ASTM C348-21

Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars

SIGNIFICANCE AND USE
5.1 This test method provides a means for determining the flexural strength of hydraulic cement mortars. Portions of the mortar prisms tested in flexure in accordance with this test method may be used for the determination of compressive strength in accordance with Test Method C349.  
5.2 The values are determined from this test method for research or reference purposes only and are not used for determining compliance with specification requirements.
SCOPE
1.1 This test method covers the determination of the flexural strength of hydraulic-cement mortars.  
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 Values in SI units shall be obtained by measurement in SI units or by appropriate conversion, using the Rules for Conversion and rounding given in IEEE/ASTM SI 10, of measurements made in other units.  
1.4 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)  
1.5 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: 31-Mar-2021
• ICS: 91.100.10 - Cement. Gypsum. Lime. Mortar
• Technical Committee: C01 - Cement
• Drafting Committee: C01.27 - Strength

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 C109/C109M-23 - Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 50 mm [2 in.] Cube Specimens)
• Effective Date: 15-Dec-2023
• 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 C125-19a - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 15-Dec-2019
• 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 C125-19 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jan-2019
• Refers: ASTM C349-18 - Standard Test Method for Compressive Strength of Hydraulic-Cement Mortars<brk/> (Using Portions of Prisms Broken in Flexure)
• Effective Date: 01-Dec-2018
• Refers: ASTM C125-18b - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Oct-2018
• Refers: ASTM C125-18a - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jul-2018
• 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

Overview

ASTM C348-21: Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars establishes the procedure for determining the flexural strength of hydraulic-cement mortar samples. Developed by ASTM International, this standard is widely referenced in research and quality control laboratories for comparing mortar types, monitoring manufacturing consistency, and supporting product development. The method provides valuable flexural strength data using prisms tested by center-line point loading and is applicable to a variety of hydraulic cement mortars, including those prepared with Portland or air-entraining cement.

All results are reported in SI units as specified by the standard. While results are intended for research or reference and not for formal specification compliance, they are fundamental in ensuring reliable, reproducible testing of mortar strength under laboratory conditions.

Key Topics

• Flexural Strength of Hydraulic-Cement Mortars: The central focus of the standard is on evaluating the ability of cement mortar prisms to resist bending forces before rupture.
• Standardized Testing Apparatus: Detailed requirements are given for equipment, such as the flexure testing device, molds, tamper, and mixing apparatus, ensuring consistency across different laboratories.
• Test Specimen Preparation: The precision in mixing, molding, curing, and storage is outlined to minimize variations and maximize comparability.
• Procedural Consistency: The method prescribes detailed procedures for molding, compacting, and finishing specimens, ensuring accurate and reproducible testing.
• SI Units Standardization: All measurements and reporting must conform strictly to the International System of Units (SI), aligned with IEEE/ASTM SI 10 guidance.
• Research & Reference Use: Results are aimed at research or reference purposes; they are not used for direct specification compliance.

Applications

The test method outlined in ASTM C348-21 is used extensively in both research and industrial laboratories for:

• Comparative Analysis: Evaluating and comparing the flexural strength of different hydraulic-cement mortar formulations to optimize mix design or assess raw material changes.
• Quality Control: Monitoring production batches for consistency in mechanical performance of mortar products.
• Academic Research: Supporting studies in cement chemistry, mortar durability, and structure-property relationships through precise flexural testing.
• Aging and Curing Studies: Assessing changes in mortar strength over time or under varying curing conditions.
• Supporting Compressive Strength Evaluation: Broken prisms from this flexural strength test may be further used for compressive strength determination, enhancing sample utility (as referenced by ASTM C349).

Proper adherence to ASTM C348-21 ensures the reliability and reproducibility of results, supporting informed decisions in product development, formulation adjustments, and academic research.

Related Standards

Several ASTM and technical standards support or relate to ASTM C348-21, including:

• ASTM C349 - Test Method for Compressive Strength of Hydraulic-Cement Mortars (Using Portions of Prisms Broken in Flexure)
• ASTM C109/C109M - Test Method for Compressive Strength of Hydraulic Cement Mortars
• ASTM C1437 - Test Method for Flow of Hydraulic Cement Mortar
• ASTM C125 / C219 - Terminology relating to concrete, hydraulic cements, and aggregates
• ASTM C230/C230M - Specification for Flow Table for Use in Tests of Hydraulic Cement
• ASTM C305 - Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars
• ASTM C670 - Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• ASTM C778 - Specification for Standard Sand
• ASTM C1005 - Specification for Reference Masses and Devices for Determining Mass and Volume
• IEEE/ASTM SI 10 - Standard for the Use of the International System of Units (SI)

Adopting ASTM C348-21 and related standards helps ensure standardized, high-quality mortar testing to support the construction and materials industry worldwide.

Keywords: flexural strength, hydraulic-cement mortar, mortar strength, cement testing, ASTM C348, standard test method, SI units, research, quality control.

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: C348 − 21
Standard Test Method for
Flexural Strength of Hydraulic-Cement Mortars
This standard is issued under the fixed designation C348; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* C219Terminology Relating to Hydraulic and Other Inor-
ganic Cements
1.1 Thistestmethodcoversthedeterminationoftheflexural
C230/C230MSpecification for Flow Table for Use in Tests
strength of hydraulic-cement mortars.
of Hydraulic Cement
1.2 The values stated in SI units are to be regarded as
C305Practice for Mechanical Mixing of Hydraulic Cement
standard. No other units of measurement are included in this
Pastes and Mortars of Plastic Consistency
standard.
C349Test Method for Compressive Strength of Hydraulic-
Cement Mortars (Using Portions of Prisms Broken in
1.3 Values in SI units shall be obtained by measurement in
SI units or by appropriate conversion, using the Rules for Flexure)
C670Practice for Preparing Precision and Bias Statements
Conversion and rounding given in IEEE/ASTM SI 10,of
measurements made in other units. for Test Methods for Construction Materials
C778Specification for Standard Sand
1.4 This standard does not purport to address all of the
C1005Specification for Reference Masses and Devices for
safety concerns, if any, associated with its use. It is the
DeterminingMassandVolumeforUseinPhysicalTesting
responsibility of the user of this standard to establish appro-
of Hydraulic Cements
priate safety, health, and environmental practices and deter-
C1437Test Method for Flow of Hydraulic Cement Mortar
mine the applicability of regulatory limitations prior to use.
IEEE/ASTM SI 10Standard for Use of the International
(Warning—Fresh hydraulic cementitious mixtures are caustic
System of Units (SI): The Modern Metric System
and may cause chemical burns to skin and tissue upon
prolonged exposure. )
3. Terminology
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard- 3.1 Definitions:
ization established in the Decision on Principles for the 3.1.1 For definitions of terms used in this test method, refer
Development of International Standards, Guides and Recom- to Terminology C125 and C219.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 4. Summary of Test Method
4.1 The test mortar used consists of one part cement and
2. Referenced Documents
2.75 parts of sand proportion by mass. Portland or air-
2.1 ASTM Standards:
entraining portland cements are mixed at specified water-
C109/C109MTest Method for Compressive Strength of
cement ratios. Water content of other cements is that sufficient
Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube
to obtain a flow of 110 6 5% with 25 drops of the flow table.
Specimens)
Test prisms, 40 by 40 by 160mm, are molded by tamping in
C125Terminology Relating to Concrete and Concrete Ag-
two layers. Prisms are cured one day in the molds and stripped
gregates
until tested by center point loading.
5. Significance and Use
ThistestmethodisunderthejurisdictionofASTMCommitteeC01onCement
5.1 This test method provides a means for determining the
and is the direct responsibility of Subcommittee C01.27 on Strength.
flexural strength of hydraulic cement mortars. Portions of the
Current edition approved April 1, 2021. Published May 2021. Originally
approved in 1954. Last previous edition approved in 2020 as C348–20. DOI:
mortar prisms tested in flexure in accordance with this test
10.1520/C0348-21.
method may be used for the determination of compressive
See the section on Safety, Manual of Cement Testing, Annual Book of ASTM
strength in accordance with Test Method C349.
Standards, Vol 04.01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.2 The values are determined from this test method for
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
research or reference purposes only and are not used for
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. determining compliance with specification requirements.
*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
C348 − 21
6. Apparatus 6.6 Tamper Guide—The tamper guide (see Fig. 2) shall be
made of metal (such as brass of Rockwell hardness not less
6.1 Weights, Weighing Devices, and Glass Graduates—
thanHRB55)notattackedbythecementmortar.Itshalllieflat
Weights, weighing devices, and glass graduates shall conform
onthemoldandshallnotprotrudeoveranyinterioredgeofthe
to the requirements of Specification C1005. The balance shall
form more than 0.40 mm. The height of the guide shall be
be evaluated for precision and accuracy at 2000g.
25mm.
6.2 Mixer, Bowl, and Paddle—An electrically driven me-
6.7 Trowel—The trowel shall have a steel blade 115 by
chanical mixer of the type equipped with paddle and mixing
250mm in length, with straight edges.
bowl, as specified in the Apparatus section of Practice C305.
6.8 Flexure Testing Device—The centerpoint loading
6.3 Flow Table and Flow Mold—Flow table and flow mold
method shall be used in making flexure tests on the prism
shall conform to Specification C230/C230M.
specimens. The device used shall be designed such that the
6.4 Specimen Molds—Molds for the 40 by 40 by 160mm
forcesappliedtothespecimenwillbeverticalonlyandapplied
prism specimens shall be triple-gang molds and shall be so
without eccentricity. A device that accomplishes this purpose,
designed that the specimens will be molded with their longi-
for use in a compression testing machine, is shown in Fig. 3.
tudinal axes in a horizontal position. The molds shall be made
Apparatus for making flexure tests of mortar specimens shall
of a hard metal, not attacked by cement mortar, and with a
be designed to incorporate the following principles:
Rockwell hardness of not less than HRB 55. The parts of the
6.8.1 The distance between supports and points of load
molds shall be matchmarked and, when assembled, shall be
application shall remain constant.
tight-fittingandpositivelyheldtogether.Thesidesofthemolds
6.8.2 The load shall be applied normal to the loaded surface
shall be sufficiently rigid to prevent spreading or warping. The
of the specimen and in such a manner as to avoid all
interior faces of the molds shall be plane surfaces with a
eccentricity of loading.
permissible variation, in any 50mm line on a surface, of
6.8.3 The direction of the reactions should be parallel to the
0.03mm for new molds and 0.05 mm for molds in use. The
direction of the applied load at all times during the test.
distance between opposite sides shall be 40 6 0.13 mm for
6.8.4 The load should be applied at a uniform rate and in a
new molds and 40 6 0.3 mm for molds in use. The height of
manner to avoid shock.
the molds shall be 40 mm with permissible variations of+0.25
6.9 Compression Testing Machine—The compression test-
and−0.15mm for new molds, and+0.25 and−0.40 mm for
ing machine used with the flexure testing device, as shown in
molds in use. The inside length of the molds shall be 160 6
Fig. 3, shall be of the hydraulic type and conform to the
2.5mm.The angle between adjacent interior faces and top and
requirements prescribed in Test Method C109/C109M.
bottom planes of the mold shall be 90 6 0.5°, measured at
pointsslightlyremovedfromtheintersectionsofthefaces.The
NOTE 1—Most hydraulic compression machines designed for breaking
baseplateshallbeapproximately10mminthicknessandshall 50 mm cubes have a relatively small diameter lower bearing surface
directly centered below the upper spherically seated head, on which
have a plane surface 200 by 180 mm with a permissible
close-fitting pedestals of appropriate heights are set for breaking 50 mm
variation in any 50 mm line on the surface of 0.03 mm.
cubes and 50 by 100 mm or 75 by 150 mm cylinders. The base plate of
6.5 Tamper—The tamper (see Fig. 1) shall be made of theflexuretestingapparatusshowninFig.3isdesignedtorestonthelow
pedestal intended for tests on 75 by 150 mm.
nonabsorptive, nonabrasive material, such as a rubber com-
NOTE 2—In the absence of self-centering arrangements on machines
pound having a Shore A durometer hardness of 80 6 10, or
withlargelowerbearingsurfaces,thecenterofthissurfacedirectlybelow
seasoned oak wood rendered nonabsorptive by immersion for
thecenteroftheuppersphericallyseatedheadshallbeaccuratelylocated.
15 min in paraffin at approximately 200 °C. The face of the
Acircle or concentric circles of appropriate diameters shall be scribed on
tamper shall be 22 by 85 mm. the lower bearing surface around this point. A cylindrical pedestal of
FIG. 1 Tamper
C348 − 21
FIG. 2 Tamper Guide Attachment
appropriate diameter and height shall be obtained. End faces of the
10. Procedure
pedestal must be plane and parallel and at 90° to the axis of the cylinder.
10.1 Proportioning, Consistency, and Mixing of Mortars—
The upper face shall have a diameter of 77.5 mm.
The proportioning, consistency, and mixing of the standard
7. Materials mortar shall be in accordance with the Procedure section of
Test Method C109/C109M.
7.1 Graded Standard Sand:
10.2 Determination of Flow—The flow shall be determined
7.1.1 The sand used for making test specimens shall be
natural silica sand and conform to Sp
...

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: C348 − 20 C348 − 21
Standard Test Method for
Flexural Strength of Hydraulic-Cement Mortars
This standard is issued under the fixed designation C348; 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 the flexural strength of hydraulic-cement mortars.
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 Values in SI units shall be obtained by measurement in SI units or by appropriate conversion, using the Rules for Conversion
and rounding given in IEEE/ASTM SI 10, of measurements made in other units.
1.4 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. )
1.5 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:
C109/C109M Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube Specimens)
C125 Terminology Relating to Concrete and Concrete Aggregates
C219 Terminology Relating to Hydraulic and Other Inorganic Cements
C230/C230M Specification for Flow Table for Use in Tests of Hydraulic Cement
C305 Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency
C349 Test Method for Compressive Strength of Hydraulic-Cement Mortars (Using Portions of Prisms Broken in Flexure)
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
C778 Specification for Standard Sand
C1005 Specification for Reference Masses and Devices for Determining Mass and Volume for Use in Physical Testing of
Hydraulic Cements
C1437 Test Method for Flow of Hydraulic Cement Mortar
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI): The Modern Metric System
3. Terminology
3.1 Definitions:
This test method is under the jurisdiction of ASTM Committee C01 on Cement and is the direct responsibility of Subcommittee C01.27 on Strength.
Current edition approved April 1, 2020April 1, 2021. Published April 2020May 2021. Originally approved in 1954. Last previous edition approved in 20192020 as
C348 – 19.C348 – 20. DOI: 10.1520/C0348-20.10.1520/C0348-21.
See the 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
C348 − 21
3.1.1 For definitions of terms used in this test method, refer to Terminology C125 and C219.
4. Summary of Test Method
4.1 The test mortar used consists of one part cement and 2.75 parts of sand proportion by mass. Portland or air-entraining portland
cements are mixed at specified water-cement ratios. Water content of other cements is that sufficient to obtain a flow of 110 6 5 %
with 25 drops of the flow table. Test prisms, 40 by 40 by 160 mm, are molded by tamping in two layers. Prisms are cured one day
in the molds and stripped until tested by center point loading.
5. Significance and Use
5.1 This test method provides a means for determining the flexural strength of hydraulic cement mortars. Portions of the mortar
prisms tested in flexure in accordance with this test method may be used for the determination of compressive strength in
accordance with Test Method C349.
5.2 The values are determined from this test method for research or reference purposes only and are not used for determining
compliance with specification requirements.
6. Apparatus
6.1 Weights, Weighing Devices, and Glass Graduates—Weights, weighing devices, and glass graduates shall conform to the
requirements of Specification C1005. The balance shall be evaluated for precision and accuracy at 2000 g.
6.2 Mixer, Bowl, and Paddle—An electrically driven mechanical mixer of the type equipped with paddle and mixing bowl, as
specified in the Apparatus section of Practice C305.
6.3 Flow Table and Flow Mold—Flow table and flow mold shall conform to Specification C230/C230M.
6.4 Specimen Molds—Molds for the 40 by 40 by 160 mm prism specimens shall be triple-gang molds and shall be so designed
that the specimens will be molded with their longitudinal axes in a horizontal position. The molds shall be made of a hard metal,
not attacked by cement mortar, and with a Rockwell hardness of not less than HRB 55. The parts of the molds shall be
matchmarked and, when assembled, shall be tight-fitting and positively held together. The sides of the molds shall be sufficiently
rigid to prevent spreading or warping. The interior faces of the molds shall be plane surfaces with a permissible variation, in any
50 mm line on a surface, of 0.03 mm for new molds and 0.05 mm for molds in use. The distance between opposite sides shall be
40 6 0.13 mm for new molds and 40 6 0.3 mm for molds in use. The height of the molds shall be 40 mm with permissible
variations of +0.25 and −0.15 mm for new molds, and +0.25 and −0.40 mm for molds in use. The inside length of the molds shall
be 160 6 2.5 mm. The angle between adjacent interior faces and top and bottom planes of the mold shall be 90 6 0.5°, measured
at points slightly removed from the intersections of the faces. The base plate shall be approximately 10 mm in thickness and shall
have a plane surface 200 by 180 mm with a permissible variation in any 50 mm line on the surface of 0.03 mm.
6.5 Tamper—The tamper (see Fig. 1) shall be made of nonabsorptive, nonabrasive material, such as a rubber compound having
a Shore A durometer hardness of 80 6 10, or seasoned oak wood rendered nonabsorptive by immersion for 15 min in paraffin at
approximately 200 °C. The face of the tamper shall be 22 by 85 mm.
6.6 Tamper Guide—The tamper guide (see Fig. 2) shall be made of metal (such as brass of Rockwell hardness not less than HRB
55) not attacked by the cement mortar. It shall lie flat on the mold and shall not protrude over any interior edge of the form more
than 0.40 mm. The height of the guide shall be 25 mm.
6.7 Trowel—The trowel shall have a steel blade 115 by 250 mm in length, with straight edges.
6.8 Flexure Testing Device—The centerpoint loading method shall be used in making flexure tests on the prism specimens. The
device used shall be designed such that the forces applied to the specimen will be vertical only and applied without eccentricity.
A device that accomplishes this purpose, for use in a compression testing machine, is shown in Fig. 3. Apparatus for making flexure
tests of mortar specimens shall be designed to incorporate the following principles:
C348 − 21
FIG. 1 Tamper
FIG. 2 Tamper Guide Attachment
C348 − 21
FIG. 3 Special Components for Adapting Compression Testing Machine for Testing 40 by 40 by 160 mm Prisms
C348 − 21
6.8.1 The distance between supports and points of load application shall remain constant.
6.8.2 The load shall be applied normal to the loaded surface of the specimen and in such a manner as to avoid all eccentricity of
loading.
6.8.3 The direction of the reactions should be parallel to the direction of the applied load at all times during the test.
6.8.4 The load should be applied at a uniform rate and in a manner to avoid shock.
6.9 Compression Testing Machine—The compression testing machine used with the flexure testing device, as shown in Fig. 3,
shall be of the hydraulic type and conform to the requirements prescribed in Test Method C109/C109M.
NOTE 1—Most hydraulic compression machines designed for breaking 50 mm cubes have a relatively small diameter lower bearing surface directly
centered below the upper spherically seated head, on which close-fitting pedestals of appropriate heights are set for breaking 50 mm cubes and 50 by
100 mm or 75 by 150 mm cylinders. The base plate of the flexure testing apparatus shown in Fig. 3 is designed to rest on the low pedestal intended for
tests on 75 by 150 mm.
NOTE 2—In the absence of self-centering arrangements on machines with large lower bearing surfaces, the center of this surface directly below the center
of the upper spherically seated head shall be accurately located. A circle or concentric circles of appropriate diameters shall be scribed on the lower bearing
surface around this point. A cylindrical pedestal of appropriate diameter and height shall be obtained. End faces of the pedestal must be plane and parallel
and at 90° to the axis of the cylinder. The upper face shall have a diameter of 77.5 mm.
7. Materials
7.1 Graded Standard Sand:
7.1.1 The sand used for making test specimens shall be natural silica sand and conform to Specification C778.
8. Number of Specimens
8.1 Three or more specimens shall be made for each period of test specified.
9. Preparing Specimen Molds
9.1 Prepare the specimen molds as prescribed in Test Method C109/C109M.
10. Procedure
10.1 Proportioning, Consistency, an
...