ACI Education Bulletin E4-03. Supersedes E4-96.
Copyright © 2003, American Concrete Institute.
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CHEMICAL ADMIXTURES FOR CONCRETE
Materials for Concrete Construction
This document discusses commonly used chemical admixtures for concrete
and describes the basic use of these admixtures. It is targeted at those in
the concrete industry not involved in determining the specific mixture
proportions of concrete or in measuring the properties of the concrete.
Students, craftsmen, inspectors, and contractors may find this a valuable
introduction to a complex topic. The document is not intended to be a stateof-the-art report, user’s guide, or a technical discussion of past and present
research findings. More detailed information is available in ACI Committee
Report 212.3R, “Chemical Admixtures for Concrete” and 212.4R, “Guide
for the Use of High-Range Water-Reducing Admixtures (Superplasticizers)
in Concrete.”
CONTENTS
Chapter 1—Introduction, p. E4-2
1.1—History
1.2—Definitions
Chapter 2—Overview, p. E4-2
2.1—Function
2.2—Standards
Chapter 3—Air-entraining admixtures, p. E4-3
3.1—History
3.2—Mechanism
3.3—Use of air-entraining admixtures
Chapter 4—Water-reducing and set-controlling
admixtures, p. E4-5
4.1—Types and composition
4.2—Type A, water-reducing admixtures
4.3—Type B, retarding, and Type D, water-reducing and
retarding admixtures
4.4—Type C, accelerating, and Type E, water-reducing
and accelerating admixtures
4.5—High-range water-reducing admixtures
4.6—Mid-range water-reducing admixtures
Chapter 5—Corrosion-inhibiting admixtures, p. E4-9
Chapter 6—Shrinkage-reducing admixtures, p. E4-9
Chapter 7—Admixtures for controlling alkali-silica
reactivity, p. E4-9
Chapter 8—Admixtures for underwater concreting,
p. E4-9
Chapter 9—Effectiveness of admixtures, p. E4-9
Chapter 10—Admixture dispensers, p. E4-10
10.1—Industry requirements and dispensing methods
10.2—Liquid admixture dispensing methods
10.3—Accuracy requirements
10.4—Application considerations and compatibility
10.5—Dispensers for high-range water-reducing admixtures
10.6—Dispenser maintenance
David M. Suchorski
Chair
James A. Farny
Secretary
Leonard W. Bell Tarek S. Khan Kenneth B. Rear
*
Richard P. Bohan Paul D. Krauss Raymundo Rivera-Villarreal
David A. Burg Colin L. Lobo Jere H. Rose
Darrell F. Elliot Stella L. Marusin Paul J. Tikalsky
James Ernzen Patrick L. McDowell Mark E. Vincent
J. Pablo Garcia Gerald R. Murphy Christopher H. Wright
Ramon F. Gutierrez Charles K. Nmai Kari L. Yuers
Morris Skip Huffman Anthony C. Powers Robert C. Zellers
Herb Johns
*
Chair of document subcommittee.E4-2 ACI EDUCATION BULLETIN
Chapter 11—Conclusion, p. E4-11
Chapter 12—List of relevant ASTM standards,
p. E4-11
Chapter 13—Glossary, p. E4-12
CHAPTER 1—INTRODUCTION
1.1—History
Admixtures have long been recognized as important components of concrete used to improve its performance.
The original use of admixtures in cementitious mixtures is
not well documented. It is known that cement mixed with
organic matter was applied as a surface coat for water resistance or tinting purposes. It would be a logical step to use
such materials, which imparted desired qualities to the surface, as integral parts of the mixture. The use of natural
admixtures in concrete was a logical progression. Materials
used as admixtures included milk and lard by the Romans;
eggs during the middle ages in Europe; polished glutinous
rice paste, lacquer, tung oil, blackstrap molasses, and
extracts from elm soaked in water and boiled bananas by the
Chinese; and in Mesoamerica and Peru, cactus juice and
latex from rubber plants. The Mayans also used bark extracts
and other substances as set retarders to keep stucco workable
for a long period of time.
1.2—Definitions
ACI 116R-00 defines the term admixture as “a material
other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to
modify its freshly mixed, setting, or hardened properties and
that is added to the batch before or during its mixing.” In ACI
212.3R it is stated that “chemical admixtures are used to
enhance the properties of concrete and mortar in the plastic
and hardened state. These properties may be modified to
increase compressive and flexural strength at all ages,
decrease permeability and improve durability, inhibit corrosion, reduce shrinkage, accelerate or retard initial set, increase
slump and workability, improve pumpability and finishability,
increase cement efficiency, and improve the economy of the
mixture. An admixture or combination of admixtures may be
the only feasible means of achieving the desired results. In certain instances, the desired objectives may be best achieved by
mixture changes in addition to proper admixture usage.”
Chemical admixtures are materials that are added to the
constituents of a concrete mixture, in most cases, specified
as a volume in relation to the mass of the cement or total
cementitious materials. The admixtures interact with the
hydrating cementitious system by physical and chemical
actions, modifying one or more of the properties of concrete
in the fresh and/or hardened states.
Concrete is composed principally of aggregates, hydraulic
cement, and water, and may contain other cementitious
materials and chemical admixtures. It will contain some
amount of entrapped air and may also contain purposely
entrained air obtained by use of a chemical admixture or airentraining cement. Chemical admixtures are also frequently
used to accelerate, retard, improve workability, reduce mixing
water requirements, increase strength, improve durability, or
alter other properties of the concrete.
There are many kinds of chemical admixtures that can
function in a variety of ways to modify the chemical and
physical properties of concrete. This bulletin provides information on the types of chemical admixtures and how they
affect the properties of concrete, mortar, and grout.
CHAPTER 2—OVERVIEW
2.1—Function
In ACI 212-3R, the reasons for the use of admixtures are
outlined by the following functions that they perform:
• Increase workability without increasing water content
or decrease the water content at the same workability;
• Retard or accelerate time of initial setting;
• Reduce or prevent shrinkage or create slight expansion;
• Modify the rate or capacity for bleeding;
• Reduce segregation;
• Improve pumpability;
• Reduce rate of slump loss;
• Retard or reduce heat evolution during early hardening;
• Accelerate the rate of strength development at early ages;
• Increase strength (compressive, tensile, or flexural);
• Increase durability or resistance to severe conditions of
exposure, including application of deicing salts and
other chemicals;
• Decrease permeability of concrete;
• Control expansion caused by the reaction of alkalies
with potentially reactive aggregate constituents;
• Increase bond of concrete to steel reinforcement;
• Increase bond between existing and new concrete;
• Improve impact and abrasion resistance;
• Inhibit corrosion of embedded metal; and
• Produce colored concrete or mortar.
2.2—Standards
Air-Entraining Admixtures ASTM C 260
Standard Specification for Air-Entraining
Admixtures for Concrete AASHTO M 154
Standard Specification for Air-Entraining
Admixtures for Concrete CRD-C 13
Chemical Admixtures ASTM C 494
Standard Specification for Chemical
Admixtures for Concrete AASHTO M 194
Standard Specification for Chemical
Admixtures for Concrete CRD-C 87
Calcium Chloride ASTM D 98
Standard Specification for Calcium Chloride AASHTO M 144
Foaming Agents ASTM C 869
Admixtures for Shotcrete ASTM C 1141
Admixtures for Use in Producing
Flowing Concrete ASTM C 1017
Grout Fluidifier For Preplaced Aggregate
Concrete ASTM C 937
Pigments For Integrally Colored Concrete ASTM C 979
*
ASTM—ASTM International
AASHTO—American Association of State Highway and Transportation Officials
CRD—Army Corps of Engineers, Chief of Research and DevelopmentCHEMICAL ADMIXTURES FOR CONCRETE E4-3
An admixture may conform to the requirements of one or
more of the above types, and may serve more than one of the
listed functions. Thus, combinations of two or more admixtures might be used in varying dosages so that optimum
results could be obtained using local materials. When using
combinations of admixtures, each admixture must be added
separately to the concrete mixture. Pre-job testing should be
conducted to ensure compatibility of the admixture system.
When using admixtures, and particularly combinations of
admixtures, testing for compatibility of the admixture system requires knowledge of the rate of slump loss (that is the
relationship between slump and time) and the setting time
under relatively hot and cold conditions (in addition to laboratory conditions). Test placements on-site are recommended to verify proper workability, finishability, and
setting time of the proposed mixture.
CHAPTER 3—AIR-ENTRAINING ADMIXTURES
3.1—History
Air-entraining admixtures are primarily used to stabilize
tiny air bubbles in concrete, produced by mixing, and protect
against damage from repeated freezing-and-thawing cycles.
The dramatic effect of freezing and thawing on concrete is of
little surprise to those who live in climates with extensive
temperature cycling. Crumbling walls and scaled sidewalks
are evidence of the devastating effect that repeated exposure
to freezing and thawing can have on concrete proportioned
with an inadequate air content and bubble spacing or
improperly cured concrete.
During the l930s, certain concrete pavements were more
able to withstand the effects of freezing and thawing than
others. Investigation showed that the more durable pavements were slightly less dense, and that the cement used had
been obtained from mills using beef tallow as a grinding aid
in the manufacturing of cement. The beef tallow acted as an
air-entraining agent, which improved the durability of the
pavements. Later, after rigorous investigation, air-entrained
concrete was specified where freezing-and-thawing resistance was needed.
The incorporation of an adequate amount and distribution of
entrained air in properly proportioned concrete that contains
sound aggregates and is protected from cycles of freezing until
the compressive strength reaches about 28 MPa (4000 psi) can
render concrete resistant to freezing-and-thawing deterioration.
Until recently, the most commonly used air-entraining admixture for concrete was a neutralized wood resin. Now, other formulations that have some enhanced performance properties,
such as improved stability, have been introduced. Today, more
than 80% of the portland-cement concrete pavements in the
United States contain an air-entraining admixture to provide
resistance to freezing and thawing and impart better workability, improved homogeneity, and decreased segregation
and bleeding.
3.2—Mechanism
Entrained air should not be confused with entrapped air.
Air entrainment is usually the result of an addition of a liquid
admixture to the concrete during batching, but may be
obtained by using a cement blended with a powdered admixture. As a result of the mixing action, these admixtures stabilize air bubbles that become a component of the hardened
concrete. The resultant air-void system consists of uniformly
dispersed voids throughout the cement paste of the concrete.
These tiny voids (between 10 and 1000 micrometers in diameter) must be present in the proper amount and spacing to be
effective at providing freezing-and-thawing protection. Concrete made with fine aggregate that is deficient in the smaller
particle sizes may benefit from air entrainment.
The space occupied by the mixing water in fresh concrete
rarely becomes completely filled with cementitious material
reaction product after the concrete has hardened. The
remaining spaces are capillary pores. Under saturated conditions, these cavities are filled with water. If this water
freezes, the resulting expansion of water to ice creates tremendous internal pressures. The expansion (approximately
9%) when water freezes produces a stress in a confined
space. This stress is far in excess of the tensile strength of
concrete. The result in non air-entrained concrete is cracking, scaling, and spalling.
Entrained air voids make these capillaries discontinuous.
Because the air voids are generally much larger than the passageways, they form tiny reservoirs that act as safety valves
during ice expansion, accommodating the increased volume.
The importance is not only the amount of entrained air but
also the size and spacing of the bubbles. The level of air content recommended by ACI Committee 201 for normalstrength concrete is listed in Table 1. It is based on different
exposure conditions and aggregate size. Adding air-entrainment can also improve the finish of the surface of slabs and
reduce the occurrence of voids and sand streaking on wall
surfaces. Air entrainment, however, is not recommended for
interior steel troweled floors. Air content in excess of 3% can
cause blisters and delamination.
3.3—Use of air-entraining admixtures
Air-entraining admixtures should be required to conform
to ASTM Specification C 260.
Air voids should not have a spacing factor larger than 0.2 mm
(0.008 in.) for adequate protection of water-saturated concrete
in a freezing-and-thawing environment. The term “spacing
Table 1—Recommended air contents for concrete
exposed to freezing and thawing (ACI 201.2R)
Nominal maximum
aggregate size, mm (in.)
Average air content, percent*
Severe exposure
†
Moderate exposure
‡
9.5 (3/8) 7-1/2 6
12.5 (1/2) 7 5-1/2
19 (3/4) 6 5
25 (1) 6 4-1/2
37.5 (1-1/2) 5-1/2 4-1/2
*
A reasonable tolerance for air content if field construction is ±1-1/2%.
†
Severe exposure—Outdoor exposure in a cold climate where the concrete may be in
almost continuous contact with moisture before freezing and where deicing compounds are used. Examples are pavements, bridge decks, and sidewalks.
‡
Moderate exposure—Outdoor exposure in a cold climate where the concrete will be
only occasionally exposed to moisture before freezing and where no deicing compounds will be used. Examples are certain exterior walls, beams, bridge decks, and
slabs not in direct contact with soil.E4-4 ACI EDUCATION BULLETIN
factor” represents the maximum distance that water would
have to move before reaching the air-void reservoir or safety
valve.
Another factor that must be considered is the size of the air
voids. For a given air content, the size of the air voids cannot
be too large if the proper spacing factor is to be achieved without using an unacceptable amount of air. The term “specific
surface” is used to indicate the average size of the air voids. It
represents the surface area of the air voids in concrete per unit
volume of air. For adequate resistance to repeated freezing and
thawing in a water-saturated environment, the specific surface
should be greater than 24 mm
2
/mm
3
(600 in.
2
/in.
3
).
With all the benefits a proper air-void system provides, there
may also be detrimental effects in concrete. Increasing the air
content will typically decrease the strength of concrete. An
increase of 1% in air content will typically decrease compressive strength by about 5% in concrete mixtures with a compressive strength in the range of 2l to 35 MPa (3000 to 5000 psi).
The air content of fresh concrete should be closely monitored. Table 2 summarizes some of the factors that influence
the entrained air content of fresh concrete.
Additional dosage rates of the various air-entraining
admixtures generally range from about 15 to 130 mL per
100 kg (1/4 to 2 fl oz. per 100 lb) of cementitious material.
Equipment for dispensing air-entrainment admixtures is discussed in Chapter 9. The measurement of entrained air content
should be performed immediately before discharging the concrete into the forms. Samples for acceptance testing, however,
should be taken from the middle of the batch in accordance
with ASTM C 172. Unit weight should also be checked.
The methods and materials for performing air-content
tests on concrete are described in ASTM Standard Test
Methods C 231 and C 173. The gravimetric method (ASTM
C 138) is not generally used in the field because it requires
knowledge of the theoretical unit weight of the concrete on
an air-free basis. Unit weights, however, should be monitored in the field to verify uniformity between batch mixture
proportions and air contents. Hardened cylinder weight
should be recorded on concrete test reports adjacent to compressive strength. Cylinders should be weighed immediately
after demolding. Air content should be measured each time
concrete is sampled, and air meters should be calibrated regularly. Inexpensive devices for quickly calibrating air meters
are available. The Chace Air Indicator, a commonly misapplied device, does not provide the degree of accuracy and
precision necessary to measure air content.
For more than 20 years, testing agencies that record hardened
cylinder weights have been aware that measured air contents
may not be reasonable when compared with hardened cylinder
weight. Lower-than-expected strength is often associated
with a low hardened cylinder weight, which is not consistent
with the measured fresh air content. Subsequent petrographic analysis of a companion cylinder often indicates an
air content significantly higher than the measured air content. The air content obtained from the petrographic analysis
adequately explains the lower-than-expected cylinder
strength, particularly if the air has coalesced around coarse
aggregate.
On-site control of air content of fresh concrete requires
coordination between the inspector-technician, the concrete
supplier, and the concrete contractor. Agreement on procedures and timing of sampling should be made before the start
of concrete placement operations. All ingredients must be
added to the concrete before testing is initiated. A minimum
of 0.04 m
3
(1.0 ft
3
) of concrete from the middle of the batch
should be discharged into a suitable container, such as a
wheelbarrow or concrete buggy, in accordance with ASTM
C 172. The remainder of the testing techniques must be perTable 2—Factors affecting the air content of concrete at a given dosage of admixture
Factor Affect on air content
Cement
An increase in the fineness of cement will decrease the air content.
As the alkali content of the cement increases, the air content may increase.
An increase in the amount of cementitious materials can decrease the air content.
Fine aggregate
An increase in the fine fraction passing the 150 µm (No. 100) sieve will decrease the amount of entrained air.
An increase in the middle fractions passing the 1.18 mm (No. 16) sieve, but retained on the 600 µm (No. 30) sieve and 300 µm (No. 50)
sieve, will increase the air content.
Certain clays may make entraining air difficult.
Coarse aggregate
Dust on the coarse aggregate will decrease the air content.
Crushed stone concrete may result in lower air than a gravel concrete.
Water
Small quantities of household or industrial detergents contaminating the water may affect the amount of entrained air.
If hard water is used for batching, the air content may be reduced.
Pozzolans and slag Fly ash, silica fume, natural pozzolans, and ground granulated blast-furnace slag can affect the dosage rate of air-entraining admixtures.
Admixtures Chemical admixtures generally affect the dosage rate of air-entraining admixtures.
Slump
For less than a 75 mm (3 in.) slump, additional admixture may be needed. An increase in slump to about 150 mm (6 in.) will
increase the air content.
At slumps above 150 mm (6 in.), air may become less stable and the air content may decrease.
Temperature
An increase in concrete temperature will decrease the air content. Increase in temperature from 21 to 38 °C (70 to 100 °F) may
reduce air contents by 25%.
Reductions from 21 to 4 °C (70 to 40 °F) may increase air contents by as much as 40%. Dosages of air-entraining admixtures must
be adjusted when changes in concrete temperatures take place.
Concrete mixer
The amount of air entrained by any given mixer (stationary, paving, or transit) will decrease as the blades become worn or become
coated with hardened concrete buildup.
Air contents often increase during the first 70 revolutions of mixing then will hold for a short duration before decreasing. Air content will increase if the mixer is loaded to less than capacity and will decrease if the mixer is overloaded. In very small loads in a
drum mixer, however, air becomes more difficult to entrain.CHEMICAL ADMIXTURES FOR CONCRETE E4-5
formed in strict accordance with ASTM test methods,
including proper remixing of the sample.
If the air content is outside specified limits, a retest should
be taken immediately. If the air content is found to be too low
or too high, the deficiency should be corrected in coordination with the producer, engineer, and testing agency.
Many factors are involved in the assurance of properly airentrained concrete. Improper concrete placement, consolidation, and finishing techniques may decrease the air content.
The configuration of the boom on a pump may affect the air
content of the concrete. Tests have shown that there is often
more air loss when the boom is in a vertical position as
opposed to when the boom is extended in a more horizontal
configuration. Attention to proper selection of all materials
involved in the proportioning of the mixture is essential, as
compatibility problems may exist with other components of
the concrete mixture. Materials complying with relevant
specifications, including air-entraining admixtures meeting
ASTM C 260, and the adherence to proper proportioning
procedures is necessary. Proper testing according to standard
practices and proper placement and curing of fresh concrete
will make a major contribution to obtaining adequate durability and resistance to deterioration by freezing and thawing.
Careful consideration should be given to the need for airentrainment of steel-troweled slabs. Steel troweling of airentrained slabs can result in surface scaling. Maximum total
air content for interior steel-troweled slabs should normally
be 3% to reduce the possibility of scaling. If steel troweling
is required, it should be kept to a minimum. Overworking the
surface may decrease air entrainment at the surface where it
is needed. This also can result in sealing in a layer of water,
which will result in scaling.
CHAPTER 4—WATER-REDUCING AND
SET-CONTROLLING ADMIXTURES
4.1—Types and composition
Water-reducing, set-controlling admixtures are added to
concrete during mixing to increase workability, improve durability, provide easier placement, control the setting time, and
produce easier finishing with less segregation of the ingredients. This is accomplished while allowing a reduction of the
total water content and providing the ability to control the time
of setting to meet changing jobsite and climatic conditions.
The strength improvement resulting from water-reducing
admixtures is primarily a result of reducing the watercementitious materials ratio and increasing cement efficiency. For a given air content, concrete strength is inversely
proportional to the water-cementitious materials ratio and,
therefore, the reduction in water needed to achieve the
desired slump and workability when a water-reducing agent
is used will effect an increase in strength. The result of waterreducing admixtures in improving strength, however, often
exceeds the results of simply reducing the water content.
Proper use of admixtures should begin by gathering available information and comparing the different types and
brands that are available. Trial mixtures, with those admixtures under consideration, should be made to determine their
effect on strength, finishability, and other construction
requirements, such as rate of slump loss and setting time.
Consideration must be given to information such as uniformity,
dispensing, long-term performance, and available service.
These are points that cannot be assessed by concrete tests but
could determine successful admixture use.
The admixture manufacturer should be able to provide
information covering typical dosage rates, times of setting,
and strength gain for local materials and conditions. The
evaluation and application of the admixture should be made
with specific job materials using the construction procedures
under anticipated ambient conditions. Laboratory tests conducted on concrete with water-reducing admixtures should
indicate the effect on pertinent properties necessary for the
construction project, including: water requirement, air content, slump, rate of slump loss, bleeding, time of setting,
compressive strength, flexural strength, and resistance to
freezing and thawing. Following the laboratory tests, field
test should be conducted to fully comprehend how the
admixtures will work in actual field conditions.
ASTM C 494, “Standard Specification for Chemical
Admixtures for Concrete,” classifies admixtures into seven
types as follows:
Type A Water-reducing admixtures;
Type B Retarding admixtures;
Type C Accelerating admixtures;
Type D Water-reducing and retarding admixture;
Type E Water-reducing and accelerating admixtures;
Type F Water-reducing, high-range, admixtures; and
Type G Water-reducing, high-range, and retarding
admixtures.
Each of the seven types of admixtures covered by ASTM C
494 is designed to function in a specific manner. ASTM C 494
outlines the physical requirements for performance of the
potential admixture to be qualified in the respective categories.
To be classified as a Type A (water-reducing) admixture,
a minimum water reduction of 5% must be obtained. Initial
and final time of setting must be no more than 1 h earlier and
not more than an 1.5 h later than the same concrete without
the admixture. Compressive strength requirements stated as
a percentage of reference are outlined at the various intervals
specified for testing. These are stated for both compressive
and flexural requirements. Drying shrinkage and freezingand-thawing resistance are also factors addressed for all
types of admixtures in ASTM C 494.
The requirements for compressive strength compared to a
control mixture allow no reduction of compressive or flexural strengths for all types except B and C.
In discussing the commercially available water-reducing
set-controlling admixtures, it is appropriate to consider five
classes of admixtures. Categorized by basic or primary
ingredients, they are as follows:
1. Lignosulfonic acids and their salts;
2. Hydroxylated polymers;
3. Hydroxylated carboxylic acids and their salts;
4. Sulfonated melamine or naphthalene formaldehyde
condensates; andE4-6 ACI EDUCATION BULLETIN
5. Polyether-polycarboxylates.
Persons involved in concrete construction should possess
a basic knowledge of proper use, application, benefits to
expect, and cautions to observe for each of these five classes.
Members of the first group, salts of lignosulfonic acids or
lignins, provide excellent water reduction and produce good
strength characteristics. Lignosulfonates tend to entrain air,
and can produce sticky, hard-to-finish concrete.
Hydroxylated polymer admixtures are widely used waterreducing admixtures. Some of the benefits associated with
these admixtures are:
1. Improved mobility of the concrete. Improved workability
and easier placement, reducing the incentive to add water;
2. May reduce segregation, particularly at higher slump
ranges;
3. May improve finished appearance and reduce stickiness in
finishing flat surfaces, even when used at increased dosages;
4. Does not entrain air and can be used at increased dosages without increasing air contents; and
5. May improve pumpability. This admixture, in a properly proportioned mixture, allows the concrete to be moved
with less pressure and provides improved lubrication.
Hydroxylated carboxylic acid-based admixtures, sometimes referred to as HC type admixtures, are designed to
reduce water also. Concrete containing HC admixtures is
mixed and placed with a higher water content than is the case
with other types of water-reducing admixtures. Some HC
admixtures promote rapid bleeding from the interior of the
concrete. This water must be removed from the surface and
the concrete revibrated to ensure proper density in the hardened
state. The benefits associated with this admixture type are
generally similar to those of the hydroxylated polymer
admixtures.
The fourth and fifth groups, sulfonated melamine or naphthalene formaldehyde condensates and polycarboxylates, are
discussed in Section 4.5.
4.2—Type A, water-reducing admixtures
The purpose of water-reducing admixtures is stated by
ACI Committee 212.3R as: “Water-reducing admixtures are
used to reduce the water requirement of the mixture for a
given slump, produce concrete of higher strength, obtain
specified strength at lower cement content, or increase the
slump of a given mixture without an increase in water content.” They also may improve the properties of concrete containing aggregates that are harsh, poorly graded, or both, or
may be used in concrete that may be placed under difficult
conditions. They are useful when placing concrete by means
of a pump or tremie.”
Typically, the use of Type A water-reducers will decrease
mixing water content by 5 to 12%, depending on the admixture, dosage, and other materials and proportions. Dosage
rates of water-reducing admixtures depend on the type and
amount of active ingredients in the admixture (that is, percent solids content). The dosage is based on the cementitious
materials content of the concrete mixture and is expressed as
milliliters per hundred kilograms (fluid ounces per hundred
pounds) of cementitious materials. Typically the dosage rate
of Type A water-reducers range from 130 to 390 mL per 100 kg
(2 to 6 fl oz. per 100 lb) of cementitious materials. Higher
dosages may result in excessive retardation of the concrete
setting time. Manufacturers recommended dosage rates
should be followed and trial batches with local materials
should be performed to determine the dosage rate for a given
concrete mixture. Usually, the primary ingredients of all
water-reducing admixtures are organic, which tend to retard
the time of setting of the concrete. This retardation may be
offset by small additions of chloride or nonchloride accelerating admixtures at the batch plant. Typically, Type A admixtures already contain some accelerators that offset this natural
retardation. Care should be taken to ensure that addition of
chloride does not exceed the ACI 318 limits for maximum
chloride-ion content in reinforced or prestressed concrete.
4.3—Type B, retarding, and Type D, water-reducing
and retarding admixtures
4.3.1 Conventional retarding admixtures—These two
types of admixtures are used for the same basic purpose: to
offset unwanted effects of high temperature, such as acceleration of set and reduction of 28-day compressive strength,
and to keep concrete workable during the entire placing and
consolidation period. Figure 1 indicates the relationship
between temperature and setting time of concrete and specifically indicates why retarding admixture formulations are
needed in warmer weather.
The benefits derived from retarding formulations include
the following:
1. Permits greater flexibility in extending the time of set
and the prevention of cold joints;
2. Facilitates finishing in hot weather; and
3. Permits full form deflection before initial set of concrete.
As with Type A admixtures, their dosage rates are based
on the amount of cementitious materials in the concrete mixture. While both Type B and Type D provide some waterreduction, Type D is more effective in achieving this goal.
The amount of retardation depends upon many factors
including: admixture concentration, dosage rate, concrete
proportions, and ambient and concrete temperatures.
Different sources and types of cement or different lots of
cements from the same source may require different amounts
Fig. 1—Relationship between temperature and setting time
of concrete.CHEMICAL ADMIXTURES FOR CONCRETE E4-7
of the admixture to obtain the desired results because of variations in chemical composition, fineness, or both. The effectiveness of the admixture seems to be related primarily to the
amount of tricalcium aluminate (C3A) and the alkali (Na
2O
and K2O) content of the cement.
The time at which the retarding admixture is introduced
into the concrete may affect the results. Allowing the cement
to become totally wet and delaying admixture addition until
all other materials are batched and mixed may result in
increased retardation and greater slump increase.
Increased retardation may also be obtained with a higher
dosage of the retarding admixture. When high dosages of
retarding admixture are used, however, rapid stiffening can
occur with some cements, resulting in severe slump loss and
difficulties in concrete placement, consolidation, and finishing.
4.3.2 Extended-set admixtures—Recent advances in
admixture technology have resulted in the development of
highly potent retarders called extended-set admixtures,
which are capable of stopping the hydration of portland
cement, thereby providing a means to control the hydration
and setting characteristics of concrete. The effectiveness of
extended-set admixtures has been attributed to their ability to
retard the reaction of all the major cement constituents,
unlike conventional retarding admixtures that only act upon
some of the cement constituents.
Extended-set admixtures are used in three primary applications: stabilization of concrete wash water, stabilization of
returned plastic concrete, and stabilization of freshly batched
concrete for long hauls. The use of extended-set admixtures
in stabilization of concrete wash water eliminates the dumping
of water that is used to wash out a ready-mixed concrete
truck drum while keeping the fins and inner drum clean. The
process is relatively simple and involves the addition of low
dosages of the extended-set admixture to the wash water to
control the hydration of concrete stuck to the fins and inside
the drum. The stabilized wash water may be included in the
mixing water for fresh concrete that is batched the next day
or after a weekend. The setting and strength development
characteristics of concrete are not adversely affected by the
use of stabilized wash water.
The use of extended-set admixtures to stabilize returned
unhardened concrete has made it possible to reuse such concrete during the same production day or the next day in lieu
of disposal. The dosage of extended-set admixture required
depends on several factors that include the ambient and concrete temperatures, the ingredients used in the manufacture
of the concrete, and the age of the concrete. Stabilized concrete is reused by batching fresh concrete on top of the stabilized concrete. In overnight applications, an accelerating
admixture may be used to reinitiate the hydration process
before adding fresh concrete. Increasingly, extended-set
admixtures are being used for long hauls and to maintain
slump and concrete temperature during transit, especially in
warm weather. For this application, the extended-set admixture is added during or immediately after batching, and the
required dosage is established based on the amount of retardation desired.
4.4—Type C, accelerating, and Type E,
water-reducing and accelerating admixtures
Accelerating admixtures are added to concrete to shorten
the setting time and accelerate the early strength development of concrete. Figure 1, which shows the relationship
between temperature and setting time of concrete, specifically indicates why accelerating admixture formulations are
needed.
Some widely used and effective chemicals that accelerate
the rate of hardening of concrete mixtures, including calcium
chloride, other chlorides, triethanolamine, silicates, fluorides, alkali hydroxide, nitrites, nitrates, formates, bromides,
and thiocyanates.
The earlier setting time and increased early strength gain
of concrete brought about by an accelerating admixture will
result in a number of benefits, including reduced bleeding,
earlier finishing, improved protection against early exposure
to freezing and thawing, earlier use of structure, and reduction of protection time to achieve a given quality. Accelerators do not act as anti-freeze agents; therefore, protection of
the concrete at early ages is required when freezing temperatures are expected.
Although calcium chloride is the most effective and economical accelerator for concrete, its potential to cause corrosion of reinforcing steel limits its use. ACI Committee 318
suggests that the water-soluble chloride-ion content should
be limited to the following levels for the conditions
described:
1. Prestressed concrete—0.06% by mass of cementitious
material; and
2. Reinforced concrete—0.15% by mass of cementitious
material.
Note that the amount of calcium chloride that may be used
is based on the cement content of the concrete mixture.
The following guidelines should be considered before
using calcium chloride or chloride-bearing admixture:
1. It should not be used in prestressed concrete because of
its potential for causing corrosion;
2. The presence of chloride ion has been associated with
corrosion of galvanized steel such as when this material is
used as permanent forms for roof decks;
3. Where sulfate-resisting concrete is required, calcium
chloride should not be used;
4. Calcium chloride should be avoided in reinforced concrete in a moist condition. In non-reinforced concrete, the
level of calcium chloride used should not exceed 2% by
weight of cementitious material;
5. Calcium chloride should be dissolved in a portion of
mixing water before batching because undissolved lumps
may later disfigure concrete surfaces;
6. Calcium chloride precipitates most air-entraining agents
so it must be dispensed separately into the mixture; and
7. Field experience and laboratory tests have demonstrated
that the use of uncoated aluminum conduit in reinforced concrete containing 1% or more of calcium chloride may lead to
sufficient corrosion of the aluminum to collapse the conduit
or crack the concrete.E4-8 ACI EDUCATION BULLETIN
Non-chloride accelerating admixtures containing salts of
formates, nitrates, nitrites, and thiocyanates are available
from admixture manufacturers. These nonchloride accelerators are effective for set acceleration and strength development: however, the degree of effectiveness of some of these
admixtures is dependent on the ambient temperature and
concrete temperature at the time of placement.
Some formulations will give protection against freezing to
concrete placed in sub-freezing ambient temperatures. These
non-chloride accelerating admixtures offer year-round versatility because they are available to be used for acceleration
purposes in cool weather and for sub-freezing protection.
The role water-reducing set-controlling admixtures play in
achieving control of concrete quality continues to grow as
the admixtures are improved. They are used in all types of
concrete construction to achieve a wide range of benefits.
4.5—High-range water-reducing admixtures
The primary difference between these admixtures and
conventional water-reducing admixtures is that high-range
water-reducing (HRWR) admixtures, often referred to as
superplasticizers, may reduce the water requirement by more
than 30%, without the side effect of excessive retardation.
By varying the dosage rate and the amount of mixing water,
an HRWR admixture can be used to produce:
1. Concrete of normal workability at a lower water-cementitious material (w/cm) ratio;
2. Highly flowable, nearly self-leveling concrete at the
same or lower w/cm as concrete of normal workability; and
3. A combination of the two; that is, concrete of moderately increased workability with a reduction in the w/cm.
When used for the purpose of producing flowing concrete,
HRWR admixtures facilitate concrete placement and consolidation.
HRWR admixtures should meet the requirements of ASTM C
494 for classification as Type F, High-Range Water-Reducing,
or Type G, High-Range Water-Reducing and Retarding,
admixtures. When used to produce flowing concrete, they
should also meet the requirements of ASTM C 1017 Type 1,
Plasticizing, or Type 2, Plasticizing and Retarding Admixtures. HRWR admixtures are organic products that typically
fall into three families based on ingredients:
1. Sulfonated melamine-formaldehyde condensate;
2. Sulfonated naphthalene-formaldehyde condensate; and
3. Polyether-polycarboxylates.
HRWR admixtures act in a manner similar to conventional
water-reducing admixtures, except that they are more efficient
at dispersing fine-grained materials such as cement, fly ash,
ground granulated blast-furnace slag, and silica fume. The
most widely used HRWR admixtures do not entrain air but
may alter the air-void system. Concrete containing HRWR
admixtures, however, may have adequate resistance to freezing and thawing even though the spacing factors may be
greater than 0.2 mm (0.008 in.). HRWR admixtures based on
polyether-polycarboxylate technology are different chemically and more effective than those based on sulfonated
melamine-formaldehyde and sulfonated naphthalene-formaldehyde condensates and, as a result, are typically added at
the batch plant. Polyether-polycarboxylate HRWRs also
retard less and develop strength faster compared to the other
HRWR formulations. Because of their increased efficiency,
polyether-polycarboxylate HRWRs are gaining widespread
acceptance, particularly in precast concrete applications and
in making self-consolidating concrete, a high-performance
concrete with high flowability that requires minimal or no
vibration for consolidation.
A characteristic of some HRWR admixtures is that their
slump-increasing effect is retained in concrete for only 30 to
60 min, by which time the concrete will revert to its original
slump. The amount of time that the concrete retains the
increased slump is dependent upon the type and quantity of
cement, the temperature of the concrete, the type of HRWR
admixture, the dosage rate used, the initial slump of the concrete, the mixing time, and the thoroughness of mixing.
Because of the limited workability time, HRWR admixtures
are typically added at the jobsite. With some HRWR admixtures, it is possible to redose the concrete to regain the
increased workability. Generally, the strength is increased
and the air content is decreased. HRWR admixtures that offer
extended slump life are also commercially available. These
HRWR admixtures are typically added at the batch plant.
HRWR admixtures can be used with conventional waterreducers or retarders to reduce slump loss and stickiness, especially in silica-fume concrete mixtures. Because a lower dosage of HRWR admixture may be required in such instances,
there may be some savings. These combinations of admixtures
may also cause unanticipated or excessive set retardation.
The strength of hardened concrete containing HRWR
admixtures is normally higher than that predicted by the
lower w/cm alone. As with conventional admixtures, this is
believed to be due to the dispersing effect of HRWR admixtures on the cement and other cementitious or pozzolanic
materials. Because the w/cm of mixtures containing HRWR
admixtures are typically low, shrinkage and permeability
may also be reduced and the overall durability of the concrete
may be increased.
A good summary of benefits and limitations for this class
of admixtures can be found in National Ready Mixed Concrete Association (NRMCA) Publication No. 158. Briefly
outlined are eight advantages and six limitations as follows:
POTENTIAL ADVANTAGES OF HRWR:
1. Significant water reduction;
2. Reduced cement contents;
3. Increased workability;
4. Reduced effort required for placement;
5. More effective use of cement;
6. More rapid rate of early strength development;
7. Increased long-term strength; and
8. Reduced permeability.
POTENTIAL DISADVANTAGES OF HRWR:
1. Additional admixture cost (the concrete in-place cost
may be reduced);
2. Slump loss greater than conventional concrete;
3. Modification of air-entraining admixture dosage;CHEMICAL ADMIXTURES FOR CONCRETE E4-9
4. Less responsive with some cement;
5. Mild discoloration of light-colored concrete; and
6. Air-void and color blemishes on exposed and formed
finishes.
Therefore, a fundamental knowledge regarding the action
of base materials will greatly assist in choosing the appropriate admixture. The choice of specific functional type will
vary with jobsite conditions.
4.6—Mid-range water-reducing admixtures
Water-reducing admixtures that provide moderate water
reduction without significantly delaying the setting characteristics of concrete are also available. Because these admixtures provide more water reduction than conventional
water-reducers but less water-reduction than high range waterreducers, they are referred to as mid-range water-reducing
admixtures. These admixtures can help reduce stickiness and
improve finishability and pumpability of concrete including
concrete containing silica fume, or manufactured or coarse
sand. Mid-range water-reducing admixtures are typically
used in a slump range of 125 to 200 mm (5 to 8 in.) and may
entrain additional air. Therefore, evaluations should be performed to establish air-entraining admixture dosage for a
desired air content.
CHAPTER 5—CORROSION-INHIBITING
ADMIXTURES
Reinforcing steel corrosion is a major concern with regard
to the durability of reinforced concrete structures. Each year,
numerous bridges and parking garage structures undergo
extensive rehabilitation to restore their structural integrity as
a result of corrosion damage. In addition to bridges and parking
structures, other reinforced concrete structures exposed to
chlorides in service are also at risk of corrosion attack. Chlorides are one of the causes of corrosion of steel in concrete.
They can be introduced into concrete from deicing salts that
are used in the winter months to melt snow or ice, from seawater, or from the concrete mixture ingredients.
There are several ways of combating chloride-induced
corrosion, one of which is the use of corrosion-inhibiting
admixtures. These admixtures are added to concrete during
batching and they protect embedded reinforcement by delaying
the onset of corrosion and also reducing the rate of corrosion
after initiation. There are several commercially available
inhibitors on the market. These include an inorganic formulation that contains calcium nitrite as the active ingredient
and organic formulations consisting of amines and esters. As
with all admixtures, the manufacturer’s recommendations
should be followed with regard to dosage.
CHAPTER 6—SHRINKAGE-REDUCING
ADMIXTURES
The loss of moisture from the concrete as it dries results in
a volume contraction termed drying shrinkage. Drying
shrinkage tends to be undesirable when it leads to cracking
due to either internal or external restraint, curling of floor
slabs, and excessive loss of prestress in prestressed concrete
applications. The magnitude of drying shrinkage can be
reduced by minimizing the unit water content of a concrete
mixture, and using good-quality aggregates and the largest
coarse-aggregate size and content consistent with the particular application. Drying shrinkage can also be reduced significantly by using shrinkage-reducing admixtures. These
are organic-based formulations that reduce the surface tension of water in the capillary pores of concrete, thereby
reducing the tension forces within the concrete matrix that
lead to drying shrinkage. Manufacturer’s recommendations
should be followed with regard to dosage and suitability for
use in freezing-and-thawing environments.
CHAPTER 7—ADMIXTURES FOR CONTROLLING
ALKALI-SILICA REACTIVITY
Alkali-silica reactivity (ASR) is a reaction between soluble
alkalies in concrete and reactive silica in certain types of
aggregate that results in the formation of a water-absorptive
gel that expands and fractures the concrete. The reaction is
typically slow and is dependent on the total amount of alkali
present in the concrete, the reactivity of the aggregates and
the availability of moisture. ASR can be mitigated by using
low-alkali cement, sufficient amounts of pozzolans or
ground granulated blast-furnace slag, and if economically
feasible, non-reactive aggregates. Alternately, ASR can be
mitigated by using lithium-based chemical admixtures. Lithium
compounds are effective in reducing ASR because they form
a nonabsorptive gel with the reactive silica in the aggregates.
The high cost of lithium-based admixtures, however, has
greatly limited their use to date.
CHAPTER 8—ADMIXTURES FOR UNDERWATER
CONCRETING
Placing concrete underwater can be particularly challenging
because of the potential for washout of the cement and fines
from the mixture reducing the strength and integrity of the
in-place concrete. Although placement techniques, such as
tremies, have been used successfully to place concrete
underwater, there are situations where enhanced cohesiveness of the concrete mixture is required, necessitating the use
of an antiwashout or viscosity-modifying admixture (VMA).
Some of these admixtures are formulated from either cellulose ether or whelan gum, and they work simply by binding
excess water in the concrete mixture, thereby increasing the
cohesiveness and viscosity of the concrete. The overall benefit is a reduction in washout of cement and fines, resistance
to dilution with water as the mixture is placed, and preservation of the integrity of the in-place concrete. Proper placement techniques should be followed even with concrete
treated with an antiwashout admixture.
CHAPTER 9—EFFECTIVENESS OF ADMIXTURES
The effectiveness of any admixture will vary depending on
its concentration in the concrete and the effect of the various
constituents of the concrete mixture, particularly the cement.
Each class of admixture is defined by its primary function. It
may have one or more secondary functions, however, and its
use may affect, positively or negatively, concrete properties
other than those desired. Therefore, adequate testing should
be performed to determine the effects of an admixture on the
plastic and hardened properties of concrete such as slump,E4-10 ACI EDUCATION BULLETIN
air content, time of setting, rate of slump loss or relationship
of slump and time, and strength development. In addition,
testing should be performed to determine the effect of the
admixture on other concrete properties that may be of interest,
for example, drying shrinkage, modulus of elasticity, or
permeability. The final decision as to the use of any admixture and the brand, class, or type, depends on its ability to
meet or enhance specific concrete performance needs.
Many of the improvements can be achieved by proper selection and application of specific admixtures. The selection process should focus on the functional qualities required by
structural demands, architectural requirements, and contractor
needs.
Whatever the approach, be it a single water-reducing
admixture or a combination approach, the use of admixtures
can be beneficial. Admixtures provide additional means of
controlling the quality of concrete by modifying some of its
properties, however, they cannot correct for poor-quality
materials, improper proportioning of the concrete, and inappropriate placement procedures.
CHAPTER 10—ADMIXTURE DISPENSERS
10.1—Industry requirements and dispensing
methods
The subject of liquid admixture dispensers covers the
entire process from storage at the producer’s plant to introduction into the concrete batch before discharge. Their operation may be separated into four functions:
1. The dispenser transports the admixture from storage to
the batch;
2. The dispenser measures the quantity of admixture
required;
3. The dispenser provides verification of the volume dispensed; and
4. The dispenser injects the admixture into or onto the
batch.
These are the basic functions. In practice, some of the
functions may be combined, for example, measurement and
verification. For reliability, the functions may be interlocked
to prevent false or inaccurate batching of the admixture and
to dispense the admixture in the optimal sequence in the concrete production process.
The various systems of dispensing, their applications to
specific types of concrete production, and the practical limitations of their operation and accuracy are the subjects that
will be discussed in this section. They are important because
the successful use of any chemical admixture stands on accurate measurement and correct addition of the material to the
concrete batch.
10.2—Liquid admixture dispensing methods
The three most commonly used dispenser systems at
ready-mix plants are Systems 1, 2, and 3.
System 1—System 1 is a fully automatic dispenser system
for interfacing with the batch plant’s automation. It is
designed for the ready-mix plant operation, which already
has admixture dispensing control capabilities built into its
computerized batch control panel. These systems are capable
of controlling multiple admixtures at the same time with various interlocks for system compliance to regulatory requirements.
The basic components of this dispenser system includes:
• A metering device for volumetric measurement;
• A measuring unit for visual verification of admixture
being dispensing;
• Air-/electric-operated valves for automatic control of the
flow of admixture in and out of the measuring unit; and
• A storage tank with fill adapters for connection to the
admixture pump.
An interface sub-junction box and cabling for connection
to the computerized batch control panel and dispenser system is used. This system may come preassembled in its own
protective enclosure or may be assembled at the plant in a
protected area.
System 2—System 2 is designed for the ready-mix plant
operation that does not have admixture dispenser control
capabilities built into its batch panel automation and, therefore, will require a stand-alone admixture batch-control unit
to automatically and simultaneously control the dispensing
of multiple admixtures. These units often have the capability
of being remote started by a signal provided through the
plant’s automation system.
The basic components of this dispenser system include:
• A metering device for volumetric measurement;
• A measuring unit for visual verification of admixture
being dispensing;
• Air-operated valves for automatic control of the flow of
admixture in and out of the measuring unit;
• A storage tank with fill adapters for connection to the
admixture pump; and
• A stand-alone control unit.
This system may come preassembled in its own protective
enclosure or may be assembled at the plant in a protected area.
System 3—System 3 is a manual dispenser system for
ready-mix plants that are not automated. The operator controls the quantity of admixture requirements by means of a
manual three-position pneumatic valve and visually verifies
the correct amount of admixture before dispensing.
The basic components of this dispenser system includes:
• A measuring unit for manual verification of the amount
of admixture being dispensed;
• Air-operated valves for manual control of the flow of
admixture in and out of the measuring unit;
• A storage tank with fill adapters for connection to a
pump; and
• A three-position pneumatic valve and miscellaneous
fittings that will be located in the batch control room of
the plant.
This system in most cases is assembled at the plant in a
protected area.
10.3—Accuracy requirements
Standards of operation for admixture dispensers are specified
by scientific groups, concrete producers’ trade organizations, and government agencies with authority over concrete
production contracts.CHEMICAL ADMIXTURES FOR CONCRETE E4-11
The NRMCA and ASTM C 94 specify a batching tolerance of 3% of the required volume or the minimum recommended dosage rate per unit of cement, whichever is greater.
(1.3.5.3) ACI 212.1R recommends an accuracy of 3% of the
required volume, or 15 mL (1/2 fl oz.), whichever is greater.
10.4—Application considerations and
compatibility
Admixture dispensing systems are complex, using parts
made of different materials. Therefore, the admixture dispensed through this system should be chemically and operationally compatible with these materials.
The basic rules of application and injection are that the
admixtures should not be mixed together. This problem is
handled in several ways:
1. Injecting admixtures into the waterline at separate
points at least 3 ft apart and only when the water is running;
2. Placing the air-entraining admixture on the fine aggregate and injecting the water-reducer into the stationary or
truck mixer along with water; and
3. Sequentially discharging the admixtures. The air-entraining
admixture is discharged first; and the water-reducer, or combination of water-reducers, is discharged later.
Recommended injection sequences for various admixtures
are as follows:
Generally, it is not necessary to distribute the admixtures
throughout the entire water batch to get good dispersion in
the mixture.
There is evidence that the timing of injection of waterreducing retarders has important effects on the length of
retardation and, to a lesser extent, the slump and air content.
A delay of 1 to 5 min between the water addition and dispersing of the retarder may result in a three-fold increase in set
retardation time with lignin and polymer retarding admixtures, a one and one-half to two-fold increase in entrained
air, and lesser increases in slump.
10.5—Dispensers for high-range water-reducing
admixtures
Some high-range water-reducing admixtures have a shortlived effect on the slump of concrete. Therefore, it is
expected that these materials will be dispensed as close to
placing time as possible. For ready-mix operations, this
might mean the use of a truck-mounted dispenser in the form
of a calibrated storage tank. The tank will be charged with
the admixture at the same time the concrete is loaded. The
user can request an increase in slump by injection of a
HRWR admixture, and the driver will dispense the required
amount into the turning drum. The volume dispensed will
be recorded on the delivery ticket. The injection should be
performed under pressure through a spray nozzle to thoroughly
disperse the admixture into the drum. Field dispensers,
consisting of a measuring unit and pump, can be used at the
job site.
10.6—Dispenser maintenance
It is incumbent on the concrete producer to take as great an
interest in the admixture dispensing equipment as in the rest
of the batch plant. Operating personnel should be trained in
the proper operation, winterization, maintenance, and calibration of admixture dispensers. Spare parts should be
retained as needed for immediate repairs. Regular cleaning
and calibration of the systems should be performed by qualified
internal personnel or by the admixture suppliers’ service
representative. Admixtures have too powerful an influence
on the quality of the concrete produced for their dispensing
to be given cursory attention.
CHAPTER 11—CONCLUSION
Air-entraining and other chemical admixtures have
become a very useful and integral component of concrete.
Admixtures are not a panacea for every ill the concrete producer, architect, engineer, owner, or contractor faces when
dealing with the many variables of concrete, but they do offer
significant improvements in both the plastic and hardened state
to all concrete. Continued research and development will
provide additional reliability, economy, and performance for
the next generation of quality concrete.
CHAPTER 12—LIST OF RELEVANT ASTM
STANDARDS
C 94 Ready-Mixed Concrete
C 138 Unit Weight, Yield, and Air Content (Gravimetric)
of Concrete
C 143 Slump of Hydraulic-Cement Concrete
C 150 Portland Cement
C 173 Air Content of Freshly Mixed Concrete by the
Volumetric Method
C 231 Air Content of Freshly Mixed Concrete by the
Pressure Method
C 260 Air-Entraining Admixtures
C 494 Chemical Admixtures
C 869 Foaming Agents Used in Making Preformed
Foam for Cellular Concrete
C 937 Grout Fluidifier for Preplaced Aggregate Concrete
C 979 Pigments for Integrally Colored Concrete
C 1012 Length Change of Hydraulic-Cement Mortars
Exposed to a Sulfate Solution
C 1017 Chemical Admixtures for Use in Producing Flowing
Concrete
C 1144 Admixtures for Shotcrete
C 1157 Hydraulic Cements
D 98 Calcium Chloride
ADMIXTURES INJECTION SEQUENCE
Air-entraining admixture With early water or on sand
Water-reducing admixtures Follow air-entraining solution
Accelerating admixtures
With water, do not mix with air-entraining
admixture
High-range water-reducing
admixtures
Immediately before discharge for placement
or with the last portion of the water at the
batch plant
Polycarboxylate high-range
water-reducing admixtures
With early water or with the last portion of the
water at the batch plantE4-12 ACI EDUCATION BULLETIN
CHAPTER 13—GLOSSARY
Admixture—A material other than water, aggregates,
hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed,
setting, or hardened properties and that is added to the batch
before or during its mixing.
Admixture, accelerating—An admixture that causes an
increase in the rate of hydration of the hydraulic cement, and
thus, shortens the time of setting, increases the rate of
strength development, or both.
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, retarding—An admixture that causes a
decrease in the rate of hydration of the hydraulic cement and
lengthens the time of setting.
Admixture, water-reducing—An admixture that either
increases slump of freshly mixed mortar or concrete without
increasing water content or maintains slump with a reduced
amount of water, the effect being due to factors other than air
entrainment.
Admixture, water-reducing high-range—A waterreducing admixture capable of producing large water reduction
or great flowability without causing undue set retardation or
entrainment of air in mortar or concrete.
Aggregate, reactive—Aggregate containing substances
capable of reacting chemically with the products of solution
or hydration of the portland cement in concrete or mortar
under ordinary conditions of exposure, resulting in some
cases in harmful expansion, cracking, or staining.
Air, entrained—Microscopic air bubbles intentionally
incorporated in mortar or concrete during mixing, usually
by use of a surface-active agent; typically between 10 and
1000 µm in diameter and spherical or nearly so.
Air, entrapped—Air voids in concrete that are not purposely entrained and are significantly larger and less useful
than those of entrained air, 1 mm in diameter or larger in size.
Air content—The total volume of air voids in cement
paste, mortar, or concrete, exclusive of pore space in aggregate
particles, usually expressed as a percentage of volume of the
paste, mortar, or concrete.
Alkali—Salts of alkali metals, principally sodium and
potassium, specifically sodium and potassium occurring in
constituents of concrete and mortar, usually expressed in
chemical analysis as the oxides Na
2O and K2O.
Alkali-aggregate reaction—Chemical reaction in either
mortar or concrete between alkalies (sodium and potassium)
from portland cement or other sources and certain constituents
of some aggregates, under certain conditions, deleterious
expansion of concrete or mortar may result.
Alkali-carbonate reaction—The reaction between the
alkalies (sodium and potassium) in portland cement and certain
carbonate rocks, particularly calcitic dolomite and dolomitic
limestones, present in some aggregates, the products of the
reaction may cause abnormal expansion and cracking of
concrete in service.
Alkali-silica reaction—The reaction between the alkalies
(sodium and potassium) in portland cement and certain siliceous rocks or minerals, such as opaline chert, strained
quartz and acidic volcanic glass, present in some aggregates;
the products of the reaction may cause abnormal expansion
and cracking of concrete in service.
Calcium chloride—A crystalline solid, CaCl
2
; in various
technical grades, used as a drying agent, as an accelerator for
fresh concrete, a deicing chemical, and for other purposes.
Cement, portland—A hydraulic cement produced by
pulverizing portland-cement clinker and usually containing
calcium sulfate.
Cementitious—Having cementing properties.
Sulfate attack—Either a chemical or physical reaction or
both that occurs between sulfates usually in soil or groundwater and concrete or mortar; the chemical reaction is primarily
with calcium aluminate hydrates in the cement-paste matrix,
often causing deterioration.
Sulfate resistance—Ability of concrete or mortar to withstand sulfate attack.
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