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OCR for page 42
B-1
ATTACHMENT B
Recommended Guidelines for Use of
Self-Consolidating Concrete in Precast,
Prestressed Concrete Bridge Elements
These proposed guidelines are the recommendations of the NCHRP Project 18-12 staff at the University of Sherbrooke. These
guidelines have not been approved by NCHRP or any AASHTO committee nor formally accepted for adoption by AASHTO.
OCR for page 43
B-3
CONTENTS
B-5 Introduction
B-6 Glossary
B-9 B.1 Guidelines for Selection of Constituent Materials
B-9 B.1.1 General
B-9 B.1.2 Cement and Cementitious Materials
B-9 B.1.2.1 Cement and Blended Cement
B-10 B.1.2.2 Fly Ash
B-10 B.1.2.3 Silica Fume
B-10 B.1.2.4 Ground Granulated Blast-Furnace Slag
B-11 B.1.2.5 Fillers
B-11 B.1.2.6 Other Supplementary Cementitious Additions
B-11 B.1.3 Aggregate Characteristics
B-11 B.1.3.1 Coarse Aggregate
B-12 B.1.3.2 Fine Aggregate
B-12 B.1.4 Chemical Admixtures
B-12 B.1.4.1 High-Range Water-Reducing Admixtures
B-13 B.1.4.2 Viscosity-Modifying Admixtures
B-13 B.1.4.3 Air-Entraining Admixtures
B-13 B.1.4.4 Set-Retarding and Set-Accelerating Admixtures
B-13 B.1.4.5 Shrinkage-Reducing Admixtures
B-14 B.1.4.6 Other Admixtures
B-14 B.1.5 Fibers
B-14 B.2 Guidelines for Selection of Workability
Test Methods
B-14 B.2.1 General
B-14 B.2.2 Filling Ability
B-14 B.2.2.1 Significance
B-15 B.2.2.2 Test Methods to Assess Filling Ability
B-15 B.2.2.3 Special Issues
B-16 B.2.3 Passing Ability
B-16 B.2.3.1 Significance
B-16 B.2.3.2 Test Methods to Assess Passing Ability
B-16 B.2.3.3 Special Issues
B-16 B.2.4 Filling Capacity
B-16 B.2.4.1 Significance
B-17 B.2.4.2 Test Method to Assess Filling Capacity
B-17 B.2.4.3 Special Issues
B-18 B.2.5 Static Stability
B-18 B.2.5.1 Significance
B-18 B.2.5.2 Test Methods to Assess Static Stability
B-18 B.2.5.3 Special Issues
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B-4
B-18 B.2.6 Dynamic Stability
B-18 B.2.6.1 Significance
B-18 B.2.6.2 Test Methods to Assess Dynamic Stability
B-19 B.2.7 Rheology
B-19 B.2.7.1 Significance
B-19 B.2.7.2 Test Methods to Assess Rheological Parameters
B-19 B.2.7.3 Special Issues
B-20 B.3 Guidelines for Mix Design
B-20 B.3.1 General
B-20 B.3.2 Mix Design Principles
B-22 B.3.2.1 Minimum Free Water Content
B-22 B.3.2.2 Moderate Water Content and Medium Concentration of VMA
B-22 B.3.2.3 Low Water Content and Low Concentration of VMA
B-22 B.3.3 Cementitious Materials Content and Water-Cementitious Material Ratio
B-22 B.3.4 Nominal Size of Coarse Aggregate
B-23 B.3.5 Air-Entrainment and Air-Void Stability
B-23 B.3.6 Mixture Robustness
B-23 B.3.7 Trial Batches
B-23 B.3.8 Recommended Range of Workability Characteristics
B-24 B.3.9 Quality Confirmation of SCC
B-26 B.4 Guidelines for Early-Age and Hardened Properties
B-26 B.4.1 General
B-26 B.4.2 Setting
B-26 B.4.3 Temperature Development
B-27 B.4.4 Release Compressive Strength
B-28 B.4.5 Flexural Strength
B-28 B.4.6 Modulus of Elasticity
B-29 B.4.7 Creep
B-30 B.4.8 Autogenous Shrinkage
B-30 B.4.9 Drying Shrinkage
B-31 B.4.10 Durability and Air-Void System
B-32 B.4.11 Bond to Prestressing Strands
B-33 B.5 Guidelines for Production and Control
B-33 B.5.1 General
B-33 B.5.2 Control of Raw Materials
B-34 B.5.3 Mixing Process and Sequence
B-34 B.5.4 Transport
B-34 B.5.5 Site Acceptance of Plastic Concrete
B-34 B.5.6 Placement Techniques and Casting Considerations
B-35 B.5.7 Temperature Control
B-36 B.5.8 Formwork Considerations and Lateral Pressure
B-36 B.5.9 Finishing
B-36 B.5.10 Curing
B-38 References
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B-5
Introduction · Greater flexibility to produce a wide variety of architectural
finishes
The competitive situation in the precast concrete construc- · Increased assembly rates and reduced labor for placement,
tion market is significantly affected by price and cost factors as vibration and finishing
well as by productivity and quality. This environment is char- · Improved working environment and safety
acterized by ever-shorter construction times, rising labor · Lower capital investment costs and higher service life of the
costs, as well as greater demand for high workability, strength, formwork elements
and durability. Technological developments and methods of · Improved surface quality with greater uniformity and fewer
production that can lead to improved concrete quality and surface imperfections
savings are therefore becoming increasingly important. Self-
consolidating concrete (SCC) represents a significant advance- Use of SCC in the precast, prestressed applications can
ment in concrete technology that provides great potential for result in specific advantages. Complex precast concrete mem-
efficiency and economy in concrete construction. bers can be prefabricated with greater ease, speed, economy,
SCC is a highly workable concrete that can flow through and higher surface quality. This can be achieved even in tightly
densely reinforced or geometrically complex structural ele- spaced areas or congested reinforcement--such as columns,
ments under its own weight without mechanical consolidation cap beams, and superstructure elements--and lead to provid-
and adequately fill the formwork with minimum risk of segre- ing uniform and aesthetically pleasing surfaces. The quality
gation. The flowability of SCC is higher than that of normal control and quality assurance measures used for producing
high-performance concrete typically used in precast, pre- SCC will help achieve structures with the desired durability
stressed concrete plants. This characteristic of SCC, coupled and service life.
with the absence of the noise associated with vibration, make These guidelines provide the information necessary for
SCC a desirable material for fabricating prestressed bridge ele- considering use of SCC in precast, prestressed bridge girders.
ments. More specifically, SCC offers the following advantages: The guidelines include information on the selection of con-
crete constituents and proportioning of concrete mixtures,
· Simplification of the concreting procedure and ability to workability characteristics, testing methods, mechanical prop-
produce heavily reinforced precast elements with virtually erties, visco-elastic properties, production and control issues,
any cross-sectional shape and durability of SCC.
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B-6
Glossary portland cement paint or other materials to reduce shrinkage,
improve workability, or act as an extender or material used to
The following definitions may be referred to in these fill an opening in a form (ACI 116).
guidelines. Some of them are general and apply to conven- Filling ability--The ability of SCC to flow into and fill
tional concrete while others are specific to SCC. Some of these completely all spaces within the formwork, under its own
definitions are based on definitions given in ACI and PCI weight, also referred to as deformability or non-restricted de-
technical documents. formability (ACI 237).
Admixture--A material, other than water, aggregates, hy- Filling capacity--The ability of SCC to flow into and fill
draulic cement, and fiber reinforcement, used as an ingredi- completely all spaces within the formwork.
ent of a cementitious mixture to modify its freshly mixed, set- Flowability--The ability of fresh concrete to flow in con-
ting, or hardened properties and that is added to the batch fined or unconfined form of any shape, reinforced or not,
before or during its mixing (ACI 116). under gravity and/or external forces, assuming the shape of
Autogenous shrinkage--The shrinkage occurring in the its container (PCI 2003).
absence of moisture exchange due to the hydration reactions Fluidity--The ease by which fresh concrete flows under
taking place inside the cement matrix (ACI 209). gravity (PCI 2003). Fluidity is the reciprocal of dynamic
Binder--A cementing material, either a hydrated cement or viscosity.
reaction products of cement or lime and reactive siliceous ma- Fly ash--The finely divided residue that results from the
terial; also materials such asphalt, resins, and other materials combustion of ground or powdered coal and that is trans-
forming the matrix of concretes, mortars, and sanded grouts. ported by flue gasses from the combustion zone to the parti-
Bingham fluid--A fluid characterized by a yield stress and cle removal system (ACI 116). Because of its spherical shape
a constant plastic viscosity, regardless of flow rate (PCI 2003). and fineness, fly ash can improve the rheology of SCC.
Bleed water--The water that rises to the surface subse- Formwork pressure--Lateral pressure acting on vertical
quent to the placing of the concrete. The rise of mixing water or inclined formed surfaces, resulting from the fluid-like be-
within, or its emergence from, newly placed concrete, caused havior of the unhardened concrete confined by the forms
by settlement and consolidation of the plastic concrete (PCI (ACI 116).
2003). Ground granulated blast-furnace slag (GGBFS)--A fine
Bleeding test--The standard test for determining the rel- granular, mostly latent hydraulic binding material that can be
ative quantity of mixing water that will bleed from a sample added to SCC to improve workability of the material (PCI
of freshly mixed concrete (ASTM C 232). 2003). GGBFS is also referred to in some cases as slag cement
Blocking--The condition in which coarse aggregate parti- (a waste product in the manufacture of pig iron and chemi-
cles combine to form elements large enough to obstruct the cally a mixture of lime, silica, and alumina).
flow of the fresh concrete between the reinforcing steel or High-range water-reducing admixture (HRWRA)--
other obstructions in the concrete formwork (PCI 2003). A water-reducing admixture capable of producing large
Cohesiveness--The tendency of the SCC constituent ma- water reduction or greater flowability without causing undue
terials to stick together, resulting in resistance to segregation, set retardation or entrainment of air in mortar or concrete
settlement, and bleeding (PCI 2003). (ACI 116).
Consistency--The relative mobility or ability of freshly J-Ring test--Test used to determine the passing ability of
mixed concrete or mortar to flow (ACI 116). SCC, or the degree to which the passage of concrete through
Consolidation--The process of inducing a closer arrange- the bars of the J-Ring apparatus is restricted (ASTM C 1621).
ment of the solid particles in freshly mixed concrete or mortar J-Ring flow--The distance of lateral flow of concrete using
during placement by the reduction of entrapped voids (ACI the J-Ring in combination with a slump cone (ASTM C 1621).
116). In SCC, consolidation is achieved by gravity flow of the L-box test--Test used to assess the confined flow of SCC
material without the need of vibration, rodding, or tamping. and the extent to which it is subject to blocking by reinforce-
Creep--Time-dependent deformation due to sustained ment (ACI 237).
load (ACI 209). Metakaolin--Mineral admixture used as binding material
Deformability--The ability of SCC to flow under its own (supplementary cementitious material) in concrete (PCI 2003).
mass and fill completely the formwork. Mixture robustness--The characteristic of a mixture that
Drying shrinkage--Shrinkage occurring in a specimen encompasses its tolerance to variations in constituent char-
that is exposed to the environment and allowed to dry (ACI acteristics and quantities, as well as its tolerance to the effects
209). of transportation and placement activities (PCI 2003).
Fillers--Finely divided inert material, such as pulverized Passing ability--The ability of SCC to flow under its own
limestone, silica, or colloidal substances, sometimes added to weight (without vibration) and completely fill all spaces
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B-7
within intricate formwork, containing obstacles, such as re- as movement of aggregate particles within fresh concrete
inforcement (ASTM C 1621). (consolidation).
Paste volume--Proportional volume of cement paste in Shear stress--The stress component acting tangentially to
concrete, mortar, or the like, expressed as volume percent of a plane (ACI 116).
the entire mixture (ACI 116). Silica fume--Very fine non-crystalline silica produced in
Plastic viscosity--The resistance of the plastic material to electric arc furnaces as a byproduct of the production of ele-
undergo a given flow. It is computed as the slope of the shear mental silicon or alloys containing silicon (ACI 116). Silica fume
stress versus shear rate curve measurements. Mixtures with can be added to SCC to improve the rheological properties.
high plastic viscosity are often described as "sticky" or "cohe- Slump flow--Test method used (upright or inverted) to
sive." Concrete with higher plastic viscosity takes longer to measure mixture filling ability (ASTM C 1611).
flow. It is closely related to T-50 and V-funnel time (higher Slump flow retention--The ability of concrete to main-
plastic viscosity: higher T-50 and V-funnel time). tain its slump flow over a given period of time.
Powder (also referred to as graded powder)--Includes ce- Slump flow spread--The distance of lateral flow of con-
ment, fly ash, GGBFS, limestone fines, material crushed to crete during the slump-flow test (ASTM C 1611). Slump flow
less than 0.125 mm (No. 100 sieve), or other non-cementi- spread is the numerical value in inches (mm) of flow deter-
tious filler (ACI 237). mined as the average diameter of the circular deposit of SCC
Powder-type SCC--SCC mixtures that rely extensively on at the conclusion of the slump flow test.
the amount and character of the fines and powder included Stability--The ability of a concrete mixture to resist seg-
in the mixture for meeting workability performance require- regation of the paste from the aggregates (ASTM C 1611).
ments (stability) (PCI 2003). Stability, Dynamic--The resistance to segregation when ex-
Pumpability--The ability of an SCC mixture to be pumped ternal energy is applied to concrete, namely during placement.
without significant degradation of workability (PCI 2003). Stability, Static--The resistance to segregation when no
Rheological properties--Properties dealing with the de- external energy is applied to concrete, namely from immedi-
formation and flow of matter (PCI 2003). ately after placement and until setting.
Rheology--The science of dealing with flow of materials, T-50 measurement (also referred to as the T-20 in. time
including studies of deformation of hardened concrete, the in North America)--The time for the concrete to reach the
handling and placing of freshly mixed concrete, and the be- 500 mm (20 in.) diameter circle drawn on the slump plate, after
havior of slurries, pastes, and the like (ACI 116). In the con- starting to raise the slump cone (ASTM C 1611).
text of SCC, rheology refers to the evaluation of yield stress, Texture--The pattern or configuration apparent in an ex-
plastic viscosity, and thixotropy to achieve desired levels of posed surface, as in concrete and mortar, including roughness,
filling ability, passing ability, and segregation resistance. streaking, striation, or departure from flatness (ACI 116).
Segregation--The differential concentration of the com- Thixotropy--The property of a material that enables it to
ponents of mixed concrete, aggregate, or the like, resulting in stiffen in a short period while at rest, but to acquire a lower
non-uniform proportions in the mass (ACI 116). In the case viscosity when mechanically agitated, the process being re-
of SCC, segregation may occur during transport, during flow versible, a material having this property is termed thixotropic
into the forms, or after placement when the concrete is in a or shear thinning (ACI 116). Thixotropy indicates formwork
plastic state. This results in non-uniform distribution of in-situ pressure and segregation resistance of SCC.
properties of the concrete. Transportability--The ability of concrete to be trans-
Segregation resistance--The ability of concrete to remain ported from the mixer to the placement site while remaining
uniform in terms of composition during placement and until in a homogeneous condition (PCI 2003).
setting (PCI 2003). Segregation resistance encompasses both V-funnel--Device used to determine the time for a given
dynamic and static stability. volume of concrete to flow out through a funnel opening
Self-consolidating concrete (SCC) (also self-compacting (PCI 2003).
concrete)--A highly flowable, non-segregating concrete that Viscosity--The resistance of a material to flow under an
can spread into place, fill the formwork, and encapsulate the re- applied shearing stress (ASTM 1611).
inforcement without any mechanical consolidation (ACI 237). Viscosity-modifying admixture (VMA)--An admixture
Service life--The time during which the structure performs used for enhancing the rheological properties of cement-
its design functions without unforeseen maintenance or repair. based materials in the plastic state to reduce the risk of segre-
Settlement--The condition in which the aggregates in gation and washout (ACI 237).
SCC tend to sink to the bottom of the form resulting in non- Visual Stability Index (VSI)--A test that involves the vi-
homogeneous concrete (PCI 2003). Surface settlement can sual examination of the SCC slump flow spread resulting
also be caused by bleeding of free water and loss of air as well from performing the slump flow test (ACI 237).
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B-8
Water-cementitious material ratio (w/cm)--The ratio of ability, passing ability, and segregation resistance, and it is af-
the mass of water, exclusive only of that absorbed by the ag- fected by rheology.
gregate, to the mass of cementitious material (hydraulic) in Yield stress--The minimum shear stress required to initi-
concrete, mortar, or grout, stated as a decimal (ACI 116). ate (static yield stress) or maintain (dynamic yield stress) flow
Workability--That property of freshly mixed concrete or (ACI 237). The yield stress is closely related to slump flow
mortar that determines the ease with which it can be mixed, (lower yield stress results in higher slump flow); it is calcu-
placed, consolidated, and finished to a homogenous condi- lated as the intercept of the shear stress versus shear rate plot
tion (ACI 116). For SCC, workability encompasses filling from rheometer flow curve measurements.
OCR for page 49
B-9
Guidelines Commentary
B.1 Guidelines for Selection of Constituent Materials
B.1.1 General
The production of SCC requires uniform quality of all con-
stituent materials, and it is therefore necessary that these ma-
terials meet standard specifications. A choice of suitable con-
stituent materials is vital to the optimization of SCC mix
design for different applications.
Constituent material qualification for SCC designated for
precast, prestressed concrete bridge elements generally follows
the requirements of AASHTO LRFD Bridge Design [2007]
and Construction [1998] Specifications. Except mixing water
and materials mentioned in the following Sections B.2.2 to
B.2.4, no materials may be incorporated into the concrete
without the authorization of the Engineer. It is important to
continually check for any change in materials or proportions
that will affect surface appearance, strength, or other charac-
teristics of SCC that may affect its overall performance.
B.1.2 Cement and Cementitious Materials
One must ensure that material additions do not adversely
affect the desired architectural appearance, where appearance
is a design requirement.
B.1.2.1 Cement and Blended Cement
All cements that conform to the AASHTO M 85 or ASTM Selection of the type of cement will depend on the overall
C 150 standard specifications can be used for the production requirements for the concrete, such as compressive strength
of SCC. The correct choice of cement type is normally dic- at early and ultimate ages, mechanical properties, durability,
tated by the specific requirements of each application or by and color considerations in architectural applications where
the availability. color and color uniformity are important.
For SCC applications where visual appearance is impor- Blended hydraulic cements that conform to the AASHTO
tant, adequate cement content and uniform w/cm should be M 240 or ASTM C 595M can also be used. Unless otherwise
adopted to minimize the color variation. Therefore, the ce- specified, Types I, II, or III cement; Types IA, IIA, or IIIA air-
ment should be from the same mill and of the same type, entrained cement; or Types IP (portland-pozzolan cement) or
brand, and color. IS (portland blast-furnace slag cement) blended hydraulic ce-
ments can be used for the construction of precast, prestressed
concrete elements. Types I, II or III cements can be used with
some replacements by supplementary cementitious materials
and other hydraulic binders. In general, fly ash and slag re-
placement values shall not exceed 20% and 40%, respectively,
to ensure high-early strength for satisfactory release of strands.
The total content of cementitious materials used in pre-
stressed concrete for a 28-day design compressive strength
of 4,000 to 8,000 psi (28 to 55 MPa) can vary from 600 to
1,000 lb/yd3 (356 to 593 kg/m3) [PCI, 1997]. The AASHTO
LRFD Bridge Design Specifications [2007] suggest that the sum
of portland cement and other cementitious materials should
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B-10
Guidelines Commentary
not exceed 800 lb/yd3 (475 kg/m3), except for Class P concrete
where the total cementitious materials should not exceed 1,000
lb/yd3 (593 kg/m3). These values for SCC designated for precast,
prestressed applications shall range between 650 and 800 lb/yd3
(386 and 475 kg/m3) [ACI Committee 237, 2007 (237R-07)].
B.1.2.2 Fly Ash
Pozzolans and slag meeting ASTM C 618, C 989, or C 1240 In some cases, higher level of fly ash replacement may re-
are supplementary cementitious material and may be added duce the ability of SCC to flow. The replacement rate of fly
to portland cements during mixing to produce SCC with im- ash also affects strength and durability. Contribution of fly
proved workability, increased strength, reduced permeability ash delays the hydration process and strength development.
and efflorescence, and improved durability. In general, Class Fly ash can also affect air entrainment since the carbon pres-
F fly ash has been shown to be effective in SCC providing in- ent in fly ash can absorb air-entraining admixture and ad-
creased cohesion and robustness to changes in water content versely affect the ability to entrain air. Therefore, specific lim-
[European Guidelines, 2005]. its on LOI which is indicative of the carbon content need to
be stated. Fly ash shall not be used with Type IP or IS cements.
Fly ash should conform to the AASHTO M 295 or ASTM
C 618 [AASHTO, 1998, 2007]. In general, the content of ce-
ment replaced with fly ash is 18% to 22% by mass [Florida
DOT, 2004].
B.1.2.3 Silica Fume
Silica fume conforming to AASHTO M 307 or ASTM C In some cases, a high level of silica fume addition can cause
1240 can be used as supplementary cementitious material in rapid surface crusting that leads to cold joints or surface de-
the proportioning of SCC for improved strength and dura- fects if delays occur in concrete delivery or surface finish (and
bility. Silica fume also improves resistance to segregation and also increases cost). According to Florida DOT [2004], the
bleeding. Special care should be taken to select the proper sil- quantity of cement replacement with silica fume should be
ica fume content. 7% to 9% by mass of cementitious materials.
B.1.2.4 Ground Granulated Blast-Furnace Slag
Ground granulated blast-furnace slag (GGFBS) meeting
AASHTO M 302 or ASTM C 989 may be used as supplemen-
tary cementitious materials. GGBFS provides reactive fines
and due to large replacement rate usually about 40% enables
a low heat of hydration.
Cement replacement by GGBFS is based on the severity of
the environment to which the concrete is exposed. The level
of GGBFS addition is 25% to 70% for slightly and moderately
aggressive environments, and 50% to 70% by mass when
used in extremely aggressive environments.
When used in combination with silica fume and/or A high proportion of GGBFS (e.g., exceeding 40%) may
metakaolin, GGBFS content should be limited to 50% to 55% however affect stability of SCC resulting in reduced robust-
of the total cementitious content, by mass of binder [Florida ness with problems of consistency control while delayed set-
DOT, 2004]. However, in precast, prestressed members, the ting can increase the risk of static segregation.
amount of slag is usually 40%. GGBFS shall not be used with
Type IP or Type IS cements.
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B-11
Guidelines Commentary
B.1.2.5 Fillers
The particle-size distribution, shape, and water absorption
of fillers may affect the water demand/sensitivity and suit-
ability for use in the production of SCC. Calcium carbonate-
based mineral fillers can enhance workability and surface fin-
ish. The fraction below 0.005 in. (0.125 mm) shall be of most
benefit to SCC flow properties. Contents of fillers should be
evaluated to ensure adequate performance of concrete, in-
cluding strength development and durability.
B.1.2.6 Other Supplementary Cementitious
Additions
Metakaolin, natural pozzolan, ground glass, air-cooled slag
and other fine fillers have also been used or considered as ad-
ditions for SCC, but their effects need to be carefully evalu-
ated for both short- and long-term effects on the fresh and
hardened concrete.
B.1.3 Aggregate Characteristics
A well-graded combined aggregate with sufficient inter-
mediate sizes is highly desirable for improved stability. Also,
if the proper particle shape and texture are selected, com-
bined aggregate grading can lead to large reductions in water,
paste, and cement contents leading to improved hardened
concrete properties.
The moisture content, water absorption, grading and Gravel, crushed stone, or combinations can be used as
variations in fines content of all aggregates should be coarse aggregate. In the case of fine aggregate, natural sand or
closely and continuously monitored and must be taken into manufactured sand can be used. Coarse and fine aggregates
account in order to produce SCC of constant quality. should conform to the grain-size distribution recommenda-
Changing the source of supply for aggregates is likely to tions of the project specifications.
make a significant change to the concrete properties and
should be carefully and fully evaluated [European Guide-
lines, 2005].
B.1.3.1 Coarse Aggregate
Unless otherwise specified in the contract documents, the Slightly gap-graded aggregates may lead to greater flow-
recommendation is to use normal-density coarse aggregate ability than continuously graded aggregate. Gap-graded ag-
meeting the requirements of AASHTO M 80 or ASTM C 33. gregate can, however, increase the risk of bleeding and segre-
The use of continuously graded aggregates is recommended. gation, and proper measures are needed to ensure adequate
The nominal maximum-size of coarse aggregate (MSA) static stability of the concrete.
should be selected based on mix requirements and minimum In the design of SCC, typically the MSA values are smaller
clear spacing between the reinforcing steel and prestressing than those of conventional vibrated concrete. The MSA is
strands, cover of the reinforcement steel, and thickness of the generally limited to 1/2 to 3/4 in. (12.5 to 19 mm). In the
member. The recommendations given in the PCI Bridge De- placement of SCC in highly congested and restricted section,
sign Manual [1997] apply. MSA value of 3/8 in. (9.5 mm) can be used.
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B-12
Guidelines Commentary
If aggregates susceptible to alkali-aggregate reactivity are
used, special precautions must be observed. These include the
use of low-alkali cement, blended cements, or pozzolans and
GGBFS.
B.1.3.2 Fine Aggregate
For normal weight concrete, fine aggregates conforming to It may be beneficial to blend natural and manufactured
AASHTO M 6 are appropriate for the production of SCC. sand to improve plastic properties of SCC. Common concrete
The fine aggregate component should be well-graded con- sand, including crushed or rounded sand and siliceous or cal-
crete sand. careous sand, can be used in SCC.
Fine aggregates for SCC should conform to the gradation
requirements of AASHTO M 6 or ASTM C 33, as presented
in Table B.1.
Table B.1. Grading requirements
for fine aggregates.
Percent passing Percent passing Particle size fractions of less than 0.005 in. (0.125 mm)
Sieve
(AASHTO M 6) (ASTM C 33) should be considered as powder material in proportioning
3
8 in. (9.5 mm) 100 100
No. 4 (4.75 mm) 95 to 100 95 to 100 SCC. Such fine content can have marked effect on rheology.
No. 8 (2.36 mm) 80 to 100 80 to 100
No. 16 (1.18 mm) 50 to 85 50 to 85
No. 30 (600 m) 25 to 60 25 to 60
No. 50 (300 m) 10 to 30 5 to 30
No. 100 (150 m) 2 to 10 0 to 10
B.1.4 Chemical Admixtures
Chemical admixtures are used in precast, prestressed con-
crete to reduce water content, improve filling ability and sta-
bility, provide air entrainment, accelerate strength develop-
ment, enhance workability retention, and retard setting time.
Because chemical admixtures can produce different results Incompatibility of admixtures with binders can lead to im-
with different binders, and at different temperatures, the se- proper air void system and delayed or accelerated setting
lection of the admixtures should be based on the plant mate- time. Therefore, before the start of the project, concrete with
rials and conditions that will be utilized in production. the job materials, including the admixtures, should be tested
For prestressed concrete, chloride-ion content in chemical to ensure compatibility. Such testing should be repeated
admixtures should be limited to 0.1%, by mass of the admix- whenever there is a change in the binder and admixtures.
ture [AASHTO, 2004].
B.1.4.1 High-Range Water-Reducing Admixtures
High-range water-reducing admixtures (HRWRA) shall The required consistency retention will depend on the ap-
conform to the requirements of ASTM C 494 Type F (water- plication. Precast concrete is likely to require a shorter reten-
reducing, high range) or G (water-reducing, high range, and tion time than cast-in-place concrete.
retarding) or ASTM C 1017. The admixture should enable the
required water reduction and fluidity during transport and
placement.
The use of Type F or G HRWRA is essential to achieve SCC
fluidity. Such HRWRA can be used in combination with reg-
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Guidelines Commentary
Type III + 20% FA (moist-cured):
A = 2.15; B = 0.89; R2 = 0.95
CEB-FIP MC90
28 1 2
fcm ( t ) = exp s 1 - fcm
t t1
fcm(t) = mean compressive strength at t days (in psi);
fcm = mean 28-day compressive strength;
s = coefficient depending on cement type (0.20 for high
early-strength cement, 0.25 for normal-hardening
cement, and 0.38 for slow-hardening cement);
t1 = 1 day.
16 non-AEA SCC + 4 AEA SCC + 2 HPC:
s = 0.19 Type I/II cement; R2 = 0.95
s = 0.20 Type III + 20% FA; R2 = 0.92
16 nonair-entrained SCC:
s = 0.20 Type I/II cement; R2 = 0.95
s = 0.23 Type III + 20% FA; R2 = 0.93
B.4.5 Flexural Strength
For precast and structural civil engineering applications, The flexural strength of SCC depends on the w/cm, coarse
SCC mixtures are typically proportioned with relatively low aggregate volume, and quality of the interface between the ag-
w/cm of 0.32 to 0.36 and with supplementary cementitious gregate and cement paste. The curing method of SCC can sig-
materials and fillers and are expected to achieve higher flex- nificantly influence the flexural strength. Moist-cured speci-
ural strength and flexural-to-compressive ratio than conven- mens can exhibit higher flexural strength because the samples
tional slump concrete [ACI Committee 237, 2007]. do not develop surface drying that could lead to premature
The flexural strength can be determined by testing in ac- microcracking development.
cordance with ASTM C 293 and C 78-02 or can be estimated
from the compressive strength. For SCC used for precast, pre-
stressed applications, the flexural strength can be estimated
with the AASHTO 2007 model, given by:
fr = 0.97 fc
= specified compressive strength of concrete (MPa)
fc
B.4.6 Modulus of Elasticity
In applications where the modulus of elasticity (MOE) is The MOE is used to calculate camber of prestressed mem-
an important design parameter, the MOE should be deter- bers at the release of the prestressing load, elastic deflections,
mined and considered in the design of the prestressed con- axial shortening and elongation, and prestress losses.
crete member. In the absence of measured data, the equation The MOE is related to the compressive strength of the con-
proposed by the AASHTO LRFD Bridge Design Specifica- crete, type and content of aggregate, as well as unit weight of the
tions [2007] is recommended to estimate the elastic modulus concrete. The modulus of elasticity is related to compressive
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Guidelines Commentary
of concrete having a unit weight of 2,427 to 4,214 lb/yd3 strength and unit weight of the concrete, aggregate type and
(1,440 and 2,500 kg/m3) and specified compressive strength content, and testing parameter, including loading rate, mois-
of up to 15,230 psi (105 MPa). For an accurate prediction, de- ture and temperature conditions of the test specimen, as well as
termine the MOE in conformance with ASTM C 469 using specimen size and shape. The content and MOE of the aggre-
the job-specific materials. gate have the largest influence on the MOE of the concrete.
The modulus of elasticity for SCC used for precast, pre- Selecting an aggregate with high modulus of elasticity will
stressed applications can be estimated using the AASHTO increase the modulus of elasticity of the concrete. Increase in
2007 equation: sand-to-coarse aggregate ratio can decrease the modulus of
elasticity of the concrete.
Ec = 0.043 1
c
.5 fc In some cases, SCC mixtures can develop modulus of elas-
ticity that can be up to 20% lower than typical values found
c = unit weight of concrete (kg/m3);
in high-performance concrete of normal consistency, which
= specified compressive strength of concrete (MPa)
fc
is mainly due to the lower coarse aggregate volume, increase
in paste content, and higher content of ultra-fine materials.
At equivalent strength, SCC made with different cement
types should develop similar modulus of elasticity when
cured and tested under identical conditions.
B.4.7 Creep
Incorrect or inaccurate design for creep and shrinkage may Length changes of prestressed members due to time-
have important undesirable consequence on stability and dependent deformation, creep, and shrinkage play a crucial
performance of the structure. role in the design of concrete structures and on structural be-
In applications where creep characteristics are important havior, especially at long term.
design parameters, this aspect should be considered in the de- Creep behavior is related to the compressive strength of the
sign and confirmed for the mixture used in the production of matrix, coarse aggregate type, relative content of aggregate, as
precast members. well as magnitude of applied load and age of loading. Creep
Perform creep testing in accordance with ASTM C 512 takes place in the cement paste and is influenced by the cap-
using the job-specific materials. The age when the load is ap- illary porosity of the paste. Cement type and w/cm can affect
plied affects creep values. For SCC used in precast, pre- creep. High early-strength cement can lead to lower creep.
stressed elements load should be applied at an early age cor- The presence of aggregate restrains creep deformation in the
responding to prestress release time. paste. Therefore, an increase in the volume and elastic mod-
In the absence of measured data, the modified AASHTO ulus of the aggregate can lower creep.
2007 prediction model can be used to predict the creep of SCC. Due to the higher volume of cement paste and fines and
smaller MSA of SCC, creep potential of SCC can be higher
AASHTO 2007
than conventional concrete made with the same raw materi-
( t , t i ) = 1.9kvs khc k f ktd t i-0.118 × A als and having the same 28-day design compression strength.
in which: kvs = 1.45 - 0.0051(V / S) 0.0
khc = 1.56 - 0.008H
35 t
kf = , ktd =
7 + fci 61 - 0.58 fci + t
where:
H = relative humidity (%). In the absence of better in-
formation, H may be taken from Figure 5.4.2.3.3-1
of AASHTO Bridge Design Specifications [2007].
kvs = factor for the effect of the volume-to-surface ratio
of the component
kf = factor for the effect of concrete strength
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Guidelines Commentary
khc = humidity factor for creep
ktd = time development factor
t = maturity of concrete (day). Defined as age of concrete
between time of loading for creep calculations, or end
of curing for shrinkage calculations, and time being
considered for analysis of creep or shrinkage effects
ti = age of concrete when load is initially applied (day)
V / S = volume-to-surface ratio (mm)
i = specified compressive strength of concrete at time of
fc
prestressing for pretensioned members and at time
of initial loading for non-prestressed members. If
concrete age at time of initial loading is unknown at
i may be taken as 0.80 f c
design time, f c i (MPa)
A = factor for the effect of cement type: 1.19 for Type
I/II cement and 1.35 for Type III + 20% FA binder
which may be used for P(SCC)
B.4.8 Autogenous Shrinkage
SCC and conventional concrete used in precast applica- Autogenous shrinkage corresponds to the macroscopic vol-
tions proportioned with relatively low w/cm (0.32 to 0.36) ume reduction due to cement hydration (chemical shrinkage)
and high content of cement and supplementary cementitious as well as self-desiccation of the cement paste. The volume of
materials could exhibit high autogenous shrinkage. This is es- the hydration products is less than the original volume of un-
pecially the case when capillary porosity is refined when using hydrated cement and water. Such reduction in volume can
silica fume. Cement type has a considerable effect in the de- lead to tensile stresses in the cement paste and microcracking.
velopment of autogenous shrinkage. Higher surface area of The reduction of relative humidity in capillary pores due to ce-
the cement can activate the reactivity of the binder, hence in- ment hydration can also result in negative pressure in the cap-
creasing the degree of autogenous shrinkage. illary pores, leading to the formation of meniscus and the de-
velopment of tensile stresses in the cement paste.
In the case of concrete proportioned with high w/cm
(higher than 0.40), autogenous shrinkage is low given the
ample presence of water in capillary pores.
B.4.9 Drying Shrinkage
In prestressed applications, shrinkage should be considered Drying shrinkage must be taken into consideration to
in the mix design and taken into consideration in the struc- avoid cracking and excessive deflection resulting from time-
tural design of the member. Proportion SCC with relatively dependent concrete deformation and loss of prestress. Drying
low binder content and w/cm to reduce drying shrinkage. shrinkage is caused by the loss of water from the concrete to
Drying shrinkage can be evaluated in accordance with the atmosphere. The increased volume of paste in SCC and re-
ASTM C 157 (AASHTO T 160). In the absence of measured duction in aggregate content and size can increase the poten-
data, the modified AASHTO 2004 or CEB-FIP MC90 shrink- tial for drying shrinkage. The presence of aggregate restrains
age models can be used to estimate drying shrinkage of SCC, shrinkage of the cement paste; therefore, the increase in ag-
as indicated below. For steam cured concretes devoid of gregate volume reduces drying shrinkage. A decrease in the
shrinkage-prone aggregates, the strain due to shrinkage, sh, MSA can necessitate higher paste volume, thus leading to
at time, t, may be taken as: higher shrinkage. Drying shrinkage increases with the increase
in powder material content, which is particularly high in SCB.
The use of fly ash in normal proportions does not signifi-
cantly influence drying shrinkage of concrete. The use of
limestone powder with Blaine fineness greater than that of
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Guidelines Commentary
AASHTO 2004 portland cement can reduce drying shrinkage of SCC. This
can be explained by the denser matrix obtained when fine
t
sh = -ks kh × 0.56 × 10-3 × A ( steam-cured ) limestone powder is used [Holschemacher and Klug, 2002].
55 + t The effect of HRWRA and VMA on shrinkage of SCC is re-
t ported to be beneficial. Indeed, the use of HRWRA reduces
26e 0.0142(V S ) + t 1064 - 3.70 (V S )
ks =
the surface tension of the water, thus decreasing the capillary
t 923 tension of pore water [Ulm et al., 1999; Acker, 1988; Acker
45 + t and Bazant, 1998; Neville, 1981; Wittman, 1976; Neville and
Meyers, 1964]. However, the air content may increase when
t = drying time (day)
using polycarboxylate-based HRWRA, which could lead to
ks = size factor
greater shrinkage.
kh = humidity factor
V / S = volume-to-surface ratio
A = cement factor: 0.918 for Type I/II cement and 1.065
for Type III + 20% FA binder which may be used
for P(SCC)
CEB-FIP MC90
(t - t c )
cso = s ( f cm )( RH )
2 Ac
2
350 + ( t - t c )
100
s(fcm) = [160 + 10sc(9 - 0.1 fcm)] × 10-6
RH = -1.55ARH; ARH = 1 - (RH/100)3
cso = drying shrinkage (mm/mm)
s = drying shrinkage obtained from RH-shrinkage
chart
sc = cement type factor
RH = relative humidity factor
fcm = mean 28-day compressive strength (MPa)
Ac = cross-sectional area (mm2)
µ = perimeter (mm)
tc = age at which drying commenced (day)
t = age of concrete (day).
B.4.10 Durability and Air-Void System
It is essential to proportion SCC with adequate stability to Segregation and bleeding have significant negative effect
ensure high performance, including durability, of the hard- on permeability and quality of the interfacial zone between
ened concrete. The durability of a concrete structure is closely cement paste and aggregate, embedded reinforcement, and
associated to the permeability of the surface layer and curing. existing surface, and hence on durability of the concrete.
The most significant durability characteristics affecting the Higher air content (6% to 9%) may be necessary in
durability of SCC used in precast, prestressed elements pro- most severe frost environments, especially when using
duction include: w/cm, cement content, degree of consolida- polycarboxylate-based HRWRA, which could result in some
tion, curing, cover over the reinforcement, and reactivity of entrapment of relatively large air voids. Coalescence of small
aggregate-cement combinations. air bubbles during agitation can occur when high air contents
Bridge structures constructed in environments prone to are obtained and when concrete is retempered with water.
freezing and thawing may become critically saturated, thus The dosage of AEA in SCC prepared with polycarboxylate-
necessitating air entrainment when exposed to cycles of freez- based HRWRA can be quite low compared with values used
ing and thawing. In some cases, the bridge deck can shelter for conventional concrete of normal consistency. Still, it is
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B-32
Guidelines Commentary
some of the precast beam elements, thus reducing the rate of critical to incorporate an AEA in concrete subjected to mod-
saturation and exposure to any deicing salt applied on the erate frost exposure conditions to secure stable and closely
bridge deck. In most cases, bridge girders can be considered to spaced air bubbles (adequate spacing factor). In general, for
be subjected to moderate exposure conditions that correspond mixtures made with a relatively low content of cementitious
to situations where deicing salts are not used or where the con- materials and a high w/cm, the air-void stability increases
crete is only occasionally exposed to moisture prior to freezing when a VMA is incorporated [Khayat, 1995].
and do not get critically saturated. Therefore, under these con- Air entrainment is necessary to stabilize small, closely
ditions, prestressed bridge girders require sufficient air content spaced, and well-distributed voids in concrete. Such voids can
for moderate exposure conditions. For example, under these be obtained when the SCC is proportioned with an effective
conditions, SCC proportioned with 1/2 in. (12.5 mm) nomi- AEA that is compatible with the HRWRA and other chemical
nal MSA would then require 4% to 7% air volume in the fresh admixtures in use.
concrete to provide adequate frost resistance.
ASTM C 457 can be used to test the air-void parameters of
the concrete, and ASTM C 666, Procedure A (AASHTO T
161, Method A), is used to test resistance to freezing and
thawing.
B.4.11 Bond to Prestressing Strands
Ensuring proper stability of SCC is essential to ensure ho- Bond between the strand and concrete is affected by the
mogenous in-situ properties, including bond to embedded re- position of the embedded reinforcements and quality of the
inforcement, which is critical for structural performance of pre- cast concrete. Bond to prestressed tendons can be influenced
cast, prestressed applications [Moustafa, 1974; Logan, 1997]. by the flow properties of the SCC, grading of the aggregate
In general, adequate concrete cover is necessary to prop- and content of fines in the matrix [Holschemacher and Klug,
erly transfer bond between prestressed tendons and concrete. 2002].
Despite the high fluidity of SCC, high static stability of the A surface settlement of 0.5% corresponds to 1.4 modifica-
SCC after placement can lead to more homogenous in-situ tion factor of prestressing strands [Khayat et al., 1997; Petrov
properties and denser matrix at the interface between the ce- et al., 2001]. It is important to note that selection of highly
ment paste and reinforcement, thus enhancing bond strength viscous SCC can result in some lack of consolidation of the
compared with normal conventional concrete subjected to concrete, which can in turn affect bond stresses between the
mechanical vibration. On the other hand, bond can be sig- concrete and prestressing strand.
nificantly affected by excessive segregation found in poorly
designed SCC. As indicated in Table B.10, in order to secure
adequate static stability, the SCC should have maximum sur-
face settlement of 0.5%, column segregation index of 5%, or
percent static segregation of 15%.
Table B.10. Recommendations to secure homogenous
in-situ properties of SCC.
Material properties Recommended values
Maximum surface settlement 0.5%
Static stability Column segregation index (Iseg) 5%
Percent static segregation (S) 15%
Plastic viscosity 0.0725 psi·s (500 Pa·s)
Viscosity
(Modified Tattersall two-point rheometer with vane device)
Core-to-cylinder compressive strength 90% (similar curing
Mechanical properties conditions)
Bond strength modification factor 1.4
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Guidelines Commentary
B.5 Guidelines for Production and Control
B.5.1 General
The need for adequate quality control is much more criti-
cal with SCC than in the case of conventional concrete. In
order to maintain a given workability, it is essential to main-
tain constant quality of all concrete constituent during SCC
production. Successful production of SCC requires greater
competence and proper control of materials and equipments
used for production.
SCC intended for use in precast plants should meet the tech-
nical requirements of the fresh concrete. The mixture needs to
be tested to ensure that required properties are achieved given
the performance specifications, casting conditions, and geom-
etry of the cast element. Before selecting the raw material and
finalizing the mix design, several factors should be known,
including the size and shape of elements to be cast.
Laboratory trials should be used to validate the material se-
lection and verify the properties of the mix design to achieve
the targeted properties. Once the optimum properties are
achieved, proper quality control for material properties should
be observed to eliminate fluctuations in fresh and hardened
properties of the concrete. Any changes in raw materials
properties should be immediately identified to allow necessary
adjustments of the mix to meet the specified properties.
B.5.2 Control of Raw Materials
Depending on the mix design, SCC may be less robust than The moisture content, water absorption, aggregate grada-
conventional concrete. SCC may therefore undergo greater tion, and variations in fines content of the aggregate should
changes in workability given small variations in the physical be continuously monitored and must be taken into account
properties of its constituents, especially in the moisture con- to produce SCC with constant characteristics. Changing the
tent of the sand, fine particle content in sand, as well as grad- source of supply for aggregate is likely to significant change
ing and shape of the sand and coarse aggregate. This would the concrete properties and should be carefully and fully eval-
necessitate frequent controls to check for any changes in ma- uated [European Guidelines, 2005].
terial properties that could affect the performance of SCC.
The maximum deviation of the sand moisture should not It is preferable to control the moisture of sand before every
exceed ± 0.2% in order to minimize the variations in fresh batch of SCB. The moisture content in coarse aggregate must be
properties of SCC. The water content of sand should be de- also taken into account and should be determined at least twice
termined just before production of SCC. a day, at the beginning of the first and second production shifts.
Changes in coarse aggregate physical characteristics (shape, When designing SCC, some factors should be taken into
texture, gradation) can affect workability. Inspection at the consideration to a greater degree than when designing con-
storage location should be conducted on coarse aggregate to ventional concrete to ensure good filling capacity, such as the
characterize their physical characteristics for every aggregate geometry configuration of cast elements and placement con-
delivery. ditions. Indeed, the nominal maximum size of coarse aggre-
gate should be selected based on mix requirements and the
minimum clear spacing between the reinforcing steel, cover
to reinforcing steel, and thickness of the member. The thick-
ness of the cast element and the congestion level of the rein-
forcement are key factors affecting workability of SCC.
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B-34
Guidelines Commentary
B.5.3 Mixing Process and Sequence
The mixing process should be properly determined given The batch volume is typically limited to 80% to 90% of the
the conditions at hand. For example, the batch volume maximum capacity of the mixer to allow efficient mixing en-
should be determined in consideration of the type of SCC ergy [JSCE, 1999]. When the mixer is alternatively used for
(consistency level), efficiency of the mixer to produce a well- mixing normal concrete and SCC, testing should be per-
dispersed and homogeneous mix, and transportation rate formed to verify that this does not result in any adverse effect
from the plant to the casting site. on SCC properties.
Just prior to mixing of the first batch, the mixer should be Mixing equipment and mixing sequence should be vali-
pre-wetted or "buttered" with SCC of approximately similar dated by testing consistency and self-consolidation properties
consistency. for a given mix design. Necessary adjustments to time and
Suitable mixing sequence should be determined given the speed of mixing should be carried out until consistent and
mixing and storage equipments available at the plant. Cement compliant results are obtained.
particles should be wetted before contact with HRWRA. Dry
mixing before water introduction is not recommended, be-
cause it may lead to build-up of fine materials in the mixer. All
batching water should be added at the same time. For example,
it has been shown that the introduction of VMA at the end of
the mixing sequence and of air-entraining admixture at the be-
ginning can provide good performance [Khayat 1995; Khayat
and Assaad, 2002]. The addition sequence of VMA should be
evaluated given the mix design and admixture in use.
B.5.4 Transport
SCC should be delivered in a continuous and timely man-
ner to ensure continuous placement of precast members with
the workability-retention period of the mixture. This is nec-
essary to avoid lift lines and other surface defects.
Transport method shall be confirmed in order to provide
SCC at the casting location that is sufficiently homogeneous
to allow successful placement in the precast element and to
achieve the targeted properties. Mixer trucks have proven to
be the best method of delivery of SCC when transporting over
rough terrain or long transport distance [PCI, 2003].
B.5.5 Site Acceptance of Plastic Concrete
The producer should determine the frequency of perform-
ing quality control testing based on available experience mix-
tures [PCI, 2003].
The quality control tests should include visual inspection Quality control for frequently used SCC is less critical than
of every batch of the concrete and any specific tests and com- in the case of SCC that is occasionally produced.
pliance parameters. For example, the slump flow and VSI
tests can be adopted. The T-50 can also be run at least once
on new mixtures and used to check the performance in the
event of mix performance problems.
B.5.6 Placement Techniques and
Casting Considerations
Prior to the production process, full-size mock-ups should In a placement case that will require multiple batches,
be cast for final approval. Placement method should be selected mixing facilities are required to ensure that concrete will be
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B-35
Guidelines Commentary
given the production capacity and transport rate to the cast- available within a short time frame with proper workability
ing point. characteristics as specified in performance specifications.
Placement techniques should be selected based on the Placement techniques of SCC can have a significant impact
total volume of the concrete to be discharged, the transporta- on the required fluidity level and flowing performance of the
tion rate, and whether the placement process is continuous concrete. For example, in the case of higher energy involved
or discontinuous. during placement, lower fluidity level for the SCC will be
In the case of placement technique involving higher en- required to achieve a given flow and filling performances.
ergy, extra care should be taken with regard to stability char-
acteristics. Relative energy involved during each placement
technique is summarized in Table B.11 [PCI, 2003].
Table B.11. Summary of different placement techniques
for SCC [Bury and Bühler, 2002].
Single Relative
Placement Discharge Discharge
discharge energy
technique rate type
volume delivered
Truck discharge High Continuous High High
Pumping Medium/High Continuous Medium High/Medium
Crane and bucket High Discontinuous Low Medium
Auger
(Tuckerbuilt) Low/Medium Continuous Medium Low/Medium
discharge
Placement of SCC in horizontal elements can be done by
starting at one end of the mold, with the discharge as close to
the form surfaces as possible. It is recommended to discharge
the SCC in the direction of desired flow to maximize the travel
distance. The recommended maximum flowing distance
should be between 10 and 33 ft (3 and 10 m), depending on
the geometry of the element [RILEM, 2000].
As in the case of conventional concrete, the free-fall dis- Free-fall distance should be fixed given the element depth
tance should be controlled to avoid concrete segregation. For to be cast and static and dynamic stability of the concrete.
example, based on the Norwegian experience, the free-fall
distance should be limited to 6.5 ft (2 m) when casting wall
and beam elements.
B.5.7 Temperature Control
The mix design should be tailored to achieve the targeted
properties specified in the performance specifications. When
the use of steam curing is required to achieve the targeted
early-age strength, the temperature of the concrete should
not exceed 160°F (71°C) [AASHTO, 1998]. Furthermore,
according to the AASHTO LRFD Bridge Construction Spec-
ifications [1998], the temperature within the curing cham-
ber shall increase at a rate not exceeding 72°F (22°C) per
hour.
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Guidelines Commentary
B.5.8 Formwork Considerations
and Lateral Pressure
Formwork for SCC can be constructed of different materi-
als, including wood, steel, plastic, fiberglass, or combination
of these materials. Formwork made with wood often leads to
less pores and bubble formation than smooth formwork. Be-
cause of the high fluidity of SCC compared with conventional
concrete, formwork should be rigid enough with accommo-
date variations in product dimensions and form, and to with-
stand lateral form pressure exerted by the plastic concrete.
Given the high fluidity of SCC compared with conventional Before applying the release agent, the wood of the form-
concrete, extra care should be taken to avoid any leakage. work should be dry to ensure good release performance and
Formwork joints should be adequately sealed. Vegetable oil has avoid appearance of air-bubbles at the formed surface of the
been shown to be a good release agent as it reduces the amount cast element.
of pores on the concrete surface [Brite-EuRam, 1998].
Depending on the casting rate and thixotropy of SCC, lat- Experience has shown that for a given casting rate, concrete
eral pressure can be lower than the theoretical hydrostatic with a higher level of thixotropy can develop lower lateral
pressure. This is especially the case when the casting rate ex- pressure, faster decay in lateral pressure, and shorter time to
ceeds 10 ft/h (3 m/h). pressure cancellation [Assaad et al., 2004]. SCC cast at 16 ft/h
Lateral pressure can be 50% to 80% of the calculated pres- (5m/h) is shown to develop maximum initial lateral pressure
sure for conventional vibrated bridge concrete with a slump of 90% of hydrostatic pressure. In general, sections measur-
consistency of 4 in. (100 mm) [RILEM, 2000]. ing up to 10 ft (3 m) in height should be designed for full
hydrostatic pressure.
Lateral pressure developed by SCC cast from the top of the
formwork is lower than in the case when the concrete is
pumped from the bottom. SCC pumped from the bottom
should be designed for full hydrostatic pressure.
B.5.9 Finishing
Finishing of SCC is easier and faster than for conventional Given the concrete properties and ambient conditions,
concrete. Finishing practices employed with conventional some surfaces may require only nominal screeding and float-
concrete can be employed with SCC. However, finishing op- ing, while other surfaces may require mild vibratory screed-
erations should be delayed slightly more than for conven- ing [ACI Committee 237, 2007; PCI, 2003].
tional superplasticized concrete [PCI, 2003].
Surface drying during finishing should be prevented. Fog Because of the relatively higher content of fines and even-
misting to increase the relative humidity would minimize rate tual presence of VMA, SCC mixtures develop little or no
of evaporation and reduce the risk of plastic shrinkage. bleed water compared with conventional concrete.
SCC exposed surfaces may dry faster than those of normal It is important to begin the finishing of the surface with
superplasticized concrete. This can happen when casting at light vibrating screeds, or other manual equipment, as soon
hot temperature or windy conditions. Also, depending on the as the correct level of the concrete in the formwork has been
SCC mixture proportioning, stiffening can increase rapidly in reached.
the period 10 to 40 minutes after casting. Setting time of the
SCC mixture should be adjusted to allow necessary time to
carry out the placement process.
B.5.10 Curing
Membrane curing, matting, foils, or appropriate materials
should be left in place for at least 4 days for cast-in-place
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Guidelines Commentary
concrete elements [Swedish Concrete Association, 2002].
This measure should be applied to SCC with low w/cm and
SCC made with high fines content or VMA. During hot or
windy weather conditions, moisture should be added by wa-
tering or by protecting the surface with wetted membranes
for proper curing.
AASHTO LRFD Bridge Construction Specifications [1998] During the waiting period, the temperature within the cur-
recommend that for concrete cured by other than steam or ra- ing chamber shall not be less than 10°C. During the applica-
diant heat methods, whenever there is a probability of air tem- tion of steam, the ambient temperature within the curing
perature below 36°F (2°C) during the curing period, the con- chamber shall not increase at an average rate greater than
crete shall be maintained at a temperature of not less than 45°F 22°C/h until the targeted temperature value is reached.
(7°C) for the first 6 days after placement. This period must be
extended if pozzolans are used as partial replacement of ce-
ment. If the compressive strength of 65% of the specified
28-day design strength is achieved in 6 days, an extended period
of controlled temperature may be waived [AASHTO, 1998].
Due to the specification in terms of early-age compressive
strength, steam curing or radiant heat curing can be used for
precast concrete members. The initial application of steam or
heat shall be from 2 to 4 hours after the initial placement of
concrete to allow the initial set of the concrete to take place
[AASHTO, 1998]. In the case of concrete incorporating a set
retarder, the waiting period shall be increased to between
4 and 6 hours after casting.
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B-38
References Khayat, K. H. (1999), "Workability, Testing, and Performance of Self-
Consolidating Concrete." ACI Materials Journal, Vol. 96, No. 3,
Acker, P. (1988), Mechanical Behavior of Concrete: Physico-Chemical pp. 346353.
Approach, Etudes et Recherches des LPC, 152, Laboratoire Central Khayat, K. H., and Assaad, J. (2002), "Air-Void Stability of Self-
des Ponts et Chaussées, 121 p. (In French) Consolidating Concrete." ACI Materials Journal, Vol. 99, No. 4,
Acker, P., and Bazant, Z. P. (1998), "Measurement of Time-Dependent pp. 408416.
Strains of Concrete, RILEM Draft Recommendations." Material and Khayat, K. H., Manai, K., and Trudel, A. (1997), "In-Situ Mechanical
Structures, RILEM, Vol. 31, No. 8 pp. 507512. Properties of Wall Elements Cast Using Self-Consolidating Con-
American Association of State Highway Transportation Officials crete." ACI Materials Journal, Vol. 94, No. 6, pp. 491500.
(AASHTO) (1998), AASHTO LRFD Bridge Construction Specifica- Khayat, K. H., Mitchell, D. Long, W. J., Lemieux, G., Hwang, S.-D.,
tions, 1st edition.
Yahia, A., Cook, W. D., Baali, L. (2007), Self-Consolidating Con-
American Association of State Highway Transportation Officials
crete for Precast, Prestressed Concrete Bridge Elements. Draft final
(AASHTO) (2004), AASHTO LRFD Bridge Design Specifications,
report, NCHRP Project 18-12. University of Sherbrooke, Quebec,
3rd edition.
Canada.
American Association of State Highway Transportation Officials
Logan, D. (1997), "Acceptance Criteria for Bond Quality of Strand for Pre-
(AASHTO) (2007), AASHTO LRFD Bridge Design Specifications,
4th edition. tensioned Prestressed Concrete Applications." PCI Journal, Vol. 42,
American Concrete Institute (ACI) Committee 116 (2000), Cement and No. 2, pp. 5290.
Concrete Terminology. Neville, A. M. (1981), Properties of Concrete, 3rd Edition, Pittman, Lon-
American Concrete Institute (ACI) Committee 237 (2007), Provisional don, 779 p.
Guidelines on Self-Consolidating Concrete. Neville, A. M., and Meyers, B. L. (1964), "Creep of Concrete: Influencing
American Concrete Institute (ACI) Committee 318 (2005), Building Factors and Prediction, Symposium on Creep of Concrete." SP-9,
Code Requirements for Structural Concrete (ACI 318-05) and Com- ACI, Detroit, pp. 133.
mentary (ACI 318R-05). Manai, K. (1995), Evaluation of the Effect of Chemical and Mineral Ad-
Assaad, J., Khayat, K. H., and Daczko, J. (2004), "Evaluation of Static mixtures on the Workability, Stability, and Performance of Self-
Stability of Self-Consolidating Concrete." ACI Materials Journal, Compacting Concrete, Master's Thesis, University of Sherbrooke,
Vol. 101, No. 3, pp. 207215. Quebec, Canada, 182 p. (In French)
Bartos, P. J. M. (1998), "An Appraisal of the Orimet Test as a Method for Moustafa, S. (1974), Pull-out Strength of Strand and Lifting Loops, Con-
On-Site Assessment of Fresh SCC Concrete." Proceedings, Interna- crete Technology Associates Technical Bulletin, 74-B5.
tional Workshop on Self-Compacting Concrete, Japan, pp. 121135. Okamura, H. (1997), "Self-Compacting High-Performance Concrete."
Brite-EuRam (1998), Report on Project SCC-BRPR-CT96-0366, Ratio- Concrete International, Vol. 19, No. 7, pp. 5054.
nal Production and Improved Working Environmental Through Ozawa, K., Tangtermsirikul, S., and Maekawa, K. (1992), "Role of Pow-
Using Self-Compacting Concrete. der Materials on the Filling Capacity of Fresh Concrete," Supple-
Bury, M. A., and Bühler, E. (2002), "Methods and Techniques for Plac- mentary Papers, 4th CANMET/ACI International Symposium on Fly
ing Self-Consolidating Concrete--An Overview of Field Experi- Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Istanbul,
ences in North American Applications." Proceedings, 1st North pp. 121137.
American Conference on the Design and Use of Self-Consolidating Petrov, N., Khayat, K. H., and Tagnit-Hamou, A. (2001), "Effect of Sta-
Concrete, ACBM, Chicago, USA, pp. 281286. bility of Self-Consolidating Concrete on the Distribution of Steel
Daczko, J., and Kurtz, M. (2001), "Development of High Volume Corrosion Characteristics Along Experimental Wall Elements,"
Coarse Aggregate Self-Compacting Concrete." Proceedings, 2nd In- Proceedings, 2nd International Symposium on Self-Consolidating
ternational Symposium on Self-Compacting Concrete, Tokyo, Concrete, Tokyo, Japan, pp. 441450.
Japan, pp. 403412. Precast/Prestressed Concrete Institute (1997), Precast Prestressed Con-
European Guidelines for Self-Compacting Concrete (2005), Specifica-
crete Bridge Design Manual, 1st edition.
tion, Production and Use, 63 p.
Precast/Prestressed Concrete Institute (PCI) (2003), Interim Guidelines
Florida DOT (2004), Standard Specifications for Road and Bridge Con-
for the Use of Self-Consolidating Concrete in Precast/Prestressed In-
struction, Florida State.
stitute Member Plants, 148 p.
Holschemacher, K., and Klug, Y. (2002), A Database for the Evaluation
RILEM Technical Committee 174-SCC (2000), Self-Compacting Con-
of Hardened Properties of SCC, Leipzig Annual Civil Engineering
Report No. 7, Universität Leipzig, pp. 123134. crete, Report 23, Edited by A. Skarendahl, O. Petersson, 154 p.
Hwang, S. D., Khayat, H. K., and Bonneau, O. (2006), "Performance- Swedish Concrete Association (2002), Self-Compacting Concrete, Rec-
Based Specifications of Self-Consolidating Concrete Used in ommendations for Use, Concrete Report No. 10(E), 84 p.
Structural Applications." ACI Materials Journal, Vol. 103, No. 2 Ulm, F.-J., Le Maou, F., and Boulay, C. (1999), "Creep and Shrinkage
pp. 121129. Coupling: New Review of Some Evidence," Creep and Shrinkage of
Japan Society of Civil Engineers (JSCE) (1999), Recommendations for Concrete, Edited by Ulm, F.-J., Prat, M., Calgaro, J.-A., Carol, I.,
Self-Compacting Concrete, Tokyo, 77 p. Special issue of Revue Française de Génie Civil, HERMES Science
Khayat, K. H. (1995), "Frost Durability of Concrete Containing Viscosity- Publications, pp. 2137.
Modifying Admixtures." ACI Materials Journal, Vol. 92, No. 6, Wittman, F. H. (1976), "On the Action of Capillary Pressure in Fresh
pp. 625633. Concrete." Cement and Concrete Research, Vol. 6, No. 11, pp. 4956.
Khayat, K. H. (1998), "Use of Viscosity-Modifying Admixture to Re- Yurugi, M., Sakata, N., Iwai, M., and Sakai, G. (1993), "Mix Propor-
duce Top-Bar Effect of Anchored Bars Cast with Fluid Concrete." tion of Highly Workable Concrete." Concrete 2000, Dundee,
ACI Materials Journal, Vol. 95, No. 2, pp. 158167. pp. 579589.
