ASTM C451-21

Standard Test Method for Early Stiffening of Hydraulic Cement (Paste Method)

SIGNIFICANCE AND USE
5.1 The purpose of this test method is to determine the degree to which a cement paste develops early stiffening or to establish whether or not a cement complies with a specification limit on early stiffening.  
5.2 When used for establishing compliance with a specification limit, the specification requirement is customarily stated in terms of the minimum allowable final penetration, in percent, calculated in accordance with the Calculation Section. When used for estimating the relative tendency of a cement to manifest early stiffening, additional information of value may be obtained if the remix procedure described in the Procedure Section is employed. Under some conditions, a judgment may be made by comparing the behavior in the initial test and in the remix procedure to differentiate a relatively less serious and less persistent tendency to early stiffening (false set) from one that is more persistent and, consequently, more serious (flash set).  
5.3 Severe false setting in a cement may cause difficulty from a placing and handling standpoint, but it is not likely to cause difficulties where concrete is mixed for a longer time than usual, as usually occurs in transit mixing, or where it is remixed prior to placing or transporting, as occurs in concrete pumping operations. It is most likely to be noticeable where concrete is mixed for a short period of time in stationary mixers and transported to the forms in non-agitating equipment, such as on some paving jobs, and when concrete is made in an on-site batch plant.  
5.4 Cements with severe false setting usually require slightly more water to produce the same consistency, which may be expected to result in slightly lower strengths and increased drying shrinkage.  
5.5 Early stiffening resulting from false set is not likely to cause a cement to fail the applicable time of setting requirement.  
5.6 Early stiffening resulting from flash set, depending on severity, can cause a cement to fail the applicable time o...
SCOPE
1.1 This test method covers the determination of early stiffening in hydraulic-cement paste.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental 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 exposure.)2  
1.4 The text of this standard 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 the standard.  
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.

General Information

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 91.100.10 - Cement. Gypsum. Lime. Mortar
• Technical Committee: C01 - Cement
• Drafting Committee: C01.30 - Time of Set

Relations

• Refers: ASTM C219-24 - Standard Terminology Relating to Hydraulic and Other Inorganic Cements
• Effective Date: 01-Apr-2024
• Refers: ASTM C670-24a - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Feb-2024
• Refers: ASTM C670-24 - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM C219-20a - Standard Terminology Relating to Hydraulic and Other Inorganic Cements
• Effective Date: 01-Aug-2020
• Refers: ASTM C305-20 - Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency
• Effective Date: 15-Jul-2020
• Refers: ASTM C219-20 - Standard Terminology Relating to Hydraulic and Other Inorganic Cements
• Effective Date: 01-Apr-2020
• Refers: ASTM C219-19a - Standard Terminology Relating to Hydraulic and Other Inorganic Cements
• Effective Date: 15-Nov-2019
• Refers: ASTM C219-19 - Standard Terminology Relating to Hydraulic Cement
• Effective Date: 01-Jun-2019
• Refers: ASTM C150/C150M-19 - Standard Specification for Portland Cement
• Effective Date: 01-Apr-2019
• Refers: ASTM C1005-18 - Standard Specification for Reference Masses and Devices for Determining Mass and Volume for Use in the Physical Testing of Hydraulic Cements
• Effective Date: 01-May-2018
• Refers: ASTM C1005-17 - Standard Specification for Reference Masses and Devices for Determining Mass and Volume for Use in the Physical Testing of Hydraulic Cements
• Effective Date: 15-Mar-2017
• Refers: ASTM C150/C150M-16 - Standard Specification for Portland Cement
• Effective Date: 15-Mar-2016
• Refers: ASTM C150/C150M-15 - Standard Specification for Portland Cement
• Effective Date: 01-Jul-2015
• Refers: ASTM C219-14 - Standard Terminology Relating to Hydraulic Cement
• Effective Date: 01-Jul-2014
• Refers: ASTM C511-13 - Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes
• Effective Date: 01-Dec-2013

Overview

ASTM C451-21: Standard Test Method for Early Stiffening of Hydraulic Cement (Paste Method) is a widely recognized ASTM standard that outlines the procedures for measuring the early stiffening of hydraulic cement paste, using the paste method. Early stiffening-manifesting as either false set or flash set-directly impacts the workability, placement, and long-term performance of concrete and mortar. This document is essential for quality control in cement production and construction, enabling determination of whether a hydraulic cement meets specification limits regarding early stiffening.

The standard prescribes the preparation and testing of cement paste samples, evaluation using the Vicat apparatus, and calculation of penetration values to quantify stiffening tendencies.

Key Topics

• Early Stiffening: The primary focus is the detection and measurement of early stiffening, a condition where cement paste develops rigidity prematurely before the expected set time.
  • False Set: Early stiffening that can be reversed by remixing, typically not associated with significant heat evolution.
  • Flash Set: Serious early stiffening that cannot be remedied through remixing, often accompanied by notable heat generation.
• Procedures: The method includes detailed steps for mixing, molding, and testing cement paste samples.
  • Use of standard apparatus such as the Vicat apparatus and trowel.
  • Measurement of initial and final penetration at specific time intervals post-mixing.
  • Optional remixing step to distinguish between false set and flash set tendencies.
• Calculation & Reporting: Results are reported as the percentage of final penetration relative to the initial, offering quantitative insight into setting behavior.
• Precision and Bias: The standard outlines repeatability expectations within and between laboratories.

Applications

ASTM C451-21 is crucial for:

• Cement Manufacturers: Evaluating product compliance with early stiffening limits, ensuring consistent quality, and validating changes in raw materials or production processes.
• Quality Control Laboratories: Routine testing of hydraulic cement during acceptance or certification processes.
• Construction and Concrete Production:
  • Assessing the suitability of cement for projects where workability and set time are critical, such as paving, precast elements, and on-site mixing.
  • Diagnosing issues with premature stiffening that may complicate placing or finishing concrete.
  • Informing adjustments to mixing or placing procedures, particularly in applications using transit mixers, concrete pumps, or non-agitating transport methods.
• Specification Compliance: Ensuring that cements do not exceed limits for early stiffening as required by project specifications or national standards.

False set is often manageable with standard mixing or delayed placement methods, while flash set poses greater risks for setting time compliance and can impact structural performance.

Related Standards

ASTM C451-21 references and works in coordination with several other standards relevant to hydraulic cement testing, including:

• ASTM C150/C150M: Specification for Portland Cement
• ASTM C183/C183M: Practice for Sampling Hydraulic Cement
• ASTM C187: Test Method for Water Required for Normal Consistency of Hydraulic Cement Paste
• ASTM C219: Terminology Relating to Hydraulic and Other Inorganic Cements
• ASTM C305: Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars
• ASTM C511: Specification for Mixing Rooms, Moist Cabinets, and Water Storage for Testing
• ASTM D1193: Specification for Reagent Water

These related standards ensure harmonized procedures for testing, terminology, sampling, and laboratory conditions, supporting international best practices for cement testing.

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Keywords: ASTM C451, early stiffening, hydraulic cement, paste method, false set, flash set, Vicat apparatus, cement quality, standard test method, cement compliance, construction materials testing.

Standards Content (Sample)

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: C451 − 21
Standard Test Method for
Early Stiffening of Hydraulic Cement (Paste Method)
This standard is issued under the fixed designation C451; 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.
1. Scope* C219 Terminology Relating to Hydraulic and Other Inor-
ganic Cements
1.1 This test method covers the determination of early
C305 Practice for Mechanical Mixing of Hydraulic Cement
stiffening in hydraulic-cement paste.
Pastes and Mortars of Plastic Consistency
1.2 The values stated in SI units are to be regarded as
C511 Specification for Mixing Rooms, Moist Cabinets,
standard. No other units of measurement are included in this
Moist Rooms, and Water Storage Tanks Used in the
standard.
Testing of Hydraulic Cements and Concretes
1.3 This standard does not purport to address all of the
C670 Practice for Preparing Precision and Bias Statements
safety concerns, if any, associated with its use. It is the
for Test Methods for Construction Materials
responsibility of the user of this standard to establish appro-
C1005 Specification for Reference Masses and Devices for
priate safety, health, and environmental practices and deter-
DeterminingMassandVolumeforUseinPhysicalTesting
mine the applicability of regulatory limitations prior to use.
of Hydraulic Cements
(Warning—Fresh hydraulic-cementitious mixtures are caustic
and may cause chemical burns to skin and tissue upon
3. Terminology
prolonged exposure.)
3.1 Definitions:
1.4 The text of this standard references notes and footnotes
3.1.1 For definitions of terms used in this test method, refer
which provide explanatory material. These notes and footnotes
to Terminology C219.
(excluding those in tables and figures) shall not be considered
as requirements of the standard.
4. Summary of Test Method
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard- 4.1 A paste is prepared with the cement to be tested, using
ization established in the Decision on Principles for the sufficient water to give a required initial penetration as mea-
Development of International Standards, Guides and Recom- sured by the Vicat apparatus at a stipulated time after comple-
mendations issued by the World Trade Organization Technical
tion of mixing. A second penetration, termed the final
Barriers to Trade (TBT) Committee. penetration, is measured at a later stipulated time. The ratio of
final penetration to initial penetration is calculated as a
2. Referenced Documents
percentage.
2.1 ASTM Standards:
5. Significance and Use
C150/C150M Specification for Portland Cement
C183/C183M Practice for Sampling and the Amount of
5.1 The purpose of this test method is to determine the
Testing of Hydraulic Cement
degree to which a cement paste develops early stiffening or to
C187 Test Method for Amount of Water Required for Nor-
establishwhetherornotacementcomplieswithaspecification
mal Consistency of Hydraulic Cement Paste
limit on early stiffening.
5.2 When used for establishing compliance with a specifi-
1 cation limit, the specification requirement is customarily stated
This test method is under the jurisdiction ofASTM Committee C01 on Cement
and is the direct responsibility of Subcommittee C01.30 on Time of Set.
in terms of the minimum allowable final penetration, in
Current edition approved Oct. 1, 2021. Published November 2021. Originally
percent, calculated in accordance with the Calculation Section.
approved in 1960. Last previous edition approved in 2019 as C451 – 19. DOI:
When used for estimating the relative tendency of a cement to
10.1520/C0451-21.
manifest early stiffening, additional information of value may
Section on Safety, Manual of Cement Testing, Annual Book of ASTM
Standards, Vol 04.01.
be obtained if the remix procedure described in the Procedure
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Section is employed. Under some conditions, a judgment may
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
be made by comparing the behavior in the initial test and in the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. remix procedure to differentiate a relatively less serious and
*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
C451 − 21
less persistent tendency to early stiffening (false set) from one 7. Reagent
that is more persistent and, consequently, more serious (flash
7.1 Mixing Water—Potable water is satisfactory for routine
set).
tests. Use reagent water for all referee and cooperative tests.
5.3 Severe false setting in a cement may cause difficulty
8. Sampling
from a placing and handling standpoint, but it is not likely to
cause difficulties where concrete is mixed for a longer time
8.1 When the test is part of acceptance testing, sample the
than usual, as usually occurs in transit mixing, or where it is
cement in accordance with Practice C183/C183M.
remixed prior to placing or transporting, as occurs in concrete
pumping operations. It is most likely to be noticeable where 9. Conditioning
concreteismixedforashortperiodoftimeinstationarymixers
9.1 Maintain the temperature and the humidity of the
and transported to the forms in non-agitating equipment, such
mixing room and the temperature of the mixing water in
as on some paving jobs, and when concrete is made in an
accordance with Specification C511 (see section titled “Re-
on-site batch plant.
quirements for Cement Mixing Rooms”).
5.4 Cements with severe false setting usually require
9.2 The dry materials shall be within the temperature range
slightly more water to produce the same consistency, which
of the mixing room prior to testing.
may be expected to result in slightly lower strengths and
increased drying shrinkage. 10. Procedure
5.5 Early stiffening resulting from false set is not likely to
10.1 Preparation of Cement Paste—Mix 500 g of cement
cause a cement to fail the applicable time of setting require- with sufficient water to produce a paste with an initial penetra-
ment.
tion of 32 6 4 mm using the following procedure.
10.1.1 Place the dry paddle and the dry bowl in the mixing
5.6 Early stiffening resulting from flash set, depending on
position in the mixer.
severity, can cause a cement to fail the applicable time of
10.1.2 Introduce the materials for a batch into the bowl and
setting requirement.
mix in the following manner:
10.1.2.1 Place all the mixing water in the bowl.
6. Apparatus
10.1.2.2 Add the cement to the water and allow 30 s for the
6.1 Vicat Apparatus, conforming to the requirements ofTest
water to absorb.
Method C187.
10.1.2.3 Start the mixer and mix at a slow speed (1406
5 r⁄min) for 30 s.
6.2 Flat Trowel, having a sharpened straight-edged steel
10.1.2.4 Stop the mixer for 15 s, and during this time scrape
blade 100 to 150 mm in length. The edges when placed on a
down into the batch any paste that may have collected on the
plane surface shall not depart from straightness by more than
sides of the bowl.
1 mm.
10.1.2.5 Start the mixer at a medium speed (285 610
...

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: C451 − 19 C451 − 21
Standard Test Method for
Early Stiffening of Hydraulic Cement (Paste Method)
This standard is issued under the fixed designation C451; 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.
1. Scope*
1.1 This test method covers the determination of early stiffening in hydraulic-cement paste.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of 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
exposure.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental 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 exposure.)
1.4 The text of this standard 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 the standard.
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:
C150/C150M Specification for Portland Cement
C183/C183M Practice for Sampling and the Amount of Testing of Hydraulic Cement
C187 Test Method for Amount of Water Required for Normal Consistency of Hydraulic Cement Paste
C219 Terminology Relating to Hydraulic and Other Inorganic Cements
C305 Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency
C511 Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic
Cements and Concretes
This test method is under the jurisdiction of ASTM Committee C01 on Cement and is the direct responsibility of Subcommittee C01.30 on Time of Set.
Current edition approved Aug. 1, 2019Oct. 1, 2021. Published August 2019November 2021. Originally approved in 1960. Last previous edition approved in 20182019
as C451 – 18.C451 – 19. DOI: 10.1520/C0451-19.10.1520/C0451-21.
Section on Safety, Manual of Cement Testing, Annual Book of ASTM Standards, Vol 04.01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
C451 − 21
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
C1005 Specification for Reference Masses and Devices for Determining Mass and Volume for Use in Physical Testing of
Hydraulic Cements
D1193 Specification for Reagent Water
3. Terminology
3.1 Definitions:
3.1.1 early stiffening, n—the early development of stiffness in the working characteristics of a hydraulic-cement paste, mortar, or
concrete; varieties include false set and flash set.
3.1.2 false set, n—the early development of stiffness in the working characteristics of a hydraulic-cement paste, mortar, or concrete
without the evolution of much heat, which stiffness can be dispelled and plasticity regained by further mixing without addition of
water; also known as “grab set,” “premature stiffening,” “ hesitation set,” and “rubber set.”
3.1.3 flash set, n—the early development of stiffness in the working characteristics of a hydraulic-cement paste, mortar, or
concrete, usually with the evolution of considerable heat, which stiffness cannot be dispelled nor can the plasticity be regained by
further mixing without addition of water; also known as “quick set.”
3.1.1 Refer to TerminologyFor definitions of C219 for definitions of other terms.terms used in this test method, refer to
Terminology C219.
4. Summary of Test Method
4.1 A paste is prepared with the cement to be tested, using sufficient water to give a required initial penetration as measured by
the Vicat apparatus at a stipulated time after completion of mixing. A second penetration, termed the final penetration, is measured
at a later stipulated time. The ratio of final penetration to initial penetration is calculated as a percentage.
5. Significance and Use
5.1 The purpose of this test method is to determine the degree to which a cement paste develops early stiffening or to establish
whether or not a cement complies with a specification limit on early stiffening.
5.2 When used for establishing compliance with a specification limit, the specification requirement is customarily stated in terms
of the minimum allowable final penetration, in percent, calculated in accordance with the Calculation Section. When used for
estimating the relative tendency of a cement to manifest early stiffening, additional information of value may be obtained if the
remix procedure described in the Procedure Section is employed. Under some conditions, a judgment may be made by comparing
the behavior in the initial test and in the remix procedure to differentiate a relatively less serious and less persistent tendency to
early stiffening (false set) from one that is more persistent and, consequently, more serious (flash set).
5.3 Severe false setting in a cement may cause difficulty from a placing and handling standpoint, but it is not likely to cause
difficulties where concrete is mixed for a longer time than usual, as usually occurs in transit mixing, or where it is remixed prior
to placing or transporting, as occurs in concrete pumping operations. It is most likely to be noticeable where concrete is mixed
for a short period of time in stationary mixers and transported to the forms in non-agitating equipment, such as on some paving
jobs, and when concrete is made in an on-site batch plant.
5.4 Cements with severe false setting usually require slightly more water to produce the same consistency, which may be expected
to result in slightly lower strengths and increased drying shrinkage.
5.5 Early stiffening resulting from false set is not likely to cause a cement to fail the applicable time of setting requirement.
5.6 Early stiffening resulting from flash set, depending on severity, can cause a cement to fail the applicable time of setting
requirement.
C451 − 21
6. Apparatus
6.1 Vicat Apparatus, conforming to the requirements of Test Method C187.
6.2 Flat Trowel, having a sharpened straight-edged steel blade 100 to 150 mm in length. The edges when placed on a plane surface
shall not depart from straightness by more than 1 mm.
6.3 Mixer, Bowl, Paddle, and Scraper, conforming to the requirements of Practice C305.
6.4 Glass Graduates, 200 or 250 mlmL capacity, conforming to the requirements of Specification C1005.
6.5 Masses and Mass Determining Devices, conforming to the requirements of Specification C1005. The devices for determining
mass shall be evaluated for continuing precise performance utilizing the procedure in Specification C1005, Appendix X1 using a
verification check mass of approximately 1000 g.
6.6 Conical Ring, made of a rigid, non-corroding, non-absorbernt material, having a height of 40 6 1 mm, an inside diameter at
the bottom of 70 6 3 mm, and an inside diameter at the top of 60 6 3 mm (see Test Method C187, Fig. 1 item G).
6.7 Plane Non-Absorptive Plate, 100 6 5 mm square, of similar planeness, cor
...