This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles

for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Designation: C94/C94M − 21a

Standard Specification for

Ready-Mixed Concrete1

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This standard is issued under the fixed designation C94/C94M; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Scope* (Warning—Fresh hydraulic cementitious mixtures are caustic

1.1 This specification covers ready-mixed concrete as de- and may cause chemical burns to skin and tissue upon
fined in 3.2.2 (Note 1). Requirements for quality of ready- prolonged use.2)
mixed concrete shall be either as stated in this specification or 1.6 This international standard was developed in accor-
as ordered by the purchaser. When the purchaser’s dance with internationally recognized principles on standard-
requirements, as stated in the order, differ from those in this ization established in the Decision on Principles for the
specification, the purchaser’s requirements shall govern. This Development of International Standards, Guides and Recom-
specification does not cover the placement, consolidation, mendations issued by the World Trade Organization Technical
curing, or protection of the concrete after delivery to the Barriers to Trade (TBT) Committee.
purchaser. 2. Referenced Documents
NOTE 1—Concrete produced by volumetric batching and continuous 2.1 ASTM Standards:3
mixing is covered in Specification C685/C685M. Fiber-reinforced con- C31/C31M Practice for Making and Curing Concrete Test
crete is covered in Specification C1116/C1116M.
Specimens in the Field
1.2 As used throughout this specification the manufacturer C33/C33M Specification for Concrete Aggregates
produces ready-mixed concrete. The purchaser buys ready- C39/C39M Test Method for Compressive Strength of Cylin-
mixed concrete. drical Concrete Specimens
1.3 The values stated in either SI units, shown in brackets, C125 Terminology Relating to Concrete and Concrete Ag-
or inch-pound units are to be regarded separately as standard. gregates
The values stated in each system may not be exact equivalents; C138/C138M Test Method for Density (Unit Weight), Yield,
therefore, each system shall be used independently of the other. and Air Content (Gravimetric) of Concrete
Combining values from the two systems may result in non- C143/C143M Test Method for Slump of Hydraulic-Cement
conformance with the standard. Concrete
C150/C150M Specification for Portland Cement
1.4 The text of this specification references notes and
C172/C172M Practice for Sampling Freshly Mixed Con-
footnotes that provide explanatory material. These notes and
crete
footnotes (excluding those in tables and figures) shall not be
C173/C173M Test Method for Air Content of Freshly Mixed
considered as requirements of the specification.
Concrete by the Volumetric Method
1.5 This standard does not purport to address all of the C231/C231M Test Method for Air Content of Freshly Mixed
safety concerns, if any, associated with its use. It is the Concrete by the Pressure Method
responsibility of the user of this standard to establish appro- C260/C260M Specification for Air-Entraining Admixtures
priate safety, health, and environmental practices and deter- for Concrete
mine the applicability of regulatory limitations prior to use. C330/C330M Specification for Lightweight Aggregates for
Structural Concrete

1 2
This specification is under the jurisdiction of ASTM Committee C09 on See Section on Safety Precautions, Manual of Aggregate and Concrete Testing,
Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 04.02.
3
C09.40 on Ready-Mixed Concrete. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2021. Published July 2021. Originally approved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
in 1933. Last previous edition approved in 2021 as C94/C94M–21. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
C0094_C0094M-21A. the ASTM website.

*A Summary of Changes section appears at the end of this standard

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 C94/C94M − 21a
C494/C494M Specification for Chemical Admixtures for 3.2.2 concrete, ready-mixed, n—concrete manufactured and
Concrete delivered to a purchaser in a fresh state.
C567/C567M Test Method for Determining Density of 3.2.3 concrete, shrink-mixed, n—ready-mixed concrete par-
Structural Lightweight Concrete tially mixed in a stationary mixer with mixing completed in a
C595/C595M Specification for Blended Hydraulic Cements truck mixer.
C618 Specification for Coal Fly Ash and Raw or Calcined
Natural Pozzolan for Use in Concrete 3.2.4 concrete, truck-mixed, n—ready-mixed concrete com-
C637 Specification for Aggregates for Radiation-Shielding pletely mixed in a truck mixer.
Concrete 3.2.5 water, target batch, n—quantity of water to be added
C685/C685M Specification for Concrete Made by Volumet- to the batch through the water measuring system after com-
ric Batching and Continuous Mixing pensating for the quantity of ice, if used, surface moisture on
C989/C989M Specification for Slag Cement for Use in the aggregates and water in the admixtures, when applicable,
Concrete and Mortars and by subtracting a quantity of water that is anticipated to be
C1017/C1017M Specification for Chemical Admixtures for added at the job site or in transit to adjust slump or slump flow
Use in Producing Flowing Concrete of the concrete batch.
C1064/C1064M Test Method for Temperature of Freshly
Mixed Hydraulic-Cement Concrete 4. Basis of Purchase
C1077 Practice for Agencies Testing Concrete and Concrete
Aggregates for Use in Construction and Criteria for 4.1 The basis of purchase shall be a cubic yard or cubic
Testing Agency Evaluation metre of fresh concrete as discharged from the transportation
C1116/C1116M Specification for Fiber-Reinforced Concrete unit.
C1157/C1157M Performance Specification for Hydraulic 4.2 The volume of fresh concrete in a given batch shall be
Cement determined from the total mass of the batch divided by the
C1240 Specification for Silica Fume Used in Cementitious density of the concrete. The total mass of the batch shall be
Mixtures determined as the net mass of the concrete in the batch as
C1602/C1602M Specification for Mixing Water Used in the delivered, including the total mixing water as defined in 9.3.
Production of Hydraulic Cement Concrete The density shall be determined in accordance with Test
C1611/C1611M Test Method for Slump Flow of Self- Method C138/C138M. The yield shall be determined as the
Consolidating Concrete average of at least three measurements, one from each of three
C1798/C1798M Specification for Returned Fresh Concrete different transportation units sampled in accordance with
for Use in a New Batch of Ready-Mixed Concrete Practice C172/C172M.
2.2 ACI Documents:4
ACI 211.1 Standard Practice for Selecting Proportions for NOTE 2—It should be understood that the volume of hardened concrete
may be, or appear to be, less than expected due to waste and spillage,
Normal, Heavyweight, and Mass Concrete over-excavation, spreading forms, some loss of entrained air, or settlement
ACI 211.2 Standard Practice for Selecting Proportions for of wet mixtures, none of which is the responsibility of the producer.
Structural Lightweight Concrete
ACI 301 Standard Specifications for Structural Concrete 5. Materials
ACI 305R Guide to Hot Weather Concreting
ACI 306R Guide to Cold Weather Concreting 5.1 In the absence of designated applicable material

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ACI 318 Building Code Requirements for Structural Con- specifications, the following material specifications shall be
crete and Commentary used:
2.3 Other Documents:5 5.2 Cementitious Materials:
NIST 105-1 National Institute of Standards and Technology 5.2.1 Hydraulic Cement—Hydraulic cement shall conform
Handbook to Specification C150/C150M, Specification C595/C595M, or
Specification C1157/C1157M.
3. Terminology
5.2.2 Supplementary Cementitious Materials—Coal fly ash
3.1 Definitions—The terms used in this specification are or natural pozzolans shall conform to Specification C618. Slag
defined in Terminology C125. cement shall conform to Specification C989/C989M. Silica
3.2 Definitions of Terms Specific to This Standard: fume shall conform to Specification C1240.
3.2.1 concrete, central-mixed, n—ready-mixed concrete 5.3 Aggregates—Normal weight aggregates shall conform
mixed completely in a stationary mixer. to Specification C33/C33M. Lightweight aggregates shall con-
form to Specification C330/C330M and heavyweight aggre-
4
Available from American Concrete Institute (ACI), P.O. Box 9094, Farmington gates shall conform to Specification C637.
Hills, MI 48333-9094, http://www.concrete.org.
5
NIST Handbook 105-1 (revised 1990), “Specifications and Tolerances for
5.4 Water—Water shall conform to Specification C1602/
Reference Standards and Field Standard Weights and Measures-1. Specifications C1602M.
and Tolerances for Field Standard Weights (NIST Class F),” National Institute of
Standards and Technology., U.S. Dept. of Commerce, http://www.nist.gov/pml/ 5.5 Air-Entraining Admixtures—Air-entraining admixtures
wmd/upload/105-1.pdf. shall conform to Specification C260/C260M (Note 3).

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 C94/C94M − 21a
5.6 Chemical Admixtures—Chemical admixtures shall con- ments for this exposure are consistent with those for Exposure Classes F2
form to Specification C494/C494M or C1017/C1017M as and F3 of ACI 318.
applicable (Note 3). 6.1.5 Which of Options A, B, or C shall be used as a basis
NOTE 3—In any given instance, the required dosage of air-entraining, for determining the proportions of the concrete to produce the
accelerating, and retarding admixtures may vary. Therefore, a range of required quality,
dosages should be allowed, which will permit obtaining the desired effect.
NOTE 4—Interchanging kinds, characteristics, types, classes, or grades 6.1.6 When lightweight concrete is specified, the equilib-
of the materials permitted in ready-mixed concrete may produce concrete rium density,
of different properties.
NOTE 7—The density of fresh concrete is the only measurable density
5.7 Returned Fresh Concrete—Returned fresh concrete, of lightweight concrete at the time of delivery. The density of fresh
when permitted by the purchaser, shall conform to Specifica- concrete is always higher than the equilibrium or oven-dry density.
tion C1798/C1798M. Therefore, for acceptance of lightweight concrete based on density at the
time of delivery, a relationship between the equilibrium density and
NOTE 5—Specification C1798/C1798M provides requirements for density of fresh concrete needs to be established. Definitions of, and
using, measuring, and reporting returned fresh concrete. These require- methods for determining or calculating equilibrium and oven-dry density,
ments are in addition to those stated herein. The purchaser may further are covered by Test Method C567/C567M.
clarify which concrete within an order, such as specific mixtures or
applications, may incorporate returned fresh concrete. 6.1.7 When high-density or heavyweight concrete is
specified, the density of fresh concrete, and
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6. Ordering Information
NOTE 8—High-density or heavyweight concrete typically contains
6.1 In the absence of designated applicable general aggregate with a relative density of 3.3 or greater conforming to
specifications, the purchaser’s order shall include the follow- Specification C637. This concrete is used for radiation shielding or other
ing: applications where higher density is required by design. For acceptance of
density at the time of delivery, a relationship between the fresh density and
6.1.1 Designated size, or sizes, of coarse aggregate, the density of hardened concrete required by design should be established.
6.1.2 Slump, or slumps, desired at the point of delivery (see
Section 7 for acceptable tolerances), 6.1.8 If desired, any of the optional requirements of Table 2
6.1.3 Slump flow, or flows, desired at the point of delivery in Specification C1602/C1602M.
(see Section 7 for acceptable tolerances), 6.1.9 Purchaser shall state any drum revolution limit as to
6.1.4 Total air content at the point of delivery for concrete when the concrete discharge must begin. If no drum revolution
that will be exposed to cycles of freezing and thawing or limit is stated by purchaser, the manufacturer shall determine
anticipated exposure of the concrete (see Section 8 for sam- and communicate the limit to the purchaser prior to delivery.
pling for air content tests and tolerances). 6.1.10 Purchaser shall state a time limit from the start of
mixing defined in 12.3 or 12.5 to when the concrete discharge
NOTE 6—Table 1 provides total air contents for concrete that vary by must be completed. If no time limit is stated by purchaser, the
exposure condition and aggregate size. Total air contents less than those
shown in Table 1 may be specified or used for concrete that is not subject manufacturer shall establish and communicate the limit to the
to freezing and thawing. This may be done to improve workability and purchaser prior to delivery. The time limit to complete dis-
cohesiveness, reduce the rate of bleeding, reduce the water content for a charge shall be stated on the delivery ticket in accordance with
given consistency, or achieve required lightweight concrete density. 14.1.14.
Specified total air contents higher than those shown in Table 1 may reduce
strength without any further improvement of durability. NOTE 9—This specification previously included a 1 1⁄2 h time limit to
Exposure conditions for freezing and thawing environments in Table 1 end of discharge since its original publication in 1935. There are many
correspond to the following: options available to the manufacturer to provide the required quality of
Moderate Exposure—Concrete exposed to freeze-thaw cycles but not concrete with end of discharge limits beyond 1 1⁄2 h or less than 1 1⁄2 h. The
in contact with the ground or with limited exposure to water, limiting the purchaser should consult with the manufacturer for available options to
ability to cause saturation of a portion of the concrete prior to freezing. establish a time limit to end of discharge prior to or at the time concrete
The concrete shall not receive deicing salts or other aggressive chemicals. is ordered. Selection of a time limit to end of discharge should consider
Examples include: exterior beams, columns, walls, girders, footings below ambient conditions, types of cementitious materials and admixtures used,
the frost line, or elevated slabs where application of deicing salt is not placement procedures, and projected transportation time between the
anticipated. The air content requirements for this exposure are consistent batch plant and the point of delivery.
with those for Exposure Class F1 of ACI 318.
Severe Exposure—Concrete exposed to freeze-thaw cycles while in 6.2 If a project specification applies, the order shall include
contact with the ground or with frequent exposure to water, potentially applicable requirements for the concrete to be produced in
causing saturation of a portion of the concrete prior to freezing. The compliance with the specification.
concrete may receive deicing chemicals or other aggressive chemicals.
Examples include: pavements, bridge decks, curbs, gutters, sidewalks, 6.3 If the type, kind, or class of cementitious materials in
canal linings, or exterior water tanks or sumps. The air content require- 5.2.1 and 5.2.2 are not designated by the purchaser, it is

TABLE 1 Total Air Content for Air-Entrained Concrete Exposed to Cycles of Freezing and Thawing
Total Air Content, %
Exposure Nominal Maximum Sizes of Aggregate, mm [in.]
Condition 9.5 [3⁄8 ] 12.5 [1⁄2 ] 19.0 [3⁄4 ] 25.0 [1] 37.5 [11⁄2 ] 50.0 [2] 75.0 [3]
(See Note 6)
Moderate 6.0 5.5 5.0 4.5 4.5 4.0 3.5
Severe 7.5 7.0 6.0 6.0 5.5 5.0 4.5

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 C94/C94M − 21a
permitted to use cementitious materials in concrete mixtures 6.6.1 When the purchaser requires the manufacturer to
that will satisfy the concrete properties and other requirements assume responsibility for the selection of the proportions for
of the purchaser as ordered. the concrete mixture with the minimum allowable cement
6.4 Option A: content specified (Note 11), the purchaser shall also specify the
6.4.1 When the purchaser requires the manufacturer to following:
assume full responsibility for the selection of the proportions 6.6.1.1 Required compressive strength as determined on
for the concrete mixture (Note 10), the purchaser shall also samples taken from the transportation unit at the point of
specify the following: discharge evaluated in accordance with Section 18. The pur-
chaser shall specify the requirements for strength in terms of
6.4.1.1 Requirements for compressive strength as deter-
tests of standard specimens cured under standard laboratory
mined on samples taken from the transportation unit at the
conditions for moist curing (see Section 18). Unless otherwise
point of discharge evaluated in accordance with Section 18.
specified the age at test shall be 28 days.
The purchaser shall specify the requirements in terms of the
6.6.1.2 Minimum cement content in kilograms per cubic
compressive strength of standard specimens cured under stan-
metre [pounds per cubic yard] of concrete.
dard laboratory conditions for moist curing (see Section 18).
6.6.1.3 If admixtures are required, the type, name, and
Unless otherwise specified the age at test shall be 28 days.
dosage to be used. The cement content shall not be reduced
NOTE 10—The purchaser, in selecting requirements for which he when admixtures are used.
assumes responsibility should give consideration to requirements for
workability, placeability, durability, surface texture, and density, in addi- NOTE 11—Option C can be distinctive and useful only if the designated
tion to those for structural design. The purchaser is referred to Standard minimum cement content is at about the same level that would ordinarily
Practice ACI 211.1 and Standard Practice ACI 211.2 for the selection of be required for the strength, aggregate size, and slump or slump flow
proportions that will result in concrete suitable for various types of specified. At the same time, it must be an amount that will be sufficient to
structures and conditions of exposure. The water-cement ratio of most ensure durability under expected service conditions, as well as satisfactory
structural lightweight concretes cannot be determined with sufficient surface texture and density, in the event specified strength is attained with
accuracy for use as a specification basis. it. For additional information refer to Standard Practice ACI 211.1 and
Standard Practice 211.2 referred to in Note 10.
6.4.2 At the request of the purchaser, the manufacturer shall,
prior to the actual delivery of the concrete, furnish a statement 6.6.2 At the request of the purchaser, the manufacturer shall,
to the purchaser, giving the dry masses of cement and saturated prior to the actual delivery of the concrete, furnish a statement
surface-dry-masses of fine and coarse aggregate and quantities, to the purchaser, giving the dry masses of cement and saturated
type, and name of admixtures (if any) and of water per cubic surface-dry masses of fine and coarse aggregate and quantities,
yard or cubic metre of concrete that will be used in the type, and name of admixture (if any) and of water per cubic
manufacture of each class of concrete ordered by the purchaser. yard or cubic metre of concrete that will be used in the
The manufacturer shall also furnish evidence satisfactory to the manufacture of each class of concrete ordered by the purchaser.
purchaser that the materials to be used and proportions selected He shall also furnish evidence satisfactory to the purchaser that
will produce concrete of the quality specified. the materials to be used and proportions selected will produce
concrete of the quality specified. Whatever strengths are
6.5 Option B: attained the quantity of cement used shall not be less than the
6.5.1 When the purchaser assumes responsibility for the minimum specified.
proportioning of the concrete mixture, he shall also specify the
6.7 The proportions arrived at by Options A, B, or C for
following:
each class of concrete and approved for use in a project shall
6.5.1.1 Cement content in kilograms per cubic metre
be assigned a designation to facilitate identification of each
[pounds per cubic yard] of concrete,
concrete mixture delivered to the project. This is the designa-
6.5.1.2 Maximum allowable water content in litres per cubic
tion required in 14.1.7 and supplies information on concrete
metre [gallons per cubic yard] of concrete, including surface
proportions when they are not given separately on each
moisture on the aggregates, but excluding water of absorption
delivery ticket as outlined in 14.2. A certified copy of all
(Note 10), and
proportions as established in Options A, B, or C shall be on file
6.5.1.3 If admixtures are required, the type, name, and at the batch plant.
dosage to be used. The cement content shall not be reduced
when admixtures are used under this option without the written 6.8 The purchaser shall ensure that the manufacturer is
approval of the purchaser. provided copies of all reports of tests performed on concrete
6.5.2 At the request of the purchaser, the manufacturer shall, samples taken to determine compliance with specification
prior to the actual delivery of the concrete, furnish a statement requirements. Reports shall be provided on a timely basis.
to the purchaser giving the sources, densities, and sieve 6.9 The manufacturer shall obtain the purchaser’s permis-
analyses of the aggregates and the dry masses of cement and sion to incorporate returned fresh concrete.
saturated-surface-dry masses of fine and coarse aggregate and
quantities, type and name of admixture (if any) and of water 7. Slump or Slump Flow
per cubic yard or cubic metre of concrete that will be used in 7.1 Unless other tolerances are indicated by the purchaser,
the manufacture of each class of concrete ordered by the the following shall apply.
purchaser. 7.1.1 When slump is stated as a “maximum” or “not to
6.6 Option C: exceed” requirement:
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 C94/C94M − 21a

Tolerances for “Maximum” or “Not to Exceed” Slumps NOTE 12—Acceptance sampling and testing in accordance with Practice
C172/C172M is not obviated by this provision. Increasing the air content
For Slump of: Tolerance may increase the slump or slump flow.

75 mm [3 in.] or less +0 and –40 mm [11⁄2 in.]

More than 75 mm [3 in.] +0 and –65 mm [21⁄2 in.] 9. Measuring Materials
7.1.1.1 The maximum or not to exceed slump provision 9.1 Except as otherwise specifically permitted, cementitious
shall be used only if a job site water addition is permitted by materials shall be measured by mass. When supplementary
the specification in accordance with 12.7. cementitious materials are used in the concrete mixtures, the
7.1.2 When slump is stated as a target or nominal slump: cumulative mass is permitted to be measured with hydraulic
Tolerances for Target or Nominal Slumps
cement, but in a batch hopper and on a scale which is separate
and distinct from those used for other materials. The mass of
For Slump of: Tolerance the hydraulic cement shall be measured before supplementary
50 mm [2 in.] and less ±15 mm [1⁄2 in.]
cementitious materials. When the quantity of cementitious
More than 50 to 100 mm [2 through 4 in.] ±25 mm [1 in.] material exceeds 30 % of the full capacity of the scale, the
More than 100 mm [4 in.] ±40 mm [11⁄2 in.] measured quantity of the hydraulic cement shall be within
7.1.3 When the purchaser states a slump flow requirement 61 % of the required mass, and the cumulative measured
for self-consolidating concrete: quantity of hydraulic cement plus supplementary cementitious
Tolerances for Slump Flow
materials shall also be within 61 % of the required cumulative
mass at each intermediate weighing. For smaller batches to a
For Slump Flow Tolerance minimum of 1 m3 [1 yd3], the measured quantity of the
Less than or equal to 550 mm [22 in.] ±40 mm [1 1⁄2 in.] hydraulic cement and the measured cumulative quantity of
hydraulic cement plus supplementary cementitious materials
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More than 550 mm [22 in. ] ±65 mm [2 1⁄2 in.]

7.1.4 The tolerances for slump or slump flow apply to the used shall be not less than the required amount nor more than
values stated in the order when adjustments in accordance with 4 % in excess. When the purchaser requires alternate methods
12.7 and 12.8 are permitted. of measuring cementitious materials, measurement methods
and reporting shall be stated in the order (see Note 13).
7.2 Concrete shall be available within the permissible range
of slump or slump flow for a period of 30 min starting either on NOTE 13—Cementitious materials in bags may be used when requested
or permitted by the purchaser.
arrival at the job site or after the initial slump adjustment
permitted in 12.7, whichever is later. The first and last 1⁄4 m3 9.2 Aggregate shall be measured by mass. The quantity of
[1⁄4 yd3] discharged are exempt from this requirement. If the aggregate weighed shall be the required dry mass plus the total
user is unprepared for discharge of the concrete from the moisture content (absorbed and surface) of the aggregate.
vehicle, the producer shall not be responsible for the limitation 9.2.1 For individual weigh batchers, the quantity of aggre-
of minimum slump or slump flow after 30 min have elapsed gate weighed shall be within 62 % of the required mass;
starting either on arrival of the vehicle at the prescribed except if the required quantity of aggregate is less than 15 % of
destination or at the requested delivery time, whichever is later. scale capacity, the quantity of aggregate weighed shall be
within 60.3 % of scale capacity.
8. Air-Entrained Concrete 9.2.2 For cumulative weigh batchers, if the required quan-
tity of aggregate is equal to or greater than 30 % of the scale
8.1 Unless otherwise specified, for air-entrained concrete capacity, the quantity of aggregate weighed shall be within
the total air contents in Table 1 shall apply based on the 61 % of the required mass at each successive weighing. If the
exposure condition stated in the purchase order. It is permitted required quantity of aggregate is less than 30 % of the scale
to reduce the total air content values in Table 1 by one capacity, the quantity of aggregate weighed shall be within
percentage point for concretes with a specified compressive 60.3 % of scale capacity at each successive weighing.
strength greater than or equal to 35 MPa [5000 psi]. Total air
content that differs from the values in Table 1 is permitted for NOTE 14—The batching accuracy limit of 0.3 % of scale capacity
concrete not exposed to cycles of freezing and thawing (Note establishes a reasonable minimum weighing tolerance that is independent
of the quantity of material being weighed.
6).
9.3 Mixing water shall consist of batch water (water
8.2 The air content of air-entrained concrete when sampled weighed or metered at the plant), ice, free moisture on the
from the transportation unit at the point of discharge shall be aggregates, wash water retained in the mixer before batching,
within a tolerance of 61.5 of the specified value. water added at the job site in accordance with 12.7 or by an
8.3 When a preliminary sample taken within the time limits automated truck mixer system in accordance with 12.8, and
of 12.7 and prior to discharge for placement shows an air water introduced from admixtures if the quantity added in-
content below the specified level by more than the allowable creases the water-cementitious materials ratio by more than
tolerance in accordance with 8.2, the manufacturer may use 0.01 (Note 15). The batch water shall be measured by mass or
additional air entraining admixture to achieve the desired air volume to an accuracy of 61.5 % of the target batch water. Ice
content level, followed by a minimum of 30 revolutions at shall be measured by mass. In the case of truck mixers, any
mixing speed, so long as the revolution limit of 6.1.9 is not wash water retained in the drum for use in the next batch of
exceeded (see Note 12). concrete shall be measured; if this proves impractical or

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 C94/C94M − 21a
impossible the wash water shall be discharged before loading applied load, whichever is greater. The minimum quantity and
the next batch of concrete. Quantity of mixing water shall be sequence of applied test loads used to verify material scales
accurate to within 63 % of the amount established by the shall conform to Table 2 and its notes.
designed mixture proportions. 10.4 All exposed fulcrums, clevises, and similar working
NOTE 15—Mixing water is the total amount of water in a batch less the parts of scales shall be kept clean. Beam scales shall be
water absorbed by the aggregates. Mixing water is used to calculate the equipped with a balance indicator sensitive enough to show
water-cementitious materials ratio (w/cm). movement when a weight equal to 0.1 % of the nominal
9.4 Chemical admixtures in powdered form shall be mea- capacity of the scale is placed in the batch hopper. Pointer
sured by mass. Liquid chemical admixtures shall be batched by travel shall be a minimum of 5 % of the net-rated capacity of
mass or volume. Admixtures measured by either mass or the largest weigh beam for underweight and 4 % for over-
volume shall be batched with an accuracy of 63 % of the total weight.
amount required or plus or minus the amount or dosage 10.5 The device for the measurement of the added water
required for 50 kg [100 lb] of hydraulic cement, whichever is shall be capable of delivering to the batch the quantity required
greater. within the accuracy required in 9.3. The device shall be so
NOTE 16—Admixture dispensers of the mechanical type capable of arranged that the measurements will not be affected by variable
adjustment for variation of dosage, and of simple calibration, are pressures in the water supply line. Measuring tanks shall be
recommended. equipped with outside taps and valves to provide for checking
10. Batching Plant their calibration unless other means are provided for readily
and accurately determining the amount of water in the tank.
10.1 Bins with adequate separate compartments shall be

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provided in the batching plant for fine and for each required NOTE 17—The scale accuracy limitations of the National Ready Mixed
Concrete Association Plant Certification meet the requirements of this
size of coarse aggregate. Each bin compartment shall be specification.
designed and operated so as to discharge efficiently and freely,
with minimum segregation, into the weighing hopper. Means 11. Mixers and Agitators
of control shall be provided so that, as the quantity desired in
the weighing hopper is approached, the material shall be shut 11.1 Mixers include stationary mixers or truck mixers.
off with precision. Weighing hoppers shall be constructed so as Agitators include truck mixers or truck agitators.
to eliminate accumulations of tare materials and to discharge 11.1.1 Stationary mixers shall be equipped with a metal
fully. plate or plates on which are plainly marked the mixing speed
of the drum or paddles, and the maximum capacity in terms of
10.2 Indicating devices shall be in full view and near the volume of mixed concrete. If used for the complete mixing
enough to be read accurately by the operator while charging the of concrete, stationary mixers shall be equipped with an
hopper. The operator shall have convenient access to all acceptable timing device that will not permit the batch to be
controls. discharged until the specified mixing time has elapsed.
10.3 Scales shall be considered accurate if their accuracy is 11.1.2 Each truck mixer or agitator shall have attached
verified through the normally used capacity in accordance with thereto in a prominent place a metal plate or plates on which
Table 2 and load indicated relative to applied test load is within are plainly marked the gross volume of the drum, the capacity
60.15 % of the total capacity of the scale or 0.4 % of the net of the drum or container in terms of the volume of mixed

TABLE 2 Minimum Field Standard Weights and Test LoadsA

Minimum
(in terms of device capacity)
Device Capacity Minimum Loads for Verification of Scale Accuracy
Field Standard
Test LoadsC
Weights
0 to 2000 kg
100 % 100 %
[0 to 4000 lb]

2001 to 20 000 kg Greater ofB Field standard weights or test load to used capacity, if greater than minimum
[4001 to 40 000 lb] 10 % or 500 kg specified.
[1000 lb] 50 %D
Strain-load testsE are permitted to be used above test load minimums. During initial
verification, a scale shall be tested to full capacity.
A
If the configuration and set up of the scale system prevents access or application of adequate field standard weights or if an unsafe condition is created by the verification
process then the use of the scale above the verified position shall be discontinued until corrective measures have been completed.
B
Field standard weights used in verifying accuracy of weighing devices shall comply with requirements of NIST Handbook 105-1.
C
The term “test load” means the sum of the combination of field standard weights and any other applied load used in the conduct of a test using substitution test methods.
Substitution Test—In the substitution test procedure, material or objects are substituted for field standard weights, or a combination of field standard weights and previously
quantified material or objects, using the scale under test as a comparator. Additional test weights or other known test loads may be added to the known test load to verify
the accuracy of higher weight ranges on the scale.
D
The scale shall be tested from zero to at least 10 % of scale capacity using field standard weights, and then to at least 50 % of scale capacity using a series of substitution
load tests that utilize field standard weights equaling at least 10 % of scale capacity.
E
A strain-load test shall be conducted to verify the accuracy from 50 % of scale capacity to the used capacity of the scale. At least one load test shall be performed in
each quarter of scale capacity. Strain-Load Test—In the strain-load test procedure, an unknown quantity of material or objects are used to establish a reference load or
tare to which field standard weights or substitution test loads are added.

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concrete, and the minimum and maximum mixing speeds of conform to the following: The mixing time shall be counted
rotation of the drum, blades, or paddles. If the concrete is truck from the time all the solid materials are in the drum. The batch
mixed as described in 12.5, or shrink mixed as described in shall be so charged into the mixer that some water will enter in
12.4, the volume of mixed concrete shall not exceed 63 % of advance of the cement and aggregate and the target batch water
the total volume of the drum or container. If the concrete is shall be in the drum by the end of the first one fourth of the
central mixed as described in 12.3, the volume of concrete in specified mixing time; or in accordance with the central
the truck mixer or agitator shall not exceed 80 % of the total concrete mixer manufacturer’s recommended charging se-
volume of the drum or container. Truck mixers and agitators quence.
shall be equipped with means to readily verify the number of 12.3.1 If no mixer performance tests are made, the accept-
revolutions of the drum, blades, or paddles. able mixing time for mixers having capacities of 0.76 m3 [1
11.2 Stationary and truck mixers shall be capable of pro- yd3] or less shall be not less than 1 min. For mixers of greater
ducing uniformly mixed concrete within the specified time in capacity, this minimum shall be increased 15 s for each cubic
12.3 or the specified number of revolutions in 12.5. The metre [cubic yard] or fraction thereof of additional capacity
capability to produce and discharge uniformly mixed concrete (see Note 19).
shall be determined in accordance with Annex A1, if required. NOTE 19—Stationary mixers of similar design bearing a Performance
Rating plate of the Concrete Plant Manufacturers Bureau have been tested
NOTE 18—The sequence or method of charging the mixer will have an for their ability to produce uniformly mixed concrete in accordance with
important effect on the uniformity of the concrete. Annex A1 for low slump (<50 mm [2 in.]) and normal slump (100–150
11.3 The agitator shall be capable of maintaining the mixed mm [4–6 in.]) concrete in a mixing time between 30 and 90 s.
concrete in a uniformly mixed condition. The capability to 12.3.2 If mixer performance tests have been made in accor-
maintain and discharge uniformly mixed concrete shall be dance with Annex A1, the acceptable mixing time is permitted
determined in accordance with Annex A1, if required. to be reduced to the time equal to or greater than that used in
11.4 Slump tests of individual samples can be used to the qualification testing. If the mixing time is so reduced the
provide a quick check of the probable degree of uniformity. maximum time of mixing shall not exceed this reduced time by
Sampling and testing shall be in accordance with Annex A1. If more than 60 s for air-entrained concrete. Mixer performance
the difference in slump exceeds the limits in Annex A1, the tests shall be repeated whenever the appearance of the concrete
mixer or agitator shall not be used unless the condition is or a comparison of coarse aggregate content of separate
corrected, except as provided in 11.5. samples as described in Annex A1 indicates that adequate
mixing has not been accomplished.
11.5 Use of the equipment not conforming to 11.2 is
permitted if operated with a longer mixing time, a smaller load, 12.4 Shrink-Mixed Concrete—Concrete that is first partially
or a more efficient charging sequence. If required, the unifor- mixed in a stationary mixer, and then mixed completely in a
mity of concrete shall be evaluated in accordance with Annex truck mixer, shall conform to the following: The time of partial
A1. mixing shall be the minimum time required to intermingle the
ingredients. After transfer to a truck mixer the amount of
11.6 Mixers and agitators shall be examined or their mass
mixing at the designated mixing speed shall be that necessary
determined as frequently as necessary to detect changes in
to meet the requirements for uniformity of concrete as indi-
condition due to accumulations of hardened concrete or mortar
cated in Annex A1. Additional turning of the mixer, if any,
and examined to detect wear of blades. If these conditions are shall be at a designated agitating speed.
considered extensive enough to affect the mixer performance,
Annex A1 establishes the basis to determine whether correction 12.5 Truck-Mixed Concrete—Concrete that is completely
of deficiencies is required or if the correction of the deficien- mixed in a truck mixer for 70 to 100 revolutions at the mixing
cies is adequate. speed designated by the manufacturer shall produce uniformly
mixed concrete as defined in Annex A1. The start of mixing
12. Mixing and Delivery shall be when all the materials have been loaded in the mixer.
If requirements for uniformity of concrete indicated in Annex
12.1 Ready-mixed concrete shall be mixed and delivered to
A1 are not met with 100 revolutions of mixing that mixer shall
the point designated by the purchaser by means of one of the
not be used until the condition is corrected, except as provided
following combinations of operations:
in 11.5. If satisfactory performance is found in one truck mixer,
12.1.1 Central-Mixed Concrete.
the performance of mixers of substantially the same design and
12.1.2 Shrink-Mixed Concrete.
condition of blades are permitted to be regarded as satisfactory.
12.1.3 Truck-Mixed Concrete.
Additional revolutions of the mixer beyond the number found
12.2 Mixers and agitators shall be operated within the limits to produce the required uniformity of concrete shall be at a
of capacity and speed of rotation designated by the manufac- designated agitating speed.
turer of the equipment.
NOTE 20—Truck mixers of similar design bearing a Performance Rating
12.3 Central-Mixed Concrete—Concrete that is mixed com- plate of the Truck Mixer Manufacturers Bureau have been tested for their
pletely in a stationary mixer and transported to the point of ability to produce uniformly mixed concrete in accordance with Annex
delivery either in a truck agitator, or a truck mixer operating at A1.
agitating speed, or in non-agitating equipment approved by the 12.6 When a truck mixer or truck agitator is used for
purchaser and meeting the requirements of Section 13, shall transporting concrete that has been completely mixed in a
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stationary mixer, any turning during transportation shall be at waived by the purchaser if the concrete is of such slump or
the speed designated by the manufacturer of the equipment as slump flow after the specified time limit has been reached that
agitating speed. it can be placed, without the addition of water, to the batch.
12.7 For concrete delivered in truck mixers, no water from 12.10 If a drum revolution limit (6.1.9) for start of discharge
the truck water system or elsewhere shall be added after the or time limit (6.1.10) for the completion of discharge is
initial introduction of water during batching, except as permit- specified by the purchaser, these limits shall govern.
ted in 12.8, and if on arrival at the job site the slump or slump
NOTE 21—Depending on the project requirements, technology is
flow needs to be increased to comply with the requirement available to the manufacturer to alter fresh concrete properties such as
stated in the purchase order. Unless otherwise stated, obtain the setting time, slump or slump flow, air content, and alter delivery and
required slump or slump flow within the tolerances stated in discharge times, or both. Discharge limitations should consider ambient
7.1.1, 7.1.2, or 7.1.3 with the addition of water, or water- conditions, placement procedures, and distance or projected transportation
time between the batch plant and the point of delivery.
reducing admixture, or both. The maximum quantity of water
or water-reducing admixture that can be added at the job site 12.11 Concrete delivered in cold weather shall have the
shall be determined by the manufacturer and shall not exceed applicable minimum temperature indicated in the following
the maximum water content for the batch as established by the table. (The purchaser shall inform the producer as to the type
designed mixture proportions. Adjusting the concrete mixture of construction for which the concrete is intended.)
with water or water-reducing admixture shall be done before Minimum Concrete Temperature as Placed
discharge of concrete, except when obtaining a preliminary
Section Size, mm [in.] Temperature, min, °C [°F]
sample in accordance with 17.6. Additional water shall be
injected into the mixer under pressure and direction of flow to <300 [<12] 13 [55]
allow for proper distribution within the mixer. After the 300–900 [12–36] 10 [50]
900–1800 [36–72] 7 [45]
additions, the drum shall be turned at least 30 revolutions at >1800 [>72] 5 [40]
mixing speed. The quantity of water or water-reducing admix- The maximum temperature of concrete produced with
ture added shall be recorded. heated aggregates, heated water, or both, shall at no time
12.8 For truck mixers with automated water or water- during its production or transportation exceed 32 °C [90 °F].
reducing admixture measurement and slump or slump flow
NOTE 22—When hot water is used rapid stiffening may occur if hot
monitoring equipment defined in 12.8.1 and if permitted by the water is brought in direct contact with the cement. Additional information
purchaser, water, or water-reducing admixture, or both, may be on cold weather concreting is contained in ACI 306R.
added during transportation to the job site. Such additional
12.12 The producer shall deliver the ready-mixed concrete
water shall be injected into the mixer under such pressure and
during hot weather at concrete temperatures as low as
direction of flow to allow for proper distribution within the
practicable, subject to the approval of the purchaser.
mixer. The water content of the batch shall not exceed that
established by the designed mixture proportions. If water or NOTE 23—In some situations difficulty may be encountered when
water-reducing admixture is added, the mixer shall be turned at concrete temperatures approach 32 °C [90 °F]. Additional information
may be found in ACI 305R.
least 30 drum revolutions at mixing speed. Said mixing shall
take place after the last water or water-reducing admixture
13. Use of Nonagitating Equipment
addition but before the start of discharge. The acceptance or
rejection of concrete based on slump or slump flow shall be in 13.1 If the use of non-agitating transportation equipment is
accordance with Section 17. approved by the purchaser, the concrete shall be manufactured
12.8.1 The automated slump or slump flow monitoring in a central mix plant. The following limitations shall apply:
equipment shall be capable of obtaining one or more physical 13.2 Bodies of nonagitating equipment shall be smooth,
measurements on the truck mixer related to concrete slump or watertight, metal containers equipped with gates that will
slump flow and providing an indication of slump or slump flow permit control of the discharge of the concrete. Covers shall be
based on pre-established correlations. The slump or slump flow provided for protection from the weather if required by the
measurement equipment shall report in terms of slump or purchaser.
slump flow. The device for the measurement of water shall be
13.3 The concrete shall be delivered to the site of the work
accurate to 63 % of the amount added with said device. The
with a satisfactory degree of uniformity. Satisfactory degree of
device for the measurement of water-reducing admixture shall
uniformity is defined in Annex A1.
be accurate to the greater of 63 % of the amount added or 630
mL [61 fl oz]. Upon request by the purchaser, the manufac- 13.4 Slump tests of individual samples obtained and tested
turer shall submit data no older than 6 months substantiating in accordance with Annex A1 can be used for a quick check of
the accuracy of the devices used for the measurement of water the probable degree of uniformity. If these slumps differ by
or water-reducing admixture. The equipment shall have con- more than the limits in Table A1.1, the nonagitating equipment
trols to prevent discharge of water at pre-set limits to avoid shall not be used unless the conditions are corrected as
exceeding the maximum water content for the batch as provided in 13.5.
established by the designed mixture proportions. 13.5 If the requirements of Annex A1 are not met when the
12.9 Discharge of the concrete shall be completed within nonagitating equipment is operated for the maximum time of
time limit as established in 6.1.10. This limitation may be
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haul, and with the concrete mixed the minimum time, the

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equipment shall only be used when operated using shorter 15. Plant Inspection
hauls, or longer mixing times, or combinations thereof that will 15.1 The manufacturer shall afford the inspector all reason-
result in the requirements of Annex A1 being met. able access, without charge, for making necessary checks of
the production facilities and for securing necessary samples to
14. Delivery Ticket Information determine if the concrete is being produced in accordance with
14.1 The manufacturer of the concrete shall furnish to the this specification. All tests and inspection shall be so conducted
purchaser with each batch of concrete before unloading at the as not to interfere unnecessarily with the manufacture and
site, a delivery ticket containing information concerning said delivery of concrete.
concrete as follows:
16. Practices, Test Methods, and Reporting
14.1.1 Name of ready-mix company and batch plant, or
batch plant number, 16.1 Test ready-mixed concrete in accordance with the
14.1.2 Serial number of ticket, following methods:
14.1.3 Date, 16.1.1 Making and Curing Concrete Test Specimens in the
14.1.4 Truck number, Field—Practice C31/C31M, using standard moist curing in
accordance with the applicable provisions of Practice C31/
14.1.5 Name of purchaser,
C31M.
14.1.6 Specific designation of job (name and location), 16.1.2 Compressive Strength Tests of Cylindrical Concrete
14.1.7 Specific class or designation of the concrete in Specimens—Test Method C39/C39M.
conformance with that employed in job specifications, 16.1.3 Density (Unit Weight) and Yield of Concrete—Test
14.1.8 Amount of concrete in cubic yards (or cubic metres), Method C138/C138M.
14.1.9 Time loaded or of first mixing of cement and 16.1.4 Air Content—Test Method C173/C173M or Test
aggregates, and Method C231/C231M.
14.1.10 Amount of water added at the request of the 16.1.5 Slump—Test Method C143/C143M.
purchaser or the purchaser’s designated representative and 16.1.6 Slump Flow—Test Method C1611/C1611M.
their initials. 16.1.7 Sampling Fresh Concrete—Practice C172/C172M.
14.1.11 Type and quantity of admixture or other adjust- 16.1.8 Temperature—Test Method C1064/C1064M.
ments made to the batch after batching. 16.2 The testing agency performing acceptance tests of
14.1.12 For trucks equipped with automated water or water- concrete shall meet the requirements of Practice C1077.
reducing admixture measurement and slump or slump flow
16.3 Testing agency reports of concrete test results used to
monitoring equipment as defined in 12.8.1, the total amount of
determine compliance with this specification shall include a
water or water-reducing admixture added by said equipment.
statement that all tests performed by the testing agency or its
14.1.13 Revolution limit to begin discharge as established agents were in accordance with the applicable test methods or
in accordance with 6.1.9. shall note all known deviations from the prescribed procedures
14.1.14 Time limit to complete discharge as established in (Note 24). The reports shall also list any part of the test
accordance with 6.1.10. methods not performed by the testing agency.
14.2 Additional information for certification purposes as

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NOTE 24—Deviation from standard test methods may adversely affect
designated by the purchaser and required by the job specifica- test results.
tions shall be furnished when requested; such information as: NOTE 25—Deviation from standard moisture and temperature curing
requirements of Practice C31/C31M is often a reason for low strength test
14.2.1 Reading of revolution counter at the first addition of results. Such deviations may invalidate the use of such test results as a
water, basis for rejection of the concrete.
14.2.2 Type, brand, and amount of cement,
14.2.3 Class, brand, and amount of coal fly ash, or raw or 17. Sampling and Testing Fresh Concrete
calcined natural pozzolans, 17.1 The contractor shall afford the inspector all reasonable
14.2.4 Grade, brand, and amount of slag cement, access and assistance, without charge, for the procurement of
14.2.5 Type, brand, and amount of silica fume, samples of fresh concrete at time of placement to determine
14.2.6 Type, brand, and amount of admixtures, conformance of it to this specification.
14.2.7 Type, brand, and amount of fiber reinforcement, 17.2 Tests of concrete required to determine compliance
14.2.8 Source and amount of each metered or weighed with this specification shall be made by a certified technician in
water, accordance with Practice C1077.
14.2.9 Information necessary to calculate the mixing water, 17.3 Samples of concrete shall be obtained in accordance
as listed in 9.3, with Practice C172/C172M, except when taken to determine
14.2.10 Maximum size of aggregate, uniformity of slump within any one batch or load of concrete
14.2.11 Mass (amount) of fine and coarse aggregate, (11.4, 13.4, and Annex A1).
14.2.12 Ingredients certified as being previously approved, 17.4 Slump or slump flow, air-content, density, and tem-
and perature tests shall be made at the time of discharge at the
14.2.13 Signature or initials of producer’s representative. option of the inspector as often as is necessary for control

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checks. In addition, these tests shall be made when specified strength, of improper sampling, molding, handling, curing, or
and always when each set of strength specimens are made. testing, it shall be discarded and the strength of the remaining
17.5 Strength tests as well as slump or slump flow, cylinder shall then be considered the test result.
temperature, density, and air content tests shall generally be NOTE 26—Additional tests may be made at other ages to obtain
made with a frequency of not less than one test for each 115 m3 information for determining form removal time or when a structure may
[150 yd3]. Each test shall be made from a separate batch. On be put in service. Specimens for such tests are cured according to the
section on Field Curing in Practice C31/C31M.
each day concrete is delivered, at least one strength test shall be
made for each class of concrete. 18.4 The representative of the purchaser shall ascertain and
record the delivery-ticket number for the concrete and the exact
17.6 If preliminary checks of slump, slump flow, or air
location in the work at which each load represented by a
content are made, a single sample shall be taken after the
strength test is deposited.
discharge of not less than 1⁄4 m3 or 1⁄4 yd3. All other require-
ments of Practice C172/C172M shall be retained. If the 18.5 To conform to the requirements of this specification,
preliminary measurement of slump (12.7) or air content (8.3) strength tests representing each class of concrete must meet the
falls outside the specified limits, address as indicated in 17.6.1 following two requirements (Note 27):
or 17.6.2 as appropriate. 18.5.1 The average of any three consecutive strength tests
17.6.1 If the measured slump or slump flow, or air content, shall be equal to, or greater than, the specified strength, f 'c, and
or both is greater than the specified upper limit, a check test 18.5.2 When the specified strength is 35 MPa [5000 psi] or
shall be made immediately on a new test sample. In the event less, no individual strength test (average of two cylinder tests)
the check test fails, the concrete shall be considered to have shall be more than 3.5 MPa [500 psi] below the specified
failed the requirements of the specification. strength, f 'c.
17.6.2 If the measured slump or slump flow, or air content, NOTE 27—Due to variations in materials, operations, and testing, the
or both is less than the lower limit, permit adjustments in average strength necessary to meet these requirements will be substan-
accordance with 12.7 or 8.3 or both, as appropriate, and obtain tially higher than the specified strength. The amount higher depends upon
a new sample. If the sample of the adjusted concrete fails, a the standard deviation of the test results and the accuracy with which that
value can be estimated from prior data as explained in ACI 214R6 and
check test shall be made immediately on a new sample of the ACI 301. Pertinent data are given in Appendix X1.
adjusted concrete. In the event the check test fails, the concrete
shall be considered to have failed the requirements of the 18.5.3 When the specified strength is greater than 35 MPa
specification. [5000 psi], no individual strength test (average of two cylinder
tests) shall be less than 0.90 f 'c.
18. Strength
19. Failure to Meet Strength Requirements
18.1 When strength is used as a basis for acceptance of
concrete, standard specimens shall be made in accordance with 19.1 In the event that concrete tested in accordance with the
Practice C31/C31M. The specimens shall be cured under requirements of Section 18 fails to meet the strength require-
standard moisture and temperature conditions in accordance ments of this specification, the manufacturer of the ready-
with the applicable provisions of Practice C31/C31M. The mixed concrete and the purchaser shall confer to determine
specimens shall be tested for compressive strength in accor- whether agreement can be reached as to what adjustment or
dance with Test Method C39/C39M. adjustments, if any, shall be made to the mixture proportions,
production process, or testing procedures.
18.2 Laboratory Personnel—The laboratory personnel per-
forming compressive strength testing of specimens used for NOTE 28—ACI 318-14, Sections 26.12.4 and R26.12.4 (commentary)
acceptance testing shall meet the personnel qualification re- address when and how low strength test results can be investigated.
quirements of Practice C1077, including an examination re-
20. Keywords
quiring performance demonstration that is evaluated by an
independent examiner. 20.1 accuracy; blended hydraulic cement; certification;
ready-mixed concrete; scales; testing
18.3 For a strength test, at least two standard test specimens
shall be made from a composite sample secured as required in
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Section 17. A test shall be the average of the strengths of the 6

ACI 214R-11, “Guide to Evaluation of Strength Test Results of Concrete,”
specimens tested at the age specified in 6.4.1.1 or 6.6.1.1 (Note available from American Concrete Institute, Farmington Hills, MI,
26). If a specimen shows definite evidence other than low www.concrete.org, 2011, 16 pp.

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 C94/C94M − 21a

ANNEX

(Mandatory Information)

A1. CONCRETE UNIFORMITY REQUIREMENTS

A1.1 Significance and Use provide recommendations for batching sequence.

A1.1.1 This annex provides procedures to evaluate the A1.2.4 For stationary mixers, mix concrete at the mixing
ability of stationary and truck mixers to produce uniformly speed and minimum duration recommended by the mixer
mixed concrete. The procedures described herein can also be manufacturer. The start of mixing time shall be from the time
used to determine the required minimum mixing revolutions in all solid materials are in the mixer. Mixing time is taken as the
truck mixers for shrink-mixed concrete and for evaluating the earlier of when the mixer is stopped or when the first material
uniformity of concrete mixtures delivered in nonagitating is discharged. Use a suitable timing device, accurate to 1 s, to
equipment. measure and record the time duration of mixing.
A1.1.2 The sequence and method of charging mixers has a A1.2.5 For truck mixers, mix concrete at a mixing speed
significant effect on the ability to produce uniformly mixed exceeding 12 r/min or at the speed recommended by the
concrete. The procedures in this annex can also be used to manufacturer. Complete mixing using between 70 and 100
evaluate the effect of batching sequence for charging or loading revolutions of the drum at mixing speed. To determine the
mixers of acceptable condition. mixer drum revolutions, the start of mixing shall be when all
the materials have been loaded in the mixer. Record the
A1.1.3 It is not the intent that this complete evaluation be number of revolutions at mixing speed.
performed on mixers at an established frequency. For equip-
ment in operation, a visual inspection of the condition of the A1.3 Sampling
mixer for blade wear and hardened concrete buildup can be
A1.3.1 Separate samples, each consisting of approximately
conducted as an alternative. If one mixer of a specific design
0.1 m3 [2 ft3] shall be taken after discharge of approximately
has been evaluated by procedures in this annex, it can be
15 % and 85 % of the load (Note A1.2). These samples shall be
assumed that mixers of essentially the same design and of
obtained within an elapsed time of not more than 15 min. The
different sizes will also produce uniformly mixed concrete. A
samples shall be secured in accordance with Practice C172/
selected portion of this evaluation, such as comparison of
C172M, but shall be kept separate to represent specific points
slump or coarse aggregate content, can also be performed as a
in the batch rather than combined to form a composite sample.
quick indication of the uniformity of concrete mixtures.
Sufficient personnel must be available to perform the required
A1.2 Concrete Mixture, Load Size, and Mixing tests promptly. Segregation during sampling and handling must
be avoided. Each sample shall be covered to prevent moisture
A1.2.1 Unless the intent is to evaluate special project
loss or contamination. Remix the minimum necessary before
situations or concrete mixtures, the concrete mixture used for
performing the tests.
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this evaluation should be typical of that produced in the

production facility. Recommended mixture characteristics in- A1.3.2 Sampling From Stationary Mixers—Samples of con-
clude the following: crete shall be obtained immediately after mixing duration is
A1.2.1.1 Cementitious materials content of 300 to completed, in accordance with one of the following proce-
350 kg ⁄m3 [500 to 600 lb/yd3], dures:
A1.2.1.2 Coarse aggregate size No. 57 or No. 67 from A1.3.2.1 Alternative Procedure 1—The mixer shall be
Specification C33/C33M, stopped, and the required samples removed by any suitable
A1.2.1.3 Fine aggregate fineness modulus 2.5 to 3.0, means from the mixer at approximately equal distances from
A1.2.1.4 Target slump of 100 to 150 mm [4 to 6 in.] or for the front and back of the drum, or
paving operations at 25 to 50 mm [1 to 2 in.], and A1.3.2.2 Alternative Procedure 2—As the mixer is being
A1.2.1.5 Air content of 4 to 6 %. emptied, individual samples shall be taken after discharge of
approximately 15 % and 85 % of the load. The method of
A1.2.2 The load size used for this evaluation shall be within sampling shall provide samples that are obtained from widely
–20 % and +10 % of the rated mixing capacity of the mixer. separated portions, but not from the very ends of the batch
A1.2.3 Use a batching sequence of concrete materials that (Note A1.2).
has been used previously with success or in accordance with A1.3.3 Sampling From Truck Mixers—The concrete shall be
the recommendation of the mixer manufacturer. Use alternative discharged at the normal operating rate for the mixer being
procedures if the purpose is to evaluate the effect of batching tested, with care being exercised not to obstruct or retard the
sequence. discharge. For the duration between obtaining samples, the
NOTE A1.1—The standards of the Truck Mixer Manufacturers Bureau, mixer shall be turned in the mixing direction at agitating speed.
TMMB 100 and of the Concrete Plant Manufacturers Bureau, CPMB 100, Obtain samples by intercepting the full discharge stream from

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 C94/C94M − 21a
the chute without stopping and starting the discharge during the tent. If a separate portion of the sample is used, the concrete
collection of the sample. sample shall be at least 15 kg [35 lb]. Place the concrete in an
A1.3.4 Sampling From Nonagitating Equipment—Obtain adequately sized container and determine the net mass of the
the two samples from approximately 15 % and 85 % of the fresh concrete.
discharge from the nonagitating equipment in accordance with A1.8.2 Wash each sample over a 4.75 mm (No. 4) sieve
Practice C172/C172M. Mix the portions obtained from each sufficiently to remove the cement and most of the fine
location into uniformly mixed samples. aggregate. Determine the mass of the wet coarse aggregate,
NOTE A1.2—No samples should be taken before 10 % or after 90 % of store in a plastic bag, and transport it to a laboratory facility.
the batch has been discharged. Due to the difficulty of determining the Dry the coarse aggregate in an oven at 230 °C [110 °F] for 16
actual quantity of concrete discharged, the intent is to provide samples that 6 2 h. Sieve the coarse aggregate over a 4.75 mm (No. 4) sieve
are representative of widely separated portions, but not the beginning and to remove any fine aggregate particles. Determine the mass of
end of the load. dry coarse aggregate in each sample.
A1.4 Slump A1.8.3 Express the mass of dry coarse aggregate as a
A1.4.1 Perform the slump test on each sample in accordance percentage of the mass of the original concrete sample:
with Test Method C143/C143M. Start the slump test within 5 c
min after the sample was obtained. coarse aggregate content, % = 3 100 (A1.3)
M

A1.5 Density (Unit Weight) and Yield where:

A1.5.1 Determine the density of each sample in accordance c = mass of dry coarse aggregate, kg [lb], and
with Test Method C138/C138M. Use the measure for measure- M = net mass of same fresh concrete sample, kg [lb].
ment of air content by Test Method C231/C231M unless the
A1.9 Compressive Strength
concrete contains a larger nominal maximum size coarse
aggregate than is appropriate for this measure. A1.9.1 Make at least three 150 × 300 mm [6 × 12 in.] or 100
× 200 mm [4 × 8 in.] cylinders from each concrete sample.
A1.5.2 Calculate the density (unit weight) of each sample as
Cure the specimens in accordance with Practice C31/C31M,
follows:
except that the cylinders shall be immersed in water immedi-
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M ately after molding with the temperature maintained between

D5 (A1.1)
V the required temperature limits for initial curing of the standard
where: curing procedures in Practice C31/C31M for the first 24 h.
Transport the cylinders to the laboratory facilities after 24 h
D = measured density (unit weight), kg/m3 [lb/ft3],
M = net mass of concrete in the measure, kg [lb], and and cure in accordance with the standard curing procedures of
V = volume of the measure, m3 [ft3]. Practice C31/C31M.
A1.5.3 From the average density (unit weight) of the two A1.9.2 Test the cylinders in accordance with Test Method
samples, calculate the yield of the batch in accordance with C39/C39M at an age of seven days. If the strength of an
Test Method C138/C138M. individual cylinder differs from the average strength of either
sample by more than 9.5 %, this value can be disregarded for
A1.6 Air Content determining the average strength for the sample.
A1.6.1 Measure the air content of each sample in accor- A1.9.3 Average the strength of the cylinders from each
dance with Test Method C231/C231M. Use Test Method sample and express that value as a percentage of the average of
C173/C173M if the concrete is made with lightweight aggre- all cylinders made from that batch. Calculate the difference in
gate or if the coarse aggregate in the concrete has an aggregate strength between each sample as a percentage of the overall
correction factor larger than 0.5 % when determined in average.
accordance with Test Method C231/C231M.
A1.10 Report
A1.7 Air-Free Density (Unit Weight)
A1.10.1 Report the following information:
A1.7.1 Calculate the air-free density (unit weight) of each A1.10.1.1 Purpose of the evaluation.
sample as follows:
A1.10.1.2 Type and description of mixer and rated mixing
D capacity.
air-free density= 3 100 (A1.2)
100 2 A A1.10.1.3 Concrete mixture proportions, batch quantities,
where: density (unit weight), and yield of the batch.
D = measured density, kg/m3 [lb/ft3], and A1.10.1.4 Mixing duration for stationary mixers or number
A = measured air content on that sample, %. of revolutions at mixing speed for truck mixers.
A1.10.1.5 Slump of each sample and the difference between
A1.8 Coarse Aggregate Content samples, mm [in.].
A1.8.1 Use the concrete in the measure used to measure A1.10.1.6 Air content of each sample and the difference
density (unit weight) to determine the coarse aggregate con- between samples, %.

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 C94/C94M − 21a
TABLE A1.1 Requirements for Uniformity of Concrete A1.10.1.8 Coarse aggregate content of each sample and the
Maximum difference between samples, %.
Test Permissible
Difference A1.10.1.9 Average strength in MPa [psi] and percent of
Air-free density (unit weight), kg/m3 [lb/ft3] 16 [1.0] overall average for each sample and the percent difference
Air content, % 1.0
Slump, mm [in.]:
between samples.
If average slump is less than 100 mm [4 in.] 25 [1.0]
If average slump is 100 to 150 mm [4 to 6 in.] 40 [1.5] A1.11 Requirements for Uniformity of Concrete
Coarse aggregate content, % 6.0
Average compressive strength at 7 days for A1.11.1 The maximum permitted difference for each prop-
each sample,A % 7.5A erty obtained from the two different samples of the same batch
A
Approval of the mixer shall be tentative, pending results of the 7-day compressive are as provided in Table A1.1. Test results conforming to the
strength tests.
limits of all five properties listed in Table A1.1 shall indicate
uniform concrete within the limits of this specification.
A1.10.1.7 Air-free density (unit weight) of each sample and
the difference between samples, kg/m3 [lb/ft3].

APPENDIX

(Nonmandatory Information)

X1. CALCULATION OF THE AVERAGE COMPRESSIVE STRENGTH (f 'cr)

NECESSARY TO MEET THE STRENGTH REQUIREMENTS OF 18.5

X1.1 Section 18.5 of this specification contains the same TABLE X1.2 Required Average Compressive Strength When Data
strength requirements as those contained in ACI 318 and Are Not Available to Establish Standard Deviation
ACI 301, except it does not require the submittal of the data Specified Strength, Required Average Strength, f 'cr
f 'c, MPa [psi] [MPa] psi
and calculation of the average strength, f 'cr necessary to meet <21 [3000] [f 'c + 7.0] f 'c + 1000
those requirements. This appendix does not include all of the 21 to 35 [3000 to 5000] [f 'c + 8.3] f 'c + 1200
detailed requirements of the ACI Code and Specification that >35 [5000] [1.10 f 'c + 5.0] 1.10 f 'c + 700
will govern a submittal for their respective purposes. The
following material is intended to guide users of this specifica-
tion when no formal submittal is required. tion between 1.16 for 15 tests and 1.00 for 30 tests. The test
X1.1.1 Table X1.1 provides the statistically based formulas record should be obtained from a similar mixture with a
to calculate the required average strength f 'cr when strength specified strength within 7 MPa [1000 psi] of the specified
test records from previous projects are available. The strength strength for the new project for which the average compressive
test results are used to establish the standard deviation, s. At strength is being determined. The equations are related to the
least 30 consecutive test results are required to obtain a robust strength acceptance criteria in 18.5 and establish less than a
estimate of the standard deviation. If the number of tests is 1 % chance of failing these criteria if concrete is produced to
between 15 and 30, the calculated standard deviation is achieve the required average strength at the same degree of
multiplied by a factor to allow for the uncertainty of the variability implied by the standard deviation used. Because the
estimated standard deviation. The factor is a linear interpola- average strength, f 'cr, must be high enough to conform to both
averages of three consecutive test results and the requirements
TABLE X1.1 Required Average Compressive Strength when Data on minimum strength of an individual test result, the highest
are Available to Establish a Standard Deviation average strength (f 'cr) determined from these two equations
Specified Strength, f 'c Required Average Strength, f 'cr governs. More detailed guidance on this subject matter is
#35 MPa [5000 psi] Use the larger from Eq X1.1 and X1.2 [X1.2M]:
f 'cr = f 'c + 1.34s (X1.1)
available in ACI 214R.6
f 'cr = f 'c + 2.33s – 500 (X1.2) X1.1.2 If it is a new mixture or strength level and a strength
[f 'cr = f 'c + 2.33s – 3.5] [X1.2M]
>35 MPa [5000 psi] Use the larger from Eq X1.1 and X1.3: test record is not available to establish a standard deviation
f 'cr = f 'c + 1.34s (X1.1) then Table X1.2 provides default levels of strength over-
f 'cr = 0.90 f 'c + 2.33s (X1.3) design.
where: X1.1.3 Table X1.3 provides calculated values of over-
f 'c = specified compressive strength,
f 'cr = required average compressive strength, and
design and required average strength for selected standard
s = standard deviation. deviations and specified strength levels that might be consid-
ered typical. More exact values are obtained from X1.1.2.

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TABLE X1.3 Overdesign Necessary to Conform to Specified Compressive Strength
Inch-Pound Units Required Overdesign SI Units
Specified Standard Deviation from Test Record, psi No data Standard Deviation from Test Record, MPa No Data
Specified
Strength, f 'c, 300 400 500 600 700 SD unknown 2.0 2.5 3.5 4.0 5.0 SD Unknown
Strength, f 'c, MPa
psi Overdesign above f 'c Overdesign above f 'c
<3000 1000 <21 7.0
3000 400 540 670 810 1130 1200 20 2.7 3.4 4.7 5.8 8.2 8.3
4000 400 540 670 810 1130 1200 30 2.7 3.4 4.7 5.8 8.2 8.3
5000 400 540 670 810 1130 1200 35 2.7 3.4 4.7 5.8 8.2 8.3
6000 400 540 670 800 1030 1300 40 2.7 3.4 4.7 5.8 7.7 9.0

14
Required Average Strength
Specified Standard Deviation from field data, psi No data Standard Deviation from field data, MPa No Data
Specified
Strength, f 'c, 300 400 500 600 700 SD unknown 2.0 2.5 3.5 4.0 5.0 SD Unknown
Strength, f 'c, MPa
psi f 'cr, Required Average Strength, psi f 'cr, Required Average Strength, MPa
<3000 f 'c + 1000 <21 f 'c + 7.0
3000 3400 3540 3670 3810 4130 4200 20 22.7 23.4 24.7 25.8 28.2 28.3
C94/C94M − 21a

4000 4400 4540 4670 4810 5130 5200 30 32.7 33.4 34.7 35.8 38.2 38.3
5000 5400 5540 5670 5810 6130 6200 35 37.7 38.4 39.7 40.8 43.2 43.3
6000 6400 6540 6670 6800 7030 7300 40 42.7 43.4 44.7 45.8 47.7 49.0

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 C94/C94M − 21a

SUMMARY OF CHANGES

Committee C09 has identified the location of selected changes to this standard since the last issue
(C94/C94M – 21) that may impact the use of this standard. (Approved June 1, 2021.)

(1) Revised 9.3.

Committee C09 has identified the location of selected changes to this standard since the last issue
(C94/C94M – 20) that may impact the use of this standard. (Approved April 1, 2021.)

(1) Added 6.1.10. (3) Revised language in 12.9, 12.10, Note 21, and 14.1.13.
(2) Added Note 9 beneath 6.1.10. (4) Added 14.1.14.

Committee C09 has identified the location of selected changes to this standard since the last issue
(C94/C94M – 19a) that may impact the use of this standard. (Approved Feb. 1, 2020.)

(1) Revised 18.1. (2) Added 18.2.

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