bridge chapter 04

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4 Concrete PlacementClasses of Structural Concrete

Concrete Plant Inspection

Types of Plants

Plant Technician

Preparations for Concrete Placement

Plan Review Site

Preparations

Weather Restrictions

Concrete Delivery

Delivery Equipment

Delivery Tickets

Field Tests

Recording Test Results

Concrete Placement

Segregation

Consolidation of Concrete

Construction oints Special Cases

Finishing Concrete Surfaces

!inishing "earing #reas

$ther Surface Treatments



Curing Substructure Concrete

Cold Water Curing

Method of Measurement and Basis for Payment



C!PT"# F$%#&

C$%CRETE P&#CE'E%T

The major topics to be discussed in this chapter are:

1) Classes of concrete

2) Concrete plants

3) Preparations for concrete delivery

4) Field tests

) Concrete placement

!) Concrete finishin"

#) Curin" methods

Technicians are re$uired to have a basic %no&led"e of concrete used in

brid"e construction and the plants that produce the concrete' (uch an

understandin" helps to form a cooperative relationship bet&een the

Technicians at the plant and the Technicians in the field'

C'!SS"S $F ST#%CT%#!' C$(C#"T"

(tructural concrete is produced as Class * Class +* and Class C' The

differences bet&een the classes are in the cement and a""re"ate contents

and &ater,cementitious ratios'

+rid"e construction often re$uires the use of all three classes of concrete'

For e-ample* the plans may re$uire Class + concrete for the footin"s*

Class for the piers and bents* and Class C for the dec%s and railin"s' The

.otes section of the /eneral Plan sheet lists the classes of concrete to beused' The +ill of 0aterials section on the detail sheets also lists these

classes' n most cases* the Contractor may substitute Class C concrete for

Class concrete and Class or Class C concrete for Class + concrete'

41



The materials used in the production of structural concrete include

combinations of the follo&in":

1) Fine and coarse a""re"ates

2) Portland cement

3) Fly ash a coal byproduct)

4) ater

) dmi-tures* includin" retarders* accelerators* &ater

reducers* and air entrainin" a"ents

C$(C#"T" P'!(T I(SP"CTI$(

T(PES $! P&#%TS

.56T cate"ori7es concrete plants as captive plants or commercial

plants' Captive plants are usually temporary plants constructed on the

jobsite) and are used primarily to produce concrete for a specific

contract' hen the contract is finished* the plant is disassembled and

moved' Commercial plants Fi"ure 41)* on the other hand* are

permanent installations'

Figure 4)*+ Commercial Plant

42



Concrete plants are inspected and certified by the 6ffice of 0aterials

0ana"ement' Commercial plants are inspected once a year' Captive plants

are inspected at the be"innin" of each construction season and &henever

they are moved to a ne& location'

P&#%T TEC)%*C*#%

There are t&o reasons for havin" Technicians at concrete plants' The first

is to insure that .56T receives the $uality of materials the Contractor

has a"reed to supply* and the second is to insure those materials are

delivered in the proper $uantities'

Plant Technicians are responsible for observin" all &ei"hin"* batchin"*

and mi-in" operations* e-cept &hen mi-in" ta%es place a&ay from the

plant site' Technicians are re$uired to ensure that all materials have been

sampled* tested* and approved' The plant scales used for batchin" cement

and a""re"ates are re$uired to be chec%ed for accuracy t&ice a day'

Plant Technicians are re$uired to maintain a cooperative relationship &ith

the Contractor and plant personnel' +ein" prepared for &or% and %no&in"

the re$uirements for the concrete are necessary to maintain this

relationship'

P#"P!#!TI$(S F$# C$(C#"T" P'!C"M"(T

The smooth delivery of concrete to the jobsite is critical' 5elays in the

delivery of the concrete or durin" the placement operation may cause

problems that are time consumin" and costly to resolve' The fieldTechnician* the Contractor* and the concrete plant Technician are re$uired

to &or% to"ether to ensure the correct concrete is delivered on time and in

the necessary $uantities'

P&#% RE+*EW

Preparin" for the delivery of concrete be"ins &ith a revie& of the plans'

The class or classes of concrete are re$uired to be chec%ed' The +ill of

0aterials section of the detail sheets is used to locate the estimated

$uantities for each class of concrete' (ubstitutions of a hi"her class of

concrete are "enerally allo&ed8 ho&ever* the Contractor is never permittedto substitute an inferior class of concrete for the class of concrete re$uired

in the plans'

The detail sheets also provide important information concernin" the

concrete pour* such as the pour se$uence and the locations and dimensions

of the construction joints and %ey&ays'

43



S*TE PREP#R#T*$%S

The Technician is re$uired to ensure that the site has been ade$uately

prepared for concrete placement' (uch preparations include that:

1) 9-cavations have been de&atered

2) Forms have been chec%ed for ade$uate bracin" and proper

elevations and ali"nment

3) Chamfer strips have been installed and are in "ood shape

4) Trash and debris have been removed from all forms

) einforcement has been tied securely and chec%ed for

proper clearance and spacin"

!) The Contractor has ade$uate manpo&er and e$uipment to

handle the pour to include a sufficient number of

vibrators and bac%ups'

WE#T)ER RESTR*CT*$%S

The Technician is re$uired to %no& the &eather forecast for the concrete

placement operation' eather conditions may influence everythin" from

the timin" and method of concrete delivery and placement to postponin"

the operation alto"ether' deally* concrete is placed in temperatures

bet&een ; and <;= F* &hen there is no threat of rain* and &hen steps have been ta%en to protect the concrete from e-cessive &ind'

n "eneral* &hen the temperature is 3= F or belo&* the temperature of the

concrete is re$uired to be bet&een ; and >;= F at the time of placin"' The

Contractor may heat the &ater and,or a""re"ates used in the concrete mi-

to achieve this ran"e of temperatures8 ho&ever* the heatin" is re$uired to

be done in accordance &ith the (pecifications for cold&eather concrete'

The Technician is re$uired to use a dial thermometer to chec% the concrete

temperature &henever the concrete is suspected to be near the

(pecifications limits'

C$(C#"T" D"'I,"#-

.o concrete may be placed &ithout a Technician on the job and another

Technician at the concrete plant' Prior to the be"innin" of concrete

delivery* the Technician is re$uired to contact the plant Technician to

doublechec% the follo&in" items:

44



1) The class of concrete to be used

2) The $uantity of concrete needed for the pour

3) The slump and air content re$uirements

4) The proposed startin" time of delivery

) The desired rate of delivery'

DE&*+ER( E,-*P'E%T

Concrete is typically delivered to the job site in mi-er truc%s* a"itator

truc%s* or in nona"itatin" e$uipment' ll delivery truc%s are re$uired to

comply &ith the e$uipment (pecifications desi"nated in (ection ./0+

0i-er truc%s Fi"ure 42) are desi"ned for mi-in" concrete at or on the&ay to the job site' For this reason* mi-er truc%s al&ays have a &ater tan%

on board and a measurin" device that is capable of controllin" the amount

of &ater that is added to the mi-' "itator truc%s deliver readymi-ed

concrete' ny &ater on the truc% is for cleanin" purposes only* not for

mi-in"'

Figure 4)0+ Mi1er Truc2s

4



hen mi-er truc%s are used* the follo&in" items are re$uired to be

chec%ed:

1) 0anufacturer?s ratin" plates are in place and le"ible

2) evolution counters are operatin" properly

3) 0i-in" speed and the number of revolutions are in

compliance &ith the (pecifications' The number of

revolutions of the drum at mi-in" speed is re$uired to be

bet&een #; and 1;;'

4) Truc%s are operated at or belo& their rated capacity

) 6ld concrete is removed from the drum

!) ash &ater is properly drained from the drum

DE&*+ER( T*C.ETS

s the concrete is delivered to the jobsite* the Technician collects a

delivery tic%et from each truc%'

hen the concrete delivered to the job site is produced at a commercial

or captive plant* the Producer?s tic%et is used to document delivery' The

Producer?s tic%et for the first load of each class of concrete delivered each

day is re$uired to contain the follo&in" information:

1) The correct contract or project number

2) The correct date

3) The producer?s name

4) The plant location

) The Contractor

!) The class of concrete delivered

#) The &ei"hts per cubic yard of all materials* includin"

admi-tures

>) The number of cubic yards delivered

<) The time of day that the &ater and cement &ere combined

1;) The plant Technician?s si"nature

4!



fter the first load is delivered* the Producer?s name* the plant

location* the Contractor* and the &ei"hts of the various materials

used in batchin" may be omitted from the Producer?s tic%ets for

the rest of the day or until the mi- desi"n is chan"ed' f the mi-

desi"n is chan"ed* the tic%et for the first load of the revised mi- is

re$uired to indicate all chan"es'

FI"'D T"STS

Conductin" and,or observin" concrete field tests is one of the most

important duties of a Technician' Typical field tests include slump*

air content* yield* and &ater,cementitious ratio' The e$uipment

used to conduct the tests is re$uired to be clean* in "ood shape* and

capable of providin" accurate results' The air meters Fi"ure 4 3)

used in air content tests and the scales used in yield tests are

re$uired to be calibrated and approved' ll test e$uipment is

provided by 5istrict Testin"'

Figure 4)3+ !ir Content Meter

The procedures for conductin" slump* air content* fle-ural

stren"th* and yield tests are detailed in the .56T /eneral

nstructions to Field 9mployees' The re$uired fre$uency for

conductin" all tests is listed in the Fre$uency 0anual' That

fre$uency of tests listed* ho&ever* is a minimum and may be

increased as specified by the plans* the (pecial Provisions* or by

the P9,P(' The follo&in" is a brief description of the purpose of



each test'

4#



(lump tests are conducted to determine the consistency of fresh

concrete and to chec% the uniformity of concrete from batch to

batch' Typical specification limits for slump for structural concrete

are bet&een 1 and 4 in' @nacceptable slump measurements usually

indicate improper mi- proportions* especially the &ater content'Contractors are not permitted to add &ater simply to ma%e the mi-

easier to pour' ny such chan"e to the mi- desi"n re$uires prior

approval'

ir content tests are conducted to determine ho& much air is

contained in the concrete' n most cases* air has been purposely

added or entrained in concrete to ma%e the concrete more durable'

llo&able air content may ran"e from to > A* dependin" on the

ma-imum si7e of the a""re"ates used in the mi-' esults outside

the specified limits indicate a re$uirement to adjust the amount of

admi-ture in subse$uent batches'

Bield tests are conducted to determine the &ei"ht per cubic foot of

fresh concrete &hich is used to determine the cement in barrels per

cubic yard' Bield tests are not used to chec% the batchin" of any

one mi- component'

Fle-ural stren"th is conducted to determine &hen forms and,or

false&or% may be removed from a structure or to determine &hen a

structure may be put into service' This test re$uires placin" fresh

concrete in a beam mold and allo&in" the concrete to set and cure

under the same conditions as the concrete used in the structure'

The concrete is then removed from the mold and bro%en in a

controlled environment by a beam brea%er' The test results may

then be used to ma%e certain assumptions re"ardin" the stren"th of

the concrete used in the structure'

ater,cementitious ratio is the ratio of the total amount of free

&ater in the a""re"ates* includin" all free &ater in the concrete* to

the amount of cement in the concrete'

REC$RD*%/ TEST RES-&TS

The results of the slump* air content* and yield tests are recordedand submitted on Form T !2' Fle-ural stren"th tests are

documented on Form T #1* and &ater,cementitious ratio is

recorded on Form T !2>'

C$(C#"T" P'!C"M"(T

Compared to the preparations leadin" up to the pour and the

testin"* the actual placement operation is relatively simple8

ho&ever* there are still items that may "o &ron"'



4>



SE/RE/#T*$%

(e"re"ation occurs &hen the coarse and fine a""re"ates used in the

concrete separate and become unevenly distributed throu"hout the mi-'

The lar"er coarse a""re"ate sin%s to the bottom &hile the fines rise to the

top' (e"re"ation al&ays leads to an inferior $uality of concrete' For the

most part* ho&ever* se"re"ation may be prevented &ith the use of proper

placement e$uipment and techni$ues'

Concrete is re$uired to be placed as close as possible to the location the

concrete occupies in the structure' The concrete should not be dumped in a

central location and then spread to the location re$uired in the structure

Fi"ure 44)'

Figure 4)4+ Concrete Placement

hen possible* concrete is re$uired to be deposited in layers no more than

24 in' thic% Fi"ure 4)' Care is re$uired be ta%en* ho&ever* to place each

successive layer before the precedin" layer has ta%en the initial set' Thisinitial set is usually 4 minutes to an hour* dependin" on the temperature'

Too much time bet&een the placement of layers usually results in a cold

joint &hich is a &ea% line of separation bet&een the layers'

Figure 4)+ Concrete 'ayers

4<



5roppin" concrete from too "reat a hei"ht causes the finer particles in the

mi- to splash a&ay from the lar"er* heavier particles' n addition* the force

of the mi- stri%in" the reinforcin" steel may shift bars out of position' The

ma-imum drop hei"ht or allo&able free fall is ft' oppers &ith fle-ible

chutes called tremies are re$uired to be used to funnel the mi- do&n into

tall* narro& forms' or%ers may be stationed inside the forms to move thechutes around to ensure an even distribution of the concrete' The hoppers

may not rest on the reinforcin" steel and are re$uired to be supported by

the form&or%'

C$%S$&*D#T*$% $! C$%CRETE

Fresh concrete naturally contains air poc%ets or voids' f the concrete &ere

left that &ay* the finished product &ould have a rou"h surface and have

$uestionable stren"th' To eliminate voids and to ensure a "ood bond to the

reinforcin" steel* the concrete is re$uired to be consolidated to a uniform

density'

The most common method of consolidatin" concrete is by vibratin" the

concrete &ith a portable spud type vibrator Fi"ure 4!)' 0ost vibrators

have an effective radius of 1> in' all around' 6nce the vibrators are

inserted* they consolidate an area appro-imately 3 ft in diameter'

Figure 4)5+ Spud ,ibrator

41;



lthou"h the procedure is a simple operation* vibratin" concrete is often

conducted incorrectly' (ome points that ensure a "ood job include:

1) Dibratin" is re$uired to be done immediately as the

concrete is placed

2) Dibrators are re$uired to be inserted and &ithdra&n

vertically and should not be dra""ed throu"h the concrete

3) Dibrators are re$uired to be inserted and &ithdra&n &ithin

seconds' 6vervibratin" forces the finer a""re"ates to the

top and drives the lar"er a""re"ates to&ard the bottom'

4) hen concrete is poured in layers* the head of the vibrator

is re$uired to penetrate throu"h the top layer and partially

throu"h the layer underneath Fi"ure 4#)'

Figure 4).+ Depth of ,ibration

) The &or%ers are re$uired to avoid contactin" thereinforcin" steel &ith the vibrator so that the bond bet&een

the steel and the concrete is not bro%en

!) The &or%ers are re$uired to avoid contactin" the form

&alls &ith the vibrator as that may loosen the forms and

may also cause honeycombin" of the concrete surface

#) The Contractor is re$uired to have a bac%up vibrator on

hand for lar"er pours in case of e$uipment problems

C$%STR-CT*$% $*%TS

The purpose of a construction joint is to join a section of fresh concrete to

a previously poured section that has already set' Construction joints are

necessary &hen a substructure unit is too lar"e to pour in one continuous

operation or &hen rain* e$uipment problems* or other conditions interrupt

the pour' @nless construction joints are specifically called for on the plans*

the Contractor is re$uired to have &ritten permission to use the

411



joints' (ome joints* ho&ever* may be described on the plans as optional*

and may be used at the Contractor?s discretion' n addition* the Contractor

may re$uest the relocation or elimination of construction joints' (uch a

chan"e is re$uired to be approved by the P9,P('

To ma%e a construction joint* either planned or unplanned* the Contractoris re$uired to form a raised %ey&ay or %ey&ays in the section to be poured

later' fter the first section has hardened* the surface is s&ept clean &ith

&ire brooms and %ept &et' f a Type construction joint is specified

Fi"ure 4>)* the surface is notched bet&een the reinforcement'

mmediately before the fresh concrete is placed* the Contractor dra&s the

forms up ti"ht a"ainst the concrete in place' To improve the bond bet&een

the sections* the Contractor may apply a bondin" epo-y to the e-posed

surface before resumin" the pour'



Figure 4)6+ Type ! Construction 7oint

To resist shear and other forces* construction joints in footin"s and inabutments for arch brid"es are re$uired to be vertical' ori7ontal

construction joints are used in &alls and columns' Eoints that are e-posed

to vie& are re$uired to be constructed strai"ht* clean* and &aterti"ht' This

is done by finishin" the concrete &ith the underside of a strai"ht

412



and level strip of &ood that is nailed to the form at

the proper elevation' .o construction joint is

allo&ed to be made in areas &here the reinforcin"

steel has been spliced' (ection ./0+* includes all

of the re$uirements for the use of construction

joints' (heet .04)B7TS)/ of the (tandard5ra&in"s for +rid"es provides additional details'

5urin" the pour* care is re$uired to be ta%en not to

disturb the position of any reinforcin" steel that is

used to tie the section bein" poured to a section that

is poured later' f the bars are displaced* they are

re$uired to be retied immediately in the proper

position' Concrete that is splashed on these bars is

re$uired to be cleaned off before the ne-t section is

poured to ensure a "ood bond' f the steel is

e-posed to the &eather for some time after the pour*the steel may re$uire coatin" &ith a cement paste or

e$uivalent to prevent the steel from rustin"'

SPEC*#& C#SES

The placement of concrete under &ater in footin"s

and for foundation seals re$uires techni$ues outside

the "eneral rules "iven above' For a complete

e-planation of the methods and re$uirements* see

(ection

./0+0/8d)f9+

FI(ISI(: C$(C#"T" S%#F!C"S

@nless other&ise authori7ed* the surface of the

concrete is finished immediately after form

removal' 6nly the minimum amount of coverin"

necessary to allo& finishin" operations to be done is

removed at one time' (ubject to approval* metal ties

may be left in the concrete for the purpose of

supportin" or bracin" subse$uent &or%' (uch ties

are re$uired to be in accordance &ith (ection

./0+*38b9 and be of a type &hich uses a cone and

rod as both spreader and tie' +efore final acceptance

of the &or%* the cones are removed and the cavities

filled* in accordance &ith (ection

./0+*38b9+

ll concrete surfaces are re$uired to be "iven a

finish immediately follo&in" the removal of any

forms'

The concrete surfaces of pier and bent caps* the



front face of mud&alls* and any other concrete

surfaces specified are re$uired to be sealed' The

material used for sealin" is re$uired to be in

accordance &ith (ection ./;' The seal is applied to

obtain a finished film thic%ness of at least 2; m

1; mils)' 0i-in"* surface preparation* and themethod of application are re$uired to be in

accordance &ith the manufacturerGs

recommendations8 ho&ever* the surfaces to be

sealed are prepared in accordance &ith (ection ./;

prior to applyin" the sealer'

413



t the time of the removal of forms* the concrete surface is scraped to

remove all fins and irre"ular projections' The surface is then po&er "round

to smooth all joints and chamfers'

fter "rindin" is completed* a paste of "rout is applied to the concrete

surface &ith a spon"e float to fill all air holes and small irre"ularities' The

paste "rout is re$uired to be ! parts of premi- mortar mi- for masonry

and 1 part &hite portland cement in accordance &ith !STM C)*/* Type

1'

fter the paste "rout ta%es the initial set* the surface of the concrete is

scraped &ith a steel dry&all %nife to remove the paste from the surface'

!*%*S)*%/ "E#R*%/ #RE#S

The brid"e seats and areas in bet&een re$uire special treatment at the

finishin" sta"e' The tops of the brid"e seats are re$uired to be finished ate-actly the ri"ht elevation and be completely level to ensure full contact

&ith the bottom of the bearin" device' The areas in bet&een the brid"e

seats are re$uired to be sloped or cro&ned sli"htly to ensure ade$uate

surface draina"e' +oth results are obtained throu"h proper finishin"

techni$ues'

$T)ER S-R!#CE TRE#T'E%TS

The plans or (pecial Provisions may provide for the use of surface

treatments other than the three classes of concrete finishes' For e-ample*

the plans may re$uire the Contactor to leave a rou"h surface te-ture ofe-posed a""re"ate' This may be done by blastin" off the surface mortar

&ith a hi"hpressure &ater hose'

The surfaces of pier and bent caps* the front face of mud&alls* and any

other areas specified are re$uired to be sealed a"ainst moisture penetration

&ith an approved concrete sealer' The surfaces to be sealed are

sandblasted to remove form oil and other forei"n matter and are re$uired

to be completely dry before the application' The sealant is applied in a

crisscross pattern and is re$uired to be a thic%ness of 1; mils' .o sealed

surface is rubbed' (ection ./; describes this operation in detail'

414



C%#I(: S%BST#%CT%#" C$(C#"T"

6nce the concrete is in place* the concrete is allo&ed to cure a

certain amount of time to achieve the full stren"th' 5urin" the

curin" period* the concrete is not to be placed under stress' Thetypical curin" period of the concrete is <! hours after the initial set'

The use of certain materials* such as fly ash or Portlandpo77olan

cement in the concrete* increases the curin" period to 12; hours'

The (pecifications describe t&o methods of curin" concrete' The

first is called the protective coverin" curin" method' This method

re$uires coverin" the surfaces to be cured &ith canvas* stra&*

burlap* sand* or other approved material and %eepin" the concrete

&et &ith &ater throu"hout the curin" period' The &ater prevents

the concrete from dryin" out too $uic%ly' (urfaces that re$uire a

Class T&o rubbin" finish are re$uired to have the protective

coverin" temporarily removed to allo& the rubbin" to continue'

The coverin" is re$uired to be restored as soon as possible'

The other curin" method re$uires the use of a membrane formin"

curin" compound' The curin" compound may be applied after the

concrete surface has received the specified finishin" treatment' @p

until then* the concrete is re$uired to be protected by the protective

coverin" method or* in the case of vertical surfaces* simply by

leavin" the forms in place'

Curin" compound is applied at a minimum rate of one "allon for

every 1; ft2 of concrete surface' The application is done in t&osta"es' The first coat is applied immediately after strippin" theforms or upon acceptance of the concrete finish' The surface isre$uired to be &etted &ith &ater and coated &ith the compound assoon as the &ater film disappears' The second application isre$uired to be"in after the first has set and accordin" to themanufacturer?s directions' 5urin" the curin" operation* alluntreated areas are re$uired to be %ept &et'

Finally* the plans may call for certain areas to be &aterproofed'

hen the application of &aterproofin" material be"ins* curin" of

those areas is no lon"er re$uired'

C$&D W#TER C-R*%/

n cold &ater &eather 3= F and belo&)* the Contractor is re$uired

to %eep the freshly poured concrete and the forms &ithin a

protective enclosure or covered &ith approved insulation material

that is at least 2 in' thic%' The air inside the enclosure or under the

insulation is re$uired to be %ept above ;= F for at least #2 hours'

f for any reason the temperature drops belo& ;= F &ithin the

enclosure* the heatin" period is re$uired to be e-tended' hen dry

heat is used to maintain the re$uired temperature* the Contractor is



re$uired to devise a means of providin" enou"h moisture

41



in the air &ithin the enclosure to prevent the concrete from dryin"

out too $uic%ly' eaters may be used to maintain the re$uired

temperature if they provide continuous operation and the

Contractor has ta%en ade$uate fireprevention and safety measures'

hen rubbin" the concrete is re$uired* the forms are removed andthe rubbin" conducted durin" the protection period' "ain* if this

means that the concrete is e-posed to temperatures belo& ;= F

before the re$uired #2 hours has transpired* the period of

protection and heatin" is re$uired to be e-tended'

M"T$D $F M"!S%#"M"(T !(D B!SIS F$# P!-M"(T

Concrete is measured and paid for by the cubic yard placed in

accordance &ith the plans or as directed' Forms* false&or%* and

other miscellaneous items re$uired to complete the &or% are not

paid for separately' The costs for these items are included in thecosts of the concrete'



41!

bridge chapter 04

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