Farm Concrete Work1

Concrete is an ideal material for foundation walls, floors, walks, steps, water tanks, and countless other jobs on the farm. It is economical, strong, durable, sanitary, and attractive in appearance. To insure most satisfactory result«, however, a working knowledge of how to make good concrete is essential. The principles outlined in the following pages are easily understood and can be readily mastered.

332. Action of Cement.—In a concrete mixture, the cement and water form a paste that, upon hardening, binds or cements the particles of sand and pebbles or crushed rock together into a permanent mass. (The hardening is caused by chemical action between the water and the cement.) The use of too much water thins or dilutes the paste and weakens it. Consequently, it is very important that the proper proportions of cement and water be used.

333. Specifying Mixtures.—Until the recent discovery that the strength, durability, and watertightness of concrete are dependent, upon the proportions of water to cement, it was customary to specify mixtures as 1 part of cement to a certain number of parts of sand and pebbles. Modern practice is to specify the amount of mixing water for each sack of cement, the amount varying according to the class of work. For example, the recommended mixture, for tanks, cisterns, and similar work, is 5 gal. of water per sack of cement for sand and pebbles of average dampness. Six gallons would be used for dry sand and pebbles (see Table VI).

334. Determining the Proportions of Sand and Pebbles.—Table VI gives recommended quantities of mixing water for different classes of concrete work and also suggests proportions of cement, to sand and pebbles to use for trial batches. It may be found that these trial proportions give a mix that is too wet, or a mix that is too stiff, or one that lacks smoothness and workability. If the mix proves to be too wet, add sand and pebbles slowly until the right degree of wetness is obtained. On the other hand, if the mix proves to be too stiff, use less sand and pebbles in the next batch. In this way the best proportions for a given job can

1 The material in this section is compiled largely from publications of the Portland Cement Association.

Table VI.—Recommended Proportions or Water to Cement and Suggested

Trial Mixes

Kind of work

Add U.S. gallon, of water to nach one-«ack batch if sand is

Suggested mixture for trial hatch

cite. in.

WCt 1 ug.-)

Damp

. 1 eu. ft, sacks

Pebbles, cu. ft.

$-Oal. Past* /or Concrete Subjected to Severe We*r, Weather, or Weak Acid and Alkali Solution»

Colored or plain topping for heary wearing frurfac/us; aK two-course work Auch iLs pavement*, walks, residence floors, etc

Fence port*. flower botea. garden furniture; work of very thin auctions; all concrete in contact with weak acid Or alkali solutions

4>4 3 H

4

4?S <H

1

IH

IK 2

H H

6-Gal. Paste for Concrete to Bo Watertight or Subjected to Moderate Wear and Weather

Watertight floors such ad base raent, dairy bam, milk houses, etc.

Watertight basement wails and pita, waUs above ground, grain bins, s»il<x=. manure pits, scale pit*, dipping vat*, dams, lawn roller*, hotbeda, cold frame?, storae* Mlltft» etc.

Water ftt»rage tanks, ciate-rns, septic tanks, sidewalks, feeding floors, barnyard pavements, driveways, barn approach«, steps, porch floors, corner postr.. gate pose*, piers, columns, sillr.. lintels, chimney capa. etc

5

W

1

3

iH

7-GaI. Paate for Concrete Not Subjected to Wear, Wither, or Water

Foundation walls, footings, retaining walls, engine base«, maw concrete. eU.. not subjected to weather, water pressure, or other exposure

flK

1

2H

4

i -

Not*.—It tn*y be neo<w«ary to u«e a richer paste than ie ah own in the tahle because the concrete may be subjected to more eevere condition a than are usual for a structure of that type. For example, a water storage tank ordinarily ia made with a 6-gaI. p&M*. However, the tank may be built in a place where the »oil water ia etrongly alkaline, in which caee a S-gtL paste is required.

Not*.—It tn*y be neo<w«ary to u«e a richer paste than ie ah own in the tahle because the concrete may be subjected to more eevere condition a than are usual for a structure of that type. For example, a water storage tank ordinarily ia made with a 6-gaI. p&M*. However, the tank may be built in a place where the »oil water ia etrongly alkaline, in which caee a S-gtL paste is required.

be determined. In general the following rules for proportioning may be given. These are based on damp sand. If the sand is absolutely dry, a condition seldom encountered, use 25 per cent less.

1. For coarse aggregate ranging from up to in., use approximately equal parts of sand and pebbles.

2. For coarse aggregate ranging from H up to % in., use about three-quarters as much sand as pebbles.

3. For coarse aggregate ranging from up to in., use about half as much sand as pebbles.

335, Workability of Mixtures,—A workable mixture is one of such plasticity and wetness that it can be placed in the forms readily, and when spaded or tamped will result in a dense concrete. In a workable mixture

Fia. 278.—A. The mix on tho left is one that does not contain enough cement-sand mortar to fill tho spaces between pebbles. Thia mix is hard to work, rough, and porous.

B. The mix in the center has an cxcess* of mortar. It i* plastic and workable but is exponsiv© owing to the small yield of concrete per bag of cement. It is alf*o likely to be porous.

C. The mix on the right contains the correct amount of mortar. With light troweling tho spaces between pebbles are filled. Note how it hang* together on the edge* of the pile. This intx given maximum yield of concrete and produces smooth, denne aurfacos.

there is sufficient cement-sand mortar to give good smooth surfaces free from rough sjjots, called honeycombing, and to bind the piece« of coarse aggregate into the mass so they will not separate out in handling. In other words there should be just enough cement-sand mortal* to fill completely the spaces between the pebbles and to insure a smooth, plastic mix. Mixtures lacking sufficient mortar will be harsh, hard to work, and difficult to finish. On the other hand, the use of too much sand should be avoided as it increases porosity and reduces the amount of concrete that can be produced with a sack of cement.

A workable mixture for one class of construction may be too stiff for another. Concrete to be deposited in thin sections, like fence posts, tank

Fio. 279-—This is how a well-graded coarse aggregate appears before and after being separated in three size». Reading from left to right, in the separated aggregate, % to lH-in % to K-in. afie, and K to ^ in. Note how the smaller piece* fit in between the larger ones in the mixed aggregate, thus producing a dense mixture.

walls, etc., must be more plastic than, if used in heavier work like foundation walls, footings, and floors. Very wet, sloppy mixtures are to be avoided as they result in weak, porous concrete.

A good rule to follow is to so proportion the amount« of sand to pebbles as to obtain the greatest volume of concrete of plasticity suitable to the character of the work. Under no circumstances should the ratio of water to cement be varied from the quantities given in Table VI.

336. Watertight Concrete.—The ratio of water to cement governs the water tightness or impermeability of the concrete, as well as its strength. A workable mixture in which not more than 6 gal. of water have been used for each sack of cement will usually produce watertight concrete. The addition of more water increases permeability. Sloppy mixtures, unless they contain a high cement content, are generally quite porous. Proper curing is also essential to obtain watertight concrete (see Art. 349, page 255).

337. Aggregates.—Sand and pebbles or broken stone are usually spoken of as aggregate. Sand is called fine aggregate, and pebbles or crushed stone, coarse aggregate. Fine aggregate, such as sand or rock screenings, includes all particles from very fine (exclusive of dust) up to those which will just, pass through a screen having meshes in. square. Coarse aggregate includes all }>ebbles or broken stone ranging from up to V/i or 2 in. The maximum size of coarse aggregate to be used is governed by the nature of the work. In thin slabs or walls the largest pieces of aggregate should never exceed one-third the thickness of the section of concrete being placed.

338. Sand.—Sand should be clean, hard, and free from fine dust, loam, clay, and vegetable matter. These materials are objectionable because they prevent a good bond between the cement and the particles of sand, thereby reducing the strength of the concrete and increasing its porosity.

Sand should be well graded, that is, the particles should not all be fine nor all coarse, but should vary from fine up to those particles that will just pass a screen having meshes Yi in. square. If the sand is well graded, the finer particles help to fill the spaces (voids) between the larger particles, thus resulting in a denser concrete and permitting the most economical use of cement in filling the remainder of the spaces and binding the sand particles together.

339. Coarse Aggregate.—Pebbles or crushcd stone to be used in a concrete mixture should be tough, fairly hard, and free from any of the impurities that would be objectionable in sand. Stone containing a considerable quantity of soft, flat, or elongated particles should not be used.

Fie*. 280,—Sample of wctl-*radcd sand before and after it has been separated in various aiaca. Particles vary from fine up to ]/i in. in «ue. Width of strips indicates amounts of cach size. This is a good aand for concrete work.

Fig. 281.—Sample of »and that lacks particlca above in. in else and how it looks when s*para4<xl into four sizes. More cement is required when sand is fine. This is not a good concrete sand.

340. Bank-run Gravel.—The natural mixture of sand and pebbles as taken from a gravel bank is usually referred to as bank-run material. In bank-run material, fine and coarse aggregates are seldom present in the right proportion to produce a good mixture. Most gravel banks contain either more sand or more pebbles than desirable. Usually there is too much sand. Money can usually be saved by screening out the sand and then recombimng the materials in the correct proportions.

341. The Silt Test.—To determine if sand has so much silt or fine material in it that it is objectionable for use in concrete, a silt test may be made as follows, using an ordinary quart milk bottle or quart fruit jar. Fill the jar to a depth of 2 in. with a representative sample of the sand to be tested. Add water until the jar or bottle is about three-fourths full and shake vigorously for 1 min., the last few shakes being in a sidewise direction to level off the sand. Allow the jar to stand for an hour, during which time any silt will be deposited in a layer above the sand. If this layer is more than % in. thick, the sand is not suitable for concrete work unless excess silt is removed by washing.

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

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