uv_bpm.pdf

Copyright 2006 by National Precast Concrete Association (NPCA)
Second Edition, 2005 All rights reserved.
No part of this manual may be reproduced in any form without permission in writing from
the National Precast Concrete Association.
The association of the manufactured concrete products industry.
10333 North Meridian Street, Suite 272 | Indianapolis, Indiana 46290
800-366-7731 | 317-571-0041 (fax) | www.precast.org
2
NATIONAL PRECAST CONCRETE ASSOCATION
NOTES
1. This manual does not claim or imply that it
addresses all safety-related issues, if any,
associated with its use. Manufacture of
concrete products may involve the use of
hazardous materials, operations and
equipment. It is the user’s responsibility to
determine appropriate safety, health and
environmental practices and applicable
regulatory requirements associated with
the use of this manual and the manufacture
of concrete products.
2. Use of this manual does not guarantee the
proper function or performance of any
product manufactured in accordance with
the requirements contained in the manual.
Routine conformance to the requirements
of this manual should result in products of
an acceptable quality according to current
industry standards.

INTRODUCTION
Precast concrete is ideally suited for utility, industrial and
communications structures. A properly manufactured and
installed precast concrete structure can last almost
indefinitely. Precast concrete is inherently durable, highly
impermeable and corrosion-resistant.
Utility, industrial and communications structures are an
important part of the manufactured concrete products
industry, and we must continue to provide project owners
and end users with the best possible products at
competitive prices. It is also important that those
products contribute to the quality, timeliness and ease of
installation of construction projects. The best practices
outlined in this manual are intended to help
manufacturers achieve these goals.
When properly designed and manufactured, precast
concrete is capable of maintenance-free performance
without the need for protective coatings, except in certain
circumstances such as highly-corrosive environments. The
“precast advantage” is further solidified through precast’s
ease of installation and strength. Because precast
concrete products typically are produced in a controlled
environment, they exhibit high quality and uniformity.
Adverse factors affecting quality which are typically
found on job sites – variable temperature, uneven curing
conditions, inconsistent material quality and
craftsmanship – are significantly reduced in a plant
environment.
High-quality concrete products are important for many
applications, most notably for underground structures
that must resist soil pressures and sustain surface loads.
The controlled manufacturing environment in a precast
concrete plant is ideal for the production of high-quality,
durable concrete products.
This manual is intended to guide manufacturers in quality
production processes for manufacturing utility vaults. The
manual is not intended to be all inclusive and the
recommendations are not intended to exclude any
materials or techniques that would help achieve the goal
of providing structurally sound, high quality products.
Attention to detail, quality materials, proper training and
a workforce dedicated to quality control will ensure that
the utility vault meets or exceeds the expectations of
contractors and end users.
3
UTILITY VAULT MANUFACTURING BEST PRACTICES MANUAL

STRUCTURAL DESIGN
4
Loading Conditions
A properly designed precast concrete utility vault must
withstand a variety of loading conditions, which vary
during manufacturing, installation, testing and service.
These structures are designed to withstand loading
conditions through rational mathematical design
calculations, by proof-of-load testing or in accordance
with ASTM C 857 “Standard Practice for Minimum
Structural Design Loading for Underground Precast
Concrete 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 designed
according to one or more of the following industry codes
and standards and as required by any regulatory groups
with 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 Precast
Concrete Utility Structures
• ASTM C 858 – Standard Specification for Underground
Precast Concrete Utility Structures
The loading conditions illustrated in the diagram(s)
should be analyzed and considered in the design of a
utility structure.
The following design characteristics have a critical impact
on the performance of utility structures.
Concrete Thickness
The concrete thickness must be sufficient to meet
minimum reinforcement cover requirements and withstand
design loading conditions.
Concrete Mix Design
Concrete must have a minimum compressive strength of
4,000 psi at 28 days. Consider methods to reduce
permeability, improve durability and increase strength.
Maintain a low water-cementitious ratio at or below 0.45.
Reinforcement
Proper design and placement is critical to withstand the
significant loads applied to utility vaults. Reinforcement
must be sufficient for required strength and service
conditions, including temperature and shrinkage effects.
Control cracking by using multiple small-diameter steel
bars rather than fewer large-diameter steel bars. Fiber
reinforcement also helps to reduce cracking and may add
some strength, but should not replace primary
reinforcement. Welded-wire reinforcement can also be
used, but particular attention should be paid to design
and location. All reinforcement should meet applicable
ASTM specifications.
Loading Diagram
*Manufacturer to specify the maximum depth of cover
Top Seam
Vault
Grade line
Groundwater
Level
+ +
Mid-Seam
Vault
Residential
Soil
Residential
Soil
Depth of
Cover
Hydrostatic
Loading
Soil
Loading
Hydrostatic
Loading
Soil
Loading
Surcharge
Surcharge

MATERIALS
The primary constituents of precast concrete are cement,
fine and coarse aggregates, water and admixtures. The
following discussion covers relevant factors in the
selection and use of these fundamental materials.
Cement
The majority of cement used in the manufactured
concrete products industry is governed by ASTM
C 150,“Standard Specification for Portland Cement.”
The five primary types of ASTM C 150 cement are:
Type I Normal
Type II Moderate Sulfate Resistance
Type III High Early Strength
Type IV Low Heat of Hydration
Type V High Sulfate Resistance
Select the cement type based on project specifications or
individual characteristics which best fit the operation and
regional conditions of each manufacturer. Note that
certain types of cement may not be readily available in
certain regions. Store cement in a manner that will
prevent 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 identify
delivery locations.
Design and maintain bin and silo compartments to
discharge freely and independently into the weighing
hopper. Cement in storage should be drawn down
frequently to prevent undesirable caking. Stack bagged
cement on pallets to permit proper air circulation and to
avoid undesirable moisture and condensation. On a short-
term basis (less than 90 days), stack the bags no more
than 14 high. For long-term storage, do not exceed seven
bags in height (or per manufacturer’s recommendations).
Use the oldest stock first. Discard any cement with lumps
that cannot be reduced by finger pressure.
Aggregates
Ensure aggregates conform to the requirements of ASTM
C33, “Standard Specification for Concrete Aggregates.”
Evaluate the aggregates and maintain documention at the
plant for potential deleterious expansion due to alkali
reactivity, unless the aggregates come from a state
department of transportation-approved source. The
maximum size of coarse aggregate should be as large as
practical, but should not exceed 20 percent of the
minimum thickness of the precast concrete utility vault or
75 percent of the clear cover between reinforcement and
the surface of the vault. Larger maximum sizes of
aggregate may be used if evidence shows that
satisfactory concrete products can be manufactured.
Aggregates are an important constituent of precast
concrete utility vaults. Nearly 75 percent of a precast
concrete utility vault’s structure consist of coarse and
fine aggregates.
The selection of appropriate aggregates is largely a
regional concern. The selection process is based on using
the best available clean, hard, durable aggregates and
proper gradations. Aggregates should conform to ASTM
C 33 – Standard Specification for Concrete Aggregates
and ACI 318 – Building Code Requirements for Structural
Concrete.
Quality of Aggregates
Concrete is exposed to continuous moist and potentially
corrosive conditions in underground applications.
Consequently, two important selection parameters are the
aggregate’s expansive properties when exposed to
moisture and its porosity. It is important to specify a
well-graded, sound, nonporous aggregate in accordance
with ASTM C33 “Standard Specification for Concrete
Aggregates.” This should be executed with limited
amounts of materials that are deleteriously reactive with
the alkalis in cement. When receiving aggregate from an
area known to have potential problems with alkali-
aggregate reaction, alkali-silica reaction or alkali-
carbonate reaction, the aggregate supplier should provide
sufficient laboratory data on the aggregate’s potential
reactivity.
5

If the only available aggregates in your area have been
found to cause excessive expansion of mortar or
concrete, appropriate precautionary measures should be
taken during the mix design process. The use of mineral
admixtures, a low water-cement ratio or a low-alkali
cement can all aid in controlling such expansive
reactions. When using mineral admixtures or a low-alkali
cement, trial batches should be tested to establish their
viability in controlling the expansive reactions.
Gradation of Aggregates
Aggregate gradation influences both the economy and
strength of a finished utility vault. The purpose of proper
gradation is to produce concrete with a maximum density
along with good workability to achieve sufficient
strength.
Well-graded aggregates help improve workability,
durability and strength of the concrete. Poorly graded or
gap-graded aggregates rely on the use of excess mortar
to fill voids between coarse aggregates, leading to
potential durability problems. Concrete mixes containing
rounded coarse aggregates tend to be easier to place and
consolidate. However, crushed aggregates clearly are
acceptable. The use of elongated, flat and flaky
aggregates is discouraged. Gap-graded aggregates
lacking intermediate sizes are also discouraged.
Aggregate Deleterious Substances
Ensure all aggregates are free of deleterious substances,
including:
• Substances that cause an adverse chemical reaction in
fresh or hardened concrete
• Clay, dust and other surface-coating contaminants
• Structurally soft or weak particles
For good bond development, ensure aggregate surfaces
are clean and free from excessive dust or clay particles.
Excessive dust or clay particles typically are defined as
material passing a #200 sieve, the limit of which is no
more than 3 percent. Friable aggregates may fracture in
the mixing and placement process, compromising the
integrity of the hardened concrete product.
Moisture Content of Aggregate
The measurement of aggregate moisture content is
important in the control of concrete workability, strength
and quality. Aggregates – particularly fine aggregates
(sands) – can collect considerable amounts of moisture
on their surfaces. Fine aggregates can hold up to 10
percent moisture by weight; coarse aggregates can hold
up to 3 percent.
Water on the surface of an aggregate that is not
calculated into the mixture proportions will increase the
water-cementitious ratio. The moisture content of
aggregates will vary throughout a stockpile and will be
affected by changes in weather conditions. Therefore,
adjust mixture proportions as necessary throughout the
production day to compensate for moisture content
changes in the aggregate.
The following methods will increase the likelihood of
uniform 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 during
batching will reduce the need to add additional cement to
offset excess water. This will maintain high-quality
standards and save on expensive raw materials.
The plant should have a program in place that manages
surface moisture content or accounts for moisture
variation during batching.
6
Figure 2 — Poorly graded mix vs. Well-graded mix design
Porous concrete resulting from
absence of fine materials. Arrows
indicate water infiltration.
Inclusion of fine materials provides
filling for spaces between coarse
aggregates.

Handling and Storage of Aggregate
Aggregate handling is an important operation. Handle and
store aggregates to prevent contamination and minimize
segregation and degradation. Accurately graded coarse
aggregate can segregate during a single improper
stockpiling operation, so handling should be minimized to
reduce the risk of particle size segregation. Also
minimize the number of handling operations and material
drop 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 should
extend high enough to prevent overlapping and cross-
contamination of different-sized aggregates.
• Avoid steep slopes in fine aggregate stockpiles. Fine
aggregate stockpiles should not have slopes greater
than the sand’s 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 taking
aggregate from the exact same location each time.
Water
Water used in mixing concrete should meet the
requirements of ASTM C 1602, “Standard Specification for
Mixing Water Used in the Production of Hydraulic
Cement Concrete.” Avoid water containing deleterious
amounts of oils, acids, alkalis, salts, organic material or
other substances that may adversely affect the properties
of fresh or hardened concrete.
Chemical Admixtures
Commonly used chemical admixtures in precast concrete
manufacturing 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 Admixtures
for Use in Producing Flowing Concrete”)
Store admixtures in a manner that avoids contamination,
evaporation and damage. Protect liquid admixtures from
freezing and extreme temperature changes, which could
adversely affect their performance. It is also important to
protect admixture batching components from dust and
temperature extremes. Ensure they are accessible for visual
observation and periodic maintenance. Perform periodic
recalibration of the batching system as recommended by
the manufacturer or as required by local regulations.
Chemical admixture performance can vary. Exercise
caution, especially when using new products. Test some
trial batches and document the results before using a
new admixture for production. Follow manufacturers’
recommendations exactly. Carefully check admixtures for
compatibility with the cement and any other admixtures
used. Do not mix similar admixtures from different
manufacturers without the manufacturer’s agreement or
testing to verify compatibility.
Additional guidelines for the use of admixtures are included
in ACI 212.3, “Guide for Use of Admixtures in Concrete.”
Avoid accelerating admixtures that contain chlorides in
order to prevent possible corrosion of reinforcing steel
elements and other embedded metal objects.
Supplementary Cementitious
Materials (SCMs)
Supplementary Cementitious Materials are often
incorporated into a concrete mix to reduce cement
contents, improve workability, increase strength and
enhance durability. The most common types of SCMs are
fly ash, silica fume and ground granulated blast furnace
slag (GGBFS) as know simply as slag. More than one
SCM may be incorporated into a mix while various types
of blended cements are also available. The following
standards establish the minimum requirements for some
of 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 and
Mortars
• ASTM C1240: Standard Specification for Use of Silica
Fume Used in Cementitious Mixtures
Ready-Mixed Concrete
Verify that the ready-mixed concrete supplier is operating
in accordance with ASTM C94, “Standard Specification
for Ready-Mixed Concrete.” Perform plastic concrete tests
(slump, temperature, air content and density) at the plant
prior to casting products. Record any added water on the
delivery batch ticket for each truck and keep it on file.
7

Concrete mix design, also known as mix proportioning, is
a broad subject – one that is specific to concrete in
general and not necessarily to utility vaults in particular.
This discussion will focus only on critical factors that
pertain to high-quality precast concrete that is
recommended when casting utility vaults.
Mix designs are selected based upon several necessary
factors including permeability, consistency, workability,
strength and durability. The elements necessary to
achieve 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 typically
measured by slump)
High water-cement ratios lead to undesirable increased
capillary porosity within the concrete. Capillary pores are
voids resulting from the consumption and evaporation of
water during the hydration or curing process. Enlarged
and interconnected capillary voids serve as pathways for
water and other contaminates to infiltrate the concrete
system. Lower water-cement ratios result in smaller and
fewer pores, reducing the concrete’s permeability.
Aggregate quality and gradation have a tremendous
impact on the concrete’s overall quality. Mix designs with
well-graded aggregates and sufficient quantities of fine
aggregate have reduced water demands (i.e., lower
water-cement ratios) while maintaining adequate
workability and ease of placement.
Proper consistency of fresh concrete is a critical element
in producing high-quality precast concrete. Fresh
concrete must be sufficiently plastic (flowable or
deformable) to be properly placed, consolidated and
finished. The size, shape and grading of aggregates,
cement content, water-cement ratio and admixtures affect
the workability of a mix.
Water-reducing admixtures and superplasticizers can
greatly increase the workability of fresh concrete without
changing the water-cement ratio. Experience has shown
that concrete with low water-cement ratios (less than
0.45) can be properly placed and consolidated with the
proper use of admixtures. However, air entrainment
should be limited to keep the air content at a maximum
of 7 percent.
The use of chemical admixtures for wet-cast concrete
(such as air-entraining admixtures, water-reducing
admixtures and superplasticizers) helps to attain
workable concrete with a low water-cement ratio. Their
use is particularly important, since most utility vaults
require heavier reinforcing and have large penetrations
that require special attention to ensure full consolidation.
In certain circumstances, and where local regulations
allow, properly designed and tested self-consolidating
concrete (SCC) can be used to improve the likelihood of
proper bond between concrete and reinforcement.
Air-entraining admixtures are designed to disperse
microscopic air bubbles throughout the concrete’s matrix
to function as small “shock absorbers” during freeze-
thaw cycles. The required air content for frost-resistant
concrete is determined by the maximum aggregate size
and severity of in-service exposure conditions (ACI 318).
Air entrainment improves workability and reduces
bleeding and segregation of fresh concrete while greatly
improving the durability of hardened concrete.
CONCRETE MIXTURE
PROPORTIONING
8

LIFTING INSERTS
Commercially manufactured lifting devices come
furnished with documented and tested load ratings. Use
the devices as prescribed by the manufacturer’s
specification sheets. Lifting devices should meet the
minimum requirements of ASTM C857, “Standard Practice
for Minimum Structural Design Loading for Underground
Precast Concrete Utility Structures.
Lifting devices designed in the plant and not
commercially manufactured must be load tested or
evaluated by a professional engineer. In general, industry
specifications require that lifting inserts have a minimum
safety factor of three (ASTM C857) or four (29 CFR
1926.704, ANSI A10.9).
According to the “NPCA Quality Control Manual for
Precast Concrete Products”:
“All lifting devices and apparatus should meet OSHA
requirements documented in ‘Code of Federal
Regulations’ Title 29 Part 1926. Other applicable codes
and standards are ANSI A10.9 and ASTM C 857.
A factor of safety of at least 4 is recommended for lifting
devices. Manufacturers of standard lifting devices should
provide test data to allow selection of appropriate
loading.
Because of their brittle nature, reinforcing bars should
not be used as lifting devices. Instead, smooth bars made
of steel conforming to ASTM A36 can be used.
9

Good concrete with a water-cement ratio less than 0.45
and a compressive strength greater than 4,000 psi is
sufficient for utility vaults. Under normal conditions,
there is no need for additional applications of asphalt,
bituminous, epoxy or cementitious coatings. However, a
protective exterior coating may be specified when a soil
analysis indicates a potential for chemical attack.
COATINGS
10

PRODUCTION PRACTICES
Quality Control
All plants must have a quality control program and
manual, 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 for
review by appropriate agencies upon request.
Participation in the NPCA Plant Certification Program and
future programs is recommended as an excellent way to
ensure product quality. Use the NPCA “Quality Control
Manual for Precast Concrete Products” as the basis for
developing a strong quality control program.
Forms
Forms must be in good condition. Frequent inspection
intervals and regular maintenance ensure that forms are
free of any damage that could cause concrete placement
difficulties or dimensional problems with the finished
product.
Use forms that prevent leakage of cement paste and are
sufficiently rigid to withstand the vibrations encountered
in the production process. Maintain forms properly,
including cleaning after each use and inspection prior to
each use, to ensure uniform concrete surfaces. Ensure
forms are level and on a solid base.
11

Fabrication drawings must be a part of every QC
program. Fabrication drawings should detail the
reinforcement requirements and all necessary information
pertaining to the product prior to casting.
Conventional Reinforcement
Fabricate reinforcing steel cages by tying or welding the
bars, wires or welded wire reinforcement into rigid
structures. The reinforcing steel cages should conform to
the tolerances defined on the fabrication drawings. If not
stated, minimum bend diameters on reinforcement
should meet the requirements set forth in ACI 318, as
defined in Table 1. Make all bends while the
reinforcement is cold. The minimum bend diameter for
concrete reinforcing welded wire reinforcement is 4db.
Table 1: Concrete Reinforcing Steel
db = nominal diameter (inch or mm) of bar
Weld reinforcement (including tack welding) in
accordance with AWS D1.4, “Structural Welding Code,
Reinforcing Steel.” This code requires either special
preheat requirements (when required) or weldable grade
reinforcement as defined by ASTM A706, “Specification
for Low-Alloy Steel Deformed and Plain Bars for Concrete
Reinforcement,” for any welding of reinforcing steel,
including tack welds. Take special care to avoid
undercutting or burning through the reinforcing steel.
Conventional reinforcement (ASTM A615, “Specification
for Deformed and Plain Billet-Steel Bars for Concrete
Reinforcement”) is produced from recycled metals that
have higher carbon contents and are likely to become
brittle if improperly welded. A brittle weld is a weak link,
which can compromise the structural integrity of the
finished product. ASTM A615/615M states: “Welding of
material in this specification should be approached with
caution since no specific provisions have been included
to enhance the weldability. When the reinforcing steel is
to be welded, a welding procedure suitable for the
chemical composition and intended use or service should
be used.”
Ensure lap splices for steel reinforcement (rebar and
welded-wire reinforcement) meet the requirements of ACI
318. Adequate development length is required to develop
the design strength of the reinforcement at a critical
section. A qualified engineer should determine
development length and clearly indicate it on shop
drawings.
Reinforcement steel should be free of loose rust, dirt and
form release agent. Cut, bend and splice reinforcing steel
in accordance with fabrication drawings and applicable
industry standards. Inspect reinforcing cages for size,
spacing, proper bends and length. Secure the reinforcing
cage in the form so that shifting will not occur during
casting. Use only chairs, wheels and spacers made of
noncorrosive materials.
It is important to place and hold reinforcement in position
as shown in the fabrication drawings. A maximum
recommended placement tolerance for the depth of
reinforcement is +1/4 inch (ACI 318). As a general rule the
variation in spacing between bars should not exceed
more than 1/12 of the designed bar spacing nor exceed
1.5 inch in variation, except for welded wire mesh
conforming to Specifications A185 or A497. The
recommended minimum concrete cover over reinforcing
steel 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
6db
8db
10db
ASTM A615 and A706
Soft Metric Bar Sizes
# 10 through # 25
# 29, # 32 and # 36
# 43 and # 57

Fiber Reinforcement
Data must be available to show conclusively that the
type, brand, quality and quantity of fibers to be included
in the concrete mix are not detrimental to the concrete or
to the precast concrete product. Fiber reinforced concrete
must conform to ASTM C1116, “Standard Specification for
Fiber-Reinforced Concrete and Shotcrete” (Type I or Type
III). The two most popular types of fibers are synthetic
and steel fibers. Steel fibers must conform to ASTM
A820, “Specification for Steel Fibers for Fiber-Reinforced
Concrete.” Do not use fibers as a replacement for
primary structural reinforcing steel. In general, fibers will
not increase the compressive or flexural strength of
concrete.
Synthetic microfibers in concrete typically reduce plastic
shrinkage cracks and improve impact resistance.
They can help reduce chipping when products are
stripped. Typical dosage rates will vary from 0.5 to 2.0
lbs/yd3. Synthetic macrofibers and steel fibers may
replace secondary reinforcement to provide equivalent
bending stress and strength when compared with welded
wire reinforcement and light-gauge steel reinforcement.
Typical dosage rates for synthetic macrofibers vary from
3.0 to 20 lbs/yd3. Steel fiber dosage rates may vary from
20 to 60 lbs/yd3. Fibers must be approved by a
regulatory agency or specifying engineer prior to
concrete placement.
Design the concrete mix so that the mix is workable and
the fibers are evenly distributed. Chemical admixtures or
adjustments to the concrete mixture design may be
necessary to achieve proper consolidation and
workability. It is important to adhere to the
manufacturer’s safety precautions and to follow
instructions when introducing the fibers into the mix.
Embedded Items
Items such as plates and inserts must be held rigidly in
place during casting. All embedded items should be
resistant to corrosion. Special consideration should be
given when welding operations are required.
Pre-Pour Inspection
A typical pre-pour checklist, as illustrated on the next
page, provides a means of documenting the required
quality checks. A qualified individual should make
inspections 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
13

14
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 Details
Reinforcing Steel
Size of Reinforcement
Spacing
Rustification
Plates and Inserts
Lifting Devices
Top Finish (wet)
REMARKS: ______________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
QC Supervisor ________________ Date _______ Inspector _______________ _______________

CASTING CONCRETE
Transporting Concrete
When transporting concrete from mixer to form, use any
method that does not contaminate the concrete, cause
delay in placing, or segregation. Concrete can be
discharged directly from the mixer into the forms – ACI
304, “Guide for Measuring, Mixing, Transporting and
Placing,” is a valuable reference.
Placing Concrete
Conventional Concrete
Keep the free fall of the concrete to a minimum and
deposit as near to its final location as possible. Do
not use vibration equipment to move fresh concrete
laterally in the forms.
Fiber Reinforced Concrete (FRC)
Follow the same practices as described for
conventional concrete, but note that the workability
of the FRC may be slightly reduced.
Self-Consolidating Concrete (SCC)
Place self-consolidating concrete into itself at a
constant pressure head from one end of the form,
allowing air to escape as the concrete flows into and
around steel reinforcement. Avoid placement
practices that add additional energy to the mix and
cause unwanted segregation, such as excessive
vibration, increased pour heights or increased
discharge rates.
Consolidating Concrete
SCC generally requires minimal consolidation efforts.
However, when using conventional concrete, consolidation
operations are required to minimize segregation and
honeycombing. Consolidation can be improved on
particular molds by using vibrators with variable
frequency and amplitude. Three types of vibration are
prevalent in the precast industry:
Internal – stick vibrator
External – vibrator mounted on forms or set on a
vibrating table
Surface – vibrator can be moved across the surface
Lower internal vibrators vertically and systematically into
the concrete without force until the tip of the vibrator
reaches the bottom of the form. When using internal
vibrators, concrete should be placed in wall sections
using lifts not exceeding two feet. Do not drag internal
vibrators horizontally. Once consolidation is complete in
one area, remove the vibrator vertically and move the
vibrator to the next area. Regardless of the vibration
method, ensure that the field of vibration overlaps with
another insertion to best consolidate the concrete and
minimize defects.
Some external vibrators are mounted on a piece of steel
attached to the form. Position them to allow for overlap
of vibration areas. Continue the vibration process until
the product is completely consolidated. Vibration is
considered complete when large bubbles (3/8” diameter
or greater) no longer appear at the surface. Care should
be taken to avoid overvibration, because segregation of
the aggregate from the cement paste can result in
lowering the concrete quality and strength.
Finishing Unformed Surfaces
Each product is to be finished according to its individual
specifications. If finishing techniques are not specified,
take care to avoid floating either too early or for too
long. Premature finishing can trap bleed water below the
finished surface, creating a weak layer of concrete
susceptible to freeze-thaw cycles and chemical attack.
Finishing with a wood or magnesium float is
recommended.
15

Two critical elements in curing concrete are maintaining
correct moisture content and maintaining correct concrete
temperature. Proper curing is important in developing
strength, durability and chemical resistance and
watertightness – all important considerations for
underground utility vaults.
Note: Concrete temperature discussed in this manual
refers to the temperature of the concrete itself, not the
ambient temperature.
The nature of precast operations poses unique challenges
to proper curing. To ensure cost-effective use of forms,
precasters often strip the forms at the beginning of the
next workday. That is an acceptable standard, according
to ACI 308, “Standard Practice for Curing Concrete.” The
time necessary to develop enough strength to strip the
forms is highly dependent on ambient temperature in the
casting 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 (plastic
coverings or applying curing compounds)
3. Applying heat (often in conjunction with moisture, with
heaters or live steam)
Choose the method(s) that best suit the particular
production operation. All three are permissible, but
preventing the loss of water (method 2) may be the
simplest choice for utility vaults. Maintaining moisture
requires constant wetting, which is labor intensive.
Alternate wetting and drying can lead to problems with
cracking. Steam curing can also be effective. Concrete
temperatures should never exceed 150 F. Both of these
techniques are described in ACI 308, “Standard Practice
for Curing Concrete,” and the PCA publication “Design
and Control of Concrete Mixtures.” Plastic coverings or
membrane-forming curing compounds require less labor
efforts and allow form stripping the next work day. There
are some special considerations for both:
1. Plastic sheeting must comply with ASTM C171,
“Standard Specification for Sheet Materials for Curing
Concrete,” which specifies a minimum thickness of 4
mm and be either white or opaque in color. PCA states
that other colors can be used depending on sun
conditions and temperature. When using multiple
sheets, overlap them by approximately 18 inches to
prevent moisture loss.
2. Curing compounds can be applied when bleed water is
no longer present on the surface. As with plastic,
white-colored compounds might reflect sunlight better
and limit temperature gain. Follow the manufacturer’s
recommendations.
CURING PROCEDURES
16

Cold and Hot Weather Concreting
In hot and cold weather, special precautions are
necessary.
Cold Weather — Hydration rates are slower during cold
weather. Concrete temperatures below 50 F are
considered unfavorable for pouring due to the extended
time required for strength gain and the possibility of
freezing. However, once concrete reaches a minimum
strength of 500 psi (usually within 24 hours) freezing has
a limited impact. Ideally, precast concrete operations
should be performed in heated enclosures that will
provide uniform heat to the products until they reach 500
psi. If necessary, heating the mixing water and/or
aggregates can increase the concrete temperature. Do not
heat water above 140 F, and do not use clumps of frozen
aggregate and ice. ACI 306, “Cold Weather Concreting,”
contains further recommendations on cold-weather
concreting.
Hot Weather – High temperatures accelerate hydration.
Do not allow fresh concrete temperature to exceed 90 F
at time of placement. Keep the temperature of the
concrete 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 concrete
temperature does not exceed 150 F. In all cases, protect
freshly cast products from direct sunlight and drying
wind. ACI 305, “Hot Weather Concreting,” contains
further recommendations on hot-weather concreting.
17

Handling Equipment
Cranes, forklifts, hoists, chains, slings and other lifting
equipment must be able to handle the weight of the
product with ease and comply with federal and local
safety requirements. Routine inspections of all handling
equipment are necessary. Qualified personnel should
make periodic maintenance and repairs as warranted. Tag
all chains and slings with individual load capacity ratings.
For U.S. plants, refer to the specific requirements of the
Occupational 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 Products
Minimum Strength Requirement – Concrete must gain
sufficient strength before stripping it from the forms. Due
to the nature of the precast business, the American
Concrete Institute recognizes that forms will usually be
stripped the next workday. Under normal conditions
(concrete temperature greater than 50° F), properly
designed concrete can reach the minimum compressive
strength for stripping within this time period. Periodic
compressive strength testing of one-day or stripping
strength cylinders is recommended to confirm that proper
concrete strength is attained.
Handle recently poured and stripped products with care.
Perform lifting and handling carefully and slowly to
ensure that dynamic loads do not damage the tank.
Always follow recognized safety guidelines.
Product Damage During Stripping – Inspect the product
immediately after stripping to check for damage.
Post-Pour Inspections
A post-pour inspection checklist, as illustrated, provides a
method of identifying and communicating quality
problems as they occur. It serves as a method of
gathering data for identification of any trends that may
be evident. After a utility vault is stripped from the form,
it should be inspected for conformance with the
fabrication drawings and any necessary repairs should be
made. All products should be clearly labeled with the
date of manufacturing and marked in accordance with
ASTM C 858.
POST-POUR OPERATIONS
18

19
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 Leak
Bowing
Exposed Reinforcement
Exposed Chairs
Plates and Inserts
Chamfer & Radius Quality
Openings / Blockouts
Lifting Devices
REMARKS: ______________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
QC Supervisor ________________ Date _______ Inspector _______________ _______________

Finished Formed Surfaces – Formed surfaces must be
relatively smooth and free of significant honeycombed
areas, air voids and “bugholes.”
Repairing Minor Defects – Defects that do not impair the
use or life of the product are considered minor or
cosmetic and may be repaired in any manner that does
not impair the product.
Repairing Honeycombed Areas – Remove all loose
material from the damaged area. Cut back the damaged
zone in horizontal or vertical planes deep enough to
remove the damaged concrete. Coarse aggregate particles
should break rather than merely dislodge when chipped.
Use only materials that are specifically developed for
concrete repair, and make repairs according to the
manufacturers’ specifications.
Repairing Major Defects – Major defects are defined as
those that impair the intended use or structural integrity
of the product. If possible, repair products with major
defects by using established repair and curing
procedures only after a qualified person evaluates the
feasibility of the repair.
Secondary Pours
For products that require secondary pours, establish
procedures to assure that the new concrete bonds
adequately to the product and becomes an integral part
of it. The surfaces of the product against which the
secondary pour is to be made should be free of laitance,
dirt, dust, grease or any other material that will tend to
weaken the bond between the original and new
concretes. If the surface is very smooth, roughen it to
help promote a good bond. As a minimum, use a high-
quality water stop, keyway and continuation of
reinforcing between pours to ensure a watertight joint.
Cold Joints
Cold joints require special care and, as a minimum,
should include a high-quality water stop, bonding agent
and continuation of reinforcing between pours.
Final Product Inspection
Utility vaults should be visually checked for required
supplementary items, embedded items and quality at the
plant prior to shipping.
Product Shipment
All vehicles used to transport products must be in good
condition and capable of handling the product without
causing damage. Utility vaults should be adequately
cured as specified prior to shipment to a job site or
distant storage areas. All products must be properly
secured with appropriate blockage and either nylon
straps or chains with guards as to avoid product damage
during shipment. NPCA’s publication Cargo Securement
for the Precast Concrete Industry outlines proper
methods for securing product. It is recommended that the
final inspection include checking these items.
FINISHING AND
REPAIRING CONCRETE
20

SEALS, FITTINGS
AND JOINTS
Careful attention to joint details, sealing materials and
penetration fittings are important to ensure quality utility
vaults. Systems in areas of high water tables may require
special methods for joint and penetration seal designs.
Joint Designs
The most common joint designs are tongue-and-groove
or lap joints.
For the manufacture of utility vaults, it is recommended
that only interlocking joints be used. In cases of
potentially significant frost heave, differential settlement
and groundwater exposure, greater attention to joint
design detail is needed. Mechanical fasteners or
secondary pours for lids on bases may be necessary in
areas with severe site conditions. The key to preventing
most differential settlement is proper bedding preparation
(especially compaction) of the site.
Sealing Materials
High-quality, preformed flexible joint sealants can be
used to achieve a dependable joint. Use only sealants
that contain less than 3 percent volatiles as defined in
ASTM D6 – Standard Test Method for Loss on Heating of
Oil 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 and
prepared, according to the sealant manufacturer’s
recommendations. Preformed flexible joint sealants must
be sufficiently pliable to compress a minimum of 50
percent at the temperature during assembly. Utility vault
sections sealed on site should not be backfilled until the
sealant has settled.
Properly splice the sealant by one of the following
methods:
• Overlap splice – Place one piece on top of the other
and carefully mold together
• Side-by-side – Place in parallel and carefully mold the
two pieces together
Sealant Size
A critical factor when evaluating the sealing potential of a
sealant is cross-sectional area. Cross-sectional area is
defined as the geometric shape of the sealant (i.e., 0.75
inches high by 1.0 inches wide). Industry experience has
shown that a sealant’s cross-sectional height must be
compressed a minimum of 30 percent to create a good
seal; 50 percent compression is desirable.
Connections and Hardware
The functionality of a utility vault is increased through
the use of high quality ancillary components such as
cable racking assemblies, pulling irons, conduit
terminators and pipe supports.
Cable racking assemblies should be specified to match
the 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 the
anticipated weight of the supported cables.
Pulling irons should be structurally engineered to resist
the anticipated cable pulling loads. Additionally, the
pulling load placed upon the wall of the utility vault
should be considered in the structural design calculations
for the vault. Pulling irons should not be used for lifting
and handling product.
21
Lap Joint Shiplap Joint
Tongue &
Groove Joint

Cable industry standards require a smooth or rolled edge
for the cable to pass over as it leaves the conduit to
enter the utility vault. End bells and conduit terminators
that are cast into the wall of the precast concrete vault at
the time of manufacture provide a quality labor saving
method to terminate conduit. These items should be sized
and located on the wall of the vault to match the duct
bank configuration.
Utility vaults may be configured to accommodate the
piping systems used for fluid conveyance. Integral
concrete sleepers, thrust blocks and pipe support
hardware may be cast into the vault. Boots and gaskets
may be incorporated at pipe entrances to ensure
watertightness and should be sized and located for the
pipe being used.
Hardware should always meet specification requirements
of the design engineer and the customer.
Access, Risers and Manholes
All access risers and manholes must be structurally
sound and watertight.
22

INSTALLATION
Proper installation is absolutely critical for maintaining
the inherent quality of plant-manufactured concrete
products and should be performed in accordance with
ASTM C 891 – Standard Practice for Installation of
Underground Precast Concrete Utility Structures. Many of
the problems experienced with troublesome utility vaults
can be attributed to incorrect procedures during
installation. In addition to damaging the structure,
improper installation techniques can lead to safety
hazards.
Site Conditions
The installation site must be accessible to large, heavy
trucks or cranes weighing up to 80,000 pounds. The
construction area should be free of trees, branches,
overhead wires or parts of buildings that could interfere
with the delivery and installation of the utility vault. Most
trucks require access within 3 to 8 feet of the excavation
to be unloaded.
Excavation
Prior to excavation, all buried utilities should be
identified and located. OSHA regulations governing
excavation work should be followed at all times; 29 CFR,
Part 1926.650-652.
Excavations should be made with approximately 18 inches
of clearance around the installed structure to allow room
for adequate compaction. More space should be
provided, as needed, if work other than installation is
required. Excavations should be sloped to comply with all
construction safety requirements.
Bedding
Proper use of bedding material is important to ensure a
long service life of the utility vault. Engineered bedding
material should be used as necessary to provide a
uniform bearing surface. A good base should ensure that
the structure would not be subjected to adverse
settlement. A minimum 4-inch-thick sand or granular bed
overlaying a firm and uniform base is recommended
unless otherwise specified. Utility vaults should not bear
on large boulders or massive rock edges.
Sites with silty soils, high water tables or other “poor”
bearing characteristics must have specially designed
bedding and bearing surfaces. In the presence of high
water tables, structures should be properly designed to
resist flotation.
Proper compaction of the underlying soil and bedding is
critical to ensure there is no differential settlement.
Placement
Prior to placement in the excavation, the structure’s
orientation should be confirmed. Inlet penetrations should
be aligned in the proper direction and the bedding
material should be checked. After placement, check to
ensure that the structure is level.
23
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 with
Construction Safety Requirements
Product Orientation to be
Determined Prior to Setting
and Checked Prior to
Backfilling
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 Level
2) Backfill Shall be Placed in Uniform, Properly
Compacted Layers Not to Exceed 24" Thick.
1'-6"
Min.
1'-6"
Min.
Figure 3

Lifting Devices
Verify lifting apparatus such as slings, lift bars, chains
and hooks for capacity, and ensure an adequate safety
factor for lifting and handling products. The capacity of
commercial lifting devices must be marked on the
devices.
All lifting devices and apparatus should meet OSHA
requirements documented in “Code of Federal
Regulations” Title 29 Part 1926. Other applicable codes
and standards are ANSI A10.9 and ASTM C857, C890 and
C913.
devices. Manufacturers of standard lifting devices should
provide test data to allow selection of appropriate
loading.
Because of their brittle nature, do not use reinforcing
bars as lifting devices. Use smooth bars made of steel
conforming to ASTM A36 instead.
apparatus, such as chains, slings, spreader beams, hooks
and shackles.
Backfilling
Backfill should be placed in uniform, mechanically
compacted layers less than 24 inches thick. This fill
should be equally and uniformly placed around the vault.
Backfill should be free of any large stones (greater than
3 inches in diameter) or other debris. Each layer should
be adequately compacted.
24

REFERENCES
Specifications
American Concrete Institute (ACI)
ACI 116R, “Cement and Concrete Terminology”
ACI 211.1, “Standard Practice for Selecting Proportions for
Normal, Heavyweight and Mass Concrete”
ACI 211.3, “Standard Practice for Selecting Proportions for
No-Slump Concrete”
ACI 212.3, “Chemical Admixtures for Concrete”
ACI 304R, “Guide for Measuring, Mixing, Transporting
and Placing Concrete”
ACI 305R, “Guide for Hot Weather Concreting”
ACI 306R, “Guide for Cold Weather Concreting”
ACI 308R, “Guide to Curing Concrete”
ACI 318, “Building Code Requirements for Structural
Concrete and Commentary”
ACI 544, “State-of-the-Art Report on Fiber Reinforced
Concrete”
ASTM International
ASTM A185, “Standard Specification for Steel Welded
Wire Reinforcement, Plain, for Concrete Reinforcement”
ASTM A496, “Standard Specification for Steel Wire,
Deformed for Concrete Reinforcement”
ASTM A497, “Standard Specification for Steel Welded
Wire Reinforcement, Deformed, for Concrete
Reinforcement”
ASTM A615, “Standard Specification for Deformed and
Plain Carbon Steel Bars for Concrete Reinforcement”
ASTM A706, “Standard Specification for Low Alloy Steel
Deformed Bars and Plain for Concrete Reinforcement”
ASTM A820, “Specification for Steel Fibers for Reinforced
Concrete”
ASTM C33, “Standard Specification for Concrete
Aggregates”
ASTM C125, “Standard Terminology Relating to Concrete
and Concrete Aggregates”
ASTM C150, “Standard Specification for Portland Cement”
ASTM C260, “Standard Specification for Air-Entraining
Admixtures for Concrete”
ASTM C494, “Standard Specification for Chemical
Admixtures for Concrete”
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 C857-95, “Practice for Minimum Structural Design
Loading for Underground Precast Concrete Utility
Structures”
ASTM C858-83, “Specification for Underground Precast
Concrete Utility Structures”
ASTM C891-90, “Practice for Installation of Underground
Precast Concrete Utility Structures”
ASTM C989: Standard Specification for Ground
Granulated Blast-Furnace Slag for Use in Concrete and
Motars
ASTM C1037-85, “Practice for Inspection of Underground
Precast Concrete Utility Structures”
ASTM C1017, “Chemical Admixtures for Use in Producing
Flowing Concrete”
ASTM C1116, “Standard Specification for Fiber Reinforced
Concrete and Shotcrete”
ASTM C1240: Standard Specification of Use of Silica
Fume Used in Cementitious Mixtures
ASTM C1602, “Standard Specification for Mixing Water
Used in the Production of Hydraulic Cement Concrete “
ASTM D6, “Standard Test Method for Loss on Heating of
Oil and Asphaltic Compounds”
American Welding Society (AWS)
AWS D1.4, “Structural Welding Code - Reinforcing Steel”
Occupational Safety and Health
Administration (OSHA)
29 CFR 1910.184 (Slings)
29 CFR 1926.650-652 (Excavation)
25

admixture – a material other than water, aggregates,
cement and fiber reinforcement, used as an ingredient
of concrete, and added to the batch immediately before
or during its mixing. Typically are liquid in
composition.
admixture, accelerating – an admixture that accelerates
the setting and early strength development of concrete.
admixture, air-entraining – an admixture that causes the
development of a system of microscopic air bubbles in
concrete, mortar or cement paste during mixing.
admixture, mineral – finely divided, powdered or
pulverized materials added to concrete to improve or
alter the properties of the plastic or hardened concrete.
admixture, water-reducing – admixture that either
increases the slump of freshly mixed concrete without
increasing the water content or that maintains the
slump 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 a
cement medium to form hydraulic-cement concrete or
mortar.
aggregate, coarse – generally pea-sized to 2 inches;
aggregate of sufficient size to be predominately
retained 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) and
almost entirely passing a No. 4 sieve (4.75 mm) and
predominately 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 in
aggregate particles, usually expressed as a percentage
of total volume of the paste, mortar or concrete.
air void – a space in cement paste, mortar or concrete
filled with air; an entrapped air void is
characteristically 1 mm or more in width and irregular
in shape; an entrained air void is typically between 10
Ìm and 1,000 Ìm in diameter and spherical in shape.
alkali-aggregate reactivity (AAR) – a chemical reaction
that occurs between the alkalies (sodium and
potassium) from portland cement or other sources and
certain constituents of some aggregates; under certain
conditions resulting in deleterious expansion of
concrete or mortar; often known as alkali-silica
reaction (ASR). Cement manufacturers often test
aggregates for AAR as a service to their customers.
ASTM – ASTM International is a not-for-profit
organization that provides a forum for producers,
users, ultimate consumers and those having a general
interest (government and academia) to meet and write
standards for materials, products, systems and
services.
bedding material – gravel, soil , sand or other material
that serves as a bearing surface on which a structure
rests and which carries the load transmitted to it.
bleeding – the separation of mixing water or its
emergence from the surface of newly placed concrete,
caused by the settlement of the solid materials.
bonding agent – a substance applied to a suitable
substrate to create a bond between it and a succeeding
layer, such as between a layer of hardened concrete
and a layer of fresh concrete.
cement, hydraulic – a cement that sets and hardens by
chemical interaction with water and is capable of doing
so under water.
cementitious material – an inorganic material or mixture
of inorganic materials that set and develop strength by
chemical reaction with water by formation of hydrates.
GLOSSARY
26

concrete – a composite material that consists essentially
of a binding medium within which are embedded
particles of fragments of aggregate, usually a
combination of fine aggregate and coarse aggregate; in
portland-cement concrete, the binder is a mixture of
portland cement and water.
concrete, fresh – concrete that possesses enough of its
original workability so that it can be placed and
consolidated by the intended methods.
compressive strength – measured maximum resistance
of a concrete or mortar specimen to axial compressive
loading; expressed as a force per unit cross-sectional
area; or the specified resistance used in design
calculations.
consistency – the relative mobility or ability of freshly
mixed concrete to flow; it is usually measured by the
slump test.
consolidation – the process of inducing a closer
arrangement of the solid particles in freshly mixed
concrete 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; as
concrete subsides, large air voids between coarse
aggregate particles are filled with mortar.
curing – action taken to maintain moisture and
temperature conditions in a freshly placed cementitious
mixture to allow hydraulic cement hydration and (if
applicable) pozzolanic reactions to occur so that the
potential properties of the mixture may devlop.
curing compound – a liquid that can be applied as a
coating to the surface of newly placed concrete to
retard the loss of water or to reflect heat so as to
provide an opportunity for the concrete to develop its
properties in a favorable temperature and moisture
environment.
dead load – a constant load that in structures is due to
the mass of the members, the supported structure, and
permanent attachments or accessories.
delayed ettringite formation (DEF) – occurs at later
ages (months to years) and the related heterogeneous
expansion in hardened concrete can produce cracking
and spalling. DEF is related to environmental or
internal sulfate attack.
deleterious substances – materials present within or on
aggregates that are harmful to hardened concrete,
often in a subtle or unexpected way. More
specifically, this may refer to one or more of the
following: materials that may be detrimentally reactive
with the alkalis in the cement (see alkali aggregate
reactivity); clay lumps and friable particles; coal and
lignite; etc.
dry-cast (no-slump concrete) – concrete of stiff or
extremely dry consistency showing no measurable
slump 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 its
length is significantly greater than its width.
entrained air – see air void; microscopic air bubbles
intentionally incorporated in mortar or concrete during
mixing, typically between 10 Ìm and 1,000 Ìm (1 mm) in
diameter and spherical or nearly so.
entrapped air – see air void; air voids in concrete that
are not purposely entrained and that are larger, mainly
irregular in shape, and less useful than those of
entrained air; typically greater than 1 mm in diameter
and may be of various shapes.
ettringite – a mineral, high-sulfate calcium
sulfoaluminate occurring in nature or formed by sulfate
attack on mortar and concrete.
27

float – a tool, usually of wood, aluminum or magnesium,
used in finishing operations to impart a relatively even
but still open texture to an unformed fresh concrete
surface.
floating – the operation of finishing a fresh concrete or
mortar surface by use of a float, preceding troweling
when that is to be the final finish.
fly ash – the finely divided residue transported by flue
gases from the combustion of ground or powdered
coal; often used as a supplementary cementitious
material in concrete.
forms (molds) – a structure for the support of concrete
while it is setting and gaining sufficient strength to be
self-supporting.
friable – easily crumbled or pulverized, as it refers to
aggregates.
gap grading – aggregate graded so that certain
intermediate sizes are substantially absent (i.e.,
aggregate containing large and small particles with
medium-size particles missing).
gradation – the particle-size distribution as determined
by a sieve analysis (i.e., ASTM C 136); usually
expressed in terms of cumulative percentages larger or
smaller 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 combining
of water with some other substance; in concrete, the
chemical process between hydraulic cement and water.
infiltration – to cause (as a liquid) to permeate
something by penetrating its pores or interstices.
initial set – a degree of stiffening of a mixture of cement
and water less than final set, generally stated as an
empirical value indicating the time in hours and
minutes required for cement paste to stiffen sufficiently
to resist to an established degree, the penetration of a
weighted test needle; often performed on a sample of
mortar sieved from a concrete sample.
live load – any load that is not permanently applied to a
structure; including transitory loading such as water,
vehicles and people.
organic impurities (re: aggregate) – extraneous and
unwanted organic materials (twigs, soil, leaves, other
debris) that are mixed in aggregates; these materials
may have detrimental effects on concrete produced
from such aggregates.
OSHA – Occupational Safety and Health Administration,
U.S. Department of Labor.
plastic concrete – see concrete, fresh.
portland cement – a hydraulic cement produced by
pulverizing portland-cement clinker, usually in
combination with calcium sulfate.
portland cement clinker – a partially fused ceramic
material consisting primarily of hydraulic calcium
silicates and calcium aluminates.
pozzolan – a siliceous or siliceous and aluminous
material that in itself possesses little or no
cementitious value but will, in finely divided form and
in the presence of moisture, chemically react with
calcium hydroxide at ordinary temperatures to form
compounds possessing cementitious properties.
psf – pounds per square foot
psi – pounds per square inch
28

secondary pour – a situation when a succeeding layer of
concrete is placed on previously-placed hardened
concrete.
segregation – the unintentional separation of the
constituents of concrete or particles of an aggregate,
resulting in nonuniform proportions in the mass.
set – the condition reached by a cement paste, mortar or
concrete when it has lost plasticity to an arbitrary
degree, usually measured in terms of resistance to
penetration or deformation; initial set refers to first
stiffening; final set refers to attainment of significant
rigidity.
silica fume – very fine non-crystalline silica produced in
electric arc furnaces as a byproduct of the production
of elemental silicon or alloys containing silicon; also
known as condensed silica fume and micro-silica. It is
often used as an additive to concrete and can greatly
increase the strength of a concrete mix.
slump – a measurement indicative of the consistency of
fresh concrete. A sample of freshly mixed concrete is
placed and compacted by rodding in a mold shaped as
the frustum of a cone. The mold is raised, and the
concrete is allowed to subside. The distance between
the original and displaced position of the center of the
top surface of the concrete is measured and reported
as the slump of the concrete. Under laboratory
conditions, with strict control of all concrete materials,
the slump is generally found to increase proportionally
with the water content of a given concrete mixture,
and thus to be inversely related to concrete strength.
Under field conditions, however, such a strength
relationship is not clearly and consistently shown.
Care should therefore be taken in relating slump
results obtained under field conditions to strength.
(ASTM C 143)
specification – an explicit set of requirements to be
satisfied by a material, product, system or service that
also indicates the procedures for determining whether
each of the requirements is satisfied.
standard – as defined by ASTM, a document that has
been developed and established within the consensus
principles 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 unformed
surface 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, to
the 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 or
other material inserted across a joint to obstruct the
seepage of water through the joint.
water table – the upper limit of the portion of the
ground wholly saturated with water.
workability of concrete – that property of freshly mixed
concrete or mortar that determines the ease with which
it can be mixed, placed, consolidated and finished to a
homogenous condition.
29

This Best Practices Manual is subject to revision at any
time by the NPCA Utility Vault Product Committee, which
must review it at least every three years.
Special thanks are given to the Utility Vault Product
Committee for updating/compiling this manual.
Steve Truax, Wieser Concrete Products Inc.
Jay Behney, By-Crete
Douglas Bowen, Bowco Industries Inc.
Todd Ebbert, San Diego Precast Concrete Inc.
Paul Heidt, Garden State Precast Inc.
Donald McNutt, Spillman Company
Michael Menard, Firebaugh Precast Inc.
Brian Rhees, Oldcastle Precast Inc.
Robert Thornton, Hughes Concrete Products
30

uv_bpm.pdf

More Related Content

Similar to uv_bpm.pdf (20)

More from osamaanter1 (8)

Recently uploaded (20)

uv_bpm.pdf