,transcriber ,notes ,text emphasis is denoted as ,italics and ,bold4 ,whole numbers and fractional parts denoted as3 #cc-c_/d4 ,u4 ,s4 ,,department ,,of ,,agriculture ,,farmers' ,,bulletin ,no4 #abgi ,,plain ,,concrete for ,,farm ,,use ,the successful and economical use of concrete involves the selection of suitable materials1 the correct proportioning of mixtures in the development of qualities to meet specific requirements1 the proper placing and the care of the green concrete4 ,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 requirements4 ,the cost of concrete depends not only upon the price of the materials and labor but also upon the judicious use of the two4 ,lack of foresight in locating the mixing plant1 in the design of forms1 and in planning the successive operations may cause unnecessary expense1 while neglect of any one of the precautions which should be observed is likely to result in unsatisfactory work4 ,the bulletin discusses the requirements of good concrete and describes the making and placing of plain concrete according to the best practice4 ,washington1 ,d4 ,c4 ,issued ,october1 #aibb ,,plain ,,concrete ,,for ,,farm ,,use4 ,t4 ,a4 ,h4 ,miller1 ,agricultural ,engineer1 ,division of ,agricultural ,engineering1 ,bureau of ,public ,roads4 ,,contents4 ,page4 ,introduction #a ,materials #a ,proportioning the materials #f ,quantities of materials required #g ,consistency #h ,estimating #i ,forms #aj ,mixing #ac ,placing #ah ,care of concrete #ba ,protection from freezing weather #ba ,contraction and expansion joints #bc ,lintels #bc ,surface finish #bd ,concrete exposed to fire #be ,water-tight concrete #bf ,,introduction4 ,portland cement concrete is the mass formed by mixing ,portland cement1 sand1 gravel 7or particles of other suitable materials71 and water4 ,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 used2 economy1 strength1 water-tightness1 fire resistance1 or resistance to wear and shock may be the chief requisite4 ,the character of the constituent materials1 the proportions in which they are used1 the consistency1 the method of mixing1 and the placing and curing of the concrete are important factors in securing the desired qualities of the finished product4 ,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 concrete4 ,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 7not reinforced7 concrete work4 ,,materials4 ,,cement4 ,portland cement is used because it is the only kind adapted to general construction4 ,other cements are manufactured but they possess individual characteristics that restrict their use4 ,the word ,portland is not a trade name1 but signifies the kind and distinguishes it from the slag1 natural1 and other cements4 ,a number of brands of ,portland cement are manufactured1 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 ,materials4 ,cement always should be tested for use in important work1 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 selected1 especially if the dealer's or manufacturer's guaranty that it meets the standard is secured4 ,the following simple test for soundness is easily made and is on the side of caution4 ,make a ball1 about #a-a_/b inches in diameter1 if neat cement and water2 place it under a wet cloth and keep it moist for #bd hours1 then put the ball in a vessel of water2 allow the water to come to the boiling point slowly and to boil for #c hours4 ,a good cement will not be affected1 but an inferior one will check1 crack1 or go to pieces entirely4 ,portland cement is shipped in paper bags1 cloth sacks1 and wooden barrels 7sometimes in bulk74 ,for the average user the cloth sack is the best container1 as it is easier to handle2 and while the manufacturers charge more for this kind of package1 they allow a rebate for the return of the sacks in good condition4 ,a sack of ,portland cement weighs #id pounds and a barrel contains the equivalent of four sacks4 ,,storing4 ,as cement readily absorbs moisture from the atmosphere1 it should be stored in a dry place2 if exposed to dampness it soon becomes lumpy1 or even a solid mass1 and in this condition it is useless and should be thrown away4 ,the lumps caused by pressure in piling the sacks are not injurious4 ,they can be pulverized easily1 thus distinguishing them from those due to dampness4 ,cement never should be stored on the ground4 ,build a raised platform for it and keep it away from the sides of the shelter4 ,as it is heavy1 care should be taken not to overload the supporting floor4 ,,fine ,,aggregate 7,,sand74 ,all grains1 small pebbles1 or particles of broken stone are considered as sand if they will pass through a wire screen with one-fourth inch meshes4 ,the particles or grains should be hard and well graded and should vary in size1 as a stronger concrete is thus obtained than when the size of the grains is nearly uniform4 ,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 #be per cent more cement4 ,the sand should be clean2 that is1 free from vegetable matter1 loam1 or any considerable amount of clay4 ,if the hands are soiled when a small quantity of sand is rubbed between them the following test should be made3 ,put #d inches of sand into a pint preserving jar1 fill with clear water to within an inch of the top1 fasten the lid1 and shake the jar vigorously until the whole is thoroughly mixed4 ,set the jar aside and allow the contents to settle4 ,the sand will settle to the bottom with the clay and loam on top of it4 ,if more than three-eighths of an inch of clay or loam shows1 the sand should be rejected or washed4 ,the difference in fineness and color shows clearly the line of division between the clay or loam and the sand4 ,illustration3 ,fig4 #a4--,sand and gravel washing trough4 ,should sand require washing the simplest way for small quantities is to build a loose board platform from #aj to #ae feet long1 with one end higher than the other4 ,on the lower end and sides nail #b by #f inch boards4 ,spread the sand over the platform in a layer #c or #d inches thick and wash with water4 ,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 water4 ,when pressure or a head is obtainable the water is most easily applied by means of a garden hose4 ,the washing should be started at the higher end and the water allowed to run through the sand and over the #b by #f inch piece at the bottom4 ,figure #a illustrates a convenient trough for washing larger quantities4 ,a small amount of clay1 provided it is not in lumps1 does not injure sand1 but amounts over #aj per cent should be washed out4 ,,coarse ,,aggregate 7,,stone1 ,,gravel1 ,,etc474 ,the larger particles used in concrete may be gravel1 broken stone1 air-cooled blast-furnace slag1 or other suitable materials4 ,the coarse aggregate should be sound and clean1 that is1 free from disintegrated or soft particles1 loam1 clay1 or vegetable matter4 ,air-cooled blast-furnace slag should weigh at least #gj pounds per cubic foot4 ,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 #b inch ring1 depending upon the work4 ,ordinarily the greatest dimension of any particle should not be over one-fourth of the thickness of the concrete work4 ,,gravel4 ,gravel which is too dirty for use usually can be detected by observation4 ,it may be washed in the same manner as sand4 ,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 cement4 ,,broken ,,stone4 ,broken stone should be clean1 hard1 and of a size suited to the character of the work1 and the same care in grading should be exercised as in the case of gravel4 ,trap1 granite1 hard limestone1 and hard sandstone are commonly used4 ,the composition and physical character of the stones should be considered1 as some possess qualities that limit their use under certain conditions 7see ,substitutes for gravel74 ,field stones are common in many localities and their use1 when crushed1 may be economical4 ,the finer particles1 after the dust is removed1 can be used as sand4 ,small stone crushers1 operated by three or four horsepower gasoline engines1 can be purchased at a relatively low price and may prove profitable if a large quantity of stone is needed4 ,,bank-,,run ,,gravel4 ,bank or creek gravel1 which will answer the purpose of sand and gravel combined1 sometimes can be obtained1 and frequently it is used in small jobs of concrete work just as it comes from the pit or creek4 ,although such gravel occasionally contains nearly the right proportions of sand and gravel1 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 each4 ,it is advisable to screen the sand and gravel and to remix them in the correct proportions1 as well-graded aggregates make stronger concrete and1 ordinarily1 enough cement will be saved to pay for the cost of screening4 ,experience has shown that it is advisable to screen bank gravel twice2 first over a screen with large meshes to eliminate particles too large for use4 ,the size of the mesh will depend upon the nature of the work involved 7see ,coarse aggregate72 then the material which has passed through this screen should be sifted again over a screen with one-fourth inch meshes4 ,all material which passes the latter screen may be considered sand and should conform to the characteristics discussed under ,fine aggregate4 ,,substitutes ,,for ,,gravel ,,or ,,stone4 ,for general work gravel or broken stone always is preferred to other coarse aggregate4 ,other materials at times are easier to obtain and1 when used with discretion1 will provide a satisfactory concrete4 ,broken terra cotta1 brick1 and old concrete1 if hard and strong1 may be used for unimportant work where no great strength is required1 but special care should be taken that the particles do not show on the finished surface4 ,the maxim that a chain is only as strong as its weakest link applies to concrete4 ,if the coarse aggregate is weaker than the cement mortar1 as in the case of some sandstones1 it should be used with caution4 ,the aggregate may have properties that render it unsuitable for use under certain conditions2 for instance1 cinders should not be used if water-tightness or strength is expected1 but they are useful for fireproofing4 ,material that disintegrates or flakes when heated is undesirable in places exposed to high temperature2 thus marble and some limestones should not be used in fireplaces4 ,some aggregates when exposed at the surface of concrete are apt to cause discolorations1 and when this would be objectionable aggregates of this type should be avoided4 ,flat or elongated slab-like fragments should be avoided1 as particles of this shape do not bond well2 slate and shale are examples4 ,,cinders4 ,cinders should be composed of hard1 clean1 vitreous clinkers1 free from sulphides1 soot1 and unburned coal or ashes4 ,as a precaution against the presence of small amounts of detrimental substances1 cinders should be soaked thoroughly with water #bd hours before being used4 ,if clean they will not discolor the hands when a small quantity is rubbed between the palms4 ,cinder concrete1 on account of its light weight1 commonly is used for filling between sleepers of floors and grading roofs1 and frequently for fireproofing1 for which it is very effective4 ,cinders should never be used when the concrete is to be subjected to heavy loads or abrasion4 ,,lava ,,rock4 ,lava rock varies widely in chemical composition and physical qualities4 ,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 work4 ,in general1 the lava rock found in the ,northwestern ,states is a suitable substitute for gravel4 ,rhyolite1 a light colored volcanic rock1 and many of the darker colored basaltic lavas can well be used for concrete for building purposes4 ,,water4 ,water should be clean and free from strong acid and alkali4 ,sea or brackish water should not be used if fresh water can be obtained4 ,,proportioning ,,the ,,materials4 ,in mixing concrete various proportions of cement1 sand1 gravel1 and water are employed1 depending upon the purpose for which the concrete is to be used4 ,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 mortar4 ,this perfection is seldom attained1 because the voids in each lot of gravel and sand vary slightly1 and in order to be absolutely safe a little more sand and cement than will just fill the voids are used4 ,the strongest concrete is not required in every structure1 and1 in many instances1 the cost of it would be unwarranted4 ,for important work involving large quantities of materials of unknown qualities1 tests should be made to determine the best proportions4 ,such tests1 being rather complicated1 are made usually in a laboratory1 and are not practical for the user of small quantities of concrete4 ,various proportions have been tested by experienced engineers to determine which1 under average conditions1 will develop the greatest strength1 best resist wear1 and assure greatest impermeability or water-tightness4 ,the mixtures given below have been found to meet the requirements indicated1 and having been adopted as arbitrary standards1 are recommended for use in farm concrete work4 ,the amount of water required is discussed under ,consistency4 ,,arbitrary ,,mixtures4 ,rich mixture4--,used for concrete subject to high stresses or where exceptional water-tightness and resistance to abrasion are desired3 #a3a-a_/b3c2 i4 e41 #a part cement1 #a-a_/b parts sand1 and #c parts gravel4 ,standard mixture4--,used generally for reinforced concrete and water-tight work3 #a3b3d2 i4 e41 #a part cement1 #b parts sand1 and #d parts gravel4 ,medium mixture4--,used for plain concrete of moderate strength3 #a3c3e2 i4 e41 #a part cement1 #c parts sand1 and #e parts gravel4 ,leaner mixtures are sometimes used after a test has proved them to be suitable for the work at hand4 ,it will be noticed that always in indicating the proportions the first number refers to the cement1 the second to the sand1 and the third to the gravel4 ,the three materials must be measured by volume1 using the same unit4 ,the cubic foot is a convenient measure1 because a sack of cement1 weighing #id pounds1 is considered to contain #a cubic foot4 ,when the coarse aggregate 7gravel1 etc47 is omitted the mixture is generally spoken of as mortar and the proportions are indicated thus1 #a3b1 meaning #a part cement and #b parts sand4 ,mortar is used for plastering1 stucco1 top coats of floors1 and for laying masonry4 ,,quantities ,,of ,,materials ,,required4 ,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 size1 because the small stones help to fill the voids between the larger ones and less sand-cement mortar is required4 ,the extra mortar thus adds to the volume of the concrete4 ,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 proportion4 ,for instance a #a3b3d mixture will not produce #f cubic yards of concrete1 if #b yards of sand and #d yards of gravel are used1 because the sand will lodge in the voids between the pebbles4 ,if #f cubic yards of concrete are desired it will be necessary to use #b4g cubic yards of sand and #e4cd cubic yards of gravel4 ,table #a shows the quantity of cement1 sand1 and gravel required under average conditions for the indicated proportions4 ,table #a4--,materials for #a cubic yard of rammed concrete4 ,proportions4 ,cement4 ,sand4 ,gravel4 ,cement4 ,sand4 ,gravel4 ---------------------------------------- ------------- ,sacks4 ,cu4 yds4 ,cu4 yds4 #a #a --- #ai4bj #j4gd --- #a #b --- #ac4dh #a4jj --- #a #b-a_/b --- #aa4jj #a4ja --- #a #c --- #aj4dj #a4af --- #a #a #b #aj4eb 4#ci #j4gh #a #a-a_/b #c #g4fd 4#db 4#he #a #b #d #f4jd 4#de 4#hi #a #b-a_/b #e #d4if 4#df 4#ib #a #c #e #d4fd 4#eb 4#hf #a #c #f #d4bd 4#dg 4#id ---------------------------------------- ------------ ,,consistency4 ,the quantity of water used in mixing has a very great influence on the strength of the concrete4 ,an excess of water weakens the concrete1 while an insufficient amount prevents thorough mixing4 ,illustration3 ,fig4 #b4--,the result of using too dry a mixture1 lack of spading and careless placing2 note irregularity of layers and poor bonding4 ,therefore1 only sufficient water should be used to produce a workable or plastic mixture4 ,recent tests have proved that to secure the greatest strength the concrete should be mixed considerably drier than has heretofore been customary4 ,of course1 for thin walls containing closely placed reinforcement1 or for water-tightness1 a fairly wet mix is necessary4 ,a little experience will show the proper amount of water to use4 ,a very rough estimate of the quantity of water required in mixing for general work is #d to #e gallons to each sack of cement4 ,three degrees of consistency 7corresponding to different proportions of water7 are used in general practice1 namely1 wet1 medium1 and dry4 ,in the light of recent investigations it is thought the wet mixture of present-day practice contains too much water4 ,the following definitions are therefore recommended3 ,wet mixture4 ,one that does not flow readily and yet can not be piled up4 ,it is recommended for thin sections when reinforcement is closely placed4 ,medium mixture4 ,one that is between the wet and dry mixture4 ,this consistency is recommended for general work4 ,dry mixture4 ,one about like damp earth4 ,if a handful is squeezed it will retain its shape4 ,this consistency requires thorough ramming to eliminate voids and is used when forms are to be removed immediately1 but should not be used where a water-tight job is expected4 ,the porous structure of the concrete in ,figure #b is due to the fact that it was placed as a dry mixture4 ,,estimating4 ,,estimating ,,concrete4 ,in estimating the amount of concrete in a given piece of work and the quantities of materials required1 the unit of measurement is usually the cubic yard 7#bg cubic feet74 ,the following examples will explain best the method of determining the quantities required3 ,example #a4--;,a wall #i inches thick1 #ab feet high1 and #cj feet long has a door opening #c feet wide and #f feet high1 also a footing #ah inches wide and #i inches deep4 ,the concrete is to be mixed in the proportions of #a3b3d4 ,the volume of the footing is found by multiplying together the dimensions expressed in feet1 thus1 #a-a_/b #c_/d #cj #cc-c_/d cubic feet4 ,similarly1 the volume in the wall is #c_/d #ab #cj1 less the door opening #c_/d #c #f #bef-a_/b cubic feet4 ,the total volume in footing and wall is #bij-a_/d cubic feet #aj-c_/d cubic yards4 ,to find the quantity of cement1 sand1 and gravel1 multiply the amounts for #a cubic yard1 indicated in line #g of ,table #a1 by #aj-c_/d1 and it will be found that #fe sacks of cement1 #d4hc cubic yards of sand1 and #i4ef cubic yards of gravel are necessary to build the wall4 ,example #b4--;,a pavement #bg feet long1 #d feet wide1 and #f inches thick has a #e-;inch base mixed in the proportions of #a3c3e and a #a-;inch surface mixed in the proportions of #a3b4 ,the volume in the base is #bg #d #e_/ab #de cubic feet #a-b_/c cubic yards4 ,the volume in the top is #bg #d #a_/ab #i cubic feet #a_/c cubic yard4 ,multiplying the quantities in line #i of ,table #a by #a-b_/c and those in line #b by it is found that the base requires #g4gd sacks cement2 #j4hf cubic yard sand2 #a4dc cubic yards gravel2 and the top requires #d4di sacks cement2 #j4cc cubic yard sand4 ,example #c4a--;,a tank #i feet inside diameter has walls #f inches thick and #d feet high 7above the floor74 ,the floor is #f inches thick1 the concrete is to be #a3b3d4 ,the volume in the floor is #aj_/b #aj_/b #bb_/g #a_/b #ci-b_/g ,cubic feet4 ,the area of the larger circle is #e #e #bb_/g #gh-d_/g cubic feet4 ,the area of the smaller circle is #d-a_/b #d-a_/b #bb_/g #fc-d_/g cubic feet4 ,the area of the wall1 therefore1 is #ae cubic feet and the volume is #ae #d #fj cubic feet4 ,the total volume in the structure is #ii-b_/g cubic feet or #c-b_/c cubic yards4 ,multiplying the quantities in line #g of ,table #a by #c-b_/c1 it is found that the following material is needed3 #bb4ad sacks of cement2 #a4fe cubic yards of sand2 #c4bg cubic yards of gravel4 #a ,a practical rule in finding the area of a circle is to multiply one-half the diameter 7radius7 by itself and the product by #bb_/g4 ,in finding the volume in the wall of a circular structure1 such as a silo or tank1 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 height4 ,,forms4 ,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 subjected4 ,concrete is plastic and will assume the shape of the form1 thus any imperfection or impression on the face of the forms will be reproduced4 ,wood is commonly used for forms1 as it can be easily worked into different shapes1 though various other materials sometimes are better adapted to special conditions4 ,cast iron1 for instance1 is suitable for casting small objects that are to be reproduced in quantities1 such as concrete block or tile2 plaster of ,paris1 glue1 or moist sand are employed for casting ornaments or to produce a fine1 smooth surface2 sheet metal is suitable when the forms can be used repeatedly or for such circular structures as silos4 ,when the sides of an excavation are not likely to cave in the earth may serve as a form4 ,,wood ,,forms4 ,wood for forms must be of a kind that is easily worked and that will retain its shape when exposed to the weather4 ,white pine is the best wood1 but is seldom used because of its cost4 ,spruce1 yellow pine1 and fir are satisfactory woods for forms and are best1 used partially green or unseasoned4 ,the edges of boards should be surfaced1 tongued and1 grooved1 or beveled in order to obtain a tight form1 so that the soft mortar will not ooze out4 ,a better surface99 is secured if the boards are dressed on one side and are free of loose knots or other imperfections4 ,as forms must be removed1 they should be so planned that they can be taken down without destroying the lumber1 especially if the boards are used for sheathing or again for forms4 ,therefore the nailing of the boards to the support should be only sufficient to keep them in place until the concrete has hardened4 ,greasing the surface next to the concrete with crude oil1 soap solution1 or linseed oil will prevent the concrete from adhering and facilitate removal4 ,,metal ,,forms4 ,metal forms can be used to advantage when the work involved is to be repeated many times4 ,if it is known or if it is probable that the forms may have to be altered1 the relative costs of wood and metal forms should be carefully determined4 ,metal forms of various types and designs may be purchased4 ,although the first cost may be high1 yet their use may lower the total cost when the work is such as to warrant it4 ,circular forms may be built as shown in ,figure #c4 ,the sheathing is generally of wood #d to #f inches wide1 or sheet metal1 and1 if of wood1 is laid perpendicular to the battens4 ,in forms of small diameter1 sheet metal sheathing is necessary if a smooth surface is desired1 as the #d-;inch boards can not be made to conform to a true circle4 ,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 battens4 ,,removal ,,of ,,forms4 ,the period of time after which forms may be removed varies according to conditions4 ,rich and dry mixtures set quickly1 and warm weather tends to hasten the setting of concrete4 ,the character of the structural member and the loadings also must be considered4 ,thus1 an unloaded wall #ab inches or more thick may be stripped of forms in from #a to #c days1 while the forms of thinner walls should remain in place from #b to #e days4 ,slab forms and the sides of beam and girder forms may be removed in from #f to #ad days if the span is not over #g feet4 ,the bottoms of beam and girder forms1 even though of a span less than #g feet1 should remain in place and braced form #aj to #ad days and even longer4 ,experience is the best guide to the time of removal1 but if there is any doubt ample time should be allowed1 especially in cold weather4 ,illustration3 ,fig4 #c4--,suggestion for circular form4 ,,building ,,and ,,setting ,,forms4 ,concrete1 while plastic1 exerts a great pressure on the confining walls1 necessitating rigid tying and bracing of the forms to keep them from bulging out of alignment4 ,the effect of the bulging of a form is corrected only at a considerable expense2 hence it is advisable to pour the concrete to a depth of not more than #b-a_/b or #c feet1 allowing it to set or harden before pouring more4 ,the form most used in concrete construction is that for a straight wall4 ,the methods of building such a form apply in general to the forms for most structural work1 though modifications may be necessary to meet particular conditions4 ,illustration3 ,fig4 #d4--;,form for basement or cellar wall4 ,the earth may be used as an outside form if it is sufficiently firm4 ,the straight wall form may be built continuous 7,figs4 #d and #e71 or in panels of a size convenient to handle1 and from stock lengths of lumber 7,fig4 #f74 ,generally the face boards are placed horizontally and secured to studs or posts4 ,the face boards may be #a or #b inches thick and from #f to #aj inches wide1 preference being given to the narrower widths1 which are less liable to cup or warp4 ,the thickness depends upon the spacing of the studs1 the number of times the forms are to be used1 and the depth of pouring4 ,ordinary sheathing1 if the joints are made tight1 is satisfactory for foundations of dwellings1 etc41 and the studs1 if #b by #d inches1 should be spaced #ah inches on centers4 ,the studs for a long1 high form had best be #d by #d inches or #b by #f inches1 spaced from #b to #c feet center to center4 ,the studs of the inside and outside forms must be tied together to prevent spreading2 this is conveniently done with ,no4 #aj wire1 as shown in ,figure #d1 or with one-half or three-quarter inch bolts1 which is the more expensive method4 ,bolts should be greased to facilitate removal4 ,temporary spacers of wood1 #a by #b inches1 of a length equal to the thickness of the wall1 should be used to prevent drawing the forms together when the wire or bolt is tightened4 ,they should be spaced at the ties1 but need not be at every wire1 and are knocked out and removed as the concreting progresses4 ,illustration3 ,fig4 #e4--,straight wall form for level ground4 ,the ties should be spaced on each stud about #b-a_/b feet vertically4 ,if more than #c feet of concrete is poured at one time the ties should be closer together1 vertically1 at the bottom of each pouring4 ,the thickness of the wall does not affect the number of ties4 ,on removing the forms the wires should be clipped close to the face of the concrete and punched back1 unless the surface is to be stuccoed4 ,if a pit hole is caused by punching back the wire it should be pointed up with mortar1 which then should be rubbed to make it blend with the general surface4 ,,mixing4 ,,preparation ,,of ,,plant4 ,before starting to mix1 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 materials4 ,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 forms4 ,it is more economical to wheel material a distance of from #aj to #be feet than to carry it in shovels4 ,eight feet is about as far as it is profitable to shovel4 ,when material is to be wheeled1 runways of planks should be provided1 because more material can be handled in a given time1 and the wear and tear on men and equipment is not so great4 ,the planks used in the runways should be thick enough to sustain the weight passing over them and should be #aj to #ab inches wide to permit foot room4 ,they should be anchored securely and made rigid1 as springy or loose boards retard progress of the work4 ,smooth joints in the planking will prevent bumping and stumbling4 ,illustration3 ,fig4 #f4--,sectional forms4 ,,number ,,of ,,men4 ,the number of men required is determined by the amount of concrete to be placed in a given time1 the method of mixing1 and the size of the batch2 that is1 the number of bags of cement mixed at one time4 ,the amount of concrete one man can mix by hand in a day depends upon the experience of the man1 the layout of the work1 and other duties required of him4 ,one man should average #a-a_/b to #a-c_/d cubic yards of concrete in eight hours1 including mixing and wheeling not more than #ej feet4 ,the gang for a one-bag batch may consist of #c men1 but a larger number make a more efficient force1 for when the concrete is mixed by hand the men can take turns at the various tasks and will not tire so easily4 ,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 profit4 ,,machine ,,mixing4 ,good concrete can be mixed by hand or machine4 ,the quantity of concrete work in prospect is the factor that determines the more economical method4 ,a small amount 7say #ajj to #bjj cubic yards7 does not warrant the purchase of a machine1 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 #ae cubic yards4 ,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 use4 ,the two types of mixers most used are the batch mixer1 which mixes and dumps a definite quantity1 and the continuous1 which discharges a constant stream of concrete4 ,the continuous type is not adapted to farm work unless the concrete can be handled as fast as it is mixed1 thus permitting the machine to work continuously4 ,illustration3 ,fig4 #g4--;,home made concrete mixer4 ,there are numerous types and various sizes of batch mixers4 ,a one-bag batch machine is most suitable for general work1 though there are smaller mixers that may prove handy4 ,some of the smallest sizes are operated by hand1 but the medium and large sizes are power operated4 ,mixers can be had with or without the power plant attached and may be stationary or on wheels1 which facilitate moving to different sites4 ,engines used for sawing wood1 the larger ones used for pumping water1 and tractors furnish sufficient power to operate an average mixer4 ,figure #g shows a homemade mixer built of discarded farm implement parts and operated by the farm engine4 ,directions for operating a mixer are generally furnished with the machine4 ,the tendency is to use too much water in mixing concrete in a machine4 ,the consistency of the mixture should be as described under the heading ,consistency on page #h4 ,the mixing should be continued for at least a minute after the drum has been charged1 but a better mixture is secured if two minutes are allowed4 ,at the end of each day's work the machine should be thoroughly washed1 and when not in use it should be well greased and covered4 ,,hand ,,mixing4 ,hand mixing is the more economical on the farm unless a large amount of work is to be done at one time4 ,few tools need be purchased1 and1 as a rule1 only farm help need be employed4 ,the following tools will be needed in mixing and placing plain concrete3 ,two or more square-end short-handled shovels1 #a heavy garden rake1 #a sprinkling can or bucket 7if a hose is not available71 #a #eb-;gallon barrel1 #b wheelbarrows with metal trays1 #a sand screen 7,fig4 #h71 #a tamper 7,fig4 #i71 #a wood float or trowel 7,fig4 #aj71 measuring boxes 7,fig4 #aa71 mixing board 7,fig4 #ab71 #a spader 7,fig4 #ac74 ,the number of shovels and wheelbarrows needed will depend upon the size of the batch1 number of men mixing1 and the layout of the work4 ,long-handled pointed shovels will be found more convenient at the sand and gravel piles4 ,a bottomless box is necessary for convenient and accurate measurement of the sand and gravel4 ,where wheelbarrow measurement of materials is practiced1 as in charging a mixer1 the capacity of the wheelbarrow should be determined by use of a measuring box4 ,the box may be made as illustrated in ,figure #aa1 from boards #ab inches wide4 ,the dimensions in ,table #b are of boxes for use in measuring quantities for mixtures of various proportions1 assuming that one bag of cement is used in a batch4 ,if two bags are used in a batch the boxes should be filled twice4 ,illustration3 ,fig4 #h4--,sand screen4 ,illustration3 ,fig4 #i4--,tampers4 ,illustration3 ,fig4 #aj4--,wooden float4 ,illustration3 ,fig4 #aa4--,measuring box4 ,illustration3 ,fig4 #ab4--,mixing ,board4 ,illustration3 ,fig4 #ac4--,spading tool4 ,table #b4--;,inside dimensions of measuring boxes for various proportions4 #a-;bag batch1 box #ab inches deep4 ,proportion4 ,box for sand4 ,box for gravel4 ----------- --------------- ---------------- ,feet4 ,feet4 #a3a3b #a by #a #a by #b #a3a-a_/b3c #a by #a-a_/b #a by #c #a3b3d #a by #b #b by #b #a3b-a_/b3e #a-a_/d by #b #b by #b-a_/b #a3c3e #a-a_/b by #b #b by #b-a_/b #a3c3f #a-a_/b by #b #b by #c ,a tight platform should be provided similar to that illustrated in ,figure #ab upon which to mix the concrete4 ,for mixing #a or #b bag batches a platform #i by #aj feet will serve4 ,,directions ,,for ,,hand ,,mixing4 ,the mixing board should be located in convenient relation to the supply of materials and the work and should be level4 ,the sand box is placed on the board1 about #b feet from one of the longer sides1 and filled level with sand2 the box is then lifted away and the sand spread in a #c or #d inch layer4 ,the cement is spread as evenly as possible on' top of the sand4 ,two men with shovels1 standing on opposite sides of the pile1 turn the sand and cement in such a way that the materials axe thoroughly mixed4 ,in turning the material it should not be simply dumped off the shovel1 but should be shaken off the ends and sides1 so that the two constituents will be mixed as they fall4 ,the mass should be turned two or three times1 or until it is of uniform color and there are no streaks of either sand or cement4 ,a man with a hoe or rake may assist by raking the top over as the two men turn4 ,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 top4 ,the box is filled with gravel and then removed1 the gravel being spread over the sand-cement mixture4 ,the mass is soaked with about one-half the quantity of water to be used1 care being taken not to wash away any of the cement4 ,the materials then should be turned over in much the same manner as was the sand-cement1 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 shovel4 ,the wet gravel picks up the sand and cement as it rolls over when dragged back4 ,the mixing should be continued until the mass is uniform1 water being added to the dry spots during the mixing until the desired consistency is obtained4 ,experience counts considerably in mixing concrete with the least amount of labor2 ordinarily three or four turnings are required to mix the materials thoroughly4 ,after the final turning the concrete should be shoveled into a compact pile and then is ready for placing in the forms4 ,,placing4 ,,placing ,,concrete4 ,the mixed concrete should be deposited in the forms within from #bj to #cj minutes from the time the water is added to the cement1 as it begins to set or harden after this time4 ,to disturb the concrete after the set has begun is risky1 as it will lose some of its strength1 the extent of the injury depending upon the seriousness of the disturbance4 ,concrete which has set before it can be placed in the forms should not be tempered or softened with water1 but should be discarded4 ,to prevent delay in placing1 all forms should be examined before the mixing is begun to see that they are properly braced1 that all chips or loose particles are removed1 that the surface of concrete which has set has been properly roughened and wetted to assure a bond1 as described on page #bj1 and that all reinforcement1 bolts1 inserts1 etc41 are properly located and secured4 ,at the lunch' period1 or at the end of a day's work1 the mixing board and equipment should be thoroughly washed1 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 workers4 ,moreover1 it will save time and wear and tear of equipment incident to cutting the surplus concrete away with a cold chisel4 ,illustration3 ,fig4 #ad4--aeib ,showing result of leaky forms and poor placing4 ,the soft cement mortar ran out1 leaving areas of honeycombed surface not necessarily harmful but unsightly4 ,in depositing concrete in the forms care should be taken that the materials do not separate4 ,if the mixing is done close to the place of depositing1 the concrete may be shoveled into the forms directly or through a chute4 ,if it is necessary to lift or transport the concrete1 buckets and wheelbarrows are convenient containers4 ,the concrete should be deposited in horizontal layers1 preferably not over #f inches thick1 and a spade or paddle should be worked up and down against the forms to push the coarse material away from the surface1 as illustrated in ,figure #ac4 ,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 surface4 ,in addition to being spaded1 stiff concrete should be rammed until water flushes to the surface4 ,tapping the forms with a hammer is a very effective way of securing a smooth surface4 ,figure #ad shows the result of improper spading4 ,fresh concrete will riot bond readily to concrete that has hardened and a seam may be formed that will permit water to trickle through4 ,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 stone1 and to clean off all loose particles4 ,the hardened concrete should be soaked with water1 the excess water removed1 and the surface then given a coat of grout 7a mixture of cement and water7 of the consistency of cream just before the new concrete is deposited4 ,when pouring of a wall is to be discontinued for some time1 provision for the bonding of future work should be made4 ,this may be done by placing short steel dowels in the concrete when it is poured1 or a rebated joint or groove may be made1 as shown in ,figure #ae4 ,in bonding a new wall to old concrete1 holes should be drilled for the dowels1 which should be grouted in1 and the old surface should be roughened1 cleaned1 and wetted2 or a groove may be cut in the old wall to receive the new concrete4 ,illustration3 ,fig4 #ae4--,method of forming horizontal rebate4 ,,placing ,,under ,,water4 ,concrete can be placed under still water if proper precautions are taken4 ,it should never be placed1 while soft1 in running water unless a form or cofferdam is used1 as the cement will be washed out4 ,when concrete is to be placed under water a form of tube or chute1 known as a tremie 7,fig4 #af71 may be used advantageously4 ,the tube should be of sheet metal1 about #h inches in diameter1 with a hopper on top1 and means should be provided for quickly raising and lowering it without jolts1 so that the concrete will feed out at the bottom without breaking the seal4 ,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 concrete1 mixed somewhat soft so that it will flow easily1 should be maintained4 ,scum or laitance is likely to form on concrete when placed under water1 and unless all of the concrete is6 poured in one operation and brought to a little above the water surface1 seams or planes of weakness will occur4 ,,care ,,of ,,concrete4 ,after the concrete has been poured1 care should be taken that it does not dry out too quickly1 and in hot weather it must be protected from the sun4 ,exposed surfaces and objects made of dry concrete should be sprayed thoroughly with water twice or oftener each day for a week or #aj days4 ,sometimes surfaces are shielded with canvas1 paper1 boards1 or layers of moist sand4 ,illustration3 ,fig4 #af4--,tremie for use in placing concrete under water4 ,,protection ,,from ,,freezing ,,weather4 ,,concreting ,,in ,,freezing ,,weather4 ,if suitable methods are used1 good concrete work can be done in cold weather1 but with more difficulty and at somewhat greater cost than when the weather is warm4 ,ordinarily it is best not to attempt to do concrete work during freezing weather4 ,however1 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 operations4 ,concrete must be protected from alternate freezing and thawing until it has set4 ,cold retards the setting and hardening of concrete2 therefore1 even though the temperature is not at the freezing point1 the concrete should be protected and special care taken not to subject it to loads4 ,the forms should be kept in place until there is no doubt that the concrete has properly hardened4 ,hot water should be poured on the concrete to make sure that apparent hardness is real and not due to a frozen condition4 ,just before the concrete is placed all ice and frost should be removed from the forms and reinforcement1 if used1 by warming the surfaces with steam or by other means4 ,concrete that has been frozen once may1 with proper care1 attain its ultimate strength1 but should it freeze a second time the chances of saving the work are very slight4 ,exposed surfaces are apt to scale or pit if the concrete is allowed to freeze before it is thoroughly hardened4 ,pleating the materials1 protecting the green concrete1 and the use of salt are precautions generally taken to prevent freezing4 ,,the ,,use ,,of ,,salt4 ,the use of salt is objectionable1 as it forms a white efflorescence on exterior surfaces and is liable to corrode the steel in reinforced concrete work4 ,the quantity of salt required varies with the temperature1 but it should not exceed #aj per cent of the weight of the water used in mixing4 ,a #aj per cent solution is eight-tenths 7approximately #ac ounces7 of a pound of salt per gallon of water and will prevent freezing at a temperature of #bb ,f4 ,lower temperatures would require a greater proportion of salt1 which would impair the strength of the concrete1 and hence is not practicable4 ,a rule1 frequently advocated1 for varying the percentage of salt is to use #a-a_/c ounces per gallon of water for each degree ,fahrenheit below freezing4 ,since it is impossible to foretell the exact drop in temperature1 the exact quantity of salt can not be predetermined1 so that provision should be made for several degrees lower than anticipated4 ,the salt should be dissolved in the mixing water1 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 work4 ,,the ,,use ,,of ,,heat4 ,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 developed4 ,in extreme weather protection may be needed for five or six days4 ,when the weather is cold but not freezing1 heating the materials will be sufficient4 ,if a freeze is expected the concrete work should be protected by wood inclosures1 paper1 or canvas1 over which1 if the surface is horizontal1 may be spread a #f or #h inch layer of straw4 ,manure should not be used to protect fresh concrete1 since the acids in it are destructive and cause unsightly stains4 ,splits or other openings in coverings may admit cold1 which may freeze parts of the work4 ,as the temperature drops 7to about #bj ,f47 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 salamanders4 ,mass work1 except in very cold weather1 will not require as careful protection as thin sections and1 as a rule1 the forms are sufficient if the exposed parts are covered4 ,,heating ,,materials4 ,the water can be heated sufficiently for use in concrete 7approximately #aej ,f47 in kettles on stoves or by steam from a boiler4 ,a metal smokestack placed horizontally with a fire in one end makes an efficient heater for the sand and gravel4 ,the materials are piled over the stack1 but not so high that their weight will crush the pipe4 ,small quantities of sand and gravel may be heated on top of metal plate with a fire under it4 ,if a small boiler is available it may be economical to use steam for heating the sand and gravel4 ,steam is effective when forced from nozzles into the piles or circulated through perforated pipes placed under the material4 ,covering the piles with canvas or other material will retain much of the heat4 ,,contraction ,,and ,,expansion ,,joints4 ,concrete expands and contracts with changes in temperature1 causing cracks to appear4 ,contraction cracks occur in thin sections exposed to wide variations in temperature and are common in sidewalks2 therefore1 large stretches of concrete should not be laid without breaks or spaces to allow for the changes in size4 ,the spaces should be filled with tar or some similar material that will yield or give when the concrete expands4 ,a joint like that shown in ,figure #ag is frequently used for thick walls4 ,a section of the wall is poured and before the next is poured the abutting end is covered with tar and paper1 the thickness of the covering depending upon the length of the section and the exposure4 ,sidewalks and similar work1 when not cast in alternate blocks1 should have a one-fourth inch space left at intervals of #dj feet4 ,the joint may be filled with tar paper or tar4 ,steel is used to take care of contraction in long or high walls and water-tight work4 ,important structures in which temperature reinforcement is necessary should be designed by one experienced in concrete design4 ,illustration3 ,fig4 #ag4--;,expansion joint showing rebate form removed and filler in place4 ,,lintels4 ,the subject of reinforced concrete is not within the province of this bulletin1 but as openings of various widths are required in the walls of most farm structures1 a general explanation is given of the reinforcement of lintels or that portion of concrete immediately above an opening1 such as a floor or window4 ,a lintel is a beam1 and when a beam bends the lower part is stretched or pulled while the upper portion is compressed4 ,good concrete will stand great pressure but is not capable of resisting any great pulling or tensile stress4 ,for this reason steel is used in the lower portion to take care of the tensile or pulling force4 ,it will be found generally satisfactory1 where no heavy or concentrated load occurs over an opening and the span is not more than #d feet1 to place two rods three-eighths of an inch in diameter in the bottom of the lintel1 so that there will be #a inch of concrete below them4 ,two diagonal rods should be placed at each top corner of a window or door1 as shown in ,figure #ah4 ,when the opening is between #d and #h feet the rods should be bent up as shown in ,figure #ai and when between #h and #ab feet1 three one-half inch rods should be used1 two of them being bent4 ,barbed wire1 old fencing1 and scrap or rusty iron is not suitable for reinforcement4 ,loose rust should be cleaned off the rods and they should be free of grease and oil4 ,illustration3 ,fig4 #ah4--,reinforcement of openings less than #d feet wide4 ,illustration3 ,fig4 #ai4--,reinforcement of openings more than #d feet wide4 ,,surface ,,finish4 ,joints and imperfections in the forms are reproduced on the concrete surfaces4 ,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 placed4 ,such imperfections do not necessarily affect the strength of the concrete1 but they do detract from the appearance 7see ,fig4 #ad74 ,too of ten the finishing of the concrete work in even the more important farm buildings is neglected4 ,with little extra trouble exposed surfaces can be given a finish which will add to the attractiveness and hence the value of the completed work4 ,rubbing off the form marks and pointing up depressions or holes greatly improves the appearance of the work4 ,the rubbing may be done with a wooden float or hard-burned brick1 using a little sand and water as an abrasive and a #a3b mortar for pointing up4 ,the surface can be worked best if the forms are removed within #bd hours or before the concrete has set too hard4 ,after the concrete has hardened it may be necessary to use a carborundum block for rubbing4 ,a pleasing finish can be secured by scrubbing the surface with a stiff fiber or wire brush1 using plenty of water to wash off the loosened particles4 ,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 effectively4 ,artistic effects can be secured by picking or tooling the surface with a bush hammer1 toothed chisel1 or pick4 ,for such treatment the concrete should be two or three weeks old to prevent breaking out the aggregate4 ,other finishes may be obtained by etching with acid to expose selected colored aggregates and by the application of stucco4 ,the limitations of the bulletin do not permit of a discussion of these more elaborate treatments4 ,,concrete ,,exposed ,,to ,,fire4 ,concrete is practically fireproof in that it can not be consumed by fire1 but unless properly made and of the right materials it will disintegrate1 at least on the surface4 ,to resist fire concrete should be mixed fairly rich1 say1 #a3a-a_/b3c1 or #a3b3d and special care should be taken to grade the sand and gravel to secure a dense mixture4 ,the aggregates should be selected with a view to their fire-resisting properties4 ,the sand should be siliceous and the larger aggregate should not disintegrate when heated2 hence1 marble1 granite1 limestone1 materials containing quartz1 and some gravels are unsuitable4 ,cinders are specially valuable1 due to their non-conductivity1 but can not be used where strength is required4 ,trap rock will resist destruction by heat and produce a strong concrete4 ,blast furnace slag is very good for this purpose4 ,fireplaces and chimneys of dwellings#b may be constructed of ordinary concrete but the back1 jambs1 and inner hearth1 which are directly exposed to the heat of the fire1 should be made of specially prepared concrete as described above or should be lined with firebrick1 although concrete made with broken hard-burned brick or terra cotta has been used successfully4 ,if suitable large-sized aggregate is not available a mixture of one part cement and three parts sand may be used4 #b ,see ,farmers' ,bulletin ,no4 #abcj1 ,chimneys and ,fireplaces1 ,u4 ,s4 ,department of ,agriculture4 ,,water-,,tight ,,concrete4 ,practical water-tightness in concrete may be secured by using a fairly rich mixture properly proportioned4 ,foreign ingredients1 membrane and surface coatings1 or other means need not be used1 except where poor workmanship is likely or where considerable damage and inconvenience may result in case of leakage4 ,under such circumstances the membrane treatment used in addition to a properly proportioned concrete1 while the most expensive method of waterproofing1 probably will give the most reliable results4 ,this treatment consists of layers of burlap or tar paper cemented to the surface and together with tar or asphalt4 ,where the membrane is subject to injury it is sometimes protected by a coating of cement mortar or brick backing4 ,first-class workmanship and special attention to details are required to secure water-tightness4 ,the essential requisite is that the voids be filled4 ,a lean mixture may be made more impervious by using hydrated lime which tends to fill the voids and makes the concrete flow easily4 ,a little more cement in the mixture would serve the same purpose4 ,the lime should not be in excess of #aj per cent of the weight of the cement and under no circumstances should unslaked lime be used4 ,the materials for water-tight concrete must be well graded1 so as to obtain a maximum density2 that is1 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 sand4 ,a #a3b3d concrete will prove practically impermeable in ordinary construction1 but if a head or pressure of water is to be resisted a #a3b3c or richer mixture may be necessary4 ,the consistency is very important4 ,a sluggishly flowing consistency is best1 for if the concrete is too wet the mortar may flow away from the stone1 leaving leaky places and1 if too dry1 the mass may prove porous4 ,the proportions and consistency must be accurately maintained for each batch and the concrete must be exceptionally well mixed4 ,it is necessary to exercise great care in the placing of the concrete4 ,where practicable1 the structure or object should be poured in one operation to avoid leaky joints1 but when this is not possible precautions should be taken to secure a tight joint between concrete of different ages4 ,the surface of concrete which has set must be cleaned of dirt and scum down to the true concrete4 ,this surface then should be well whetted and painted immediately with a creamy mixture of cement and water before placing the new concrete4 ,a good plan1 when discontinuing work on structures intended to hold liquids1 is to embed a #f or #h 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 concrete4 ,a wall thick enough to resist the stresses put upon it will generally resist percolation of water1 but #f inches may be considered as a minimum4 ,contraction and expansion must be controlled to avoid the occurrence of leaks4 ,to guard against cracks due to unequal settlement or other causes1 most concrete designed for water-tightness should be reinforced4 ,in some mass work1 special contraction joints1 as described on page #bc may be necessary4 ,rules for the use of reinforcement and contraction joints can not be given1 as the requirements in each case vary with the conditions to be met4 99 99 99 99 99 ,,organization ,,of ,,the ,,united ,,states ,,department ,,of ,,agriculture ,october #ba1 #aibi ,secretary of ,agriculture ,arthur ,m4 ,hyde4 ,assistant ,secretary ,r4 ,w4 ,dunlap4 ,director of ,scientific ,work ,a4 ,f4 ,woods4 ,director of ,regulatory ,work ,walter ,g4 ,campbell4 ,director of ,extension ,work ,c4 ,w4 ,warburton4 ,director of ,personnel and ,business ,w4 ,w4 ,stockberger4 ,administration ,director of ,information ,m4 ,s4 ,eisenhower4 ,solicitor ,r4 ,w4 ,williams4 ,weather ,bureau ,charles ,f4 ,marvin1 ,chief4 ,bureau of ,animal ,industry ,john ,r4 ,mohler1 ,chief4 ,bureau of ,dairy ,industry ,o4 ,e4 ,reed1 ,chief4 ,bureau of ,plant ,industry ,william ,a4 ,taylor1 ,chief4 ,forest ,service ,r4 ,y4 ,stuart1 ,chief4 ,bureau of ,chemistry and ,soils ,h4 ,g4 ,knight1 ,chief4 ,bureau of ,entomology ,c4 ,l4 ,marlatt1 ,chief4 ,bureau of ,biological ,survey ,paul ,g4 ,redington1 ,chief4 ,bureau of ,public ,roads ,thomas ,h4 ,mac,donald1 ,chief4 ,bureau of ,agricultural ,economics ,nils ,a4 ,olsen1 ,chief4 ,bureau of ,home ,economics ,louise ,stanley1 ,chief4 ,plant ,quarantine and ,control ,c4 ,l4 ,marlatt1 ,chief4 ,administration ,grain ,futures ,administration ,j4 ,w4 ,t4 ,duvel1 ,chief4 ,food1 ,drug1 and ,insecticide ,walter ,g4 ,campbell1 ,director of ,administration ,regulatory ,work1 in ,charge4 ,office of ,experiment ,stations ,e4 ,w4 ,allen1 ,chief4 ,office of ,cooperative ,extension ,work ,c4 ,b4 ,smith1 ,chief4 ,library ,claribel ,r4 ,barnett1 ,librarian4 ,this bulletin is a contribution from ,bureau of ,public ,roads ,thomas ,h4 ,mac,donald1 ,chief4 ,division of ,agricultural ,engineering ,s4 ,h4 ,mc,crory1 in ,charge4 ,u4 ,s4 ,,government ,,printing ,,office3 #aibi 99 99 99 99 99 ,transcriber ,notes ,all illustrations were moved so as to not split paragraphs4