MACHINERY''''S HANDBOOK 27th CD 2 Episode 8 pps

The mini-mum requirements for tensile strength in pounds, for briquettes one square inch in cross-section, should be as follows: For cement 24 hours old in moist air, 175 pounds.. For ce

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To find the square of a given whole number, divide the number by 10 and find the row in the first column that contains the whole number portion of the result The selected row contains the square of given number under the column corresponding to the last digit in the number

Example:The square of 673, found in row labeled 67, under column labeled 3, is given as 452,929.

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Squares of Mixed Numbers from ⁄64 to 6, by 64ths

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Squares of Mixed Numbers from 6 ⁄64 to 12, by 64ths

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Squares and Cubes of Numbers from 1⁄32 to 6 15⁄16

No Square Cube No Square Cube No Square Cube

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Squares and Cubes of Numbers from 7 to 21 ⁄8

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Squares and Cubes of Numbers from 58 to 75⁄8

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Squares and Cubes of Numbers from 76 to 93⁄8

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Powers, Roots, and Reciprocals From 1 to 50

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No Square Cube Sq Root Cube Root Reciprocal No.

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Multiplication Table for Common Fractions and Whole Numbers From 1 to 9

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Area and Volume of Spheres Surface Area and Volume of Spheres From 1⁄64 to 14 3⁄4

* The figures given in the table can be used for English and Metric (SI) units

d = diameter Surface = πd2 Volume = πd3 ÷ 6

Dia Surface Volume Dia Surface Volume Dia Surface Volume

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Surface Area and Volume of Spheres From 15 to 75⁄2

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Circumferences and Areas of Circles From 1⁄64 to 9 7⁄8

Diameter Circumference Area Diameter Circumference Area Diameter Circumference Area

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Circumferences and Areas of Circles From 10 to 27⁄8

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Diameter Circumference Area Diameter Circumfernce Area Diameter Circumfernce Area

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meter Circum- ference Area

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Table of Decimal Equivalents, Squares, Cubes, Square Roots, Cube Roots, and Logarithms of Fractions from 1⁄64 to 1, by 64ths

Fraction Decimal Log Square Log Cube Log Sq Root Log Cube Root Log

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CEMENT, CONCRETE, LUTES, ADHESIVES, AND SEALANTS

Cement

The cements used in concrete construction are classified as:

1) Portland cements

2) Natural cements

3) Pozzuolanic, pozzuolan, or slag cements

These different classes are all hydraulic cements as they will set or harden under water.When the powdered cement is mixed with water to a plastic condition, the cement sets orsolidifies as the result of chemical action After the preliminary hardening or initial set, thecement slowly increases in strength, the increase extending over months or years

Portland Cement.— Portland and natural cements are the kinds most commonly used.

Portland cement should be used for all structures which must withstand stresses and formasonry that is either under water or heavily exposed to water or the weather According

to the specifications of the American Society for Testing Materials, the specific gravity ofPortland cement must be not less than 8:1 If the tested cement is below this requirement Asecond test should be made on a sample ignited at a low red heat The ignited cementshould not lose more than four per cent of its weight A satisfactory Portland cement mustnot develop initial set in less than 30 minutes; it must not develop hard set in less than 1hour; but the time required for developing hard set must not exceed 10 hours The mini-mum requirements for tensile strength in pounds, for briquettes one square inch in cross-section, should be as follows:

For cement 24 hours old in moist air, 175 pounds

For cement 7 days old, one day in moist air and six days in water, 500 pounds.For cement 28 days old, one day in moist air and 27 days in water, 600 pounds.For one part of cement and three parts of standard Ottawa sand, 7 days old, one day inmoist air and six days in water, 200 pounds

For one part of cement and three parts of standard Ottawa sand, 28 days old, one day inmoist air and 27 days in water, 275 pounds

The cements must under no circumstances show a decrease in strength during the timeperiods specified

Natural Cement.—Natural cement is used in mortar for ordinary brick work and stone

masonry, street sub-pavements, as a backing or filling for massive concrete or stonemasonry, and for similar purposes Natural cement does not develop its strength as quicklyand is not as uniform in composition as Portland cement It should not be used for columns,beams, floors or any structural members which must withstand considerable stress Natu-ral cement is also unsuitable for work that is exposed to water Foundations which are sub-jected to moderate compressive stresses may be made of natural cement, which is alsosatisfactory for massive masonry where weight rather than strength is the essential feature The American Society for Testing Materials gives the following specifications for natu-ral cement: An initial set must not develop in less than 10 minutes, and the hard set must notdevelop in less than 30 minutes, but must develop in less than three hours The minimumrequirements for tensile strength in pounds, for briquettes one inch in cross-section, are asfollows:

For natural cement 24 hours old in moist air, 75 pounds

For natural cement 7 days old, one day in moist air and six days in water, 150 pounds.For natural cement 28 days old, one day in moist air and 27 days in water, 250 pounds.For one part of cement and three parts of standard Ottawa sand, 7 days old, one day inmoist air and six days in water, 50 pounds

For one part of cement and three parts of standard Ottawa sand, 28 days old, one day inmoist air and 27 days in water, 125 pounds

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stantly exposed to fresh or salt water and for drains, sewers, foundation work underground,etc It is not suitable where masonry is exposed to dry air for long periods Pozzuolaniccement sets slowly but its strength increases considerably with age While this cement isrelatively cheap, it is not as strong, uniform, or reliable as Portland and natural cements,and is not used extensively.

Concrete Concrete.—The principal ingredients of concrete are the matrix or mortar and the “coarse

aggregate.” The matrix consists of cement and sand mixed with water, and the coarse

aggregate is usually broken stone or gravel What is known as rubble concrete or

cyclo-pean masonry contains large stones which are used for reducing the cost of massive damsand walls These rubble stones may vary from a few per cent to over one-half the volume.When concrete without much strength but light in weight is required, cinders may be used.This cinder concrete is porous and is used for light floor construction or fire-proofing

Concrete Mixtures.—In the mixing of concrete, it is desirable to use as little cement as is

consistent with the required strength, because the cement is much more expensive than theother ingredients The proportioning of the ingredients is usually by volume and mixturesare generally designated by giving the amount of each ingredient in a fixed order, as 1 : 2:

5, the first figure indicating the amount of cement by volume, the second the amount ofsand, and the third the amount of broken stone or gravel

For ordinary machine foundations, retaining walls, bridge abutments, and piers exposed

to the air, a 1 : 21⁄2 : 5 concrete is satisfactory; and for ordinary foundations, heavy walls,etc., a lean mixture of 1 : 3 : 6 may be used For reinforced floors, beams, columns, andarches, as well as for machine foundations which are subjected to vibration, a 1 : 2 : 4 con-crete is generally used This composition is also employed when concrete is used underwater For water tanks and similar structures subjected to considerable pressure andrequired to be water-tight, mixtures rich in cement and composed of either 1 : 1 : 2 or 1 : 11⁄2:

3 concrete are used Portland cement should preferably be used in concrete construction

Sand, Gravel, and Stone for Concrete.—The sand used must be free from dust, loam,

vegetable, or other organic matter; it should pass, when dry, through a screen with holes of

1⁄4-inch mesh The gravel should consist of clean pebbles free from foreign matter andshould be of such coarseness that it will not pass through a screen of 1⁄4-inch mesh Gravelcontaining loam or clay should be washed by a hose before mixing The broken stoneshould be of a hard and durable kind, such as granite or limestone This stone should passthrough a 21⁄2-inch screen

Amount of Water for Mixing Concrete.—The amount of water required to combine

chemically with cement is about 16 per cent by weight, but in mixing concrete a greateramount than this must be used, because of losses and the difficulty of uniformly distribut-ing the water In hot weather more water is required than in cool weather because of the lossdue to evaporation The same applies when absorbent sand is used, or when the concrete isnot rammed tightly An excess of water is not desirable, because this excess will flow awayand carry some of the cement with it The water must be free from oils, acids, and impuri-ties that would prevent a proper chemical combination with the cement It is important tomix the ingredients thoroughly Lime cement, sand and stone should be mixed while dry,preferably using a machine Enough water should then be added to produce a mixturewhich will flow readily and fill different parts of the form

Reinforced Concrete.—Concrete reinforced with steel is widely used, especially where

the concrete must resist tensile as well as compressive stresses This reinforcement may be

in the form of round bars twisted square bars, corrugated bars, expanded metal, steel mesh,

or wire fabric The proportions for reinforced concrete structures are usually 1 : 2 : 4, or 1

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lateral spacing between reinforcement bars should not be less than three times the bardiameter from center to center, with a clear space between the bars of at least one inch Thedistance from the side of a beam to the center of the nearest bar should be not less than twodiameters.

Strength of Concrete.—The strength varies greatly depending upon the quality and

pro-portions of the ingredients and the care in mixing and depositing in the forms The pressive strength of concrete which, after having been mixed and laid, has set 28 days,varies from 1000 to 3300 pounds per square inch, according to the mixture used If made inthe proportion 1 : 3 : 6, using soft limestone and sandstone a compressive strength of only

com-1000 pounds per square inch may be expected, whereas a mixture of 1 : 1 : 2, made with softlimestone and sandstone, will show a strength of 2200 pounds per square inch A mixture

of 1 : 3 : 6, made from granite or trap rock, will have a compressive strength of 1400 poundsper square inch, while a mixture of 1 : 1 : 2, made from granite or trap rock, will have astrength of 3300 pounds per square inch Other mixtures will have values between thosegiven The richer in cement in proportion to sand, gravel, and stone, the stronger will be theconcrete The strongest concretes are also obtained by using granite or trap rock Amedium strength is obtained by using gravel, hard limestone, or hard sandstone, whereasthe least strength is obtained by using soft limestone or sandstone Concrete may also bemixed with cinders, but, in this case, very inferior strength is obtained; the richest mixtureswill only give a strength of about 800 pounds per square inch

Durability of Concrete in Sea Water.—Experiments have been made to determine the

durability of different mixtures of concrete when exposed to sea water It has been foundthat the mixtures that give the best results are those that are richest in cement Mixtures of

1 : 1 : 2, for example, will give much better results than mixtures of 1 : 3 : 6 Also, very wetmixtures seem to give better results than those that are comparatively dry when deposited

It has also been found that, in order to insure the permanence of Portland cement concrete

in sea water, the cement must contain as little lime and alumina as possible and must also

be free from sulfates, and the proportion of sand and stones in the concrete must be suchthat the structure is practically non-porous Natural cement should never be used for con-crete exposed to sea water

Waterproofing Concrete.—Several formulas for making concrete waterproof have been

successfully used but some of them are too expensive for general application One of thesimplest, cheapest, and most effective is that developed by the U.S Geological Survey Aheavy residual mineral oil of 0.93 specific gravity, mixed with Portland cement, makes itwaterproof and does not weaken when the concrete consists of, say, cement, 1 part, sand, 3parts, and oil, not more than 10 per cent, by weight, of the cement Concrete mixed with oilrequires about fifty per cent longer time to set hard, and the compressive strength is slightlydecreased but not seriously The bond or grip of oil concrete on steel is much decreasedwhen plain bars are used, but formed bars, wire mesh, or expanded metal act as effectively

in it as in ordinary concrete

Resistance to Acids and Oils.—Concrete of a good quality, that has thoroughly

hard-ened, resists the action of acids and mineral oils as well as other building materials, butvegetable oils containing fatty acids produce injurious effects by combining with the lime

in the cement and causing disintegration of the concrete

Lutes and Cements

Luting and cementing materials for various purposes in the laboratory and shops may beclassified as follows: water- and steam-proof; oil-proof; acid-proof; proof to hydrocarbongases; chlorine-proof; elastic; general purposes; marine glue; gaskets; machinists; leather(belting); crucible; iron; and stone

Tiêu đề	Squares of Numbers from 1 to 999
Trường học	Unknown
Chuyên ngành	Mechanical Engineering
Thể loại	Reference
Năm xuất bản	2024
Thành phố	Unknown

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