Concrete VibrationHandbookConcrete VibrationHandbook

2 CONCRETE VIBRATION HANDBOOK

Cement

Pound-for-pound this is the most expensiveingredient in concrete. Several types of cement areavailable to meet different construction criteria.

Water content—curing

In order to begin the hydration process, water isneeded to act as a catalyst. Water content willdetermine the strength, workability andplaceability of the mix. An increase in watercontent will improve the concrete’s workabilitybut will decrease its ultimate strength and durabil-ity. For example, a standard mix with four gallonsof water per bag of cement, or 0.36 W/C ratio(water-to-cement ratio), yields a compressivestrength of about 6,300 lbs.Five gallons, or 0.44 W/Cratio, lowers it to about5,100 lbs., a strength lossof 21%.

Proper curing is alsoimportant to the relativestrength and durability ofconcrete. Several meth-ods of curing are recom-mended by ACI (Ameri-can Concrete Institute) inorder to control the waterretention of the slab.28 days is considered thebenchmark for ultimateconcrete strength and represents 96% to 98% ofthe total strength over its lifetime. Impropercuring will result in excess water loss, lowercompressive strengths, shrinkage and cracking.

Aggregates

Aggregates consist of small particles, such asrocks and stones, which are divided into twogrades, fine and coarse, and comprise the largestvolume of concrete ingredients (typically 70%).The amount of cement used over a given areadepends on aggregate size — the finer the aggre-gate, the larger the surface area. Also, the shapeof the aggregate affects the amount of vibrationrequired, since rough aggregate shapes holdmore air than smooth.

Vibration (Consolidation)

Right after placement, concrete contains up to20% entrapped air. The amount varies according

to the type of mix and itsslump, the placementmethod, form size, and theamount of reinforcing steelused. Concrete vibration canimprove the compressivestrength of the concrete byabout 3% to 5% for eachpercent of air removed.Vibration consolidatesconcrete in two stages: firstby moving the concreteparticles, then by removingentrapped air.

Vibration settles the concreteby subjecting the individual

particles to a rapid succession of impulses, caus-ing differential motion (each particle movingindependently of the other). The particles con-solidate as trapped air are forced to the surface,

Concrete is the combination of four basic components:

water, cement, sand (small aggregate) and rock (large aggregate).

When mixed together, hydration, or curing, occurs, where the cement paste

acts as a glue binding all the surrounding aggregates.

2

Concrete VibrationHandbookConcrete VibrationHandbook

CONCRETE VIBRATION HANDBOOK 3

SLUMP TESTSLUMP TEST

allowing the concrete to flow into corners,around rebar and flush against the form face.This eliminates voids (honeycombing) and bringspaste to the surface to assist in finishing. Sinceconcrete flows better with vibration, the mix cancontain less water, thereby providing greaterstrength for the finished product.

Until both vibration stages are complete, theconcrete isn’t fully consolidated. If the vibrator isremoved too soon, some of the smaller bubblesdon’t have enough time to move to the surface.

Following are terms used in the process of con-crete vibration:

CENTRIFUGAL FORCE—a measure of the ability tomove the mix based on the speed of rotation andsize of the eccentric rotor. The higher the force, theheavier the mix it can move.

AMPLITUDE—a measurement of the outermostdistance the vibrator head will move from its staticaxis; important with large aggregate mixes.

FREQUENCY— measured by vibrations perminute, or VPM, the speed at which the vibratorhead moves within the confines of its amplitude.High VPM vibrators (up to 12,000 VPM) will

primarily affect fine particles. This is ideal be-cause the majority of the trapped air occursaround these particles. High VPM gives thecement paste the opportunity to coat these fineparticles after the air is removed, thus helping tounify the mass. Frequency liquefies or moves theconcrete mix. The greater the VPM, the greaterthe ability to liquefy stiff mixes.

Concrete slump

Depending on the structure’s specifications, theconcrete used for floors, walls, columns, etc., mayneed a specific consistency. On most jobs, samplesof the concrete used on the pour are taken fromthe redi-mix truck and tested to determine thatthe concrete has been mixed to the requiredspecifications. One of these tests is known as the“slump test.” Several samples are taken from thesame batch of mix at regular intervals during thepour. The concrete is placed in a cone-shapedform and rodded to settle the contents (see SlumpTest below). The cone is removed and placed nextto the concrete shaped by the cone (Figure 5). Astraight-edge is placed across the cone, extendingover the concrete next to it, and the “slump” ismeasured after approximately 1½ minutes.

3

CONCRETE VIBRATION HANDBOOK

11111 22222 33333 44444 55555 66666 77777 88888

NMULOC NMULOC NMULOC NMULOC NMULOC foeulavdetsegguS foeulavetamixorppA

noitacilppA noitacilppA noitacilppA noitacilppA noitacilppAPUORG PUORG PUORG PUORG PUORG

daehfo.aiD)mm(.ni

dednemmoceR,ycneuqerfsnoitarbiv.nimrep

egarevAedutilpma)mm(.ni

lagufirtneCecrof

)gk(.sbl

fosuidaRnoitca

)mc(.ni

foetaRetercnoc

tnemecalp.rhrep.sdy

111114/# 1- 2/!

)04-02(000,51-0009

30.0-510.0)8.0-4.0(

006-001)272-54(

42-6)16-51(

51-5

srebmemnihtyrevnietercnocgniwolfdnacitsalPtnemelppusotdesuebyaM.secalpdenifnocdna

erehwkrowdesserts-erpniyllaicepse,srotarbivregraldesuoslA.smrofninoitsegnocesuacstcuddnaselbac

.snemicepstsetyrotarobalgnitacirbafrof

222221 4/! 2- 2/!

)06-03(005,21-0058

40.0-20.0)0.1-5.0(

0001-003)354-631(

23-02)18-15(

54-21

-erp,smaeb,snmuloc,sllawnihtnietercnoccitsalP.stniojnoitcurtsnocgnoladnasbalsniht,seliptsac

nisrotarbivregraltnemelppusotdesuebyaM.saeradenifnoc

333333-2 2/!

)09-05(000,21-0008

50.0-520.0)3.1-6.0(

0002-007)709-713(

84-82)221-17(

06-42

)pmuls]mm08[.ni3nahtssel(etercnoccitsalpffitS,snmuloc,sllawsahcusnoitcurtsnoclarenegni

yrailixuA.sbalsyvaehdnaselipdesserts-erp,smaebdnaetercnocssamfosmrofottnecajdanoitarbiv

-llufedivorpotdetnuom-gnagebyaM.stnemevap.sbalstnemevapfonoitarbivlanretnihtdiw

Concrete vibrators

Concrete vibrators are divided into two majorcategories: external and internal.

EXTERNAL VIBRATORS are attached directly to theconcrete form, thereby vibrating the concretethrough the form.

RANGE OF CHARACTERISTICS, PERFORMANCEAND APPLICATION OF INTERNAL VIBRATIONS

The slump equals the distance the concrete dropsafter sitting for this period of time.

The greater the drop, the higher the slump andthe wetter the mix. Low slump (0-2") is consid-ered a “stiff ” mix. These mixes need the mosthelp in consolidation. 2" to 4" is considered to bea low/medium slump; a 4" to 6" slump is a soft orwet mix and is probably the most widely used;over 6" is considered a flowing mix. These slumpdesignations are approximations, generallyaccepted as “rule of thumb,” and necessary tomatch the appropriate vibrator to the applica-tion.

INTERNAL VIBRATORS utilize a vibrating head thatis placed directly into the concrete mix. Internalvibrators fall into two major categories: flex-shaftand high-cycle.

FLEX-SHAFT VIBRATORS consist of a universalmotor connected to a flexible shaft casing with awire core and a head on the other end of theshaft. The motor turns the shaft, which turns thehead. Flex-shaft vibrators have specific applica-tions, such as small pours that require a minimalamount of vibration (i.e. thin slabs, narrow walls,

4

FLEX-SHAFTVIBRATOR

CONCRETE VIBRATION HANDBOOK

bases and small footings). In these cases, flex-shaft vibrators are usually sufficient. In pourswith heavy rebar concentration, flex shafts can beused since small diameter heads (&/8" to 2") canavoid hang-ups in the rebar (see table on page 3).

Stiff concrete cannot be used in this situation;concrete slumps of 3" or more are commonlyvibrated with the flex shaft.

HIGH-CYCLE VIBRATORS are so-named because ofthe electrical requirement of 180 Hz (cycles per

second) indicating that the alternating currentreverses direction 180 times per second. (Not tobe confused with the VPM rating of vibratorsalso known as “high-cycle”or “high-frequency.”)This allows the use of an induction motor, whichcan provide plenty of power in a smaller packagethan universal motors. With this small packagedmotor, the eccentric rotor can be directly coupledto the motor that is enclosed in the head, elimi-nating the need for a flexible shaft. (The longhandling hose between the motor/head and thepower source contains electrical wires only.) Thisallows the high-cycle to be used on 1" to 3" slumpconcrete, especially in production situations.

Why high-cycle vibrators?

Due to the nature of the universal motor, flex-shaftvibrator motors will continually lose power as theload increases. The stronger the load (such as low-slump concrete), the greater the power loss.The principle advantage is that the180-cycle induction motor used inhigh-cycle vibrators will lose onlyabout 5% of its VPM under load.Additionally, the flexible shaft willcreate friction loss with each bend,

further slowing the effective VPM at the head. Thedifference is performance in low- to medium-slump concrete. A high-cycle vibrator will run atapproximately 10,800 VPM even in low slump(concrete moves best at 10,000 to 11,500 VPM). In astiff mix, a flex shaft will operate around 9,000 VPMor lower, causing the operator to leave the vibratorin the concrete longer. In addition, the high cyclecreates more centrifugal force and has a longerhead, subjecting more of the mix to vibration.These factors allow the operator to vibrate a greatercubic yardage of mix.

Applications for high-cycle vibrators include anywork requiring low- to medium-slump concrete,including dams, large retaining walls, slab pours onhigh-rise buildings and parking lots, tilt-up walls,and other types of standard construction work.

Micon high-cycle vibrator

Multiquip’s microcomputer-controlled (Micon)fully-patented high-cycle vibrator is a majortechnological advancement allowing contractorsto maximize their productivity. The Micon deliv-ers the performance of a high-cycle vibrator whileoffering many exclusive features.

Why Micon high-cycle?

One advantage of the Micon is that it uses stan-dard 60 Hz electrical current in place of the special180 Hz generators that are required to powerhigh-cycle vibrators. The Micon controller auto-matically converts the 120 volt, 60 Hz current intothe 58 volt, 400 Hz current required by the motor.

A microcomputer located within the controllerfunctions as the “brain” of the Micon, monitoringthe vibrator’s performance while submerged inconcrete. This enables it to perform with

MICONHIGH-CYCLEVIBRATOR

HIGH-CYCLEVIBRATOR

5

CONCRETE VIBRATION HANDBOOK

unparalleled efficiency and achieve superiorconcrete consolidation regardless of the slumpconditions. For example, a conventional vibratorplaced in a stiff mix will experience a drop-off infrequency and RPMs. With the Micon, this loss isdetected by the controller which signals themotor to increase its speed to compensate for theloss. Its capacity to maintain a frequency of up to12,000 vpm makes it ideal for zero-slump condi-tions.

The controller also safeguards against commonproblems such as overheating, motor burnout andfluctuations in current. Built-in sensors con-stantly monitor the system, shutting down themotor at the first sign of a problem.

External vibrators

External vibrators attach directly to the form walland consolidate without actually touching theconcrete (hence, “external”). External vibration ispreferred in situations where columns or heavyconcentrations of rebar could result in the tan-gling of an internal head. External vibrators areuseful for precast production work, as they can bepermanently placed and thereby save on labor.

Selling high-cycle vibrators

When high-cycle concrete vibrator technology firstbecame available, the new vibrators requiredgenerators designed specifically for that purpose(240 volt, 3 phase, 180 Hz) with some auxiliary 115volt DC power. These single-purpose high-cyclegenerators were large, heavy and expensive; theiruse was strictly limited to high-cycle applications.

In the past, high-cycle vibrator sales were minimalbecause of the restrictive power supply require-ments. Nevertheless, contractors preferred to usehigh-cycle for the following reasons:

Less maintenance than flex-shaft units.

Higher and more consistent centrifugal force(and area of compaction) than flex-shaft.

Eliminates problem of a motor dropping intothe concrete mix or mix getting into the motor.Nominal RPM loss under load.

Higher productivity rates than flex shaft.

Greater ability to handle stiff mixes and high-production work.

The introduction of Multiquip’s GDP series 60/180cycle generators allows the contractor to use onemachine for both general 60 Hz applications andhigh-cycle power (180 Hz). Multiquip’s 60/180 cyclegenerators are unique in that they are lighter, farless expensive and offer more standard features—ata lower list price—than other brands.

Multiquip’s high-cycle vibrators are ideal for rentalcompanies as they can handle a large range ofconcrete vibration applications and can be poweredby the same generator used for standard AC tools.And they are built with large, heavy-duty perma-nently lubricated bearings to give maximum perfor-mance, durability and long life.

Micon high-cycle vibrator systems are designed forcontinuous work with low- or zero-slump con-crete. These units are also available with an ex-tended rigid vibrator head that incorporates anextension pipe attached directly to the head. Incertain situations where the handling hose on thevibrator is too flexible to position the vibrating head(in tight spots or against sloping form-faces), thehead extension (5.8" in length) allows the operatorto place the head in precise locations, assuringproper concrete consolidation. The Micon systemgives the operator all the advantages of high-cyclevibrators plus additional performance and theability to use a 120 volt,60 Hz power supply.

When selling concrete vibrators, eliminate thepossibility of over-equipping or under-equippingcustomers by utilizing the above information todetermine specific job applications. Required dataincludes the dimensions of the form, form material,concrete slump, the extent of rebar concentration,the number of pours needed and available powersupply at the jobsite.

6

CONCRETE VIBRATION HANDBOOK

Vibration procedures

Before using a vibrator, check for properoperation and VPMs using a simple handtachometer (wire-type.)It is good practice always to have a sparevibrator on the job.Concrete in walls and columns are placed inlifts of various depths, usually 12" to 24".Vibrate the first lift with the head all the wayto the bottom of the form as the vibrationforce extends laterally from the head, notbelow the tip of the head. The vibrator mustalways be used vertically.Place the vibrator into the highest levels ofconcrete first, and when a fairly even surface isobtained, insert it at regular intervals (1½times the radius of influence) for consolidation.Observe the vibration action on the surface tocalculate the radius, and place accordingly tocreate an overlap; it is better to err on the sideof more overlap than not enough.

Vibrate with the head totally submerged in theconcrete, maintaining consistency of spacingand vibration time.Keep the vibrator stationary for 5 to 15 secondsdepending on the mix and the force of thevibrator. Less time will not allow for properconsolidation or entrapped air to escape; toomuch can cause segregation, sand streaks and/or loss of entrained air. The surface should becovered with a thin sheet of paste (mortar) andair bubbles should no longer rise to the surface.Pull the vibrator slowly out of the mix soconcrete can fill in behind the head. Whenplacing the next lift, insert the vibrator at least6" into the previous lift to stitch the layerstogether—this eliminates cold joints.Never use vibrators to spread concrete andalways stay 2" away from form faces andbottom slabs.

MULTIQUIP60/180 HIGH-CYCLE GENERATOR

GDP-5000H

7

Stow Flex-Shaft Vibrators1-, 2- & 3-HP electric motors5.5-HP Honda gasoline engineFlex shafts from 2ft. to 21ft.Heads from &/8" to 2%/8"

Mikasa Flex-Shaft Vibrators2- & 3-HP electric motors5.5-HP HondaFlex shafts from 3ft. to 21ft.Heads from &/8" to 2#/8"

Mikasa High-Cycle Vibrators2.0- & 4.5-amp motors2" and 2#/8" heads5kVA 180 Hz/4kW 60 Hz generator

Micon Micro-Computer-ControlledHigh-Cycle Vibrators

10- and 20-amp controllers1.25" to 2.8" heads

Vibrator selection

Ask for our full-color “Concrete Vibrators” brochureshowing our complete range of vibrator equipment

MULTIQUIP INC. PO BOX 6254, CARSON, CA 90749

310-537-3700 • 800-421-1244 • FAX: 310-537-3927E-MAIL: mq@multiquip.com • www.multiquip.com

CV

-219 (10/03) © C

OP

YR

IGH

T 2003, M

ULT

IQU

IP IN

C.