ASTM C1040/C1040M-16a

Standard Test Methods for In-Place Density of Unhardened and Hardened Concrete, Including Roller Compacted Concrete, By Nuclear Methods

SIGNIFICANCE AND USE
4.1 These test methods are useful as rapid, nondestructive techniques for the in-place determination of the density of unhardened concrete. The backscatter test method is also useful for the same purpose on hardened concrete. The fundamental assumptions inherent in the test methods are that Compton scattering is the dominant interaction and that the material under test is homogeneous.  
4.2 These test methods are suitable for control and for assisting in acceptance testing during construction, for evaluation of concrete quality subsequent to construction, and for research and development.  
Note 1: Care must be taken when using these test methods in monitoring the degree of consolidation, which is the ratio of the actual density achieved to the maximum density attainable with a particular concrete. The test methods presented here are used to determine the actual density. A density measurement, by any test method, is a function of the components of the concrete and may vary, to some extent, in response to the normal, acceptable variability of those components.  
4.3 Test results may be affected by reinforcing steel, by the chemical composition of concrete constituents, and by sample heterogeneity. The variations resulting from these influences are minimized by instrument design and by the user's compliance with appropriate sections of the test procedure. Results of tests by the backscatter test method may also be affected by the density of underlying material. The backscatter test method exhibits spatial bias in that the apparatus's sensitivity to the material under it decreases with distance from the surface of the concrete.
Note 2: Typically, backscatter gauge readings represent the density in the top 75 to 100 mm [3 to 4 in.] of material.
SCOPE
1.1 These test methods cover the determination of the in-place density of unhardened and hardened concrete, including roller compacted concrete, by gamma radiation. For notes on the nuclear test see Appendix X1.  
1.2 Two test methods are described, as follows:    
Section  
Test Method A—Direct Transmission
Test Method B—Backscatter  
8
9  
1.3 The values stated in either SI units 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 non-conformance with the standard.  
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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Published
• Publication Date: 14-Dec-2016
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: C09 - Concrete and Concrete Aggregates
• Drafting Committee: C09.45 - Roller-Compacted Concrete

Relations

• 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 C29/C29M-23 - Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
• Effective Date: 01-Oct-2023
• Refers: ASTM C125-19a - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 15-Dec-2019
• Refers: ASTM C125-19 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jan-2019
• 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 C125-18 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jan-2018
• Refers: ASTM C29/C29M-17 - Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
• Effective Date: 01-Jan-2017
• Refers: ASTM C125-16 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 15-Dec-2016
• Refers: ASTM C29/C29M-16 - Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
• Effective Date: 01-Feb-2016
• Refers: ASTM C125-15b - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 15-Dec-2015
• Refers: ASTM C125-15a - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jul-2015
• Refers: ASTM C125-15 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Feb-2015
• Refers: ASTM C125-14 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Aug-2014

Overview

ASTM C1040/C1040M-16a is the standard test method for determining the in-place density of both unhardened and hardened concrete, including roller-compacted concrete, using nuclear methods. Issued by ASTM International, this standard provides two testing approaches: direct transmission and backscatter, leveraging gamma radiation as a rapid, nondestructive technique. The standard is widely utilized in the construction industry for quality control, acceptance testing, and research, offering advantages like speed, minimal disturbance to the structure, and reliable results when properly implemented.

Key Topics

• Nuclear Density Measurement
  The standard describes nuclear test methods that utilize the interaction of gamma rays (primarily Compton scattering) with concrete material to determine its density. Test methods are applicable to a range of concrete types, including roller-compacted and conventional mixtures.

• Test Methods

  • Direct Transmission: Measures density at varying depths within unhardened concrete using a probe inserted into the material.
  • Backscatter: Applicable to both unhardened and hardened concrete, the gauge sits on the surface and measures density primarily in the upper layer.

• Calibration and Precision
  The document stipulates device calibration and adjustment processes to address variations in concrete composition and ensure that readings are accurate and comparable. Instrument precision and proper standardization are critical for consistent results.

• Influencing Factors
  Results can be affected by the presence of reinforcing steel, the chemical makeup of the aggregate, and the homogeneity of the concrete. The backscatter method, in particular, may reflect the properties of underlying materials and is sensitive to surface conditions.

• Safety and Compliance
  Since nuclear devices use gamma radiation, adherence to regulatory requirements and robust safety practices is mandatory.

Applications

The ASTM C1040/C1040M-16a standard is essential for:

• Construction Quality Control
  Enabling real-time monitoring of concrete density during placement for both traditional and roller-compacted applications.

• Acceptance Testing
  Providing in-place density measurements to verify concrete meets project specifications during and after construction.

• Post-Construction Evaluation
  Used to assess the quality of hardened concrete structures without the need for coring or damaging the material.

• Research and Development
  Helpful in testing new concrete formulations or methods, facilitating comparisons and optimization of mixtures.

Typical users include contractors, construction inspectors, materials engineers, and quality assurance professionals. The rapid, nondestructive nature of nuclear density testing enhances productivity and confidence in material performance for paving, slabs, pavements, and structural concreted elements.

Related Standards

The following ASTM standards are commonly referenced in connection with ASTM C1040/C1040M-16a:

• ASTM C29/C29M - Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
• ASTM C125 - Terminology Relating to Concrete and Concrete Aggregates
• ASTM C138/C138M - Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete
• ASTM C670 - Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials

Understanding and applying ASTM C1040/C1040M-16a in combination with these related standards ensures comprehensive and accurate assessment of concrete density, supports regulatory compliance, and promotes construction quality and safety in concrete infrastructure projects.

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: C1040/C1040M − 16a
Standard Test Methods for
In-Place Density of Unhardened and Hardened Concrete,
Including Roller Compacted Concrete, By Nuclear Methods
This standard is issued under the fixed designation C1040/C1040M; 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* 3. Terminology
1.1 These test methods cover the determination of the 3.1 Definitions:
in-place density of unhardened and hardened concrete, includ- 3.1.1 For definitions of terms used in these test methods,
ing roller compacted concrete, by gamma radiation. For notes
refer to Terminology C125.
on the nuclear test see Appendix X1.
4. Significance and Use
1.2 Two test methods are described, as follows:
4.1 These test methods are useful as rapid, nondestructive
Section
techniques for the in-place determination of the density of
Test MethodA—Direct Transmission 8
unhardened concrete. The backscatter test method is also
Test Method B—Backscatter 9
useful for the same purpose on hardened concrete. The
1.3 The values stated in either SI units or inch-pound units
fundamental assumptions inherent in the test methods are that
are to be regarded separately as standard. The values stated in
Compton scattering is the dominant interaction and that the
each system may not be exact equivalents; therefore, each
material under test is homogeneous.
system shall be used independently of the other. Combining
4.2 These test methods are suitable for control and for
values from the two systems may result in non-conformance
assisting in acceptance testing during construction, for evalu-
with the standard.
ation of concrete quality subsequent to construction, and for
1.4 This standard does not purport to address all of the
research and development.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- NOTE 1—Care must be taken when using these test methods in
monitoring the degree of consolidation, which is the ratio of the actual
priate safety and health practices and determine the applica-
density achieved to the maximum density attainable with a particular
bility of regulatory limitations prior to use.
concrete.The test methods presented here are used to determine the actual
density. A density measurement, by any test method, is a function of the
2. Referenced Documents
components of the concrete and may vary, to some extent, in response to
the normal, acceptable variability of those components.
2.1 ASTM Standards:
C29/C29M Test Method for Bulk Density (“Unit Weight”) 4.3 Test results may be affected by reinforcing steel, by the
and Voids in Aggregate
chemical composition of concrete constituents, and by sample
C125 Terminology Relating to Concrete and Concrete Ag- heterogeneity. The variations resulting from these influences
gregates are minimized by instrument design and by the user’s compli-
C138/C138M Test Method for Density (Unit Weight),Yield, ance with appropriate sections of the test procedure. Results of
and Air Content (Gravimetric) of Concrete tests by the backscatter test method may also be affected by the
C670 Practice for Preparing Precision and Bias Statements density of underlying material. The backscatter test method
for Test Methods for Construction Materials exhibits spatial bias in that the apparatus’s sensitivity to the
material under it decreases with distance from the surface of
the concrete.
NOTE 2—Typically, backscatter gauge readings represent the density in
These test methods are under the jurisdiction of ASTM Committee C09 on
Concrete and ConcreteAggregatesand are the direct responsibility of Subcommittee the top 75 to 100 mm [3 to 4 in.] of material.
C09.45 on Roller-Compacted Concrete.
Current edition approved Dec. 15, 2016. Published January 2017. Originally
5. Apparatus
approved in 1985. Last previous edition approved in 2016 as C1040/C1040M – 16.
DOI: 10.1520/C1040_C1040M-16A.
5.1 The exact details of construction of the apparatus may
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
vary,buttheapparatusasawholeshallsatisfytherequirements
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
for system precision stated in Annex A1. The system shall
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. consist of the following:
*A Summary of Changes section appears at the end of this standard
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
C1040/C1040M − 16a
NOTE 4—Calibration curves are supplied by gauge manufacturers, or
5.1.1 Gamma Source—An encapsulated and sealed radio-
can be established using blocks of known density or prepared containers
isotopic source, such as cesium-137 (see X1.3).
of uniform, unchanging material compacted to known densities. Materials
5.1.2 Detector—Any type of gamma detector, such as a
consideredsatisfactoryforuseinblocksincludegranite,aluminum,chalk,
Geiger-Müller tube, scintillation crystal, or proportional coun-
limestone, and magnesium.
ter.
6.2 Adjusting Calibration Curves—Prior to use, adjust the
5.1.3 Probe—For direct transmission measurements, either
instrument’s calibration curve, if necessary, to compensate for
thegammasourceorthedetectorshallbehousedinaprobefor
chemical composition effects. Such an adjustment is necessary
inserting in a preformed hole in the material to be tested. The
wheneverthechemicalcompositionoftheconcretetobetested
probe shall be marked in increments of 50 mm [2 in.] for tests
differs significantly from that for which the calibration curve
with probe depths from 50 to 300 mm [2 to 12 in.]. The probe
was established. An adjustment is also necessary if the testing
shall be so made mechanically, that when moved manually to
equipment has been changed. Adjustment is particularly im-
the marked depth desired, it will be held securely in position at
portant for backscatter test method measurements. Determine
that depth.
the necessary adjustments using the same mode of operation
5.1.4 Readout Instrument—A suitable scaler or direct read-
and at the same depth (if using direct transmission) as that
out meter.
intendedfortesting.Arecommendedprocedureformakingthis
5.1.5 Gauge Housing—The source, detector, readout instru-
adjustment is as follows:
ment and appropriate power supplies shall be in housings of
6.2.1 Prepare a concrete mix similar in composition to the
rugged construction that are moisture and dust proof.
material to be tested subsequently.
5.1.6 Reference Standard—Ablock of uniform, unchanging
6.2.2 Fill the calibration adjustment container with concrete
density provided for checking equipment operation, back-
and consolidate to produce a uniform, homogeneous material
ground count, and count-rate reproducibility.
with approximately the density that will be achieved in the
5.1.7 Guide Plate and Hole-Forming-Device—For direct
construction.
transmission measurements, a guide plate and a device, such as
NOTE 5—Consolidation may be achieved by the procedure used for unit
apinordrillrod,havinganominaldiameterslightlylargerthan
weight testing (Test Method C138/C138M) or by other methods, such as
theprobe,forformingaholenormaltotheconcretesurfaceare
spading the concrete and then dropping the ends of the container
required.
alternately on a rigid surface.
5.1.8 Calibration Adjustment Container—The container
6.2.3 Strike off the container with strike-off plate or bar.
shall be rigid and watertight, with minimum inside dimensions
Take care to make the concrete surface flat and flush with the
large enough to allow the calibration curve adjustment proce-
container edges.
dure (6.2) to be followed with no effect of the finite size of the
container on the instrument’s responses. The volume of the
NOTE 6—A2 mm [ ⁄16 in.] average difference between the concrete
container shall be established following the procedure outlined surface and the container edges in a 150 mm [6 in.] deep container will
producea1to2% error in the weighed density of the concrete.
in Test Method C29/C29M.
6.2.4 Weigh the concrete in the container to the nearest 0.2
NOTE 3—For backscatter measurements, a container 450 by 450 by 150
kg [0.5 lb] and determine the weighed density as follows:
mm [18 by 18 by 6 in.] will meet this requirement for most equipment
currently available commercially. For 50-mm [2-in.] depth direct trans-
W
c
mission measurements, a container 600 by 600 by 100 mm [24 by 24 by
W 5 (1)
V
4 in.] will meet this requirement.
where:
5.1.9 Scale—The scale shall be accurate to within 0.2 kg
3 3
[0.5lb]ofthetestloadatanypointwithintherangeofuse.The W = weighed density of concrete, kg/m [lb⁄ft ],
W = mass of the concrete, kg [lb], and
range of use shall be considered to extend from the weight of
c
3 3
V = volume of the container, m [ft ].
thecalibrationadjustmentcontainerempty,totheweightofthe
3 3
measure plus the contents at 2600 kg/m [160 lb/ft ].
6.2.5 Immediately take three automatically timed direct
5.1.10 Strike-Off Plate or Bar—This shall be a flat metal or
transmission or backscatter readings with the instrument cen-
glass plate or metal bar with a length at least 50 mm [2 in.]
tered on the surface of the concrete in the container. Rotate the
greater than the length, width, or diameter of the calibration
base of the instrument 90° around the vertical axis, with
adjustment container.The strike-off must be rigid, straight, and
subsequent rotations of 180 and 270° from the original
smoothenoughtofinishtheconcretesurfaceflatandflushwith
position. Obtain three additional automatically timed counts at
the edges of the calibration adjustment container.
each position. The instrument must be centered over the
surface of the concrete in each rotated position to prevent edge
6. Calibration
effects on the instrument reading.
6.2.6 Using the applicable calibration curve, determine the
6.1 Calibration curves are established by determining the
density from the average of the 12 counts obtained in 6.2.5.
nuclear count rate of each of several materials at different and
6.2.7 Determine the difference between the two density
known densities, plotting the count rate (or count ratio) versus
readings obtained in 6.2.4 and 6.2.6.
each known density, and placing a curve through the resulting
points. The method used to establish the curve must be the 6.2.8 Repeat 6.2.2 – 6.2.7 on two additional concrete mixes
same as that used to determine the density. The materials used of the same proportions. Determine the adjustment factor by
for calibration must be of uniform density. averaging the three values obtained in 6.2.7 and 6.2.8. If one of
C1040/C1040M − 16a
the three values differs from the average by more than 25 TEST METHOD A—DIRECT TRANSMISSION (FOR
3 3
kg/m [1.5 lb/ft ], discard it as a statistical outlier and recalcu- UNHARDENED CONCRETE)
late the adjustment factor as the average of the remaining two
8. Procedure
values.
6.2.9 Use the adjustment factor determined in 6.2.8 to plot
8.1 Selectatestlocationsuchthat,whenthegaugeisplaced
a corrected count-rate calibration curve which shall be parallel
in test position:
to the original calibration curve and offset by the amount
8.1.1 Any point on the source-detector axis shall be at least
indicated in 6.2.8. Alternatively, the value of the adjustment
230 mm [9 in.] from any pavement edge or object.
factor shall be attached to the instrument and applied to all
8.1.2 Reinforcing steel shall not be present in the volume
density determinations arrived at from an original (unadjusted)
bounded by the extended probe and the detector tubes.
calibration curve.
8.1.3 The test location shall contain concrete to a depth 25
mm[1in.]greaterthanthattowhichtheprobewillbeinserted.
NOTE 7—In some circumstances, for example, where chemical compo-
In thin concrete overlay projects, this may require the removal
sition changes are minimal, calibration curve adjustments may be estab-
lished on permanent, uniform, hardened concrete blocks.
of the underlying (original) concrete 25 to 50 mm [1 to 2 in.]
down over a small area before placement of the overlay.
7. Standardization
8.2 Smooth the surface with a wood float. If necessary, use
7.1 Standardization of the equipment on the reference stan-
the guide plate and hole-forming device (5.1.7) to make a hole
dard is required at the start of each day and whenever test
slightly larger than the probe and perpendicular to the surface.
measurements are suspect.
In some concretes, the probe may be inserted directly into the
concrete without the use of the guide plate and hole-forming
NOTE 8—In some older instrument models, count rates are strongly
device.
influenced by the ambient temperature; frequent standardization may be
necessary.
8.3 Insert the probe so that the side of the probe facing the
7.2 Warm-up time shall be in accordance with the manufac-
center of the gauge is in intimate contact with the side of the
turer’s recommendations.
hole. Keep all other radioactive sources at such a distance from
the gauge that the readings will not be affected.
7.3 Take at least five readings on the reference standard,
more if recommended by the manufacturer, or take one 4 min
NOTE 9—The recommended minimum distance from other nuclear
density gauges is 10 m [
...

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: C1040/C1040M − 16 C1040/C1040M − 16a
Standard Test Methods for
In-Place Density of Unhardened and Hardened Concrete,
Including Roller Compacted Concrete, By Nuclear Methods
This standard is issued under the fixed designation C1040/C1040M; 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 These test methods cover the determination of the in-place density of unhardened and hardened concrete, including roller
compacted concrete, by gamma radiation. For notes on the nuclear test see Appendix X1.
1.2 Two test methods are described, as follows:
Section
Test Method A—Direct Transmission 8
Test Method B—Backscatter 9
1.3 The values stated in either SI units 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 non-conformance with the standard.
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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C29/C29M Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
C125 Terminology Relating to Concrete and Concrete Aggregates
C138/C138M Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in these test methods, refer to Terminology C125.
4. Significance and Use
4.1 These test methods are useful as rapid, nondestructive techniques for the in-place determination of the density of unhardened
concrete. The backscatter test method is also useful for the same purpose on hardened concrete. The fundamental assumptions
inherent in the test methods are that Compton scattering is the dominant interaction and that the material under test is
homogeneous.
4.2 These test methods are suitable for control and for assisting in acceptance testing during construction, for evaluation of
concrete quality subsequent to construction, and for research and development.
NOTE 1—Care must be taken when using these test methods in monitoring the degree of consolidation, which is the ratio of the actual density achieved
to the maximum density attainable with a particular concrete. The test methods presented here are used to determine the actual density. A density
These test methods are under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregatesand are the direct responsibility of Subcommittee C09.45
on Roller-Compacted Concrete.
Current edition approved July 1, 2016Dec. 15, 2016. Published August 2016January 2017. Originally approved in 1985. Last previous edition approved in 20132016 as
C1040/C1040M – 08C1040/C1040M – 16.(2013). DOI: 10.1520/C1040_C1040M-16.10.1520/C1040_C1040M-16A.
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
C1040/C1040M − 16a
measurement, by any test method, is a function of the components of the concrete and may vary, to some extent, in response to the normal, acceptable
variability of those components.
4.3 Test results may be affected by reinforcing steel, by the chemical composition of concrete constituents, and by sample
heterogeneity. The variations resulting from these influences are minimized by instrument design and by the user’s compliance
with appropriate sections of the test procedure. Results of tests by the backscatter test method may also be affected by the density
of underlying material. The backscatter test method exhibits spatial bias in that the apparatus’s sensitivity to the material under
it decreases with distance from the surface of the concrete.
NOTE 2—Typically, backscatter gauge readings represent the density in the top 75 to 100 mm [3 to 4 in.] of material.
5. Apparatus
5.1 The exact details of construction of the apparatus may vary, but the apparatus as a whole shall satisfy the requirements for
system precision stated in Annex A1. The system shall consist of the following:
5.1.1 Gamma Source—An encapsulated and sealed radioisotopic source, such as cesium-137 (see X1.3).
5.1.2 Detector—Any type of gamma detector, such as a Geiger-Müller tube, scintillation crystal, or proportional counter.
5.1.3 Probe—For direct transmission measurements, either the gamma source or the detector shall be housed in a probe for
inserting in a preformed hole in the material to be tested. The probe shall be marked in increments of 50 mm [2 in.] for tests with
probe depths from 50 to 300 mm [2 to 12 in.]. The probe shall be so made mechanically, that when moved manually to the marked
depth desired, it will be held securely in position at that depth.
5.1.4 Readout Instrument—A suitable scaler or direct readout meter.
5.1.5 Gauge Housing—The source, detector, readout instrument and appropriate power supplies shall be in housings of rugged
construction that are moisture and dust proof.
5.1.6 Reference Standard—A block of uniform, unchanging density provided for checking equipment operation, background
count, and count-rate reproducibility.
5.1.7 Guide Plate and Hole-Forming-Device—For direct transmission measurements, a guide plate and a device, such as a pin
or drill rod, having a nominal diameter slightly larger than the probe, for forming a hole normal to the concrete surface are required.
5.1.8 Calibration Adjustment Container—The container shall be rigid and watertight, with minimum inside dimensions large
enough to allow the calibration curve adjustment procedure (6.2) to be followed with no effect of the finite size of the container
on the instrument’s responses. The volume of the container shall be established following the procedure outlined in Test Method
C29/C29M.
NOTE 3—For backscatter measurements, a container 450 by 450 by 150 mm [18 by 18 by 6 in.] will meet this requirement for most equipment currently
available commercially. For 50-mm [2-in.] depth direct transmission measurements, a container 600 by 600 by 100 mm [24 by 24 by 4 in.] will meet
this requirement.
5.1.9 Scale—The scale shall be accurate to within 0.2 kg [0.5 lb] of the test load at any point within the range of use. The range
of use shall be considered to extend from the weight of the calibration adjustment container empty, to the weight of the measure
3 3
plus the contents at 2600 kg/m [160 lb/ft ].
5.1.10 Strike-Off Plate or Bar—This shall be a flat metal or glass plate or metal bar with a length at least 50 mm [2 in.] greater
than the length, width, or diameter of the calibration adjustment container. The strike-off must be rigid, straight, and smooth enough
to finish the concrete surface flat and flush with the edges of the calibration adjustment container.
6. Calibration
6.1 Calibration curves are established by determining the nuclear count rate of each of several materials at different and known
densities, plotting the count rate (or count ratio) versus each known density, and placing a curve through the resulting points. The
method used to establish the curve must be the same as that used to determine the density. The materials used for calibration must
be of uniform density.
NOTE 4—Calibration curves are supplied by gauge manufacturers, or can be established using blocks of known density or prepared containers of
uniform, unchanging material compacted to known densities. Materials considered satisfactory for use in blocks include granite, aluminum, chalk,
limestone, and magnesium.
6.2 Adjusting Calibration Curves—Prior to use, adjust the instrument’s calibration curve, if necessary, to compensate for
chemical composition effects. Such an adjustment is necessary whenever the chemical composition of the concrete to be tested
differs significantly from that for which the calibration curve was established. An adjustment is also necessary if the testing
equipment has been changed. Adjustment is particularly important for backscatter test method measurements. Determine the
necessary adjustments using the same mode of operation and at the same depth (if using direct transmission) as that intended for
testing. A recommended procedure for making this adjustment is as follows:
6.2.1 Prepare a concrete mix similar in composition to the material to be tested subsequently.
6.2.2 Fill the calibration adjustment container with concrete and consolidate to produce a uniform, homogeneous material with
approximately the density that will be achieved in the construction.
NOTE 5—Consolidation may be achieved by the procedure used for unit weight testing (Test Method C138/C138M) or by other methods, such as
spading the concrete and then dropping the ends of the container alternately on a rigid surface.
C1040/C1040M − 16a
6.2.3 Strike off the container with strike-off plate or bar. Take care to make the concrete surface flat and flush with the container
edges.
NOTE 6—A2 mm [ ⁄16 in.] average difference between the concrete surface and the container edges in a 150 mm [6 in.] deep container will produce
a 1 to 2 % error in the weighed density of the concrete.
6.2.4 Weigh the concrete in the container to the nearest 0.2 kg [0.5 lb] and determine the weighed density as follows:
W
c
W 5 (1)
V
where:
3 3
W = weighed density of concrete, kg/m [lb ⁄ft ],
W = mass of the concrete, kg [lb], and
c
3 3
V = volume of the container, m [ft ].
6.2.5 Immediately take three automatically timed direct transmission or backscatter readings with the instrument centered on
the surface of the concrete in the container. Rotate the base of the instrument 90° around the vertical axis, with subsequent rotations
of 180 and 270° from the original position. Obtain three additional automatically timed counts at each position. The instrument
must be centered over the surface of the concrete in each rotated position to prevent edge effects on the instrument reading.
6.2.6 Using the applicable calibration curve, determine the density from the average of the 12 counts obtained in 6.2.5.
6.2.7 Determine the difference between the two density readings obtained in 6.2.4 and 6.2.6.
6.2.8 Repeat 6.2.2 – 6.2.7 on two additional concrete mixes of the same proportions. Determine the adjustment factor by
averaging the three values obtained in 6.2.7 and 6.2.8. If one of the three values differs from the average by more than 25
3 3
kg/m [1.5 lb/ft ], discard it as a statistical outlier and recalculate the adjustment factor as the average of the remaining two values.
6.2.9 Use the adjustment factor determined in 6.2.8 to plot a corrected count-rate calibration curve which shall be parallel to
the original calibration curve and offset by the amount indicated in 6.2.8. Alternatively, the value of the adjustment factor shall be
attached to the instrument and applied to all density determinations arrived at from an original (unadjusted) calibration curve.
NOTE 7—In some circumstances, for example, where chemical composition changes are minimal, calibration curve adjustments may be established on
permanent, uniform, hardened concrete blocks.
7. Standardization
7.1 Standardization of the equipment on the reference standard is required at the start of each day and whenever test
measurements are suspect.
NOTE 8—In some older instrument models, count rates are strongly influenced by the ambient temperature; frequent standardization may be necessary.
7.2 Warm-up time shall be in accordance with the manufacturer’s recommendations.
7.3 Take at least five readings on the reference standard, more if recommended by the manufacturer, or take one 4 min or longer
count if the instrument is equipped with automatic standard count storage.
7.4 If more than one of the individual readings is outside the limit set by Eq 2, repeat the standardization. If the second attempt
does not satisfy Eq 2, check the system for a malfunction. If no malfunction is found, establish a new N (average count) by taking
o
the average of a minimum of 10 counts on the reference standard.
N 2 N ,1.96 =N (2)
? s o? o
where:
N = count currently measured in checking the instrument operation, and
s
N = average count previously established on the reference standard.
o
In instruments where the count has been prescaled, that is, divided by a constant factor k before it is displayed, Eq 2 shall be
replaced by the following:
N 2 N ,1.96 =N /k (3)
? s o? o
7.4.1 If automatic standard count storage is used and the newly established count is outside the limit set by Eq 2, repeat the
standardization.
7.4.2 If the second attempt does not satisfy Eq 2, check the system for a malfunction.
7.4.3 If no malfunction is found, establish a new N equal to the average count found in 7.4.2.
o
7.5 If a new N differs by more than 10 % from the standard count at which the calibration curve (6.1) was established,
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recalibrate the instrument.
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