ASTM C685/C685M-17

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C685/C685M − 14 C685/C685M − 17
Standard Specification for
Concrete Made by Volumetric Batching and Continuous
Mixing
This standard is issued under the fixed designation C685/C685M; 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*
1.1 This specification covers concrete made from materials continuously batched by volume, mixed in a continuous mixer, and
delivered to the purchaser in a freshly mixed and unhardened state as hereinafter specified. Requirements for quality of concrete
shall be either as hereinafter specified or as specified by the purchaser. When the requirements of the purchaser differ from this
specification, the purchaser’s specification shall govern. This specification does not cover the placement, consolidation, finishing,
curing, or protection of the concrete after delivery to the purchaser. Tests and criteria for batching accuracy and mixing efficiency
are specified herein.
1.2 The values stated in either SI units, shown in brackets, or inch-pound units are to be regarded separately as standard. The
values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other.
Combining values from the two systems may result in nonconformance with the standard.
1.3 This specification references notes and footnotes which provide explanatory material. These notes and footnotes (excluding
those in tables and figures) shall not be considered as requirements of this specification.
1.4 This standard does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of
the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. (Warning—Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and
tissue upon prolonged use. )
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
C31/C31M Practice for Making and Curing Concrete Test Specimens in the Field
C33C33/C33M Specification for Concrete Aggregates
C39/C39M Test Method for Compressive Strength of Cylindrical Concrete Specimens
C94/C94M Specification for Ready-Mixed Concrete
C125 Terminology Relating to Concrete and Concrete Aggregates
C127 Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate
C136C136/C136M Test Method for Sieve Analysis of Fine and Coarse Aggregates
C138/C138M Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete
C143/C143M Test Method for Slump of Hydraulic-Cement Concrete
C150/C150M Specification for Portland Cement
C172/C172M Practice for Sampling Freshly Mixed Concrete
This specification is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregatesand is the direct responsibility of Subcommittee C09.40 on
Ready-Mixed Concrete.
Current edition approved Dec. 15, 2014Dec. 1, 2017. Published February 2015December 2017. Originally approved in 1971. Last previous edition approved in 20112014
as C685/C685M–11.–14. DOI: 10.1520/C0685_C0685M-14.10.1520/C0685_C0685M-17.
See Section on Safety Precautions, Manual of Aggregate and Concrete Testing, Annual Book of ASTM Standards, Vol 04.02.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C685/C685M − 17
C173/C173M Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method
C231C231/C231M Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method
C260C260/C260M Specification for Air-Entraining Admixtures for Concrete
C330C330/C330M Specification for Lightweight Aggregates for Structural Concrete
C494/C494M Specification for Chemical Admixtures for Concrete
C567C567/C567M Test Method for Determining Density of Structural Lightweight Concrete
C595/C595M Specification for Blended Hydraulic Cements
C618 Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
C637 Specification for Aggregates for Radiation-Shielding Concrete
C989/C989M Specification for Slag Cement for Use in Concrete and Mortars
C1017/C1017M Specification for Chemical Admixtures for Use in Producing Flowing Concrete
C1064/C1064M Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete
C1077 Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency
Evaluation
C1157/C1157M Performance Specification for Hydraulic Cement
C1240 Specification for Silica Fume Used in Cementitious Mixtures
C1602/C1602M Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete
2.2 ACI Documents:
CP-1 Technician Workbook for ACI Certification of Concrete Field Testing Technician-Grade I
211.1 Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete
211.2 Standard Practice for Selecting Proportions for Structural Lightweight Concrete
301 Standard Specifications for Structural Concrete
304.6R Guide for Use of Volumetric-Measuring and Continuous-Mixing Concrete Equipment
305R Hot Weather Concreting
306R Cold Weather Concreting
318 Building Code Requirements for Structural Concrete and Commentary
2.3 Other Documents:
Bureau of Reclamation Concrete Manual
VMMB 100-01 Volumetric Mixer Standards of the Volumetric Mixer Manufacturers Bureau
3. Terminology
3.1 Definitions: For definitions of terms used in this specification, refer to Terminology C125.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 manufacturer, n—of concrete, the producer of the concrete.
3.2.2 purchaser, n—of concrete, the buyer of the concrete.
4. Basis of Purchase
4.1 The basis of purchase shall be the cubic yard or cubic metre of fresh concrete as it is continuously discharged from the
batching and mixing apparatus.
4.2 The volume of fresh concrete in a given batch shall be determined by, or calculated from, a calibrated indicating device
driven directly by the batching apparatus.
NOTE 1—It should be understood that the volume of hardened concrete may be, or may appear to be, less than expected due to waste and spillage,
over-excavation, spreading forms, some loss of entrained air, or settlement of wet mixtures, none of which are the responsibility of the manufacturer.
A
TABLE 1 Recommended Total Air Content for Air-Entrained Concrete
Total Air Content, %
B,C
Exposure Condition Nominal Max Sizes of Aggregate, in. [mm]
3 1 3 1
⁄8 [9.5] ⁄2 [12.5] ⁄4 [19.0] 1 [25.0] 1 ⁄2 [37.5] 2 [50.0] 3 [75.0]
Mild 4.5 4.0 3.5 3.0 2.5 2.0 1.5
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
A
For air-entrained concrete, when specified.
B
For description of exposure conditions, refer to ACI Standard Practice 211.1, Section 6.3.3 with attention to accompanying footnotes.
C
Unless exposure conditions dictate otherwise, it is permissible to reduce air contents recommended above by up to 1 % for concretes with specified compressive
strength, f' , of 5000 psi [35 MPa] or above.
c
Available from American Concrete Institute (ACI), P.O. Box 9094, Farmington Hills, MI 48333-9094, http://www.aci-int.org.
Available from Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.
Available from the Volumetric Mixer Manufacturers Bureau, 900 Spring Street, Silver Spring, MD 20910, www.vmmb.org.
C685/C685M − 17
5. Materials
5.1 In the absence of designated applicable specifications covering requirements for quality of materials, the following
specifications shall govern:
5.2 Cementitious Materials:
5.2.1 Hydraulic Cement—Hydraulic Cement shall conform to Specification C150/C150M, Specification C595/C595M, or
Specification C1157/C1157M (Note 2).
5.2.2 Supplementary Cementitious Materials—Coal Fly Ash or natural pozzolans shall conform to Specification C618. Slag
Cement shall conform to Specification C989/C989M. Silica Fume shall conform to Specification C1240.
NOTE 2—These different cementitious materials will produce concretes of different properties and should not be used interchangeably.
5.3 Aggregates—Normal weight aggregates shall conform to Specification C33C33/C33M. Lightweight aggregates shall
conform to Specification C330C330/C330M and heavyweight aggregates shall conform to Specification C637.
5.4 Water—Water shall conform to Specification C1602/C1602M.
5.5 Air-Entraining Admixtures—Air-entraining admixtures shall conform to Specification C260C260/C260M (Note 3).
5.6 Chemical Admixtures—Chemical admixtures shall conform to either Specification C494/C494M or C1017/C1017M, as
applicable (Note 3).
NOTE 3—In any given instance, the required dosage of air-entraining, accelerating, and retarding admixtures may vary. Therefore, a range of dosages
should be allowed which will permit obtaining the desired effect.
6. Ordering Information
6.1 In the absence of designated applicable general specifications, the purchaser shall specify the following:
6.1.1 Designated size or sizes of coarse aggregate,
6.1.2 Slump or slumps desired at the point of delivery (see 10.3),
6.1.3 When air-entrained concrete is specified, the air content of samples taken at the point of discharge from the transportation
unit (see 10.4 and Table 1 for the total air content and tolerances) (Note 4),
6.1.4 When structural lightweight concrete is specified, the density as fresh density, equilibrium density, or oven-dry density
(Note 5), and
6.1.5 Which of Options A, B, or C shall be used as a basis for determining the proportions of the concrete to produce the
required quality (see 6.2, 6.3, or 6.4).
NOTE 4—In selecting the specified air content, the purchaser should consider the exposure conditions to which the concrete will be subjected. Air
contents less than shown in Table 1 may not give the required resistance to freezing and thawing, which is the primary purpose of air-entrained concrete.
Air contents higher than the levels shown may reduce strength without contributing any further improvement of durability.
NOTE 5—The density of fresh concrete, which is the only density determinable at the time of delivery, is always higher than the equilibrium density,
or oven-dry density. Definitions of, and methods for determining or calculating equilibrium density and oven-dry density, are covered in Test Method
C567C567/C567M.
6.2 Option A:
6.2.1 When the purchaser requires the manufacturer to assume full responsibility for the selection of the proportions for the
concrete mixture, the purchaser shall also specify the following:
6.2.1.1 Requirements for compressive strength as determined on samples taken from the mixer at the point of discharge and
evaluated in accordance with Section 11. The purchaser shall specify the requirements in terms of the compressive strength of
standard specimens cured under standard curing conditions for moist curing. Unless otherwise specified, the age at test shall be
28 days, and
6.2.2 At the request of the purchaser, the manufacturer shall, prior to the actual delivery of the concrete, furnish a statement to
the purchaser, giving the dry mass of cement and saturated surface-dry mass of fine and coarse aggregate and quantities, type, and
name of admixtures (if any) and of water per cubic yard or cubic metre of concrete that will be used in the manufacture of each
class of concrete ordered by the purchaser. The manufacturer shall also furnish evidence satisfactory to the purchaser that the
materials to be used and proportions selected will produce concrete of the quality specified.
6.3 Option B:
6.3.1 When the purchaser assumes responsibility for the proportioning of the concrete mixture, the purchaser shall also specify
the following:
6.3.1.1 Cement content in pounds per cubic yard or kilograms per cubic metre of concrete, or equivalent units,
6.3.1.2 Maximum allowable water content in gallons per cubic yard or litres or kilograms per cubic metre of concrete or
equivalent units, including surface moisture on the aggregates, but excluding water of absorption (Note 6), and
6.3.1.3 If admixtures are required, the type, name, and dosage range to be used. Admixtures shall not be used as a substitute
for a portion of specified amounts of cement without the written approval of the purchaser.
NOTE 6—The purchaser, in selecting requirements for which he assumes responsibility should give consideration to requirements for workability,
placeability, durability, surface texture, and density, in addition to those for structural design. The purchaser is referred to ACI Standard Practice 211.1
C685/C685M − 17
for normal weight concrete, and ACI Standard Practice 211.2 for lightweight concrete, for the selection of proportions that will result in concrete suitable
for various types of structures and conditions of exposure. The water-cement ratio of most structural lightweight concretes cannot be determined with
sufficient accuracy for use as a specification basis.
6.3.2 At the request of the purchaser, the manufacturer shall, prior to the actual delivery of the concrete, furnish a statement to
the purchaser giving the sources, densities, and sieve analyses of the aggregates and the dry mass of cement and saturated
surface-dry mass of fine and coarse aggregate and quantities, type, and name of admixture (if any) and of water per cubic yard
or cubic metre of concrete that will be used in the manufacture of each class of concrete ordered by the purchaser.
6.4 Option C:
6.4.1 When the purchaser requires the manufacturer to assume responsibility for the selection of the proportions for the concrete
mixture with the minimum allowable cement content specified, the purchaser shall also specify the following in addition to the
requirements of 6.1.1 through 6.1.5:
6.4.1.1 Required compressive strength as determined on samples taken from the mixer at the point of discharge and evaluated
in accordance with Section 11. The purchaser shall specify the requirements for strength in terms of tests of standard specimens
cured under standard curing conditions for moist curing. Unless otherwise specified, the age at test shall be 28 days.
6.4.1.2 Minimum cement content in pounds per cubic yard or kilograms per cubic metre of concrete (Note 7), and
6.4.1.3 If admixtures are required, the type, name, and dosage range to be used. The cement content shall not be reduced when
admixtures are used.
6.4.2 At the request of the purchaser, the manufacturer shall, prior to the actual delivery of the concrete, furnish a statement to
the purchaser, giving the dry mass of cement and saturated surface-dry mass of fine and coarse aggregate and quantities, type, and
name of admixture (if any) and of water per cubic yard or cubic metre of concrete that will be used in the manufacture of each
class of concrete ordered by the purchaser. The manufacturer shall also furnish evidence satisfactory to the purchaser that the
materials to be used and proportions selected will produce concrete of the quality specified. Whatever strengths are attained the
quantity of cement used shall not be less than the minimum specified.
NOTE 7—Option C can be distinctive and useful only if the designated minimum cement content is at about the same level that would ordinarily be
required for the strength, aggregate size, and slump specified. At the same time, it must be an amount that will be sufficient to ensure durability under
expected service conditions, as well as satisfactory surface texture and density, in the event specified strength is attained with it. Attention is directed to
ACI Standard Practices 211.1 and 211.2 for additional information on mixture proportions.
6.5 The proportions arrived at by Options A, B, or C for each class of concrete and which are approved for use in a project shall
be assigned a designation (7CV.PK7, etc.) to facilitate identification of each concrete mixture delivered to the project. This is the
designation required in 15.1.7 and supplies information on concrete proportions when they are not given separately on each
delivery ticket as outlined in 15.2. However, each delivery of concrete shall be covered by a delivery ticket showing enough
information to establish that the mix conforms to the mix designs previously approved for the work.
6.6 The purchaser shall ensure that the manufacturer is provided copies of all reports of tests performed on concrete samples
taken to determine compliance with specification requirements. Reports will be provided on a timely basis.
7. Controlling and Measuring Materials
7.1 Cement, fine and coarse aggregates, water, and admixtures shall be measured by volume. Devices such as counters,
calibrated gate openings, control valves, or flowmeters shall be available for controlling and determining the quantities of the
ingredients discharged. The entire measuring and dispensing mechanism shall produce the specified proportions of each ingredient
within the tolerances in 7.8.
NOTE 8—The recommendations of the equipment manufacturer in the operation of the equipment and in calibrating and using the various gages,
revolution counters, speed indicators, or other control devices should be followed.
7.2 All indicating devices that bear on the accuracy of proportioning and mixing of concrete shall be in full view and near
enough to be read by the operator while concrete is being produced. The operator shall have convenient access to all controls.
7.3 The proportioning and indicating devices shall be individually checked by following the equipment manufacturer’s
recommendations as related to each individual concrete batching and mixing unit. Adequate standard volume measures, scales, and
weights shall be made available for the checking accuracy of the proportioning mechanism.
7.4 Yield Check—Essentially, the volume of concrete discharged from the mixer is checked by first determining the mass of the
amount of concrete discharged during some number of revolutions, or as determined by some other output indicator; this is then
followed immediately by a determination of the density. The mass of concrete discharged divided by the density is equal to the
number of cubic feet or cubic metres mixed and discharged during the chosen interval. The accuracy of the output indicator is thus
checked by this expedient. For further guidance and a suggested calibration procedure, refer to ACI 304.6R and VMMB 100-01.
3 3
NOTE 9—It is recommended that about 2.5 to 3.0 ft [0.070 to 0.085 m ] be discharged for this purpose; this amount of concrete will weigh from 350
to 500 lb [160 to 225 kg] and can be discharged into and contained in a 35 or 55-gal [130 to 210-dm ] drum or other suitable container which in turn
can be placed on a scale of adequate capacity. The output of a batcher-mixer unit may be indicated by the number of revolutions, travel of a belt, or
changes in gage readings; if so, these figures should be used as a measure of output.
C685/C685M − 17
7.5 Proportioning Check—Whenever the sources or characteristics of the ingredients are changed, or the characteristics of the
mixture are noted to have changed, the purchaser is permitted to require a check of the fine aggregate content and the coarse
3 3
aggregate content by use of the washout test. Essentially, in the washout test, 1 ft [0.03 m ] of concrete is washed through a No.
4 [4.75-mm] sieve and through a No. 100 [150-μm] sieve; that retained on the No. 4 sieve is normally considered coarse aggregate
whereas that passing the No. 4 and retained on the No. 100 sieve is considered fine aggregate. Corrections to the quantity of
aggregates (per cubic foot or cubic metre of concrete) shall be made if the original sieve analysis of each aggregate is available.
7.6 The rate of water supplied the continuous mixer shall be measured by a calibrated flowmeter coordinated with the cement
and aggregate feeding mechanism, and with the mixer. The device for the control of water shall be capable of delivering to the
batch the required quantity. The rate shall be capable of being adjusted in order to control slump at the desired levels and to
determine that the water-cement (permitted or required) ratios are being met.
7.7 Liquid admixtures shall be dispensed through a controlled flowmeter.
7.8 Tolerances in proportioning the various ingredients are as follows:
Cement, mass % 0 to +4
Fine Aggregate, mass % ±2
Coarse Aggregate, mass % ±2
Admixtures, mass or volume % ±3
Water, mass or volume % ±1
The tolerances are based on a volume/mass relationship established by calibration of the measuring devices furnished as an
integral part of the whole equipment.
NOTE 10—It is noted that to meet these tolerances, attention should be given to:
(1) Degree of compaction of the cement,
(2) Grading and other physical characteristics of the fine and coarse aggregates,
(3) Moisture content and bulking factor of the fine aggregate,
(4) Viscosity of the admixture, and
(5) Other factors of influence, for example, mechanical condition and weather.
8. Mixing Mechanism
8.1 The continuous mixer shall be an auger-type mixer or any other type suitable for mixing concrete to meet the required
consistency and uniformity requirements (see 14.2.3).
8.2 Each batching and mixing unit, or both, shall carry in a prominent place a metal plate or plates on which is plainly marked
the gross volume of the unit in terms of mixed concrete. The mixer shall produce a thoroughly mixed and uniform concrete.
NOTE 11—Slump and air content tests of samples taken in accordance with 14.2.3 can be made for a quick check of the probable degree of uniformity.
9. Mixing and Delivery
9.1 The batcher-mixer unit shall contain in separate compartments all the necessary ingredients needed for the manufacture of
concrete. The unit shall be equipped with calibrated proportioning devices to vary the mix proportions and it shall produce concrete
as required by this specification and those of the project.
9.2 Cold Weather Concrete—Concrete delivered in cold weather shall have the applicable minimum temperature indicated in
the following table. (The purchaser shall inform the producer as to the type of construction for which the concrete is intended.)
Minimum Concrete Temperature as Placed
Section Size, <12 12 to 36 36 to 72 >72
in. [mm] [<300] [300 to 900] [900 to 1800] [>1800]
Temperature, 55 50 45 40
min, °F (°C) [13] [10] [7] [5]
The maximum temperature of concrete produced with heated aggregates, heated water, or both, shall at no time during its
production or transportation exceed 90 °F [32 °C].
NOTE 12—When hot water is used rapid stiffening may occur if hot water is brought in direct contact with the cement. Additional information on cold
weather concreting is contained in ACI 306R.
9.3 The producer shall deliver the concrete during hot weather at concrete temperatures as low as pra
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