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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-quently covered 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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325.9R-4 MANUAL OF CONCRETE PRACTICE
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 1
1/2 in.
(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
1/2 in. (63 mm) maximum
size] is specified. When the nominal maximum
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CONCRETE PAVEMENTS AND BASES 325.9R-5
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 or
boards, 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 to
batching 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 sealants
The recommendations in ACI 504R should befollowed 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 inserts
2.8.1 - 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 can
be 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 may
be 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 not
be 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 deformation
before and during concrete placing.2.9.8 Stakes - Stakes used to support
expansion joint fillers should be metal. Theirlength and stiffness should be adequate to keepthe fillers in proper position during the concrete
placement.
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 for
product 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 prescribed
procedures. 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 will
provide correct information if the samples arecarelessly taken, and not representative of thematerial sampled. Procedures should be set upfor gathering samples in a manner which
provides 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 standard
procedures. Test methods appropriate for use incontract documents are listed inChapter 14.
3.3-Flexural strength of concrete as basisof design
Specimens for flexural strength tests to beused as the basis for the laboratory
proportioning 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 or
preliminary 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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control, companion compressive cylinders shouldalso be made. These cylinders should bemolded and cured in accordance with ASTM C192 and tested in accordance with ASTM C 39to establish the correlation between the flexuraland compressive strengths.
3.4-Strength tests of field concrete
3.4.1 Strength test specimens - Specimens,either compressive or flexural, should be madein the field in accordance with ASTM C 31 insufficient numbers to assure job control; forexample, two sets each day for fast moving
projects, one set on projects with low tomoderate production rates. Flexural specimensshould be tested in accordance with ASTM C78. Compressive specimens should be tested inaccordance with ASTM C 39. More elaboratetesting programs can be developed using themethods described in ACI 214.
3.4.2 Accelerated strength tests - ASTM C 684includes three methods, any one of which maybe used to predict the compressive strength ofconcrete at later ages for acceptance purposes orfor process control as the concrete is producedand used. Results are available within 24 to 48hrs, depending on the method used. Choice ofthe method should be based on this factor andconvenience, since cooperative testing programsand practical experience show the three methodshave equal precision. Currently, these methodsare being used with 6 x 12 in. (152 x 305 mm)cylinders only, but there is no theoretical reasonwhy they could not be used with flexural beams.The size of beam specimens involved, however,
restricts use of the methods for practicalpurposes to cylinders subsequently tested incompression.
3.4.3 Tests of in-place concrete - In the eventof low compressive tests, core testing of in-placeconcrete should be conducted in accordancewith ASTM C 42 evaluated in accordance withACI 318, Chapter 4. Beams sawed from thepavement should not be used to evaluate in-place concrete strength.
3.5-Job control acceptance criteriaWhether compressive or flexural strengths are
used for acceptance, the acceptance criteriashould allow occasional low tests. Low strengthresults should be evaluated in accordance withACI 318, Chapter 4, Section 4.7.4.1. Theconcrete proportion should be consideredadequate when the average of any threeconsecutive tests equals or exceeds the specified
strength and no one test falls more than 500 psi(3.5 MPa) low in compression or 75 psi (0.5MPa) low in flexure. The mixture should bereproportioned in the event of compressive orflexural strengths failing to meet this criteria.
3.6-Gradation, specific gravity, andabsorption of aggregates
Concrete uniformity is difficult to controlunless aggregates are tested with a frequencyconsistent with the production rate.
3.6.1 Grading - Fine and coarse aggregategrading should be closely monitored using thesieve analysis procedures of ASTM C 136.
3.6.2Coarse aggregate - The bulk specificgravity in a saturated-surface-dry condition andthe absorption of coarse aggregate should bedetermined in accordance with ASTM C 127.
3.6.3Fine aggregate - The bulk specific gravityin a saturated-surface-dry condition and theabsorption of fine aggregate should bedetermined in accordance with ASTM C 128.
3.7-Air contentThe air content of plastic concrete may be
determined in accordance with standardmethods of test for air content: (1) gravimetric,ASTM C 138; (2) volumetric, ASTM C 173; or(3) pressure method, ASTM C 231. Forconcretes made with blast-furnace slag,lightweight aggregate, or other vesicular porousaggregates, the volumetric (rolling) method must
be used.
3.8-Consistency
3.8.1 - Consistency is usually determined inAccordance with ASTM C 143. See Fig. 3.8.1.
Fig. 3.8.1-Testing devices. (a) airpressure
meter, (b) slump cone, (c) rollameter
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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 rural
pavements 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 soil
backfilling 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 (Courtesy
Construction 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 forms
4.4.1 Materials and dimensions - Formscapable 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 as
a 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
/16in. (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 be
provided 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, and1/4 in. (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. 4.4.1shows a standard paving form.
4.4.2Form 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 from
play 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 should
be 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 concrete
placement, the forms should be left in place fora sufficient additional time to assure that
pavement 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 REINFORCEMENT
5.1-GeneralJoints are placed in concrete pavements to
control 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 the
pavement. 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 the
proper 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 then
bent out for insertion into the adjacent lane.Current ASTM specifications for reinforcing
bars 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 (seeFig. 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 of
tie bars that are bent into keyways and
restraightened
5.3.1Transverse 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.5.3.1.1Expansion 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
5.3.1.2 Expansion 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 being
placed. 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 joints
Transverse groove or weakened planecontraction 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 in
position 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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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-time
paving, showing dowel bar assembly (with caps
making design also useable for expansion joints,providing expansion joint material is used),
keyway, hookbolt dowels, preformed compression
seal, and optional transverse joint base plate to
prevent infiltration where untreated granular bases
are used
5.5-Transverse construction joints
Unless other prescribed joints occur at thesame 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 the
proper shape containing a keyway and tie barssimilar to that described in Section 5.2.2. Anequally effective joint can be formed by omittingthe keyway and increasing the size of tie bars todowel bar dimensions.
Transverse construction joints should not beformed 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 last
placed. 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 hasdried, 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 metaldowel 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 assemblies
5.7.1 - 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. Onwidened curves, the longitudinal center jointshould be placed so that it will be equidistantfrom the edges of the slab. Joints should be setto 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 concrete
pressure from disturbing their alignment.
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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 not
be 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 to
prevent 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 toSection2.7.5. Fig. 5.8.4 shows a machine used to install
preformed joint material.
Fig. 5.8.4-Machine used for installation of
preformed 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 pavement
and 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 reinforcement
5.9.1 - When steel reinforcement for jointedpavements 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 of
bar 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 should
be 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 the
placement 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 should
be 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 exposed
particularly during hot, windy weather. Probably30 min should be considered a reasonablemaximum exposure time. The positioning of thereinforcement during concrete operations should
be checked and if necessary, corrected.
Fig. 5.9.5-Mesh installations on two-course
pavement, employing forms. Mesh cart towed
by 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 proper
position. At each transverse joint a checkshould be made to assure proper clearance
between mesh ends and the joint.
5.9.7 - Where continuously reinforcedconcrete pavement is specified, steel in thequantity, fabrication, and grade shown on the
plans 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 its
positioning 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 cannot
be overemphasized. The danger of failure atsplices at early ages can be minimized byarranging the splices in a skewed or staggered
pattern 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 after the first fewhours. For these reasons, and of course foreconomy, considerable extra care in
proportioning is justified (see ACI 211.1).The concrete produced should be required to
attain 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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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 should
be 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-step
procedure 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 (seeSection 2.2), certainblends of cementing materials (seeSection2.4.2), or both are used in the work. Specifiedconcrete strengths for design and durability
purposes should generally not be less than:Flexural strength with third-point loading - 650
psi (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 on
principles 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 may
be 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 opening
pavement sections.The user is referred to the American Concrete
Pavement Associations Technical Bulletin onFast Track Paving
4for additional information.
CHAPTER 8-MIXING CONCRETE
8.1-Batching plants
Batching plants used to supply concrete forpaving and concrete bases should be of sizesadequate to supply well-mixed concrete at the
production rate specified or anticipated by thecontractor. Plants should be in good repair andoperate reliably. Guidance for establishing plantrequirements and judging the adequacy of a
batching 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 be
provided. 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 materials
8.2.1 - Bulkcement is normally used on highproduction 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 of
plus 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 or
by volume. Accuracy of weighing chemicaladmixtures should be within plus or minus 3
percent of the required weight. Volumetricmeasurements should be within an accuracy of
plus or minus 3 percent of the total amountrequired. A suitable device for measuring anddispensing the liquid admixture should be
provided. 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 mixer
performance 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 (30C) 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 be
possible 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 mesh
placed 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.
9.3.2Procedure - The entire area of thepavement should be consolidated in a manner aseffective as possible. Particular attention should
be given to edges, the area along the centerline,
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and at other joints. Mechanical mesh placersmay provide some consolidation. Slipform
pavers 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 as
possible, and all operations of mixing, delivering,and spreading concrete should be coordinated to
provide 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 and
procedures 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 to
prohibit new and improved types. If properlyused, tube finishers are effective, but see Section10.5 for procedures needed to assure nonskid
surfaces.9.4.3Procedure - 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 when
paving with any type of full-scale pavingequipment, the operation should be stopped and
procedures 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 beedged unless formed by sawing. Construction
joints are also sometimes edged, but with a shortradius tool unless they are to be grooved andfilled. 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 toallow 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 andintersection 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 onthe 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 1/2 in. (3 mm) asmeasured with a 10 ft (3 m) straightedge in thelongitudinal direction. Deviations of more than1/8
in. (3 mm), but less than 1/2in. (13 mm)should be corrected by grinding in such amanner as not to result in a polished surface. Ifmore than 1/2in. (13 mm), the pavement should
be corrected by grinding if the pavement iswithin thickness tolerances, evaluated as to itsserviceability, or removed and replaced. A
greater tolerance, up 1/4in. (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) in10 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 entiresurface 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 beattained earlier.
10.1.1 Membrane curing - Immediately afterthe 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
2of surface (one L per 3
m2), 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 immediately
before transfer to the distributor and keptthoroughly 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 asubstitute 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. The
paper 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 be
place 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 should
be discarded. Curing paper should be placedonly on a moist surface. If the surface appearsdry 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 curing
period. 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 acceptable
point. Polyethylene sheets covered with hay orstraw serve both purposes. See ACI 306R andACI 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 rain
So that the concrete may be properlyprotected 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. Such
protective 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 BE
SUBSEQUENTLY COVERED WITH ASURFACE 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 recommended
practices. 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-Econocrete
Econocrete may be considered as a concretebase for various surface courses.
11.4-ProportioningProportioning of concrete for bases should be
done in accordance with the recommendationsof ACI 211.1 andChapter 6 of this report.
11.5-Transverse weakened-plane joints
Concrete bases may be provided withexpansion and/or contraction joints, and should
be 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 WEATHER
CONCRETING
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 it
be considered necessary to determine the
thickness of pavement after placement, thepavement thickness should be determined bymeasurement of cores drilled from the
pavement. 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 be
performed 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 of
pavements, 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 the
pavement.Other construction equipment such as
subgrade 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 the
pavement until the joints have been sealed.Any portion of a pavement damaged by
traffic, 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
http://304r_89.pdf/http://305r_91.pdf/http://306r_88.pdf/http://3061_90.pdf/http://308_92.pdf/http://309r_96.pdf/http://3114r_95.pdf/http://304r_89.pdf/http://304r_89.pdf/http://304r_89.pdf/http://305r_91.pdf/http://306r_88.pdf/http://3061_90.pdf/http://3061_90.pdf/http://308_92.pdf/http://308_92.pdf/http://309r_96.pdf/http://309r_96.pdf/http://3114r_95.pdf/http://3114r_95.pdf/http://309r_96.pdf/http://308_92.