Construction Methods - Chapter07.pdf - po ang - Januszek66

ProductionofAggregate,

Concrete,andAsphaltMixes

Theproductionofhigh-qualityconcreteandasphaltmixesrequiresasupplyofaggregate

(gravel,sand,andmineralfiller)meetingthespecifiedgradationandotherrequirements.

Mostcommonly,suchaggregateisproducedbycrushingrockorgravelandblendingit

withsandandothermineralsasrequired.Otherconstructionoperationswhichrequire

crushedstoneincludehighwayandairfieldbasecourses,drainagefacilities,asphaltsurface

treatments,beddingforpipelines,andrailroadballast.Thefollowingsectionsdescribethe

majorstepsintheproductionofaggregate,concretemixes,andasphaltmixes.

7–1PRODUCTIONOFAGGREGATE

Toproducequalityaggregate,rockorgravelmustbeexcavated,loaded,andtransportedto

anaggregateprocessingplant(crushingplant)suchasthatshowninFigure7–1.Herethe

rawmaterialiswashedifnecessary,crushed,screened,sorted,andblendedifnecessary,

andstoredorloadedintohaulunits.Sandsarenotcrushedbutoftenrequirewashingand

dewateringbeforeuse.

RockCrushers

RockcrusherssuchastheoneshowninFigure7–2utilizemechanicalactiontoreducerock

orgraveltoasmallersize.Theprincipaltypesofrockcrushersandtheircharacteristicsare

showninTable7–1andincludejawcrushers,impactcrushers,coneorgyratorycrushers,

androllcrushers.

Jawcrushers (Figure7–3a)utilizeafixedplateandamovingplatetocrushstonebe-

tweenthetwojaws.Jawcrushersareprincipallyusedasprimarycrushers. Impactcrush-

ers (Figure7–3b)usebreakersorhammersrotatingathighspeedtofracturetheinputstone.

Therearevarioustypesofimpactcrushersincludingimpactbreakers,horizontalandver-

ticalshaftimpactors,hammermills,andlimemills. Cone or gyratorycrushers (Figure7–3c)

useaneccentricallyrotatingheadtocrushstonebetweentherotatingheadandthecrusher

185

186

CHAPTER7

Figure7–1 Aggregateprocessingplant.(CourtesyofCedarapids,Inc.)

body. Rollcrushers (Figure7–3d)producefracturingofstonebypassingthematerialbe-

tweentwoormorecloselyspacedrollers. Limemills aresimilartohammermillsbutarede-

signedtoproduceafineproductfromlimestone.

Thegradationofcrusheroutputdependsoncrushertypeandsize,crushersetting,

feedsize,crusherspeed,andotheroperatingconditions.Thebestestimateofthegradation

ofaparticularcrusheroutputwillbeobtainedfromthecrushermanufacturer’sdataorpre-

viousexperience.However,Tables7–2and7–3presentrepresentativeoutputgradations

forjawandrollercrushersrespectively.Thesetableswillbeusedintheexamplesandprob-

lemswhichfollow.Noticethatasignificantfractionofcrusheroutputislargerthanthese-

lectedcrusherclosedsidesetting.

Thecrusherwhichfirstreceivesrawstoneisknownasthe primarycrusher. Ifthe

productispassedtoanothercrusher,thiscrusherisknownasa secondarycrusher. Simi-

larly,ifyetanotherstageofcrushingisrequired,thethirdcrusherinlineisknownasa

tertiarycrusher. Screensareusedtosortcrusheroutputandfeedoversizematerialbackfor

recrushing.Ifthematerialmakesasinglepassthroughthecrusherandnoneisfedbackto

thecrusher,thisisclassifiedas opencircuit crushing.Whensomematerialisfedbackto

thecrusherforrecrushing,thecrusherisoperatingin closedcircuit.

Figure7–2 Portableconecrusher.(CourtesyofKolberg-Pioneer,Inc.,and

JohnsonCrushersInternational)

Table7–1 Principaltypesofrockcrushersandtheircharacteristics

Maximum Reduction

Crushing

CrusherType FeedSize

Ratio ProductSize

S tage

Jawcrusher 50(1270mm) 6to1

3 ′′ –20 ′′ (76–508mm) Primary

Impactbreakers 60(1524mm) 20to1

2 –16(51–406mm) Primary

Horizontalsecondary 16(406mm) 6–8to1

3 /4–4(19–102mm) Secondary/

impactor

Tertiary

Standardheadcone 14(356mm) 12to1

3 /4–4(19–102mm) ′′

Hammermill 8(203mm) 20to1

#4–1 1

′′ (4.8–38mm) ′′

Fineheadcone 8(203mm) 4–6to1

1 /4–2(6.4–51mm) ′′

Tripleroll 8(203mm) 4–5to1

1 /4–2(6.4–51mm) ′′

Dualroll

6(152mm) 2–2.5to1

1 /4–3(6.4–76mm) ′′

Limemill

4(101mm) 20to1

#10–#4(1.7–4.8mm) ′′

Verticalshaftimpactor 3(76mm) 4–8to1

3 /8 ′′ –1 1

′′ (9.5–38mm) ′′

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188

CHAPTER7

Figure7–3 Majortypesofrockcrushers.

FeedersandScreens

Feeders (Figure7–4)areusedtosupplygravelorstonetoacrusher.Typesoffeedersin-

cludeapronfeeders,reciprocatingplatefeeders,vibratingfeeders,andbeltfeeders.An

apronfeeder consistsofahopperboxmountedaboveaplatefeederwhichoperateslikea

conveyortofeedstoneintoacrusher.Apronfeedersoftenincorporateagrizzlytoremove

oversizestonefromthecrusherinput.A grizzly issimplyasetofwidelyspacedbarsorrods

whichservetoremoveoversizedmaterialwhichmightjamthecrusher.A reciprocating

Table7–2 Gradationofjawcrusheroutput(percentpassing—opencircuit)

CrusherClosedSideSetting

ScreenSizein.

3 4 5 6 7 8

in. mmmm 19 25 32 38 51 64 76 102 127 152 178 203

1 1

2 1

10254

100 97 87 84

8203

96 88 81 73

7178

100 90 82 74 65

6152

100 94 83 69 64 55

5127

100 98 86 75 63 55 47

4102

97 90 75 62 51 43 36

376

100 86 78 58 47 37 32 27

100 100 93 78 66 48 38 31 25 23

251

100 98 96 82 64 52 39 29 25 21 18

38 100 96 90 84 65 47 39 29 22 20 17 14

32 99 91 83 74 55 40 33 25 20 17 15 12

125

9 4

7 9

6 8

5 8

4 3

3 1

2 6

1 9

1 6

1 4

1 1

1 0

19 80 61 55 43 31 23 20 15 13 11 9

13 58 41 33 30 22 16 14 11 9

10 41 29 25 22 17 13 11 8

2 7

2 0

1 8

1 6

1 2

#4 4.8 20 15 13 12 9

#8 2.4 10 8

#16 1.2 7

#30 0.6 4

0 .8 0.6 0.6

#50 0.3 2

1 0.6 0.5 0.4 0.4

#100 0.2 1

0 .5 0.5 0.4 0.3 0.3 0.2 0.2

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