheet metal to half its width in the concrete so that the +other half will project into the new concrete. + +A wall thick enough to resist the stresses put upon it will generally +resist percolation of water, but 6 inches may be considered as a minimum. + +Contraction and expansion must be controlled to avoid the occurrence of +leaks. To guard against cracks due to unequal settlement or other causes, +most concrete designed for water-tightness should be reinforced. In some +mass work, special contraction joints, as described on page 23 may be +necessary. Rules for the use of reinforcement and contraction joints can +not be given, as the requirements in each case vary with the conditions +to be met. + + + * * * * * + + + ORGANIZATION OF THE + UNITED STATES DEPARTMENT OF AGRICULTURE + + October 21, 1929 + + _Secretary of Agriculture_ Arthur M. Hyde. + _Assistant Secretary_ R. W. Dunlap. + _Director of Scientific Work_ A. F. Woods. + _Director of Regulatory Work_ Walter G. Campbell. + _Director of Extension Work_ C. W. Warburton. + _Director of Personnel and Business W. W. Stockberger. + Administration_ + _Director of Information_ M. S. Eisenhower. + _Solicitor_ R. W. Williams. + _Weather Bureau_ Charles F. Marvin, _Chief_. + _Bureau of Animal Industry_ John R. Mohler, _Chief_. + _Bureau of Dairy Industry_ O. E. Reed, _Chief_. + _Bureau of Plant Industry_ William A. Taylor, _Chief_. + _Forest Service_ R. Y. Stuart, _Chief_. + _Bureau of Chemistry and Soils_ H. G. Knight, _Chief_. + _Bureau of Entomology_ C. L. Marlatt, _Chief_. + _Bureau of Biological Survey_ Paul G. Redington, _Chief_. + _Bureau of Public Roads_ Thomas H. MacDonald, _Chief_. + _Bureau of Agricultural Economics_ Nils A. Olsen, _Chief_. + _Bureau of Home Economics_ Louise Stanley, _Chief_. + _Plant Quarantine and Control C. L. Marlatt, _Chief_. + Administration_ + _Grain Futures Administration_ J. W. T. Duvel, _Chief_. + _Food, Drug, and Insecticide Walter G. Campbell, _Director of + Administration_ Regulatory Work, in Charge_. + _Office of Experiment Stations_ E. W. Allen, _Chief_. + _Office of Cooperative Extension Work_ C. B. Smith, _Chief_. + _Library_ Claribel R. Barnett, _Librarian_. + + +This bulletin is a contribution from + + _Bureau of Public Roads_ Thomas H. MacDonald, _Chief_. + _Division of Agricultural Engineering_ S. H. McCrory, _in Charge_. + + + U. S. GOVERNMENT PRINTING OFFICE: 1929 + + + * * * * * + + +Transcriber Notes + + +All illustrations were moved so as to not split paragraphs. + + + + + + +End of the Project Gutenberg EBook of USDA Farmers' Bulletin No. 1279: Plain +Concrete for Farm Use, by T. A. H. Miller + +*** END OF THE PROJECT GUTENBERG EBOOK 59379 *** |