uv_bpm utility vaults precast npca

7/21/2019 Uv_bpm Utility Vaults Precast NPCA

1/30


2/30

opyright 2006 by National Precast Concrete Association (NPCA)econd Edition, 2005 All rights reserved.

No part of this manual may be reproduced in any form without permission in writing fromhe National Precast Concrete Association.

he association of the manufactured concrete products industry.0333 North Meridian Street, Suite 272 | Indianapolis, Indiana 4629000-366-7731 | 317-571-0041 (fax) | www.precast.org

2

NATIONAL PRECAST CONCRETE ASSOCATION

NOTES1. This manual does not claim or imply thataddresses all safety-related issues, if anyassociated with its use. Manufacture ofconcrete products may involve the use ohazardous materials, operations andequipment. It is the users responsibility determine appropriate safety, health andenvironmental practices and applicableregulatory requirements associated withthe use of this manual and the manufactu

of concrete products.

2. Use of this manual does not guarantee thproper function or performance of anyproduct manufactured in accordance withthe requirements contained in the manuaRoutine conformance to the requirementsof this manual should result in products an acceptable quality according to currenindustry standards.


3/30

INTRODUCTION

Precast concrete is ideally suited for utility, industrial andcommunications structures. A properly manufactured andinstalled precast concrete structure can last almostindefinitely. Precast concrete is inherently durable, highlyimpermeable and corrosion-resistant.

Utility, industrial and communications structures are animportant part of the manufactured concrete productsindustry, and we must continue to provide project ownersand end users with the best possible products atcompetitive prices. It is also important that those

products contribute to the quality, timeliness and ease ofinstallation of construction projects. The best practicesoutlined in this manual are intended to helpmanufacturers achieve these goals.

When properly designed and manufactured, precastconcrete is capable of maintenance-free performancewithout the need for protective coatings, except in certaincircumstances such as highly-corrosive environments. Theprecast advantage is further solidified through precastsease of installation and strength. Because precast

concrete products typically are produced in a controlledenvironment, they exhibit high quality and uniformity.Adverse factors affecting quality which are typicallyfound on job sites variable temperature, uneven curingconditions, inconsistent material quality andcraftsmanship are significantly reduced in a plantenvironment.

High-quality concrete products are important for manyapplications, most notably for underground structuresthat must resist soil pressures and sustain surface loads.The controlled manufacturing environment in a precastconcrete plant is ideal for the production of high-quality,durable concrete products.

This manual is intended to guide manufacturers in qualityproduction processes for manufacturing utility vaults. Themanual is not intended to be all inclusive and therecommendations are not intended to exclude any

materials or techniques that would help achieve the goalof providing structurally sound, high quality products.Attention to detail, quality materials, proper training anda workforce dedicated to quality control will ensure thatthe utility vault meets or exceeds the expectations ofcontractors and end users.

UTILITY VAULT MANUFACTURING BEST PRACTICES MAN


4/30

STRUCTURAL DESIGN

4


Loading ConditionsA properly designed precast concrete utility vault mustwithstand a variety of loading conditions, which vary

during manufacturing, installation, testing and service.These structures are designed to withstand loadingconditions through rational mathematical designcalculations, by proof-of-load testing or in accordancewith ASTM C 857 Standard Practice for MinimumStructural Design Loading for Underground PrecastConcrete Utility Structures.

Consider the following in the design: Surface surcharge loads Concentrated wheel and other traffic loads Lateral loads Presumptive soil bearing capacity Buoyant forces Connections and penetrations Point loads

Precast concrete utility vaults should be designedaccording to one or more of the following industry codesand standards and as required by any regulatory groupswith jurisdiction: ACI 318 Building Code Requirements for Structural

Concrete AASHTO Specification for Highway Bridges ASTM C 857 Standard Practice for Minimum

Structural Design Loading for Underground PrecastConcrete Utility Structures

ASTM C 858 Standard Specification for UndergroundPrecast Concrete Utility Structures

The loading conditions illustrated in the diagram(s)should be analyzed and considered in the design of autility structure.

The following design characteristics have a critical impaon the performance of utility structures.

Concrete ThicknessThe concrete thickness must be sufficient to meetminimum reinforcement cover requirements and withstadesign loading conditions.

Concrete Mix DesignConcrete must have a minimum compressive strength o

4,000 psi at 28 days. Consider methods to reducepermeability, improve durability and increase strength.Maintain a low water-cementitious ratio at or below 0.4

ReinforcementProper design and placement is critical to withstand thesignificant loads applied to utility vaults. Reinforcementmust be sufficient for required strength and serviceconditions, including temperature and shrinkage effectsControl cracking by using multiple small-diameter steelbars rather than fewer large-diameter steel bars. Fiber

reinforcement also helps to reduce cracking and may adsome strength, but should not replace primaryreinforcement. Welded-wire reinforcement can also beused, but particular attention should be paid to designand location. All reinforcement should meet applicableASTM specifications.

Loading Diagram*Manufacturer to specify the maximum depth of cover

Top SeamVault

Grade line

GroundwaterLevel

+ +

Mid-SeamVault

ResidentialSoil

ResidentialSoil

Depth ofCover

HydrostaticLoading

SoilLoading

HydrostaticLoading

SoilLoading

SurchargeSurcharge


5/30

MATERIALSThe primary constituents of precast concrete are cement,fine and coarse aggregates, water and admixtures. Thefollowing discussion covers relevant factors in the

selection and use of these fundamental materials.

CementThe majority of cement used in the manufacturedconcrete products industry is governed by ASTMC 150,Standard Specification for Portland Cement.The five primary types of ASTM C 150 cement are:

Type I NormalType II Moderate Sulfate ResistanceType III High Early Strength

Type IV Low Heat of HydrationType V High Sulfate Resistance

Select the cement type based on project specifications orindividual characteristics which best fit the operation andregional conditions of each manufacturer. Note thatcertain types of cement may not be readily available incertain regions. Store cement in a manner that willprevent exposure to moisture or other contamination.Bulk cement should be stored in watertight bins or silos.If different types of cement are used at a facility, store

each type in a separate bin or silo. Clearly identifydelivery locations.

Design and maintain bin and silo compartments todischarge freely and independently into the weighinghopper. Cement in storage should be drawn downfrequently to prevent undesirable caking. Stack baggedcement on pallets to permit proper air circulation and toavoid undesirable moisture and condensation. On a short-term basis (less than 90 days), stack the bags no morethan 14 high. For long-term storage, do not exceed seven

bags in height (or per manufacturers recommendations).Use the oldest stock first. Discard any cement with lumpsthat cannot be reduced by finger pressure.

AggregatesEnsure aggregates conform to the requirements of ASTMC33, Standard Specification for Concrete Aggregates.

Evaluate the aggregates and maintain documention at theplant for potential deleterious expansion due to alkalireactivity, unless the aggregates come from a statedepartment of transportation-approved source. Themaximum size of coarse aggregate should be as large aspractical, but should not exceed 20 percent of theminimum thickness of the precast concrete utility vault or75 percent of the clear cover between reinforcement andthe surface of the vault. Larger maximum sizes ofaggregate may be used if evidence shows thatsatisfactory concrete products can be manufactured.

Aggregates are an important constituent of precastconcrete utility vaults. Nearly 75 percent of a precastconcrete utility vaults structure consist of coarse andfine aggregates.

The selection of appropriate aggregates is largely aregional concern. The selection process is based on usingthe best available clean, hard, durable aggregates andproper gradations. Aggregates should conform to ASTMC 33 Standard Specification for Concrete Aggregatesand ACI 318 Building Code Requirements for StructuralConcrete.

Quality of AggregatesConcrete is exposed to continuous moist and potentiallycorrosive conditions in underground applications.Consequently, two important selection parameters are theaggregates expansive properties when exposed tomoisture and its porosity. It is important to specify awell-graded, sound, nonporous aggregate in accordancewith ASTM C33 Standard Specification for ConcreteAggregates. This should be executed with limitedamounts of materials that are deleteriously reactive withthe alkalis in cement. When receiving aggregate from anarea known to have potential problems with alkali-aggregate reaction, alkali-silica reaction or alkali-carbonate reaction, the aggregate supplier should providesufficient laboratory data on the aggregates potentialreactivity.



6/30

If the only available aggregates in your area have beenfound to cause excessive expansion of mortar orconcrete, appropriate precautionary measures should betaken during the mix design process. The use of mineraladmixtures, a low water-cement ratio or a low-alkalicement can all aid in controlling such expansivereactions. When using mineral admixtures or a low-alkali

cement, trial batches should be tested to establish theirviability in controlling the expansive reactions.

Gradation of AggregatesAggregate gradation influences both the economy andstrength of a finished utility vault. The purpose of propergradation is to produce concrete with a maximum densityalong with good workability to achieve sufficientstrength.

Well-graded aggregates help improve workability,

durability and strength of the concrete. Poorly graded orgap-graded aggregates rely on the use of excess mortarto fill voids between coarse aggregates, leading topotential durability problems. Concrete mixes containingrounded coarse aggregates tend to be easier to place andconsolidate. However, crushed aggregates clearly areacceptable. The use of elongated, flat and flakyaggregates is discouraged. Gap-graded aggregateslacking intermediate sizes are also discouraged.

Aggregate Deleterious SubstancesEnsure all aggregates are free of deleterious substances,including:

Substances that cause an adverse chemical reaction infresh or hardened concrete

Clay, dust and other surface-coating contaminants Structurally soft or weak particles

For good bond development, ensure aggregate surfacesare clean and free from excessive dust or clay particlesExcessive dust or clay particles typically are defined asmaterial passing a #200 sieve, the limit of which is nomore than 3 percent. Friable aggregates may fracture inthe mixing and placement process, compromising theintegrity of the hardened concrete product.

Moisture Content of AggregateThe measurement of aggregate moisture content isimportant in the control of concrete workability, strengand quality. Aggregates particularly fine aggregates(sands) can collect considerable amounts of moistureon their surfaces. Fine aggregates can hold up to 10percent moisture by weight; coarse aggregates can holup to 3 percent.

Water on the surface of an aggregate that is not

calculated into the mixture proportions will increase thewater-cementitious ratio. The moisture content ofaggregates will vary throughout a stockpile and will beaffected by changes in weather conditions. Therefore,adjust mixture proportions as necessary throughout theproduction day to compensate for moisture contentchanges in the aggregate.

The following methods will increase the likelihood ofuniform moisture content:

Enclose storage of daily production quantities Store aggregates in horizontal layers Have at least two stockpiles Allow aggregate piles to drain before use Avoid the use of the bottom 12 inches of a stockpile Continuously sprinkle aggregate stock piles (climate

dependent) Store entire stockpile indoors or under cover

Careful monitoring of aggregate moisture content durinbatching will reduce the need to add additional cementoffset excess water. This will maintain high-qualitystandards and save on expensive raw materials.

The plant should have a program in place that managesurface moisture content or accounts for moisturevariation during batching.

6


Figure 2 Poorly graded mix vs. Well-graded mix design

Porous concrete resulting from

bsence of fine materials. Arrows

ndicate water infiltration.

Inclusion of fine materials provides

filling for spaces between coarse

aggregates.


7/30

Handling and Storage of AggregateAggregate handling is an important operation. Handle andstore aggregates to prevent contamination and minimizesegregation and degradation. Accurately graded coarseaggregate can segregate during a single improperstockpiling operation, so handling should be minimized toreduce the risk of particle size segregation. Alsominimize the number of handling operations and materialdrop heights to avoid breakage.

The following methods can prevent segregation: Store aggregates on a clean, hard, well-drained base to

prevent contamination. Bin separation walls shouldextend high enough to prevent overlapping and cross-contamination of different-sized aggregates.

Avoid steep slopes in fine aggregate stockpiles. Fineaggregate stockpiles should not have slopes greaterthan the sands angle of repose (i.e., natural slope,

typically 1:1.5) to prevent unwanted segregation. Remove aggregates from a stockpile by working

horizontally across the face of the pile. Avoid takingaggregate from the exact same location each time.

WaterWater used in mixing concrete should meet therequirements of ASTM C 1602, Standard Specification forMixing Water Used in the Production of HydraulicCement Concrete. Avoid water containing deleteriousamounts of oils, acids, alkalis, salts, organic material or

other substances that may adversely affect the propertiesof fresh or hardened concrete.

Chemical AdmixturesCommonly used chemical admixtures in precast concretemanufacturing include: Accelerating admixtures (ASTM C494, Specification for

Chemical Admixtures for Concrete) Air entrainment admixtures (ASTM C260, Specification

for Air-Entraining Admixtures for Concrete) Water-reducing admixtures (ASTM C494, Specification

for Chemical Admixtures for Concrete) High-range water-reducing admixtures or

superplasticizers (ASTM C1017, Chemical Admixturesfor Use in Producing Flowing Concrete)

Store admixtures in a manner that avoids contamination,evaporation and damage. Protect liquid admixtures fromfreezing and extreme temperature changes, which couldadversely affect their performance. It is also important toprotect admixture batching components from dust and

temperature extremes. Ensure they are accessible for visualobservation and periodic maintenance. Perform periodicrecalibration of the batching system as recommended bythe manufacturer or as required by local regulations.

Chemical admixture performance can vary. Exercisecaution, especially when using new products. Test some

trial batches and document the results before using anew admixture for production. Follow manufacturersrecommendations exactly. Carefully check admixtures forcompatibility with the cement and any other admixturesused. Do not mix similar admixtures from differentmanufacturers without the manufacturers agreement ortesting to verify compatibility.

Additional guidelines for the use of admixtures are includedin ACI 212.3, Guide for Use of Admixtures in Concrete.Avoid accelerating admixtures that contain chlorides inorder to prevent possible corrosion of reinforcing steelelements and other embedded metal objects.

Supplementary CementitiousMaterials (SCMs)Supplementary Cementitious Materials are oftenincorporated into a concrete mix to reduce cementcontents, improve workability, increase strength andenhance durability. The most common types of SCMs arefly ash, silica fume and ground granulated blast furnaceslag (GGBFS) as know simply as slag. More than oneSCM may be incorporated into a mix while various typesof blended cements are also available. The followingstandards establish the minimum requirements for someof the common SCMs and blended cements. ASTM C595: Standard Specification for Blended

Hydraulic Cements ASTM C618: Standard Specification for Coal Fly Ash and

Raw or Calcined Natural Pozzolan for Use in Concrete ASTM C989: Standard Specification for Ground

Granulated Blast-Furnace Slag for Use in Concrete andMortars

ASTM C1240: Standard Specification for Use of SilicaFume Used in Cementitious Mixtures

Ready-Mixed ConcreteVerify that the ready-mixed concrete supplier is operatingin accordance with ASTM C94, Standard Specificationfor Ready-Mixed Concrete. Perform plastic concrete tests(slump, temperature, air content and density) at the plantprior to casting products. Record any added water on thedelivery batch ticket for each truck and keep it on file.



8/30

Concrete mix design, also known as mix proportioning, isa broad subject one that is specific to concrete ingeneral and not necessarily to utility vaults in particular.This discussion will focus only on critical factors thatpertain to high-quality precast concrete that isrecommended when casting utility vaults.

Mix designs are selected based upon several necessaryfactors including permeability, consistency, workability,strength and durability. The elements necessary toachieve high-quality precast concrete include:

Low water-cement ratio (less than 0.45) Minimum compressive strength of 4,000 psi at 28 days Use of quality aggregates Appropriate concrete consistency (concrete that can be

readily placed by traditional methods; this is typicallymeasured by slump)

High water-cement ratios lead to undesirable increasedcapillary porosity within the concrete. Capillary pores arevoids resulting from the consumption and evaporation ofwater during the hydration or curing process. Enlarged

and interconnected capillary voids serve as pathways forwater and other contaminates to infiltrate the concretesystem. Lower water-cement ratios result in smaller andfewer pores, reducing the concretes permeability.

Aggregate quality and gradation have a tremendousimpact on the concretes overall quality. Mix designs withwell-graded aggregates and sufficient quantities of fineaggregate have reduced water demands (i.e., lowerwater-cement ratios) while maintaining adequateworkability and ease of placement.

Proper consistency of fresh concrete is a critical elementin producing high-quality precast concrete. Fresh

concrete must be sufficiently plastic (flowable ordeformable) to be properly placed, consolidated andfinished. The size, shape and grading of aggregates,cement content, water-cement ratio and admixtures affethe workability of a mix.

Water-reducing admixtures and superplasticizers cangreatly increase the workability of fresh concrete withochanging the water-cement ratio. Experience has shownthat concrete with low water-cement ratios (less than0.45) can be properly placed and consolidated with the

proper use of admixtures. However, air entrainmentshould be limited to keep the air content at a maximumof 7 percent.

The use of chemical admixtures for wet-cast concrete(such as air-entraining admixtures, water-reducingadmixtures and superplasticizers) helps to attainworkable concrete with a low water-cement ratio. Theiruse is particularly important, since most utility vaultsrequire heavier reinforcing and have large penetrationsthat require special attention to ensure full consolidatio

In certain circumstances, and where local regulationsallow, properly designed and tested self-consolidatingconcrete (SCC) can be used to improve the likelihood oproper bond between concrete and reinforcement.

Air-entraining admixtures are designed to dispersemicroscopic air bubbles throughout the concretes matrto function as small shock absorbers during freeze-thaw cycles. The required air content for frost-resistantconcrete is determined by the maximum aggregate sizeand severity of in-service exposure conditions (ACI 318)

Air entrainment improves workability and reducesbleeding and segregation of fresh concrete while greatlimproving the durability of hardened concrete.

CONCRETE MIXTUREPROPORTIONING

8



9/30

LIFTING INSERTS

Commercially manufactured lifting devices comefurnished with documented and tested load ratings. Usethe devices as prescribed by the manufacturersspecification sheets. Lifting devices should meet theminimum requirements of ASTM C857, Standard Practicefor Minimum Structural Design Loading for UndergroundPrecast Concrete Utility Structures.

Lifting devices designed in the plant and notcommercially manufactured must be load tested orevaluated by a professional engineer. In general, industry

specifications require that lifting inserts have a minimumsafety factor of three (ASTM C857) or four (29 CFR1926.704, ANSI A10.9).

According to the NPCA Quality Control Manual forPrecast Concrete Products:All lifting devices and apparatus should meet OSHArequirements documented in Code of FederalRegulations Title 29 Part 1926. Other applicable codesand standards are ANSI A10.9 and ASTM C 857.

A factor of safety of at least 4 is recommended for liftingdevices. Manufacturers of standard lifting devices shouldprovide test data to allow selection of appropriateloading.

Because of their brittle nature, reinforcing bars shouldnot be used as lifting devices. Instead, smooth bars madeof steel conforming to ASTM A36 can be used.



10/30

Good concrete with a water-cement ratio less than 0.45and a compressive strength greater than 4,000 psi issufficient for utility vaults. Under normal conditions,there is no need for additional applications of asphalt,bituminous, epoxy or cementitious coatings. However, aprotective exterior coating may be specified when a soanalysis indicates a potential for chemical attack.

COATINGS

10



11/30

PRODUCTION PRACTICES

Quality ControlAll plants must have a quality control program andmanual, including but not limited to the following:

Documented mix designs Pre-pour inspection reports Form maintenance logs Post-pour inspection reports Performance and documentation of structural and

watertightness testing discussed in this manual Plant quality control procedures

Raw materials Production practices Concrete mixes Reinforcement fabrication and placement Concrete testing Storage and handling

Records of the above listed items should be available forreview by appropriate agencies upon request.Participation in the NPCA Plant Certification Program andfuture programs is recommended as an excellent way to

ensure product quality. Use the NPCA Quality ControlManual for Precast Concrete Products as the basis fordeveloping a strong quality control program.

FormsForms must be in good condition. Frequent inspectionintervals and regular maintenance ensure that forms arefree of any damage that could cause concrete placementdifficulties or dimensional problems with the finishedproduct.

Use forms that prevent leakage of cement paste and aresufficiently rigid to withstand the vibrations encounteredin the production process. Maintain forms properly,including cleaning after each use and inspection prior toeach use, to ensure uniform concrete surfaces. Ensureforms are level and on a solid base.



12/30

Fabrication drawings must be a part of every QCprogram. Fabrication drawings should detail thereinforcement requirements and all necessary informationpertaining to the product prior to casting.

Conventional ReinforcementFabricate reinforcing steel cages by tying or welding thebars, wires or welded wire reinforcement into rigidstructures. The reinforcing steel cages should conform tothe tolerances defined on the fabrication drawings. If notstated, minimum bend diameters on reinforcement

should meet the requirements set forth in ACI 318, asdefined in Table 1. Make all bends while thereinforcement is cold. The minimum bend diameter forconcrete reinforcing welded wire reinforcement is 4db.

Table 1: Concrete Reinforcing Steel

db = nominal diameter (inch or mm) of bar

Weld reinforcement (including tack welding) inaccordance with AWS D1.4, Structural Welding Code,Reinforcing Steel. This code requires either specialpreheat requirements (when required) or weldable gradereinforcement as defined by ASTM A706, Specification

for Low-Alloy Steel Deformed and Plain Bars for ConcreteReinforcement, for any welding of reinforcing steel,including tack welds. Take special care to avoidundercutting or burning through the reinforcing steel.

Conventional reinforcement (ASTM A615, Specificationfor Deformed and Plain Billet-Steel Bars for ConcreteReinforcement) is produced from recycled metals thathave higher carbon contents and are likely to becomebrittle if improperly welded. A brittle weld is a weak linwhich can compromise the structural integrity of thefinished product. ASTM A615/615M states: Welding ofmaterial in this specification should be approached withcaution since no specific provisions have been includedto enhance the weldability. When the reinforcing steel ito be welded, a welding procedure suitable for the

chemical composition and intended use or service shoube used.

Ensure lap splices for steel reinforcement (rebar andwelded-wire reinforcement) meet the requirements of A318. Adequate development length is required to develothe design strength of the reinforcement at a criticalsection. A qualified engineer should determinedevelopment length and clearly indicate it on shopdrawings.

Reinforcement steel should be free of loose rust, dirt anform release agent. Cut, bend and splice reinforcing stein accordance with fabrication drawings and applicableindustry standards. Inspect reinforcing cages for size,spacing, proper bends and length. Secure the reinforcincage in the form so that shifting will not occur duringcasting. Use only chairs, wheels and spacers made ofnoncorrosive materials.

It is important to place and hold reinforcement in positas shown in the fabrication drawings. A maximum

recommended placement tolerance for the depth ofreinforcement is +1/4 inch (ACI 318). As a general rule variation in spacing between bars should not exceedmore than 1/12 of the designed bar spacing nor exceed1.5 inch in variation, except for welded wire meshconforming to Specifications A185 or A497. Therecommended minimum concrete cover over reinforcingsteel is 3/4 inch (ASTM C858).

REINFORCEMENT

12


ASTM A615 and A706

Inch-Pound Bar Sizes

# 3 through # 8# 9, # 10 and # 11

# 14 and # 18

Minimum Bend

Diameter

6db8db10db

ASTM A615 and A706

Soft Metric Bar Sizes

# 10 through # 25# 29, # 32 and # 36

# 43 and # 57


13/30

Fiber ReinforcementData must be available to show conclusively that thetype, brand, quality and quantity of fibers to be includedin the concrete mix are not detrimental to the concrete orto the precast concrete product. Fiber reinforced concretemust conform to ASTM C1116, Standard Specification forFiber-Reinforced Concrete and Shotcrete (Type I or TypeIII). The two most popular types of fibers are syntheticand steel fibers. Steel fibers must conform to ASTMA820, Specification for Steel Fibers for Fiber-ReinforcedConcrete. Do not use fibers as a replacement for

primary structural reinforcing steel. In general, fibers willnot increase the compressive or flexural strength ofconcrete.

Synthetic microfibers in concrete typically reduce plasticshrinkage cracks and improve impact resistance.

They can help reduce chipping when products arestripped. Typical dosage rates will vary from 0.5 to 2.0lbs/yd3. Synthetic macrofibers and steel fibers mayreplace secondary reinforcement to provide equivalent

bending stress and strength when compared with weldedwire reinforcement and light-gauge steel reinforcement.Typical dosage rates for synthetic macrofibers vary from3.0 to 20 lbs/yd3. Steel fiber dosage rates may vary from20 to 60 lbs/yd3. Fibers must be approved by aregulatory agency or specifying engineer prior toconcrete placement.

Design the concrete mix so that the mix is workable andthe fibers are evenly distributed. Chemical admixtures oradjustments to the concrete mixture design may be

necessary to achieve proper consolidation andworkability. It is important to adhere to themanufacturers safety precautions and to followinstructions when introducing the fibers into the mix.

Embedded ItemsItems such as plates and inserts must be held rigidly inplace during casting. All embedded items should beresistant to corrosion. Special consideration should begiven when welding operations are required.

Pre-Pour InspectionA typical pre-pour checklist, as illustrated on the nextpage, provides a means of documenting the requiredquality checks. A qualified individual should makeinspections prior to each pour. Correct any deviations

prior to the start of placement activities.

Pre-Pour Operations Include: Preparing and setting forms Positioning steel reinforcement according to structural

design Placing blockouts Positioning embedded items



14/3014


PRE-POUR CHECKLIST

PRODUCT: ________________________________________________ Job No. ____________

Casting Date Sun Mon Tues Wed Thurs Fri Sat

Form Condition

Form Cleanliness

Form Joints

Release Agent/Retarder

Design Length (ft/in)

Set-Up Length (ft/in)

Design Width (ft/in)

Set-Up Width (ft/in)

Design Depth (ft/in)

Set-Up Depth (ft/in)

Blockouts

Squareness

End and Edge DetailsReinforcing Steel

Size of Reinforcement

Spacing

Rustification

Plates and Inserts

Lifting Devices

Top Finish (wet)

REMARKS: ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

QC Supervisor ________________ Date _______ Inspector _______________ _______________


15/30

CASTING CONCRETE

Transporting ConcreteWhen transporting concrete from mixer to form, use anymethod that does not contaminate the concrete, causedelay in placing, or segregation. Concrete can bedischarged directly from the mixer into the forms ACI304, Guide for Measuring, Mixing, Transporting andPlacing, is a valuable reference.

Placing Concrete

Conventional Concrete

Keep the free fall of the concrete to a minimum anddeposit as near to its final location as possible. Donot use vibration equipment to move fresh concretelaterally in the forms.

Fiber Reinforced Concrete (FRC)

Follow the same practices as described forconventional concrete, but note that the workabilityof the FRC may be slightly reduced.

Self-Consolidating Concrete (SCC)

Place self-consolidating concrete into itself at aconstant pressure head from one end of the form,allowing air to escape as the concrete flows into andaround steel reinforcement. Avoid placementpractices that add additional energy to the mix andcause unwanted segregation, such as excessivevibration, increased pour heights or increaseddischarge rates.

Consolidating ConcreteSCC generally requires minimal consolidation efforts.

However, when using conventional concrete, consolidationoperations are required to minimize segregation andhoneycombing. Consolidation can be improved onparticular molds by using vibrators with variablefrequency and amplitude. Three types of vibration areprevalent in the precast industry:

Internal stick vibratorExternal vibrator mounted on forms or set on a

vibrating tableSurface vibrator can be moved across the surface

Lower internal vibrators vertically and systematically intothe concrete without force until the tip of the vibratorreaches the bottom of the form. When using internalvibrators, concrete should be placed in wall sectionsusing lifts not exceeding two feet. Do not drag internalvibrators horizontally. Once consolidation is complete in

one area, remove the vibrator vertically and move thevibrator to the next area. Regardless of the vibrationmethod, ensure that the field of vibration overlaps withanother insertion to best consolidate the concrete andminimize defects.

Some external vibrators are mounted on a piece of steelattached to the form. Position them to allow for overlapof vibration areas. Continue the vibration process untilthe product is completely consolidated. Vibration isconsidered complete when large bubbles (3/8 diameter

or greater) no longer appear at the surface. Care shouldbe taken to avoid overvibration, because segregation ofthe aggregate from the cement paste can result inlowering the concrete quality and strength.

Finishing Unformed SurfacesEach product is to be finished according to its individualspecifications. If finishing techniques are not specified,take care to avoid floating either too early or for toolong. Premature finishing can trap bleed water below thefinished surface, creating a weak layer of concrete

susceptible to freeze-thaw cycles and chemical attack.Finishing with a wood or magnesium float isrecommended.



16/30

Two critical elements in curing concrete are maintainingcorrect moisture content and maintaining correct concretetemperature. Proper curing is important in developingstrength, durability and chemical resistance andwatertightness all important considerations forunderground utility vaults.

Note: Concrete temperature discussed in this manualrefers to the temperature of the concrete itself, not theambient temperature.

The nature of precast operations poses unique challengesto proper curing. To ensure cost-effective use of forms,precasters often strip the forms at the beginning of thenext workday. That is an acceptable standard, accordingto ACI 308, Standard Practice for Curing Concrete. Thetime necessary to develop enough strength to strip theforms is highly dependent on ambient temperature in thecasting area. The Portland Concrete Association (PCA)lists three methods of curing:

1. Maintaining water moisture by wetting (fogging,

spraying, wet coverings, etc.)2. Preventing the loss of water by sealing (plasticcoverings or applying curing compounds)

3. Applying heat (often in conjunction with moisture, withheaters or live steam)

Choose the method(s) that best suit the particularproduction operation. All three are permissible, butpreventing the loss of water (method 2) may be thesimplest choice for utility vaults. Maintaining moisturerequires constant wetting, which is labor intensive.Alternate wetting and drying can lead to problems withcracking. Steam curing can also be effective. Concretetemperatures should never exceed 150 F. Both of thesetechniques are described in ACI 308, Standard Practicefor Curing Concrete, and the PCA publication Designand Control of Concrete Mixtures. Plastic coverings or

membrane-forming curing compounds require less laboefforts and allow form stripping the next work day. Theare some special considerations for both:

1. Plastic sheeting must comply with ASTM C171,Standard Specification for Sheet Materials for CurinConcrete, which specifies a minimum thickness of 4mm and be either white or opaque in color. PCA statthat other colors can be used depending on sunconditions and temperature. When using multiplesheets, overlap them by approximately 18 inches to

prevent moisture loss.2. Curing compounds can be applied when bleed water no longer present on the surface. As with plastic,white-colored compounds might reflect sunlight betteand limit temperature gain. Follow the manufacturersrecommendations.

CURING PROCEDURES

16



17/30

Cold and Hot Weather ConcretingIn hot and cold weather, special precautions arenecessary.

Cold Weather Hydration rates are slower during coldweather. Concrete temperatures below 50 F areconsidered unfavorable for pouring due to the extendedtime required for strength gain and the possibility offreezing. However, once concrete reaches a minimumstrength of 500 psi (usually within 24 hours) freezing hasa limited impact. Ideally, precast concrete operations

should be performed in heated enclosures that willprovide uniform heat to the products until they reach 500psi. If necessary, heating the mixing water and/oraggregates can increase the concrete temperature. Do notheat water above 140 F, and do not use clumps of frozenaggregate and ice. ACI 306, Cold Weather Concreting,contains further recommendations on cold-weatherconcreting.

Hot Weather High temperatures accelerate hydration.Do not allow fresh concrete temperature to exceed 90 F

at time of placement. Keep the temperature of theconcrete mix as low as possible using a variety of means,including:

Shading the aggregate piles Wetting the aggregates (mix design must be adjusted

to account for the additional water) Using chilled water

Note: During the curing process, ensure that the concretetemperature does not exceed 150 F. In all cases, protect

freshly cast products from direct sunlight and dryingwind. ACI 305, Hot Weather Concreting, containsfurther recommendations on hot-weather concreting.



18/30

Handling EquipmentCranes, forklifts, hoists, chains, slings and other liftingequipment must be able to handle the weight of theproduct with ease and comply with federal and localsafety requirements. Routine inspections of all handlingequipment are necessary. Qualified personnel shouldmake periodic maintenance and repairs as warranted. Tagall chains and slings with individual load capacity ratings.For U.S. plants, refer to the specific requirements of theOccupational Safety and Health Administration (OSHA).For Canadian plants, refer to the specific requirements of

the Canadian Centre for Occupational Health and Safety(CCOHS).

Stripping and Handling ProductsMinimum Strength Requirement Concrete must gainsufficient strength before stripping it from the forms. Dto the nature of the precast business, the AmericanConcrete Institute recognizes that forms will usually bestripped the next workday. Under normal conditions(concrete temperature greater than 50 F), properlydesigned concrete can reach the minimum compressivestrength for stripping within this time period. Periodiccompressive strength testing of one-day or strippingstrength cylinders is recommended to confirm that prop

concrete strength is attained.

Handle recently poured and stripped products with carePerform lifting and handling carefully and slowly toensure that dynamic loads do not damage the tank.Always follow recognized safety guidelines.

Product Damage During Stripping Inspect the producimmediately after stripping to check for damage.

Post-Pour Inspections

A post-pour inspection checklist, as illustrated, providemethod of identifying and communicating qualityproblems as they occur. It serves as a method ofgathering data for identification of any trends that maybe evident. After a utility vault is stripped from the forit should be inspected for conformance with thefabrication drawings and any necessary repairs should made. All products should be clearly labeled with thedate of manufacturing and marked in accordance withASTM C 858.

POST-POUR OPERATIONS

18



19/30


POST-POUR CHECKLIST

PRODUCT: ________________________________________________ Job No. ____________

Casting Date:_________ Sun Mon Tues Wed Thurs Fri Sat

Inspection Date:______

Mark Number

Stripping Strength

Top Finish

Bottom Finish

Surface Texture

As Cast Length (ft/in)

As Cast Width (ft/in)

As Cast Depth (ft/in)

Cracks or Spalls

Squareness

Chamfers

Honeycomb / Grout LeakBowing

Exposed Reinforcement

Exposed Chairs

Plates and Inserts

Chamfer & Radius Quality

Openings / Blockouts

Lifting Devices

REMARKS: ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

QC Supervisor ________________ Date _______ Inspector _______________ _______________


20/30

Finished Formed Surfaces Formed surfaces must berelatively smooth and free of significant honeycombedareas, air voids and bugholes.

Repairing Minor Defects Defects that do not impair theuse or life of the product are considered minor orcosmetic and may be repaired in any manner that doesnot impair the product.

Repairing Honeycombed Areas Remove all loosematerial from the damaged area. Cut back the damaged

zone in horizontal or vertical planes deep enough toremove the damaged concrete. Coarse aggregate particlesshould break rather than merely dislodge when chipped.Use only materials that are specifically developed forconcrete repair, and make repairs according to themanufacturers specifications.

Repairing Major Defects Major defects are defined asthose that impair the intended use or structural integrityof the product. If possible, repair products with majordefects by using established repair and curing

procedures only after a qualified person evaluates thefeasibility of the repair.

Secondary PoursFor products that require secondary pours, establishprocedures to assure that the new concrete bondsadequately to the product and becomes an integral partof it. The surfaces of the product against which thesecondary pour is to be made should be free of laitance,dirt, dust, grease or any other material that will tend toweaken the bond between the original and new

concretes. If the surface is very smooth, roughen it tohelp promote a good bond. As a minimum, use a high-quality water stop, keyway and continuation ofreinforcing between pours to ensure a watertight joint.

Cold JointsCold joints require special care and, as a minimum,should include a high-quality water stop, bonding agenand continuation of reinforcing between pours.

Final Product InspectionUtility vaults should be visually checked for requiredsupplementary items, embedded items and quality at thplant prior to shipping.

Product Shipment

All vehicles used to transport products must be in goodcondition and capable of handling the product withoutcausing damage. Utility vaults should be adequatelycured as specified prior to shipment to a job site ordistant storage areas. All products must be properlysecured with appropriate blockage and either nylonstraps or chains with guards as to avoid product damaduring shipment. NPCAs publication Cargo Securementfor the Precast Concrete Industryoutlines propermethods for securing product. It is recommended that tfinal inspection include checking these items.

FINISHING ANDREPAIRING CONCRETE

20



21/30

SEALS, FITTINGSAND JOINTSCareful attention to joint details, sealing materials andpenetration fittings are important to ensure quality utilityvaults. Systems in areas of high water tables may requirespecial methods for joint and penetration seal designs.

Joint DesignsThe most common joint designs are tongue-and-grooveor lap joints.

For the manufacture of utility vaults, it is recommendedthat only interlocking joints be used. In cases of

potentially significant frost heave, differential settlementand groundwater exposure, greater attention to jointdesign detail is needed. Mechanical fasteners orsecondary pours for lids on bases may be necessary inareas with severe site conditions. The key to preventingmost differential settlement is proper bedding preparation(especially compaction) of the site.

Sealing MaterialsHigh-quality, preformed flexible joint sealants can beused to achieve a dependable joint. Use only sealantsthat contain less than 3 percent volatiles as defined in

ASTM D6 Standard Test Method for Loss on Heating ofOil and Asphaltic Compounds.

The characteristics of a high-quality sealant include: Workability over a wide temperature range Adhesion to clean, dry surfaces Good performance over time (must not shrink, harden

or oxidize)

It is important that all joints be properly cleaned andprepared, according to the sealant manufacturersrecommendations. Preformed flexible joint sealants mustbe sufficiently pliable to compress a minimum of 50percent at the temperature during assembly. Utility vaultsections sealed on site should not be backfilled until thesealant has settled.

Properly splice the sealant by one of the followingmethods: Overlap splice Place one piece on top of the other

and carefully mold together Side-by-side Place in parallel and carefully mold thetwo pieces together

Sealant SizeA critical factor when evaluating the sealing potential of asealant is cross-sectional area. Cross-sectional area isdefined as the geometric shape of the sealant (i.e., 0.75inches high by 1.0 inches wide). Industry experience hasshown that a sealants cross-sectional height must becompressed a minimum of 30 percent to create a good

seal; 50 percent compression is desirable.

Connections and HardwareThe functionality of a utility vault is increased throughthe use of high quality ancillary components such ascable racking assemblies, pulling irons, conduitterminators and pipe supports.

Cable racking assemblies should be specified to matchthe characteristics of the type of cable to be supported.The assemblies and their hardware for attachment to the

wall of the vault should be engineered to carry theanticipated weight of the supported cables.

Pulling irons should be structurally engineered to resistthe anticipated cable pulling loads. Additionally, thepulling load placed upon the wall of the utility vaultshould be considered in the structural design calculationsfor the vault. Pulling irons should not be used for liftingand handling product.


Lap Joint Shiplap JointTongue &

Groove Joint


22/30

Cable industry standards require a smooth or rolled edgefor the cable to pass over as it leaves the conduit toenter the utility vault. End bells and conduit terminatorsthat are cast into the wall of the precast concrete vault atthe time of manufacture provide a quality labor savingmethod to terminate conduit. These items should be sizedand located on the wall of the vault to match the ductbank configuration.

Utility vaults may be configured to accommodate thepiping systems used for fluid conveyance. Integral

concrete sleepers, thrust blocks and pipe supporthardware may be cast into the vault. Boots and gasketsmay be incorporated at pipe entrances to ensurewatertightness and should be sized and located for thepipe being used.

Hardware should always meet specification requirementsof the design engineer and the customer.

Access, Risers and ManholesAll access risers and manholes must be structurally

sound and watertight.

22



23/30

INSTALLATION

Proper installation is absolutely critical for maintainingthe inherent quality of plant-manufactured concreteproducts and should be performed in accordance withASTM C 891 Standard Practice for Installation ofUnderground Precast Concrete Utility Structures. Many ofthe problems experienced with troublesome utility vaultscan be attributed to incorrect procedures duringinstallation. In addition to damaging the structure,improper installation techniques can lead to safetyhazards.

Site ConditionsThe installation site must be accessible to large, heavytrucks or cranes weighing up to 80,000 pounds. Theconstruction area should be free of trees, branches,overhead wires or parts of buildings that could interferewith the delivery and installation of the utility vault. Mosttrucks require access within 3 to 8 feet of the excavationto be unloaded.

ExcavationPrior to excavation, all buried utilities should be

identified and located. OSHA regulations governingexcavation work should be followed at all times; 29 CFR,Part 1926.650-652.

Excavations should be made with approximately 18 inchesof clearance around the installed structure to allow roomfor adequate compaction. More space should beprovided, as needed, if work other than installation isrequired. Excavations should be sloped to comply with allconstruction safety requirements.

BeddingProper use of bedding material is important to ensure along service life of the utility vault. Engineered beddingmaterial should be used as necessary to provide auniform bearing surface. A good base should ensure thatthe structure would not be subjected to adversesettlement. A minimum 4-inch-thick sand or granular bedoverlaying a firm and uniform base is recommendedunless otherwise specified. Utility vaults should not bearon large boulders or massive rock edges.

Sites with silty soils, high water tables or other poorbearing characteristics must have specially designedbedding and bearing surfaces. In the presence of highwater tables, structures should be properly designed toresist flotation.

Proper compaction of the underlying soil and bedding iscritical to ensure there is no differential settlement.

PlacementPrior to placement in the excavation, the structures

orientation should be confirmed. Inlet penetrations shouldbe aligned in the proper direction and the beddingmaterial should be checked. After placement, check toensure that the structure is level.


Not less

than 60

4" Sand or Granular Bedding (Minimum)

Properly Compacted Base to Prevent Settling

Underground Utilities to be Located Prior to Excavation in Accordance to OSHA Regulations

Excavation Slope to Comply withConstruction Safety Requirements

Product Orientation to beDetermined Prior to Setting

and Checked Prior toBackfilling

Site to be Accessible to

Heavy Trucks & Cranes

(Up to 80,000 lbs.) in an

Area Free of Trees and

Overhead Obstructions

Product Notes:

1) After Placement, Check That the Structure is L

2) Backfill Shall be Placed in Uniform, Properly

Compacted Layers Not to Exceed 24" Thick.

1'-6"Min.

1'-6"Min.

Figure 3


24/30

Lifting DevicesVerify lifting apparatus such as slings, lift bars, chainsand hooks for capacity, and ensure an adequate safetyfactor for lifting and handling products. The capacity ofcommercial lifting devices must be marked on thedevices.

All lifting devices and apparatus should meet OSHArequirements documented in Code of FederalRegulations Title 29 Part 1926. Other applicable codesand standards are ANSI A10.9 and ASTM C857, C890 anC913.

A factor of safety of at least 4 is recommended for liftidevices. Manufacturers of standard lifting devices shouprovide test data to allow selection of appropriateloading.

Because of their brittle nature, do not use reinforcingbars as lifting devices. Use smooth bars made of steelconforming to ASTM A36 instead.

A factor of safety of at least 5 is recommended for liftiapparatus, such as chains, slings, spreader beams, hooand shackles.

BackfillingBackfill should be placed in uniform, mechanicallycompacted layers less than 24 inches thick. This fill

should be equally and uniformly placed around the vauBackfill should be free of any large stones (greater tha3 inches in diameter) or other debris. Each layer shouldbe adequately compacted.

24



25/30

REFERENCES

SpecificationsAmerican Concrete Institute (ACI)ACI 116R, Cement and Concrete TerminologyACI 211.1, Standard Practice for Selecting Proportions for

Normal, Heavyweight and Mass ConcreteACI 211.3, Standard Practice for Selecting Proportions for

No-Slump ConcreteACI 212.3, Chemical Admixtures for ConcreteACI 304R, Guide for Measuring, Mixing, Transporting

and Placing ConcreteACI 305R, Guide for Hot Weather Concreting

ACI 306R, Guide for Cold Weather ConcretingACI 308R, Guide to Curing ConcreteACI 318, Building Code Requirements for Structural

Concrete and CommentaryACI 544, State-of-the-Art Report on Fiber Reinforced

Concrete

ASTM InternationalASTM A185, Standard Specification for Steel Welded

Wire Reinforcement, Plain, for Concrete ReinforcementASTM A496, Standard Specification for Steel Wire,

Deformed for Concrete ReinforcementASTM A497, Standard Specification for Steel Welded

Wire Reinforcement, Deformed, for ConcreteReinforcement

ASTM A615, Standard Specification for Deformed andPlain Carbon Steel Bars for Concrete Reinforcement

ASTM A706, Standard Specification for Low Alloy SteelDeformed Bars and Plain for Concrete Reinforcement

ASTM A820, Specification for Steel Fibers for ReinforcedConcrete

ASTM C33, Standard Specification for Concrete

AggregatesASTM C125, Standard Terminology Relating to Concrete

and Concrete AggregatesASTM C150, Standard Specification for Portland CementASTM C260, Standard Specification for Air-Entraining

Admixtures for ConcreteASTM C494, Standard Specification for Chemical

Admixtures for ConcreteASTM C595, Standard Specification for Blended

Hydraulic CementsASTM C618, Standard Specification for Coal Fly Ash and

Raw or Calcined Natural Pozzolan for Use in ConcreteASTM C857-95, Practice for Minimum Structural Design

Loading for Underground Precast Concrete UtilityStructures

ASTM C858-83, Specification for Underground Precast

Concrete Utility StructuresASTM C891-90, Practice for Installation of UndergroundPrecast Concrete Utility Structures

ASTM C989: Standard Specification for GroundGranulated Blast-Furnace Slag for Use in Concrete andMotars

ASTM C1037-85, Practice for Inspection of UndergroundPrecast Concrete Utility Structures

ASTM C1017, Chemical Admixtures for Use in ProducingFlowing Concrete

ASTM C1116, Standard Specification for Fiber Reinforced

Concrete and ShotcreteASTM C1240: Standard Specification of Use of SilicaFume Used in Cementitious Mixtures

ASTM C1602, Standard Specification for Mixing WaterUsed in the Production of Hydraulic Cement Concrete

ASTM D6, Standard Test Method for Loss on Heating ofOil and Asphaltic Compounds

American Welding Society (AWS)AWS D1.4, Structural Welding Code - Reinforcing Steel

Occupational Safety and HealthAdministration (OSHA)29 CFR 1910.184 (Slings)29 CFR 1926.650-652 (Excavation)



26/30

admixture a material other than water, aggregates,cement and fiber reinforcement, used as an ingredientof concrete, and added to the batch immediately beforeor during its mixing. Typically are liquid incomposition.

admixture, accelerating an admixture that acceleratesthe setting and early strength development of concrete.

admixture, air-entraining an admixture that causes the

development of a system of microscopic air bubbles inconcrete, mortar or cement paste during mixing.

admixture, mineral finely divided, powdered orpulverized materials added to concrete to improve oralter the properties of the plastic or hardened concrete.

admixture, water-reducing admixture that eitherincreases the slump of freshly mixed concrete withoutincreasing the water content or that maintains theslump with a reduced amount of water due to factors

other than air entrainment.

aggregate granular material, such as sand, gravel,crushed stone or iron blast-furnace slag used with acement medium to form hydraulic-cement concrete ormortar.

aggregate, coarse generally pea-sized to 2 inches;aggregate of sufficient size to be predominatelyretained on a No. 4 sieve (4.75 mm).

aggregate, fine general coarse sand to very fine;aggregate passing the 3/8 inch sieve (9.5 mm) andalmost entirely passing a No. 4 sieve (4.75 mm) andpredominately retained on the No. 200 sieve (75 mm).

air content the volume of air voids in cement paste,mortar, or concrete, exclusive of pore space inaggregate particles, usually expressed as a percentageof total volume of the paste, mortar or concrete.

air void a space in cement paste, mortar or concretefilled with air; an entrapped air void ischaracteristically 1 mm or more in width and irregulain shape; an entrained air void is typically between 10

m and 1,000 m in diameter and spherical in shape.

alkali-aggregate reactivity (AAR) a chemical reactionthat occurs between the alkalies (sodium andpotassium) from portland cement or other sources ancertain constituents of some aggregates; under certaconditions resulting in deleterious expansion of

concrete or mortar; often known as alkali-silicareaction (ASR). Cement manufacturers often testaggregates for AAR as a service to their customers.

ASTM ASTM International is a not-for-profitorganization that provides a forum for producers,users, ultimate consumers and those having a generainterest (government and academia) to meet and writstandards for materials, products, systems andservices.

bedding material gravel, soil , sand or other materiathat serves as a bearing surface on which a structurerests and which carries the load transmitted to it.

bleeding the separation of mixing water or itsemergence from the surface of newly placed concretecaused by the settlement of the solid materials.

bonding agent a substance applied to a suitablesubstrate to create a bond between it and a succeedlayer, such as between a layer of hardened concrete

and a layer of fresh concrete.

cement, hydraulic a cement that sets and hardens bychemical interaction with water and is capable of doiso under water.

cementitious material an inorganic material or mixtuof inorganic materials that set and develop strength bchemical reaction with water by formation of hydrate

GLOSSARY

26



27/30

concrete a composite material that consists essentiallyof a binding medium within which are embeddedparticles of fragments of aggregate, usually acombination of fine aggregate and coarse aggregate; inportland-cement concrete, the binder is a mixture ofportland cement and water.

concrete, fresh concrete that possesses enough of itsoriginal workability so that it can be placed andconsolidated by the intended methods.

compressive strength measured maximum resistanceof a concrete or mortar specimen to axial compressiveloading; expressed as a force per unit cross-sectionalarea; or the specified resistance used in designcalculations.

consistency the relative mobility or ability of freshlymixed concrete to flow; it is usually measured by theslump test.

consolidation the process of inducing a closer

arrangement of the solid particles in freshly mixedconcrete during placement by the reduction of voids,usually accomplished by vibration, centrifugation,rodding, tamping or some combination of these actions.Consolidation facilitates the release of entrapped air; asconcrete subsides, large air voids between coarseaggregate particles are filled with mortar.

curing action taken to maintain moisture andtemperature conditions in a freshly placed cementitiousmixture to allow hydraulic cement hydration and (if

applicable) pozzolanic reactions to occur so that thepotential properties of the mixture may devlop.

curing compound a liquid that can be applied as acoating to the surface of newly placed concrete toretard the loss of water or to reflect heat so as toprovide an opportunity for the concrete to develop itsproperties in a favorable temperature and moistureenvironment.

dead load a constant load that in structures is due tothe mass of the members, the supported structure, andpermanent attachments or accessories.

delayed ettringite formation (DEF) occurs at laterages (months to years) and the related heterogeneousexpansion in hardened concrete can produce crackingand spalling. DEF is related to environmental orinternal sulfate attack.

deleterious substances materials present within or on

aggregates that are harmful to hardened concrete,often in a subtle or unexpected way. Morespecifically, this may refer to one or more of thefollowing: materials that may be detrimentally reactivewith the alkalis in the cement (see alkali aggregatereactivity); clay lumps and friable particles; coal andlignite; etc.

dry-cast (no-slump concrete) concrete of stiff orextremely dry consistency showing no measurableslump after removal of the slump cone.

differential settlement the uneven sinking of material(usually gravel or sand) after placement.

elongated aggregate a particle of aggregate where itslength is significantly greater than its width.

entrained air see air void; microscopic air bubblesintentionally incorporated in mortar or concrete duringmixing, typically between 10 m and 1,000 m (1 mm) indiameter and spherical or nearly so.

entrapped air see air void; air voids in concrete thatare not purposely entrained and that are larger, mainlyirregular in shape, and less useful than those ofentrained air; typically greater than 1 mm in diameterand may be of various shapes.

ettringite a mineral, high-sulfate calciumsulfoaluminate occurring in nature or formed by sulfateattack on mortar and concrete.



28/30

float a tool, usually of wood, aluminum or magnesium,used in finishing operations to impart a relatively evenbut still open texture to an unformed fresh concretesurface.

floating the operation of finishing a fresh concrete ormortar surface by use of a float, preceding trowelingwhen that is to be the final finish.

fly ash the finely divided residue transported by flue

gases from the combustion of ground or powderedcoal; often used as a supplementary cementitiousmaterial in concrete.

forms (molds) a structure for the support of concretewhile it is setting and gaining sufficient strength to beself-supporting.

friable easily crumbled or pulverized, as it refers toaggregates.

gap grading aggregate graded so that certainintermediate sizes are substantially absent (i.e.,aggregate containing large and small particles withmedium-size particles missing).

gradation the particle-size distribution as determinedby a sieve analysis (i.e., ASTM C 136); usuallyexpressed in terms of cumulative percentages larger orsmaller than each of a series of sizes (sieve openings)or the percentages between certain ranges of sizes(sieve openings).

hydration formation of a compound by the combiningof water with some other substance; in concrete, thechemical process between hydraulic cement and water.

infiltration to cause (as a liquid) to permeatesomething by penetrating its pores or interstices.

initial set a degree of stiffening of a mixture of cemand water less than final set, generally stated as anempirical value indicating the time in hours andminutes required for cement paste to stiffen sufficiento resist to an established degree, the penetration of weighted test needle; often performed on a sample omortar sieved from a concrete sample.

live load any load that is not permanently applied tostructure; including transitory loading such as water,vehicles and people.

organic impurities (re: aggregate) extraneous andunwanted organic materials (twigs, soil, leaves, otherdebris) that are mixed in aggregates; these materialsmay have detrimental effects on concrete producedfrom such aggregates.

OSHA Occupational Safety and Health AdministrationU.S. Department of Labor.

plastic concrete see concrete, fresh.

portland cement a hydraulic cement produced bypulverizing portland-cement clinker, usually incombination with calcium sulfate.

portland cement clinker a partially fused ceramicmaterial consisting primarily of hydraulic calciumsilicates and calcium aluminates.

pozzolan a siliceous or siliceous and aluminousmaterial that in itself possesses little or no

cementitious value but will, in finely divided form anin the presence of moisture, chemically react withcalcium hydroxide at ordinary temperatures to formcompounds possessing cementitious properties.

psf pounds per square foot

psi pounds per square inch

28



29/30

secondary pour a situation when a succeeding layer ofconcrete is placed on previously-placed hardenedconcrete.

segregation the unintentional separation of theconstituents of concrete or particles of an aggregate,resulting in nonuniform proportions in the mass.

set the condition reached by a cement paste, mortar orconcrete when it has lost plasticity to an arbitrarydegree, usually measured in terms of resistance to

penetration or deformation; initial set refers to firststiffening; final set refers to attainment of significantrigidity.

silica fume very fine non-crystalline silica produced inelectric arc furnaces as a byproduct of the productionof elemental silicon or alloys containing silicon; alsoknown as condensed silica fume and micro-silica. It isoften used as an additive to concrete and can greatlyincrease the strength of a concrete mix.

slump a measurement indicative of the consistency offresh concrete. A sample of freshly mixed concrete isplaced and compacted by rodding in a mold shaped asthe frustum of a cone. The mold is raised, and theconcrete is allowed to subside. The distance betweenthe original and displaced position of the center of thetop surface of the concrete is measured and reportedas the slump of the concrete. Under laboratoryconditions, with strict control of all concrete materials,the slump is generally found to increase proportionallywith the water content of a given concrete mixture,

and thus to be inversely related to concrete strength.Under field conditions, however, such a strengthrelationship is not clearly and consistently shown.Care should therefore be taken in relating slumpresults obtained under field conditions to strength.(ASTM C 143)

specification an explicit set of requirements to besatisfied by a material, product, system or service thatalso indicates the procedures for determining whethereach of the requirements is satisfied.

standard as defined by ASTM, a document that hasbeen developed and established within the consensusprinciples of the Society.

superplasticizer see admixture, water-reducing.Superplasticizers are also known as high-range water-

reducing admixtures.

surcharge a surface load applied to the structure,transferred through the surrounding soil.

trowelling smoothing and compacting the unformedsurface of fresh concrete by strokes of a trowel.

water-cement ratio the ratio of the mass of water,exclusive only of that absorbed by the aggregates, tothe mass of portland cement in concrete, mortar or

grout; stated as a decimal and abbreviated as w/c.

waterstop a thin sheet of metal, rubber, plastic orother material inserted across a joint to obstruct theseepage of water through the joint.

water table the upper limit of the portion of theground wholly saturated with water.

workability of concrete that property of freshly mixedconcrete or mortar that determines the ease with which

it can be mixed, placed, consolidated and finished to ahomogenous condition.



30/30

This Best Practices Manual is subject to revision at anytime by the NPCA Utility Vault Product Committee, whichmust review it at least every three years.

Special thanks are given to the Utility Vault ProductCommittee for updating/compiling this manual.

Steve Truax, Wieser Concrete Products Inc.Jay Behney, By-CreteDouglas Bowen, Bowco Industries Inc.Todd Ebbert, San Diego Precast Concrete Inc.

Paul Heidt, Garden State Precast Inc.Donald McNutt, Spillman CompanyMichael Menard, Firebaugh Precast Inc.Brian Rhees, Oldcastle Precast Inc.Robert Thornton, Hughes Concrete Products


uv_bpm utility vaults precast npca

Documents