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325.9R-2 MANUAL OF CONCRETE PRACTICE

CONTENTS

Chapter 1-Introduction

Chapter 2-Materials2.1-Sources2.2-Chemical admixtures2.3-Aggregates2.4-Cement and cementitious materials

2.5-Curing materials2.6-Expansion joint filler2.7-Joint sealants2.8-Nonbituminous inserts2.9-Reinforcing steel and accessories2.10-Water

9.6-Edging

Chapter 3-Sampling and testing ofmaterials for quality assurance3.1-Sampling

of design

3.5-Job control acceptance criteria

3.2-Test methods3.3-Flexural strength of concrete as basis

3.4-Strength tests of field concrete

3.6-Gradation, specific gravity, and absorptionof aggregates

3.7-Air content3.8-Consistency ing

Chapter 4-Subgrade or subbase prepara-tion and forms4.1-General4.2-Fine grading4.3-Requirements and checking of the

4.4-Stationary formsfinished grade

14.1

Chapter 5-Installation of joints and rein-forcement

5.1-General5.2-Longitudinal joints5.3-Isolation or expansion joints

5.4-Weakened plane contraction joints5.5-Transverse construction joints5.6-Load transfer devices5.7-Installation of dowel assemblies

5.9-Placing reinforcement

Chapter 6-Concrete properties andproportions of materials6.1-General statement6.2-Properties for pavements and bases6.3-Proportioning

5.8-Joint sealing

Chapter 7-High-early-strength concrete7.1-Methods of production

Chapter 8-Mixing concrete

8.1-Batching plants8.2-Measurement and handling of materials8.3-Central-mixed concrete8.4-Ready-mixed concrete

Chapter 9-Placing and finishing concrete9.1-Placing

9.2-Spreading9.3-Consolidation9.4-Finishing9.5-Texturing of surface

9.7-Ramps and intersections9.8-Surface requirements

Chapter 10-Curing and protecting concrete10.1-Curing10.2-Cold weather curing10.3-Protection of finished pavement10.4-Protection against rain

Chapter 11-Concrete bases to be subse-quentlycovered with a surface course

11.1-General11.2-Materials11.3-Econocrete11.4-Proportioning11.5-Transverse weakened-plane joints11.6-Surface finishing11.7-Curing for base courses

Chapter 12-Cold and hot weather concret-

12.1-Cold weather concreting12.2-Hot weather concreting

Chapter 13-Miscellaneous13.1-Thickness tolerances

Chapter 14-References-Recommended references

14.2-Cited references

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Fig. 1a -Step by step paving procedure

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Fig. 1b-A slipform paving operation showing paver components (Courtesy CMI Corp.)

CHAPTER 2-MATERIALS

2.1-SourcesMaterials should be furnished only from

sources of supply approved before shipments arestarted, and used only so long as the materialsmeet the requirements of the specifications.The basis of approval of such sources should bethe ability to produce materials of the qualityand in the quantity required. Unless local con-ditions indicate a need for modification, it isrecommended that materials meet the standardspecifications listed in the following section.

2.2-Chemical admixturesAdmixtures may be used to modify the prop-

erties of concrete so that it will be more suitable

for a particular purpose. Their use to obtaindesirable characteristics should be based onappropriate evaluation of their effects on specif-ic combinations of materials and on economicconsiderations. Air-entraining admixturesshould be used to improve durability and work-ability. Water-reducing admixtures may reducetotal water content and water-to-cementitiousmaterials ratio, thus increasing compressivestrength, flexural strength, and durability, anddecreasing permeability, shrinkage, and creep.Some admixtures accelerate the time of settingof concrete, permitting earlier finishing, removal

of forms, and opening of lanes to traffic, as wellas reduce the time of protection from freezingduring cold weather. Others can retard the timeof setting of concrete where rapid setting isundesirable. Many retarding admixtures acceler-ate strength gain once initial set is attained

ACI 212.3R and TRB Special Report 1191

should be consulted when considering the use ofadmixtures in concrete. Experience records onuse of specific admixture with concreting materi-als commonly used in the area should also beconsidered. When admixtures are required bythe general specifications, or permitted by theengineer, they should conform to the appropri-ate specifications as follows:

ASTM C 260ASTM C 494ASTM C 618ASTM C 989

2.3-Aggregates2.3.1 - Aggregates should conform to the

quality requirements of ASTM C 33. For evalu-ating potential reactivity of an aggregate, meth-ods are provided in the appendix of ASTM C33. The danger of aggregate-alkali reactiondifficulties can be reduced by following therecommendations in ACI 201.2R. The desiredgradation limits for the project should be stipu-lated, along with permissible day-to-day varia-tions within the limits of the specifications.

Coarse aggregates should be furnished in atleast two separate sizes, with the separation atthe

3/4 in. (19 mm) sieve when combined mate-

rial graded from No. 4 (4.75 mm) to 11/

2in.

(37.5 mm) nominal maximum size (or 2 in. (50mm) maximum size] is specified and at the 1 in.(25 mm) sieve when combined material gradedfrom No. 4 (4.75 mm) to 2 in. (50 mm) nominalmaximum size [or 2

1/

2in. (63 mm) maximum

size] is specified. When the nominal maximum

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size of coarse aggregate is 1 in. (25 mm) or less,such separation is not necessary.

2.3.2 - Aggregates should be handled andstored in a manner which minimizes segregation,degradation, contamination, or mixing ofdifferent kinds and sizes. A preferred methodof stockpiling coarse aggregates to minimize

segregation is construction of the stockpile insuccessive horizontal layers not more than 6 ft (2m) thick, with each layer completed over theentire stockpile area before the next is started.If operation of hauling equipment on a stockpileis necessary all ramps and runways on thestockpile should be covered by suitable mats orboards, or rubber tired vehicles should be usedto minimize degradation. Rejected material,may be reprocessed and returned to thestockpile provided the reprocessed materialsmeet the applicable specifications. Comparablecare should be used in removal of aggregates

from stockpiles to prevent segregation.Information about stockpiling in specificsituations can be obtained from ACI 304R andACI 221R.

2.3.3 - Frozen aggregates or aggregatescontaining frozen lumps should be thawedbefore use. Washed fine aggregates and fineaggregates produced or manipulated byhydraulic methods should be allowed to drainfor at least 12 hrs before use. Stockpiles, or carsand barges equipped with seep holes areconsidered to offer suitable opportunity fordrainage.

2.3.4 - Aggregates should have a reasonablyuniform moisture content when delivered to themixer. Wetting of dry aggregates prior tobatching will effect cooling by evaporation andmay, if carefully done, minimize moisturevariations and reduce excessive absorption ofmixing water.

2.4-Cement and cementitious materialsThe cement type or types to be used should

be specified and should conform to therequirements of applicable ASTM standards aslisted below. All cement used on a given project

should be from the same source unless otherwisepermitted by the specifications. For furtherguidance on cementitious materials see ACI 223,ACI 225R, ACI 226.1R, and ACI 226.3R.

2.4.1 - Cementitious materials used may

consist of any of the following:2.4.1.1 - Portland cement (ASTM C 150)2.4.1.2 - Blended hydraulic cements (ASTM C

595)2.4.1.3 - Other special types, such as expansive

cements (ASTM C 845).2.4.2 - When hydraulic cements listed in

Section 2.4.1.1 are to be batched on the job withanother cementing material, the batchedingredient may be one of the following:

2.4.2.1 - Ground granulated, blast furnace,slag (ASTM C 989)

2.4.2.2 - Fly ash (ASTM C 618)2.4.2.3 - Natural pozzolan (ASTM C 618)2.4.2.4 - Silica fume

2.5-Curing materialsThe specifications should stipulate the type or

types of curing material to be used and requireconformance to the appropriate specification

below. The general requirements of curingpractice as recommended by ACI 308 should befollowed.

2.5.1 - Burlap should be made from jute orkenaf and, at the time of use, should be in goodcondition, free from holes, dirt, clay, or anyother substance which interferes with itsabsorptive quality. It should not contain anysubstance which would have a deleterious effecton the concrete. Additional details are inAASHTO M 182. Burlap that will not absorbwater readily when dipped or sprayed and thatweighs less than 7 oz/yd

2(240 g/m

2) when clean

and dry should not be used. Burlap made intomats should be handled with care to avoidmarring the finished surface of the concrete.

2.5.2 - Waterproof paper and impermeablesheets should conform to the water retentionrequirements of ASTM C 171.

2.5.3 - Liquid membrane-forming compoundsshould conform to the requirements of ASTM C309. Type 2, white pigmented curing compoundis generally preferred for concrete pavements.Type 1, clear or translucent, and Type 3, lightgray pigmented, are also used.

2.6-Expansion joint fillerExpansion joint filler should be of the type

specified and conform to one of the followingspecifications, depending on the conditions of itsuse.

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2.6.1 - ASTM D 1751.2.6.2 - ASTM D 1752.2.6.3 - ASTM D 994.

2.7-Joint sealantsThe recommendations in ACI 504R should be

followed in the selection of joint materials.Among the current specifications for joint

sealants are:2.7.1 - ASTM D 1850.2.7.2 - ASTM D 1190.2.7.3 - Federal Specification SS-S-200.2.7.4 - ASTM D 1854.2.7.5 - ASTM D 2628 and ASTM D 2835.2.7.6 - AASHTO M 282.2.7.7 - ASTM D 3406.Information on other sealants which may be

used, such as silicone, may be found in ACI504R.

2.8-Nonbituminous inserts2.8.1 - ASTM D 2828.

2.9-Reinforcing steel and accessoriesThe desired types of reinforcing steel and

accessories should be specified in accordancewith the following applicable specifications:

2.9.1 Steel wire fabric reinforcement - ASTM A185, ASTM A 497 or ASTM A 884.

2.9.2Bar mats - ASTM A 184. Member sizeand spacing should be shown on the plans. Allintersections of longitudinal and transverse barsshould be securely wired, clipped, or welded

together in the plant of the steel supplier.2.9.3 Reinforcing bars - Reinforcing bars

should conform to the requirements of one ofthe following standard specifications:

2.9.3.1 - ASTM A 615, Grade 40 or Grade 60.2.9.3.2 - ASTM A 616, Grade 50 or Grade 60.2.9.3.3 - ASTM A 617, Grade 40 or Grade 60.2.9.3.4 - Guidance for the use of fiber

reinforced concrete can be found in ACI 544.1R.2.9.3.5 - ASTM A 775 specifies materials,

surface preparation procedures, and coatingrequirements for protective epoxy coatings.

2.9.4 Surface condition - Reinforcing steel

should be free from dirt, oil, paint, grease, orother organic materials that may adversely affector reduce bond with the concrete. Rust, millscale, or a combination of both should beconsidered acceptable provided the minimumdimensions, weight, and physical properties of a

hand wire brushed test specimen are not lessthan the applicable ASTM specificationrequirements.

2.9.5 Tie bars - Tie bars should be deformedsteel bars conforming to the requirements of thespecifications for reinforcing bars except thatonly grades of steel bars should be used that canbe bent and restraightened without damage

when this procedure is indicated. Tie bars canhave various shapes to conform to the placementmethod: straight for embedment from thesurface, bent to form legs for preplacement ongrade, sinuous to develop bond when inserted infreshly slipformed edge. Joint hook bolts maybe used as an alternate to tie bars. Such boltsshould not be less than

1/2 in. (13 mm) in

diameter and should be equipped with adequatecouplings.

2.9.6Dowels - Dowels should be plain roundbars conforming to the requirements of thespecifications for plain round bars, ASTM A615, A 616, and A 617. Dowel bars should notbe burred, roughened, or deformed out of roundin such a manner as to hinder slippage in theconcrete. When metal expansion caps are usedfor expansion joints, they should cover the endsof the dowels for not less than 2 in. (50 mm) normore than 3 in. (75 mm). Caps should be closedat one end, and should provide for adequateexpansion. It should be of such rigid design thatthe closed end will not collapse duringconstruction. Epoxy coatings have also beenused on dowels to prevent corrosion.

2.9.7 Chairs - Chairs which are used tosupport reinforcing steel, dowels, or tie bars onsubbases must be of adequate strength anddesign to resist displacement or deformationbefore and during concrete placing.

2.9.8 Stakes - Stakes used to supportexpansion joint fillers should be metal. Theirlength and stiffness should be adequate to keepthe fillers in proper position during the concreteplacement.

2.10-Water

Water used in mixing or curing concrete

should be clean and free from injurious amountsof oil, salt, acid, vegetable matter, or othersubstances harmful to the finished product.Water obtained from natural sources should bewithdrawn in a manner which excludes silt, mud,grass, or other foreign materials. Water should

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CONCRETE PAVEMENTS AND BASES 325.9R-7

be secured only from previously approvedsources or sources approved after testing inaccordance with AASHTO T 26. Nonpotablewater should be used only if it produces mortarcubes having 7- and 28-day strengths equal tothe strength of similar specimens made withdistilled water when tested in accordance withASTM C 109.

CHAPTER 3-SAMPLING AND TESTING OF

MATERIALS FOR QUALITY ASSURANCEThe type of quality assurance program

required to establish that the concrete asproduced, and after incorporation in the work,meets the requirements of the specification willdepend on the nature and size of the project.On small jobs only a limited amount of samplingand testing can be justified, but on major work itis important to use a quality assurance program

based on statistical concepts. The programshould require that the contractor, the concreteproducer, and suppliers of constituent materialsbe responsible for product quality control, andthat the owner be responsible for acceptance.This requires that the producer, supplier, orcontractor sample and test the product tocontrol the process and the materials being usedso that they are both within the specified limits,and so that the resulting concrete is of uniformquality. Because it is difficult and costly toreplace defective concrete and because suitabletests do not yet exist which can fully define the

required properties of concrete after hardening,the owner may wish to elect to sample and testthe freshly mixed concrete as produced prior toincorporation in the work, or to sample and testany of the constituent materials. Such tests bythe owner for acceptance purposes should notrelieve the contractor of his responsibilities forproduct control. Guidelines for developingquality assurance programs will be found in ACI121R, ACI 221R, ACI 311.4R, ACI 311.5R andACI SP-2 (ACI 311.1R).

On projects where flexural testing may beunreliable or prohibitively expensive,

compressive testing may be used for job controlprovided adequate correlations are establishedbetween flexural and compressive strength forthe concrete mixture used on the job (seeSection 3.3).

3.1-SamplingSamples of materials on which the acceptance

or rejection of material is based should becarefully taken in accordance with prescribedprocedures. Samples for inspection orpreliminary tests should be required of theproducer.

3.1.1 - It is impossible to overemphasize theimportance of proper sampling. No amount ofcare and accuracy in subsequent testing willprovide correct information if the samples arecarelessly taken, and not representative of thematerial sampled. Procedures should be set upfor gathering samples in a manner whichprovides the maximum possible information onthe average characteristics, and the nature andextent of variability of materials.

3.1.2 - Methods of sampling materials and theproper size of samples for various tests are oftenstipulated in the test methods. Sample sizes

must be adequate for all tests to be conducted.Procedures for obtaining samples of materialsare covered in AASHTO or ASTM standardsand are referenced in the appropriate materialsspecifications of Chapter 2.

3.2-Test methodsMaterials should be tested in accordance with

methods referred to in the appropriate contractspecifications, or other recognized standardprocedures. Test methods appropriate for use incontract documents are listed in Chapter 14.

3.3-Flexural strength of concrete as basisof design

Specimens for flexural strength tests to beused as the basis for the laboratoryproportioning of concrete mixtures should bemolded and cured in accordance with ASTM C192 and tested in accordance with ASTM C 78.The average flexural strength of concrete asdetermined by the laboratory test should not beless than 650 psi (4.5 MPa) at 28 days. If knowncharacteristics of the available materials orpreliminary tests indicate difficulty in attainingthis strength economically, a minimum average

flexural strength of 600 psi (4.1 MPa) may beused provided the slab thickness is designedaccordingly.

For projects where it is desirable to usecompressive strength testing as the basis for job

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CHAPTER 4-SUBGRADE OR SUBBASEPREPARATION AND FORMS

4.1-GeneralOnly that portion of the final fine grading of

the underlying base course, subbase course,select materials, or treated base materialreferred to as subbase construction operation,which is usually considered as incidental to the

paving operation, is within the scope of thisguide. For more specific information coveringother aspects of incidental pavementconstruction such as clearing and grubbing,removal of structures and obstructions,excavations and embankments, or theconstruction of special subbases with or withoutcementing agents, reference should be made tothe AASHTO Guide Specifications for HighwayConstruction

2or to the various state highway

standard specifications for road construction.Essential preparatory work prior to the paving

operation includes such items as fine grading,

making minor adjustment, to the surface of thesubgrade or subbase (or underlying material ifrequired), adding moisture and recompactingany disturbed material, and preparing the finalfinished surface to conform to the grade andcross section shown on the plans.

Accurate trimming is important to the pavingcontractor from the standpoint of the amount ofconcrete needed to complete the job. Subbasesof adequate stability will benefit pavementsmoothness. Where slipform methods are used,it is recommended that a minimum width ofsubbase should be 2 ft (0.61 m) greater on eachside than the width of the driving lanes to

accommodate the slipform tracks. Not allconcrete pavement is placed on special subbases.Most city streets and many light traffic ruralpavements are placed directly on the preparedsubgrade. On heavy duty routes or whereserious frost problems exist special granularsubbases with or without a cementing agent arefrequently used. Care should be taken to insurethat utility trenches are properly filled andcompacted prior to fine grading and paving.Controlled low strength concrete fill may beused for this purpose in lieu of conventional soilbackfilling techniques.

4.2-Fine gradingWhen forms are to be used in the paving

operation, fine grading is usually done withequipment which rides on the forms after they

have been properly aligned and set to grade.High areas are trimmed to proper elevation.Low areas should be filled and compacted incompliance with the specified compactionrequirements of the underlying material. If theequipment is controlled with an automaticguidance system operating from a wire guideline,the grading equipment can run directly on the

unfinished surface. (see Fig. 4.2). Thisequipment is often used on large projects. Finegrading of cement treated subbases should becompleted prior to initial hardening of the basematerial, which takes 4 to 6 hr. Trimmedcement treated base (CTB) material should beremoved from the surface of the subbase or usedto fill low spots.After the grade or subbase has been placed andcompacted to the required density, the grade onwhich the pavement is to be constructed shouldthen be brought to the proper profile. If thedensity of the base is disturbed by the grading

operations, it should be corrected by additionalcompaction before concrete is placed. Thegrade should be constructed sufficiently inadvance of the placing of the concrete that thetwo operations do not interfere. If any traffic isallowed to use the prepared grade, the gradeshould be checked and corrected immediatelyahead of the placing of the concrete.

Fig. 4.2-Subgrade trimmer operating from

stringline for both line and grade (CourtesyConstruction Machinery, Inc.)

4.3-Requirements and checking of thefinished grade

Prior to placing concrete, the underlyingmaterial should be checked for conformity tospecified density and cross section. The crosssection can be checked by means of an approvedtemplate riding on the forms or by use of a

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stringline if forms are not required Theunderlying material should be wetted downsufficiently in advance of placing concrete toinsure that the material is in a moist conditionwhen concrete is placed. The underlyingmaterial should be free of foreign matter, wasteconcrete, and debris.

4.4-Stationary forms4.4.1 Materials and dimensions - Forms

capable of supporting the loads imposed by theconstruction equipment should be used. A testto evaluate the load capability of straight metalforms has requirements that forms should notdeflect more than

1

/4 in. (6 mm) when tested asa simple beam with a span of 10 ft (3 m) and aload equal to that of the finishing machine orother construction equipment that will operateon them. The two form thicknesses in generaluse are

1/

4in. (6 mm) and

5/

16in. (8 mm). If

the forms are to support heavy pavingequipment they should have a thickness of not

less than5

/16 in. (8 mm). It is recommendedthat forms have a depth equal to the specifiedthickness of the concrete, and a base width thatis equal to three-quarters of the depth but notless than 8 in. (200 mm). Forms should beprovided with adequate devices for securesetting so that when in place they will withstand,without visible spring or settlement, the impactand vibration of the consolidating and finishingequipment. Flange braces should extendoutward on the base not less than two-thirds theheight of the form. Built-up forms, made fromsmaller sizes, are not recommended on projectswhere the total pavement area is greater than2000 yd

2(1670 m

2). If built-up forms are used,

the increase in depth should be not more than25 percent of the original form depth. Whenchecked for straightness, forms should not varyby more than

1/8 in. (3 mm) in 10 ft (3 m) from

the true plane surface on the top, and1/

4in. (6

mm) in 10 ft (3 m) along the face of the form.Forms should contain provisions for locking theends of abutting form sections together tightly.Flexible or curved forms are recommended foruse when the curve has a radius of 100 ft (30 m)or less. Fig. 4.4.1 shows a standard paving form.

4.4.2 Form setting - It is essential that the

foundation under the forms be compacted andcut to grade so that the forms, when set, areuniformly supported for their entire length and

Fig. 4.4.1-Standard paving forms

are at the proper elevation. It is preferable thatthe grade be established by cutting.Foundations below the established grade shouldbe filled to grade in lifts of

1/2 in. (12.7 mm) or

less for 18 in. (460 mm) each side of the formand thoroughly compacted according to jobspecifications. The alignment and gradeelevations of the forms should be checked andcorrections made by the contractor immediately

before placing the concrete. When any form hasbeen disturbed or after any unstable grade hasbeen corrected, the form should be reset andrechecked. Forms should be set sufficiently inadvance of concrete placement to permitinspection of the work. After the forms havebeen set to the correct grade, the subgrade orsubbase should be thoroughly tamped,mechanically, or by hand, at both the inside andoutside edges of the base of the forms. Formsshould be staked into place with not less thanthree pins for each 10 ft (3 m) section. Formsections should be tightly locked, and free fromplay or movement in any direction. The formsshould not deviate from true line by more than1

/4 in. (6 mm) at any point. No excessivesettlement or springing of forms under thefinishing machine should occur. Forms shouldbe cleaned and oiled prior to the placing ofconcrete.

4.4.3Removal of forms - Forms should remainin place at least 8 hr after placing the concrete.If the air temperature is below 50F (10C) atany time during the 8 hr following concreteplacement, the forms should be left in place fora sufficient additional time to assure thatpavement edges will not be damaged Curing of

the exposed concrete pavement edges shouldbegin immediately after removal of the forms.

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CHAPTER 5-INSTALLATION OF JOINTS

AND REINFORCEMENT5.1-General

Joints are placed in concrete pavements tocontrol the location of cracks, and in someinstances, provide relief for expansion due totemperature and moisture changes. ACI 504R

contains information on joint sealants.5.1.1 - All longitudinal and transverse jointsshould conform to the details and positionsshown on the plans.

5.1.2 - Plans and specifications should beexplicit as to location and type of joints at rampentrances and intersections, and where normalspacing is altered due to end-of-day oremergency construction joints.

5.1.3 - All transverse joints should beconstructed in line for the full width of thepavement. Faces of joints should be normal tothe surface of the pavement.

5.1.4 - Special care should be taken to preventuneven riding surfaces at formed joints. Ifedging is required or permitted, a 10 ft (3 m)straight edge should be used to assure thatdisplaced concrete has not resulted in high spots.Joint forming insets placed ahead of the screedsmay tip; if placed behind they are liable to resultin high spots.

5.1.5 - Keyways, when required, should beaccurately formed by material of sufficientstrength to assure a full keyway and accuratealignment. Keyways may also be extruded to theproper dimensions by a slipform paver.

5.2-Longitudinal joints5.2.1 Weakened plane joints - Longitudinal

weakened plane joints may be formed in theconcrete by sawing. Care must be exercised toinsure that the depth of the separation isadequate to prevent random cracking, usuallyabout one-third of the slab depth. If sealingcannot be done ahead of traffic, backer rodshould be installed before the pavement isopened.

5.2.1.1 Sawing - The timing of the sawingoperation should be late enough to avoid

raveling of the new concrete, but soon enoughso that random cracking does not occur. Wherecracking has occurred at the proposed jointlocation, the sawing of that joint should beomitted. Whatever the sawing method, diamond

blades, wet abrasive, or dry abrasive blades, careshould be exercised that sawing is delayedsufficiently to prevent a rough, eroded joint.Longitudinal joints are less prone to randomcracking due to late sawing than transverse

joints.5.2.2 Construction joints - Longitudinal keyed

construction joints (i.e., joints between lanesplaced separately) can be formed with either theslipform methods or standard steel forms andkeyway. Consideration can be given toelimination of keyways in this joint wherestabilized subbases are used. If permitted by thespecifications, tie bars may be bent against theform during casting of the first lane, and thenbent out for insertion into the adjacent lane.Current ASTM specifications for reinforcingbars do not guarantee that bars can be bent andrestraightened without breakage. Hence, if thismethod is specified, precautionary steps should

be taken to assure adequate performance. Onestate highway department has alleviated theproblem of tie bars which will not tolerate a 90-deg bend with subsequent straightening; they usea 60-deg bend initially, and then a straightening60-deg bend to produce a skewed but adequatetie bar arrangement (see Fig. 5.2.2).

Joint hook bolts conforming to the provisionsof Section 2.9.5 may be used. Hook bolts andcouplings should be provided with approvedfasteners for attachment to the pavement formsto maintain them in correct position duringconcreting and subsequent removal of forms.

Slipform pavers should be equipped with asuitable device for the installation of tie bars, orother approved means of holding the lanes incontact should be provided.

5.3-Isolation or expansion jointsIsolation or expansion joints should be placed

between all structures and features such as catchbasins and manholes projecting through, into, oragainst the pavement. Unless otherwiseindicated on the plans, such joints should be notless than

1/4 in. (6 mm) thick and of the

premolded type. A need for thicker joints can

often be predicted. Expansion joint fillersshould be firmly held in place and not dislodgedso that concrete cannot enter the expansionspace at bottom, sides, or top.

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Fig. 5.2.2 - Method for minimizing breakage oftie bars that are bent into keyways andrestraightened

5.3.1 Transverse expansion joints - Transverseexpansion joints should be constructed at rightangles to the centerline of the pavement, unless

otherwise required, and should extend the fullwidth of the pavement.5.3.1.1 Expansion joints at bridge ends -

Bridge ends should be protected from excessivepressures due to pavement expansion by theinstallation of ample width expansion joints inthe pavement near ends of bridges. Anchorslabs should not be depended on to prevent allmovement. Some state highway agenciesconstruct an asphalt section in lengths up to 50ft (15 m) to provide positive protection againstcompressive damage for abutments. (NCHRPSynthesis 159)

3

5.3.1.2Expansion joints where dowels areused - These joints should be formed by securelystaking in place approved load transfer deviceswhich consist of welded assemblies of dowels,supporting and spacing devices, and joint filler.The filler may be the premolded type, redwood

board, or other approved material. The fillershould extend downward to the bottom of theslab, and unless otherwise prescribed, the topedge should be held about

1/2 in. (13 mm)

below the finished surface of the pavement. Thetop edge of the filler should be protected by ametal channel while the concrete is beingplaced. The joint assemblies should be

protected against damage until they are installedin the work. Joint assemblies damaged duringtransportation, or by careless handling, or whilein storage should be replaced or repaired andshould not be used until they have beenapproved by the engineer.

5.3.1.3Joint filler - The designated joint fillershould be punched or drilled to the exactdiameter and at the location of the dowels. Itshould be furnished in lengths equal to thewidth of one lane. Where more than one lengthis used in a joint the abutting ends of the fillershould be held in alignment. Care should beexercised so that when the filler is cut awayduring paving, for example, to accommodate theflanges on the wheels of the paving train, plugsof concrete do not develop across the joint. Thesupporting assembly should furnish positivesupport of the filler in a position normal to thesurface.

5.4-Weakened plane contraction jointsTransverse groove or weakened plane

contraction joints should be constructed in thesame manner as provided for weakened plane

longitudinal joints except that some type of loadtransfer may need to be provided whereexpected traffic volume and the magnitude ofthe loads will be heavy. In this case it isrecommended that slip dowels or other loadtransfer devices be provided. Many heavilytraveled pavements without dowels have beensuccessful where high quality bases wereemployed (cement or asphalt stabilized) but, ingeneral, some type of load transfer isrecommended. Dowels should be firmly held inposition by welded assemblies for supporting andspacing the dowels. Alternately machine

placement can be used. Accurate positioningmust be assured for proper functioning ofdowels. A positive marking system should beused to assure that sawed or tooled grooves areover the midlengths of the dowels. Grooves

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CONCRETE PAVEMENTS AND BASES 325.9R-13

should be not less than one-fourth the slabdepth.

Fig. 5.4 shows a detail of a longitudinal joint,a transverse contraction joint, and a dowel barassembly.

Fig. 5.4 -Detail of longitudinal joint and

transverse contraction joint for lane-at-a-timepaving, showing dowel bar assembly (with caps

making design also useable for expansion joints,providing expansion joint material is used),keyway, hookbolt dowels, preformed compressionseal, and optional transverse joint base plate to

prevent infiltration where untreated granular basesare used

5.5-Transverse construction jointsUnless other prescribed joints occur at the

same points, transverse construction jointsshould be made at the end of each day or whereinterruptions occur in the concreting operation.

Weather conditions should govern the length of

delays which are considered cause for requiringthe setting of a joint. A 30-min delay could beconsidered a reasonable limit during hot, dry,windy weather; up to an hour or more may betolerated when conditions are less severe.

Transverse construction joints should beformed by staking in place a bulkhead of theproper shape containing a keyway and tie barssimilar to that described in Section 5.2.2. Anequally effective joint can be formed by omitting

the keyway and increasing the size of tie bars to

dowel bar dimensions.Transverse construction joints should not be

formed to make a slab less than 10 ft (3 m)long. If sufficient concrete is not available toplace a slab at least 10 ft (3 m) long, theconstruction joint should be formed at the

preceding joint location. The spacing of

subsequent transverse joints should be measuredfrom the transverse contraction joints lastplaced. In lane-at-a-time construction,construction joints not located in the adjacentlane should be keyed and tied to prevent theformation of sympathy cracks.

5.6-Load transfer devices5.6.1Dowels - Dowel bars should have a

diameter consistent with slab depth and beplaced at the mid-depth of the slab. Properhorizontal and vertical alignment should beassured by either approved dowel assemblydevices, or by approved machine placement.

Good consolidation of concrete around thedowels is essential to good performance.

5.6.2.Dowel coating - The free or unbondedend of each dowel should be coated with acorrosion inhibitor. When the inhibitor has

dried, the free end of each bar should be

completely coated with a thin brush coat of alubricant immediately before it is placed inposition. An excessive coating should beavoided. The free ends of the dowel bars forexpansion joints should be provided with metal

dowel caps. Approved types of epoxy coateddowels can be used in lieu of lubricated dowels.Consideration may also be given to other typesof coatings for the purpose of preventing bond,corrosion, or both.

5.7-lnstallation of dowel assemblies5.7.1 - Dowel assemblies should be put in

place on prepared subbase or subgrade.Transverse dowel assemblies should be placed atright angles to the centerline of the pavementexcept when otherwise detailed on the plans.Doweled joints required or permitted to be setat angles other than normal to the centerlinewill require careful detailing and installation toassure freedom of movement. Dowels should besecurely held in the required position. On

widened curves, the longitudinal center jointshould be placed so that it will be equidistant

from the edges of the slab. Joints should be set

to the required line and grade and should besecurely held in the required position by stakes,an approved installing device, or other approvedmethod (see section 5.4). Dowels should beinstalled in a way that prevents concretepressure from disturbing their alignment.

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325.9R-14 MANUAL OF CONCRETE PRACTICE

If joints are constructed in sections, thereshould be no offsets between adjacent units.Dowel bars should be checked for exact positionand alignment as soon as the joint assembly isstaked in place on the subgrade or subbase, andthe joint should be tested to determine whetherit is firmly supported. Any joint not firmlysupported should be reset. Wires or bars used

to hold assemblies in position for shipmentshould be cut before concrete is placed if theycould cause restraint to early shrinkage of newconcrete.

5.8-Joint sealingACI 504R should be referred to in selecting

proper joint shape factors and joint sealants.5.8.1 - The tops of expansion joints and all

edged and sawed joints should be sealed withthe specified sealing material before traffic ispermitted on the pavement. Joint openingsshould be thoroughly cleaned of all foreign

matter before the sealing material is placed. Allcontact faces of joints should be cleaned toremove loose material, and should be surfacedry when hot-poured sealing material is used.When sawing of green concrete is required orpermitted, extra care should be exercised toremove the slurry coating deposited along thesides of saw cuts.

5.8.2 - Sealing material should be installed inthe joint openings to conform to the detailsshown on the plans. The installation should bedone in such a manner that the material will notbe spilled on the exposed surfaces of theconcrete. Any excess material on the surface ofthe concrete pavement should be removedimmediately and the pavement surface cleaned.

5.8.3 - Poured joint sealing materials shouldnot be placed when temperatures are such as toprevent proper installation. The manufacturersrecommendations may be useful in preparingspecification limits.

5.8.4 - Where preformed joint material, suchas neoprene (preformed compression sealants),is used the uncompressed width of such jointmaterial should be properly balanced with the

joint opening, which in turn should be of a widthconsistent with the length of the slab andtemperature ranges expected. The installingdevice should assure that the preformed materialis not stretched more than 3 percent duringinsertion in the joint opening since the result of

such stretching may be a drastic shortening ofthe useful life of the material. The seal and theinstallation lubricant should conform to Section2.7.5. Fig. 5.8.4 shows a machine used to installpreformed joint material.

Fig. 5.8.4-Machine used for installation ofpreformed neoprene contraction joint strip. The

material and reel are not pictured. Machine is

self-propelled and capable of installation of the

strip with little length change.

5.8.5 - Edge seals are sometimes specified andthese may be useful in preventing infiltration.Such systems have exhibited varying degrees ofsuccess and their use should be based onexperience (Fig. 5.8.5).

Fig. 5.8.5-A method sometimes used to

prevent entrance of water between pavementand asphalt shoulder. (1 in. = 25.4 mm)

5.8.6 - Some jointing materials areincompatible and should not be used in directcontact with each other without an inert divider.Some bituminous materials, for example, shouldnot be in contact with a joint seal of the two

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component, polysulfide type. They may beseparated with a neoprene tape, or otherrelatively inert material.

5.9-Placing reinforcement5.9.1 - When steel reinforcement for jointed

pavements is used it should consist of welded

wire fabric or bar mats in accordance withSections 2.9.1 and 2.9.2. The surface conditionof the steel with respect to foreign matter andrust should conform to the requirements inSection 2.9.4. Width of fabric sheets or bar matsshould be such that, when properly placed in thework, the extreme longitudinal members of thesheet or mat will be located not less than 2 in.(50 mm) or more than 6 in. (150 mm) from theedges of the slab. The length of fabric sheets ofbar mats should be as shown on the plans andshould be such that, when properly placed in thework, the reinforcement will clear all transverse

contraction joints by not less than 6 in. (150mm) as measured from the center of the joint tothe ends of the longitudinal members of thesheet or mat.

5.9.2 - When reinforcing bar assemblies arcshown on the plans, the bars should be firmlyfastened together at all intersections. Adjacentends should lap not less than 30 diameters (seeSection 5.9.7).

5.9.3 - Where bars are fabricated into matform by positive welding at all intersections, thelaps for longitudinal bars should be a minimumof 30 diameters. If the mat pattern is such that

the edge longitudinal bars or the end transversebars of the mats overlap, the lap should be madeso that the bars overlap each other by at least 2in. (50 mm).

5.9.4 - Steel fabric sheets should be lapped asshown on the plans. Sheets should be securelytied together to prevent displacement,particularly from being pulled by the pavingtrain.

5.9.5 - When reinforced concrete is placed intwo lifts (see Fig. 5.9.5) the initial layer shouldbe uniformly struck off at a depth not less than

2 in. (50 mm) below the finished surface norgreater than middepth of slab below theproposed surface of the pavement, and thereinforcement placed thereon. The concreteshould be struck off to the entire width of theplacement and a sufficient length to permit the

sheet or mat of reinforcement to be laid fulllength on the concrete in its final positionwithout farther manipulation of thereinforcement. Adjacent mats or sheets shouldbe tied to prevent an opening from occurringbetween the mats. The balance of the requiredconcrete should be placed after the

reinforcement is in place. The first course ofstruck-off concrete should not be exposedparticularly during hot, windy weather. Probably30 min should be considered a reasonablemaximum exposure time. The positioning of thereinforcement during concrete operations shouldbe checked and if necessary, corrected.

Fig. 5.9.5-Mesh installations on two-course

pavement, employing forms. Mesh cart towedby spreader

5.9.6 - When concrete is placed in a singlecourse, wire fabric sheets or bar mats may belaid in proper horizontal alignment on the fulldepth of struck-off concrete and machinevibrated or tamped to proper elevation. Careshould be exercised that the installing machinesare designed and adjusted so that they will notleave cleavage planes over steel members nordrag the sheets or mats from their properposition. At each transverse joint a checkshould be made to assure proper clearancebetween mesh ends and the joint.

5.9.7 - Where continuously reinforcedconcrete pavement is specified, steel in thequantity, fabrication, and grade shown on theplans should be installed so that thereinforcement will have a minimum cover of 2in. (50 mm) and the longitudinal members will

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325.9R-16 MANUAL OF CONCRETE PRACTICE

5.9.8 Verifying location of reinforcing - A gageshould be used to determine the location of thereinforcing in a pavement. Insertion to thedepth of the reinforcing location will indicate itspositioning in the fresh concrete.

not fall below the middepth of the slab, unlessotherwise specified or shown on the plans.

When the concrete is placed in a singlecourse, the steel should be placed on supportsthat will retain the steel in its specified positionwhile the concrete is being deposited, or elsemechanical placement as described in Section5.9.6 should be used (Fig. 5.9.7). When

transverse bars are not used, the steel can beplaced through tubes in a concrete spreader.Equipment is also available to place steel withtransverse bars in single course construction.When the concrete is placed in two courses, theprocedure outlined in Section 5.9.5 should befollowed.

Lap splices for individual bars, prefabricatedbar mats, or deformed welded wire fabric matsare usually designated on plans and should becarefully checked in the work. The importanceof adequate laps and proper placement cannotbe overemphasized. The danger of failure atsplices at early ages can be minimized byarranging the splices in a skewed or staggeredpattern from one pavement edge to the other.Splice lengths should be shown on the plans orspecifications and should not be less than 30diameters, nor less than 16 in. (400 mm).

Fig. 5.9.7-Bar on chairs, spliced, for single

course slipform operation

CHAPTER 6-CONCRETE PROPERTIES

AND PROPORTIONS OF MATERIALS6.1-General

Concrete pavements, and in most respectsconcrete bases, are exposed to severe treatment.In addition to the pounding of traffic, manyfactors are present tending to destroy them.They are subjected to rapid change in extremesof temperature, abrasion, usually saltapplications, as well as the certainty of erraticsubgrade support at alI ages afterthe first fewhours. For these reasons, and of course foreconomy, considerable extra care inproportioning is justified (see ACI 211.1).

The concrete produced should be required toattain strength compatible with the structuraldesign. It should contain entrained air withinthe range recommended for the aggregate sizeand the area in which it is to be used, and mostimportantly, it should have a water-cement, orwater-cementitious material ratio not higherthan that recommended for the anticipatedexposure. When a blend of cementing materialsis used as provided in Section 2.4.2, the water-cementitious material ratio should beappropriate for making highly durable concretewith these materials.

6.2-Properties for pavements and bases

6.2.1 Water and air content- Water contentshould be kept as low as practicable to producedense and durable concrete with the required airvoid system. Total air content should conformto ACI 201.2R, Table 1.4.3, for exposureconditions anticipated.

6.2.2 Maximum size of coarse aggregate-Observations of existing concrete in the areamay be helpful if aggregate quality is uncertain.Some reduction in the maximum size of

aggregate may improve resistance to Dcracking. Guidance for improving resistance toD cracking can be found in ACI 221R.

6.2.3 Chemical admixtures - One or moreadmixtures may be helpful in most situations,but none should be used without the same

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CONCRETE PAVEMENTS AND BASES 325.9R-17

careful evaluation before the start of work usingjob materials as should be done for concretewithout admixtures. Evaluations are preferablymade by means of full scale trial batches. Referto ACI 212.3R or TRB Special Report 119.

1

6.2.4 Skid resistance - It has been found thatlow water-cement ratios are helpful in

maintaining the skid resistant qualities ofconcrete pavement surfaces. Some aggregatesare more susceptible than others to polishing,and local experience in high traffic areas shouldbe observed. The contribution of fineaggregates to skid resistance is discussed inSection 9.5.

6.2.5Air entrainment - Where freezing andthawing cycles occur, all concrete must contain asatisfactory air void system to improve itsdurability. In practice this is specified in termsof the volume of entrained air required asrelated to the nominal maximum size of coarse

aggregate used. See the recommendations ofACI 201.2R.

6.3-ProportioningSpecifications should establish limits for these

basic mixture proportioning factors: eithermaximum water-cement or water-cementitiousmaterial ratio or minimum strength or minimumcement content. In addition, minimum andmaximum air content, maximum slump, andmaximum size of aggregate should be specified.Preliminary batch weights can be developedfrom experience, from tables of approximate

relationships (see ACI 211.1), or from small trialbatches. Regardless of how batch weights areinitially determined, they should be finallyestablished from full-size batches at the start ofthe work. ACI 211.1 contains a step-by-stepprocedure for determining batch weights andtables of approximate relationships.

Where minimum cement content is specifiedas the criterion of quality of concrete pavement,the committee recommends a minimum of 564lb/yd

3of cement per cubic yard (334.6 kg/m

3)

unless local experience demonstrates that thisminimum can be decreased.

If one of the alternate permitted mixtureproportioning factors, i.e., required strengthconsistent with specified air content and slump isemployed, less cement per cubic yard ofconcrete might be used, especially if certain

chemical admixtures (see Section 2.2), certainblends of cementing materials (see Section2.4.2), or both are used in the work. Specifiedconcrete strengths for design and durabilitypurposes should generally not be less than:Flexural strength with third-point loading - 650psi (4.5 MPa) at 28 days; Compressive

strength-4000 psi (27.6 MPa) at 28 days.Specification for statistical control limits toachieve these strengths should be based onprinciples stated in ACI 214.

CHAPTER 7-HIGH-EARLY-STRENGTH

CONCRETE

7.1-Methods of productionHigh strength at an early age may be desired

to permit placing some key sections of pavementinto use at the earliest possible moment, or forother reasons. High-early-strength concrete maybe produced by in the following ways.

7.1.1 - Use of high-early-strength portlandcement Type III or IIIA, by either method ofproportioning in lieu of normal portland cement(Type I or IA, or Type II or IIA).

7.1.2 - Reducing the water-cement ratio by useof additional normal portland cement (Type I orIA or Type II or IIA).

7.1.3 - Use of calcium chloride as aningredient of the concrete in the followingquantities: (1) between 1 and 2 lb (0.45 to 0.91kg) per 100 lb (45.5 kg) of Type I cement or (2)between 0.8 to 1.6 lb (0.36 to 0.73 kg) per 100 lb(45.5 kg) of Type III cement. Calcium chloride

should be added in solution. It is convenient toproportion the solution so that 1 qt (0.95 L)contains one lb (0.45 kg) of calcium chloride foruse with Type I cement and that 1 qt (0.95 L)contains 0.8 lb (0.36 kg) calcium chloride for usewith Type II cement. It should be recognizedthat the use of calcium chloride very likely willreduce the natural ability of concrete to inhibitcorrosion of embedded metals such as tie bars,mesh, or dowels.

7.1.4 - Use of an appropriate acceleratingadmixture meeting the requirement of ASTMC 494.

7.1.5 - Currently, fast track pavingconstruction practices are under developmentwhich use rapid strength gaining concreteproportions of various material compositions.During 1986 and 1987, several projects were

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325.9R-18 MANUAL OF CONCRETE PRACTICE

successfully completed so that the pavementscould be opened to traffic in 12-24 hr. Thehigh-early-strength technology being developedin these systems may lend itself to quick openingpavement sections.

The user is referred to the American ConcretePavement Associations Technical Bulletin onFast Track Paving

4for additional information.

CHAPTER 8-MIXING CONCRETE

8.1-Batching plantsBatching plants used to supply concrete for

paving and concrete bases should be of sizesadequate to supply well-mixed concrete at theproduction rate specified or anticipated by thecontractor. Plants should be in good repair andoperate reliably. Guidance for establishing plantrequirements and judging the adequacy of abatching plant can be found in Certification ofReady Mixed Concrete Production Facilities

(QC-3)5, Sections 9, 10, and 11 of ASTM C 94,ACI 304R, and ACI 311.5R.

Plants should contain separate bins orcompartments for each aggregate size specified.

Bulk cement and other cementitious materialsshould be stored in closed bins or silos. Ifcombined bins or double silos are used, storagecompartments for cement and othercementitious materials must be separated bydouble walls.

Suitable batching equipment with weighhoppers, scales, and batching controls should beprovided. Cementitious materials should beweighed in separate hoppers and should not beweighed cumulatively with aggregates. Weighingequipment should meet the requirements andaccuracies specified in ASTM C 94.

8.2-Measurement and handling of materials8.2.1 - Bulkcement is normally used on high

production paving projects. Cement should bemeasured by weight within a maximum allowableerror of 1 percent.

8.2.2 - Aggregates should be weighed within amaximum allowable error plus or minus 2

percent.8.2.3 - Mixing water may be measured byweight or by volume. Measurement of the watershould be within a maximum allowable error ofplus or minus 1 percent of the total mixingwater. The use of wash water as a portion of

the mixing water for succeeding batches shouldnot be permitted unless the quantity of washwater is accurately measured.

8.2.4 - Chemicaladmixtures, other than fly ashand other cementitious materials, should be usedin liquid form and may be batched by weight orby volume. Accuracy of weighing chemicaladmixtures should be within plus or minus 3

percent of the required weight. Volumetricmeasurements should be within an accuracy ofplus or minus 3 percent of the total amountrequired. A suitable device for measuring anddispensing the liquid admixture should beprovided. If an air-entraining admixture is usedtogether with a chemical admixture, eachadmixture should be measured and added to theconcrete mix separately to avoid all contact witheach other until they are in the mix. All othercementitious materials should be measured byweight to an accuracy of plus or minus 3percent.

8.3-Central-mixed concrete

8.3.1 Stationary mixers - Stationary mixers atthe site should meet the standards of theConcrete Plant Manufacturers Bureau.

6

Regardless of mixer size, the required minimummixing time for an individual mixer should bespecified as that which, as shown by tests, willresult in satisfactory mixing. The mixing timeshould not be less than 60 sec. Where mixerperformance tests are not made, minimummixing time should be in accordance with ASTMC 94. Preblending of materials is necessary toobtain a uniform mixture with large batches andshort mixing times.

Mixing of concrete should continue for therequired mixing time after all ingredients,including water (and admixture if added with thewater), are in the mixing compartment of themixer before any part of the batch is released.Transfer time in multiple drum mixers should becounted as part of the mixing time.

8.3.2 Transporting mixed concrete - Whennonagitating hauling equipment is used fortransporting concrete to the delivery point,

discharge should be completed within 45 minafter mixing. In case of emergency, the haultime may be increased to that which will notresult in undue loss of slump or separation ofthe mixture (see ASTM C 94). Underconditions contributing to quick stiffening of the

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concrete or when the temperature of theconcrete at point of discharge is 85F (3OC) orabove, the time between mixing and dischargeshould not exceed 30 min.8.4-Ready-mixed concrete

Ready-mixed concrete should be mixed,handled, and transported to the site in

accordance with ASTM C 94. Truck mixersshould conform to the requirements of theTruck Mixer Manufacturers Bureau of theNational Ready Mixed Concrete Association.Suitable equipment should be provided fortransferring the concrete from the transportingvehicle and distributing it uniformly, withoutsegregation, on the grade.

CHAPTER 9-PLACING AND FINISHING

CONCRETE

9.1-Placing

9.1.1Equipment - Placing equipment should becapable of transporting the mixed concrete fromthe mixer or hauling equipment and depositing itnear its final position on the grade with aminimum of segregation, and without damage tothe grade. On large jobs, screw, belt, or hoppertype spreaders are available and should berequired. These generally operate from theshoulder and carry the concrete the full width ofthe slab. If transit mixers are used, with onlychutes available to deposit the concrete on thegrade, lane-at-a-time paving is advisable. Whenplain pavement is constructed with a slipform

paver, concrete may be dumped on the grade infront of the paver from dump trucks. Haulingequipment should not be allowed to operate onthe grade in front of the paver if rutting occurs.

9.1.2 Special situations - Where widths vary atramps and intersections, it will not always bepossible to use ideal methods. However, it isequally important to require that concrete notbe dumped haphazardly and shoved or vibratedinto its final position. Hand shoveling may benecessary to avoid segregation.

9.2-Spreading

9.2.1Equipment- For large jobs, paddle orauger type spreaders, belt spreaders, and hopperand auger type spreaders are available andshould be required, unless slipform pavers areused. Slipform paving machines include built-in

equipment for proper spreading. All should beoperated with care in a prescribed and uniformmanner to minimize segregation. See Fig. 9.2.1

On smaller projects spreading can beaccomplished in a number of ways such as withmixer powered strikeoff, hand tools, or a plank,but in any case the concrete should be spread to

the proper depth for consolidation and finishing.

Fig. 9.2.1 -Concrete spreader. Dowel basket,hookbolts, lane-at-a-time construction

9.2.2 Two-course construction - When mesh isto be used, and is to be placed by hand, theconcrete below the mesh is struck off, the meshplaced and tied, and the top course spread. Onlarge projects two spreaders are sometimes used.More commonly, the concrete is struck off to itsfull depth and the mesh vibrated or tamped toits proper position. Mechanical mesh depressingmachines are also available.

9.3-Consolidation

9.3.1Methods - A guide to properconsolidation can be found in ACI 309R.Spading at joints and edges, screeding,mechanical tampers, and vibrators are alleffective to some degree but do notautomatically assure dense concrete. Vibrators,either internal (spud), or surface types (pan ortube), are capable of producing good results.However, surface vibrators should be used withcare to prevent excess mortar from rising to thesurface. Surface vibration may not provideadequate consolidation for thick pavements.

9.3.2 Procedure - The entire area of thepavement should be consolidated in a manner aseffective as possible. Particular attention shouldbe given to edges, the area along the centerline,

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and at other joints. Mechanical mesh placersmay provide some consolidation. Slipformpavers are equipped with gang mounted internalvibrators and are operated within the concretemass to consolidate the concrete as the pavermoves forward. Vibrators should be stoppedwhen the paver is stopped.

9.3.3 Special situations - Extra care is required

to assure proper consolidation around dowelbars and supporting baskets, at edges andcorners or around drains, and at irregularsections related to ramps or intersections.

9.4-Finishing

9.4.1 Slipform pavers - Slipform pavers aredesigned to spread, consolidate, screed, and floatfinish the freshly placed concrete in one pass ofthe machines to provide a well consolidated andhomogenous pavement requiring a minimum ofhand finishing to meet surface tolerances. Themachines should vibrate the concrete pavement

for its full width and depth. Vibration is usuallysupplied by gang mounted spud type internalvibrators.

Slipform pavers should be operated with asnearly a continuous forward movement aspossible, and all operations of mixing, delivering,and spreading concrete should be coordinated toprovide uniform progress with stopping of apaver held at a minimum. When it is necessaryto stop a paver, the vibratory elements shouldalso be stopped. Slipform pavers are capable oftaking grade from a subbase or subgradeaccurately trimmed with automated equipment,or sensing devices working off a stringline.

9.4.1.1Edge Slump - Edge slump is ofparticular concern with slipform pavers,especially for thick pavements. It must be keptto an absolute minimum, within projectspecifications. This is accomplished by properconcrete proportion use of low slump concreteand proper operation of the paver. If edgeslump requiring significant hand work occurs,the paving operation should be stopped andprocedures altered. Specifications generallyrequire edge slump to be no more than

1/4 in. (6

mm).9.4.2Equipment- Requirements for finishingequipment should not be so restrictive as toprohibit new and improved types. If properlyused, tube finishers are effective, but see Section10.5 for procedures needed to assure nonskid

surfaces.9.4.3 Procedure - Regardless of the type of

equipment used, good results are attainable if allmachines are coordinated, properly adjusted,and operated by experienced personnel.Slipform pavers should carry a constant, uniformroll of concrete ahead of the strike-off device tosubmerge the internal vibrators and equalize the

depth of concrete placed by the spreader. It isalmost impossible for following equipment in thetrain to completely equalize the depth if aspreader has a tendency to leave too much, toolittle, or erratic amounts of concrete.

9.4.4Hand finishing - If a significant amountof hand finishing becomes necessary whenpaving with any type of full-scale pavingequipment, the operation should be stopped andprocedures altered to eliminate the need forhand work. No water should be added to thesurface for finishing purposes.

9.5-Texturing of surfaceThe surface of a pavement should include

both fine and coarse texture. The fine texture(grittiness) is formed by the sand in the cement-mortar layer. The coarse texture is formed bythe ridges of mortar left by the method oftexturing.

A wide variety of skid-resistant texturepatterns can be applied to concrete surfaces.Different textures may be desirable at differentlocations on the same project. The texturemethod selected should be compatible with theenvironment, speed, and density of traffic, andtopography and geometrics of the pavement.

An adequately skid-resistant texture can bebuilt into concrete pavements by using one ormore of the following texturing methods: burlapdrag, brooming, wire combs, and other typessuch as rug backing, plastic combs, etc. (see Fig9.5).

Superior skid resistance may be required toprovide additional safety in critical areas such astoll plazas, busy intersections, airport runways,or other locations where frequent braking,acceleration, or cornering occurs. This may be

accomplished by providing deeper than normaltexturing, grooving, or if necessary, byintroducing aluminum oxide, silicon carbide, orother wear-resistant particles into the surface ofthe concrete. ACI 325.6R provides furtherguidance on texturing pavements.

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Fig. 9.5-Different textures used to increase skid resistance: (1) burlap drag (2) wire comb, (3) heavy nylon

bristle broom, (4) fine nylon bristle broom, (5) natural bristle broom, (6) grooving tool plus natural bristlebroom, and (7) planer. (Courtesy Missouri State Highway Commission)

9.6-Edging

The edges along the formline and atexpansion joints should be smoothed with anedging tool. Contraction joints should also be

edged unless formed by sawing. Constructionjoints are also sometimes edged, but with a shortradius tool unless they are to be grooved and

filled. Profile recording devices are commonlyused to determine smoothness of a highwaypavement surface. Accumulated measurement

of deviation from a plane surface for a chosenlength of pavement indicates ride characteristicsof the pavement. Measurements should betaken within 24 hr of concrete placement to

allow correction early in the pavement curingprocess.

9.7-Ramps and intersections

Past practice has been to use irregular rampwidths and sections of odd shape whichgenerally precluded the use of highlymechanized equipment. While these pavedareas cost about double the same amount of

mainline pavement, they seldom are of equalquality and tend to show deterioration earlierthan the rest of the project. Extra effort shouldbe expended to place and finish ramp and

intersection concrete without resorting to unduly

high slump concrete or other expedients. Everyeffort should be made tostandardize ramp widths to the maximum extentpossible consistent with traffic considerations.Ramp design which permits hauling concrete on

the subbase also contributes to reducedconstruction costs due to the restricted haulingspace available on most ramps.

9.8-Surface requirements

9.8.1High-speed roads - High-speed roads areroads carrying traffic with an average speed over45 mph (72 km/h). Surfaces of these roads aregenerally required to be within

1

/8 in. (3 mm) asmeasured with a 10 ft (3 m) straightedge in thelongitudinal direction. Deviations of more than1

/8in. (3 mm), but less than

1

/2 in. (13 mm)should be corrected by grinding in such amanner as not to result in a polished surface. Ifmore than

1

/2 in. (13 mm), the pavement shouldbe corrected by grinding if the pavement iswithin thickness tolerances, evaluated as to its

serviceability, or removed and replaced. A

greater tolerance, up 1/4 in. (6 mm) in 10 ft (3m), can be permitted for surface deviationsmeasured in the transverse direction.

9.8.2Ramps, intersections, and low-speedroads - Surface tolerances may be difficult to

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325.9R-22 MANUAL OF CONCRETE PRACTICE

meet for these pavements. Extra effort shouldbe made to use construction techniques whichwill produce surface tolerances comparable tothose on the mainline. However, surfacetolerance can be increased to

1/4 in. (6 mm) in

10 ft (3 m) in these sections.

CHAPTER 10-CURING AND PROTECTING

10.1-CuringCONCRETE

Immediately after the finishing operations havebeen completed and the water film hasevaporated from the surface or as soon asmarring of the concrete will not occur, the entire

surface of the newly placed concrete should becovered and curing in accordance with one ofthe methods in Sections 10.1.1 through 10.1.5.In all cases in which curing requires the use ofwater, the curing operation should have priorright to all water supply or supplies. ACI 308should be used as a guide. This

recommendation requires 7 days curing attemperatures above 40F (4C) but provides forshorter curing periods if 70 percent or more ofspecified compressive or flexural strength can be

attained earlier.10.1.1 Membrane curing - Immediately after

the water film has disappeared from the surfaceof the pavement, the surface should beuniformly coated with liquid membrane curingmaterial by a suitable means of an approvedmechanical spray machine at the rate of not lessthan 1 gal. per 150 ft

2

of surface (one L per 3m

2), or as recommended by the manufacturer.

To insure uniform consistency and dispersion ofthe pigment in the curing material, it should beagitated in the supply container immediatelybefore transfer to the distributor and kept

thoroughly agitated during application. Irregularareas or sections of pavement where the use of amechanical spraying machine is impracticablemay be sprayed with approved hand sprayingequipment. The sides of the pavement slabshould be coated within 60 min after theremoval of forms. Any areas of the coatingwhich are damaged within the specified curingperiod should be immediately repaired.

10.1.2 Mono-molecular coatings - This type ofmembrane coating material may be desirableunder adverse drying construction conditions toretard surface evaporation. This is not a

substitute for curing.

10.1.3 Cotton mats or burlap - The surface andedges of the pavement should be entirelycovered with mats. Prior to being place, themats should be saturated thoroughly with water.The mats should be so placed as to cause themto remain in intimate contact with the surface,but these should not be placed until the surfacehas hardened sufficiently to prevent marring.

They should be maintained fully wetted and inposition for the specified curing period.

10.1.4 Waterproof paper - As soon as thepavement has hardened sufficiently to preventmarring of the surface, the pavement should beentirely covered with waterproof paper. Thepaper units should be lapped 12 in (300 mm).The waterproof paper should be sufficiently wideto overlap and completely cover the sides of theslab after the forms have been removed unlessadditional strips of paper are furnished forcuring the sides. The curing paper should beplace and maintained in intimate contact with

the surface and sides of the pavement during thecuring period. Damaged curing paper whichcannot be effectively patched or repaired shouldbe discarded. Curing paper should be placedonly on a moist surface. If the surface appears

dry it should be wetted by a spray fine enoughto prevent damage to the fresh concrete.

10.1.5 White polyethylene sheeting - The surfaceand sides of the pavement should be entirelycovered with white polyethylene sheeting. Itshould be placed while the surface of theconcrete is still moist. If the surface appears dryit should be wetted with a fine spray before the

sheeting is placed. Adjacent sheets should belapped 18 in. (460 mm). The sheeting should beweighted to keep it in contact with the pavementsurface and it should be large enough to extend

beyond the pavement edge and completely coverthe sides of the slab after the forms have beenremoved. The polyethylene sheeting shouldremain in place for the duration of the curingperiod. A minimum polyethylene thickness of 4mils (1 mm) should be specified. Specialinsulating sheeting materials are sometimes usedfor cold weather or fast-track paving.

10.1.6 Curing of saw cuts - Saw cuts inpavement being cured should be protected fromrapid drying. This is often accomplished withtwisted paper or fiber cords or ropes, or withgummed polyethylene strips, or other approvedmaterial.

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CONCRETE PAVEMENTS AND BASES 325.9R-23

10.2-Cold weather curingCold weather curing should provide protection

from freezing without overlooking the primarygoal of retaining moisture for the time necessaryto bring cement hydration to an acceptablepoint. Polyethylene sheets covered with hay orstraw serve both purposes. See ACI 306R and

ACI 306.1.

10.3-Protection of finished pavementThe contractor should protect the pavement

and its appurtenances against both public trafficand traffic caused by his own employees andagents. This should include the use of flaggersto direct traffic and the erection andmaintenance of warning signs, lights, barricades,and pavement bridges or crossovers. Anydamage to the pavement, occurring prior toopening to the public should be repaired or thepavement replaced. (See Section 13.1.2).

10.4-Protection against rainSo that the concrete may be properly

protected against the effects of rain before theconcrete has sufficiently hardened, thecontractor should be required to have availableat all times materials for the protection of thesurface of the unhardened concrete. Suchprotective materials should consist of burlap orcotton mats, curing paper, or plastic sheetingmaterial. In addition, when the slipform methodof paving is used, the contractor should berequired to have an acceptable plan for the

emergency protection of the surface and edges.When rain appears imminent, all pavingoperations should stop and all personnel shouldtake the necessary steps for complete protectionof the unhardened concrete. Additionalinformation can be found in Reference 7.

CHAPTER 11-CONCRETE BASES TO BESUBSEQUENTLY COVERED WITH A

SURFACE COURSE

11.1-GeneralThis work consists of constructing a course of

portland cement concrete base, with or without

reinforcement as specified, on a prepared gradein compliance with these recommendedpractices. The recommendations of Chapter 9should be followed unless modified by thefollowing.

11.2-MaterialsRecommendations for materials to be

included in the work are given in Chapter 2.

11.3-EconocreteEconocrete may be considered as a concrete

base for various surface courses.

11.4-ProportioningProportioning of concrete for bases should be

done in accordance with the recommendationsof ACI 211.1 and Chapter 6 of this report.

11.5-Transverse weakened-plane jointsConcrete bases may be provided with

expansion and/or contraction joints, and shouldbe constructed according to therecommendations provided for constructingsimilar joints in concrete surface courses.

11.6-Surface finishingNo intentional effort should be made toroughen the pavement surface. Final finishshould be left as smooth as possible withoutextraordinary finishing effort in order to keepthe coefficient of friction low. The finishedsurface should not deviate more than

1/4 in. (6

mm) between two contact points when testedwith a 10-ft (3-m) straightedge parallel to thecenterline.

11.7-Curing for base coursesBase courses should be cured as carefully, and

in the same manner, as surface courses. Waxbase membranes are considered bond breakers,and should not be used on patches that areexpected to bond with concrete overlays.

CHAPTER 12-COLD AND HOT WEATHERCONCRETING

12.1-Cold weather concretingNumerous problems are encountered in winter

concreting operations which make advancedplanning necessary. Materials for protection ofthe subgrade and underlying base courses, and

for curing of the concrete should be on hand atthe jobsite prior to the start of concretingoperations. Special winter concreting practicesare covered in ACI 306R and ACI 306.1.

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325.9R-24 MANUAL OF CONCRETE PRACTICE

12.2-Hot weather concretingDuring hot weather concreting, necessary

precautions should be taken to place theconcrete at the coolest temperature practicable.The concrete temperatures must be controlled toassure proper placing, consolidation, finishing,and curing, and to prevent plastic shrinkagecracking. For useful information for preventing

problems that can develop during hot weatherconcreting, refer to ACI 305R.

CHAPTER 13-MISCELLANEOUS

13.1-Thickness tolerancesAll pavements and base courses should be

constructed to the thickness shown on thedrawings. Careful checking of form elevations,and measurements of the depth to the subgradeor underlying base course by stringlinemeasurements will generally suffice. Should itbe considered necessary to determine the

thickness of pavement after placement, thepavement thickness should be determined bymeasurement of cores drilled from thepavement. Cores should be taken at intervals asrequired by the Engineer. The cores shouldhave a diameter of at least 4 in. (100 mm).Measurement of individual cores should beperformed in accordance with ASTM C 174.

13.1.1 Thickness tolerances for pavements and

bases - Acceptance of the work should be based,in part, on the result of test cores taken fromthe finishing work. Consideration should begiven to providing for partial payment of the

contract unit price per square yard for the workthrough a price adjustment based on therecommendations contained in the AASHTOGuide Specifications for Highway Construction.

2

13.1.2 Opening to traffic and construction trafficlimitations - The finished pavement should beprotected against damage from the constructionoperations and traffic until final acceptance.

As a construction expedient in pavingintermediate lanes or closure lanes ofpavements, the operation of equipment on thepreviously placed lanes may be permitted underthe conditions outlined below. Vehicle loadsshould not exceed design axle load.

In no case should hauling equipment orconcrete mixer trucks be permitted on newlypaved lanes until the pavement has attained astrength sufficient to carry the traffic without

being damaged. The transverse and longitudinaljoints should be sealed or otherwise protectedbefore any construction traffic is permitted.Rapid strength gain concrete mixtures may bespecified to provide earlier opening of thepavement.

Other construction equipment such assubgrade planers and concrete finishing

machines may be permitted to ride on the edgesof previously constructed pavement slabs whenthe concrete is at least 72 hr old and hasattained a minimum flexural strength of 400 psi(3 MPa). All edges of slabs should be protectedfrom damage.

Pavements carrying construction equipmenttraffic should be kept clean. Spillage of materialor concrete should be removed immediatelyafter occurrence.

Traffic should be excluded from the pavementby erecting and maintaining barricades and signsuntil the concrete is at least 14 days old, or for a

longer period if necessary to gain adequatestrength. No traffic should be permitted on thepavement until the joints have been sealed.

Any portion of a pavement damaged bytraffic, construction equipment, or other causesprior to final acceptance by the Engineer shouldbe repaired or replaced by and at the expense ofthe Contractor by procedures and methods asapproved.

CHAPTER 14-REFERENCES

14.1 Recommended references

The documents of the various standards-producing organizations and ACI documentsreferred to in this document are listed belowwith their serial designation.

American Association of State Highway andTransportation OfficialsM 182 Burlap Cloth Made from Jute or

Kenaf

M 282 Joint Sealants -- Hot Poured --Elastomeric Type for PortlandCement Concrete Pavement

T 26 Quality of Water to be Used inConcrete

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CONCRETE PAVEMENTS AND BASES

American Concrete Institute121R Quality Assurance Systems for

201.2R

211.1

212.3R

214

221R

223

225R

226.1R

226.3R

304R

305R

306R

306.1

308

309R

311.4R

Concrete Construction

Guide to Durable Concrete

Standard Practice for Selecting

Proportions for Normal,Heavyweight, and Mass Concrete

Chemical Admixtures forConcrete

Recommended Practice forEvaluation of Strength TestResults of Concrete

Guide for Use of Normal WeightAggregates in Concrete

Standard Practice for Shrinkage-Compensating Concrete

Guide to the Selection and Use ofHydraulic Cements

Ground Granulated Blast-FurnaceSlag as a CementitiousConstituent in Concrete

Use of Fly Ash in Concrete

Guide for Measuring, Mixing,

Transporting, and PlacingConcrete

Hot Weather Concreting

Cold Weather Concreting

Standard Specifications for ColdWeather Concreting

Standard Practice for CuringConcrete

Guide for Consolidation ofConcrete

Guide for Concrete Inspection

311.5R

318

325.6R

504R

544.1R

SP-2(311.1R)

ASTMA 184

A 185

A 497

A 615

A 616

A 617

A 775/A 775M

A 884

C 31

325.9R-25

Batch Plant Inspection and FieldTesting of Ready-Mixed Concrete

Building Code Requirements forReinforced Concrete

Texturing Concrete Pavements

Guide to Joint Sealants forConcrete Structures

State-of-the-Art Report on FiberReinforced Concrete

ACI Manual of ConcreteInspection

Specification for FabricatedDeformed Steel Bar Mats for

Concrete Reinforcement

Specification for Welded SteelWire Fabric for ConcreteReinforcement

Specification for WeldedDeformed Steel Wire Fabric forConcrete Reinforcement

Specification for Deformed andPlain Billet-Steel Bars forConcrete Reinforcement

Specification for Rail-SteelDeformed and Plain Bars forConcrete Reinforcement

Specification for Axle-SteelDeformed and Plain Bars forConcrete Reinforcement

Specification for Epoxy CoatedReinforcing Steel Bars

Specification for Epoxy-Coated

Steel Wire and Welded WireFabric for Reinforcement

Methods of Making and CuringConcrete Test Specimens in the Field

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325.9R-26

C 33

C 39

C 42

C 78

C 94

C 109

C 127

C 128

C 136

C 138

C 143

C 150

C 171

C 173

MANUAL OF CONCRETE PRACTICE

Specification for Concrete

Aggregates

Test Method for CompressiveStrength of Cylindrical ConcreteSpecimens

Method of Obtaining and Testing

Drilled Cores and Sawed Beamsof Concrete

Test Method for FlexuralStrength of concrete (UsingSimple Beam with Third-PointLoading)

Specification for Ready-MixedConcrete

Test Method for CompressiveStrength of Hydraulic Cement

Mortars (Using 2-in. or 50 mmCube Specimens)

Test Method for Specific Gravityand Absorption of Coarse

Aggregate

Test Method for Specific Gravityand Absorption of Fine Aggregate

Test Method for Sieve Analysis ofFine and Coarse Aggregates

Test Method for Unit Weight,Yield, and Air Content(Gravimetric of Concrete)

Test Method for Slump ofPortland Cement Concrete

Specification for Portland Cement

Specification for Sheet Materialsfor Curing Concrete

Test Method for Air Content of

Freshly Mixed Concrete forVolumetric Method

C 192

C 231

C 260

C 309

C 494

C 595

C 618

C 684

C 845

C 989

D 994

D 1190

D 1751

Test Method of Making andCuring Concrete Test Specimens

in the Laboratory

Test Method for Air Content ofFreshly Mixed Concrete by thePressure Method

Specification for Air-EntrainingAdmixtures for Concrete

Specification for LiquidMembrane-Forming Compoundsfor Curing Concrete

Specification for ChemicalAdmixtures for Concrete

Specification for BlendedHydraulic Cements

Specification for Fly Ash and Rawor Calcined Natural Pozzolan forUse as a Mineral Admixture inPortland Cement Concrete

Method of Making, AcceleratedCuring, and Testing of ConcreteCompression Test Specimens

Specification for ExpansiveHydraulic Cement

Specifications for Ground Iron

Blast-Furnace Slag for Use inConcrete and Mortars

Specification for PreformedExpansion Joint Filler for

Concrete (Bituminous Type)

Specification for Concrete JointSealer, Hot-Poured Elastic Type

Specification for PreformedExpansion Joint Fillers forConcrete Paving and Structural

Construction (Nonextruding andResilient Bituminous Types)

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CONCRETE PAVEMENTS AND BASES 325.9R-27

D 1752

D 1850

D 1854

D 2628

D 2828

D 2835

D 3406

D 3569

Specification for PreformedSponge Rubber and CorkExpansion Joint Fillers forConcrete Paving and StructuralConstruction

Specification for Concrete JointSealer, Cold Application Type

Specification for Jet-Fuel-Resistant Concrete Joint Sealer,Hot-Poured Elastic Type

Specification for PreformedPolychloroprene Elastomeric JointSeals for Concrete Pavements

Specification for NonbituminousInserts for Contraction Joints inPortland Cement ConcreteAirfield Pavement, Sawable Type

Specification for Lubricant forInstallation on PreformedCompression Seal in ConcretePavements

Specification for Joint Sealants,Hot-Poured, Elastomeric-Type,for Portland Cement ConcretePavements

Specification for Joint Sealant,Hot-Poured, Elastomeric, Jet-

Fuel-Resistant Type, for PortlandCement Concrete Pavements

Federal standards

SS-S200 Sealing Compound, TwoComponents, ElastomericPolymer Type, Jet-Fuel-Resistant,Cold Applied, Concrete Paving

AASHTO standards can be obtained fromthe American Association of State Highway andTransportation Officials, 341 National PressBuilding, Washington, D. C. 20004.

ACI publications are available from theAmerican Concrete Institute, P.O. Box 19150,Detroit, Mich. 48219

ASTM standards may be obtained from theAmerican Society for Testing and Materials,1916 Race St., Philadelphia, PA 19103.

TRB standards may be obtained from theTransportation Research Board, 2101Constitution Ave., N. W., Washington, D. C.20418.

Federal standards are available through theSuperintendent of Documents, U.S. GovernmentPrinting Office, Washington, D. C. 20402.

14.2 Cited references1. Admixtures in Concrete: Accelerators, Air Entrainers,

Water Reducers, Retarders, Pozzolans, Special ReportNo.119, Transportation Research Board, Washington, D. C.,

1971, 32 pp.

2. Guide Specification for Highway Construction,American Association of State Highway and TransportationOfficials, Washington, D. C., 1984.

3. Design and Construction of Bridge Approaches,NCHRP Synthesis 159, Transportation Research Board,Washington, D. C.

4. Technical Bulletin on Fast Track Paving, AmericanConcrete Pavement Association, Arlington Heights, Ill.

5. Certification of Ready Mixed Concrete ProductionFacilities, QC-3, National Ready Mixed Concrete

Association, Silver Spring, MD.

6. CPMB 100--Concrete Plant Standards of the CPMB,Eighth Revision, 1986.

7. Concrete Pavements Exposed to Rain DuringConstruction, American Concrete Pavement Association,Arlington Heights, IL

This report was submitted to letter ballot of thecommittee and was approved according toInstitute procedures.