No Job Name Designation C 1150 – 96 Standard Test Method for The Break Off Number of Concrete 1 This standard is issued under the fixed designation C 1150; the number immediately following the designa[.]
Trang 1Designation: C 1150 – 96
Standard Test Method for
This standard is issued under the fixed designation C 1150; 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 ( e) indicates an editorial change since the last revision or reapproval.
1 Scope
1.1 This test method2covers determination of the break-off
number of hardened concrete in test specimens or structures,
by measuring the force required to cause failure of a pre-cast or
drilled core specimen loaded as a cantilever
1.2 The values stated in SI units are to be regarded as the
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
appro-priate safety and health practices and determine the
applica-bility of regulatory limitations prior to use.
2 Referenced Documents
2.1 ASTM Standards:
E 178 Practice for Dealing with Outlying Observations3
C 670 Practice for Preparing Precision and Bias Statements
for Test Methods for Construction Materials4
C 823 Practice for Examination and Sampling of Hardened
Concrete in Constructions4
3 Summary of Test Method
3.1 The principle of the break-off test is illustrated in Fig 1
A plastic sleeve with an annular seating ring is inserted in fresh
concrete to form a cylindrical test specimen and a counter bore
After the concrete has hardened, the sleeve is removed and a
force is applied at the uppermost section of the cylinder so as
to break the cylindrical test specimen from the concrete mass
The test result is reported as a break-off number, which is the
maximum pressure recorded by the gage measuring the
hy-draulic pressure in the loading mechanism In hardened
con-crete, in cases where the plastic sleeve has not been installed,
a concrete coring machine with a specially shaped coring drill
bit may be used to drill a similarly shaped test specimen
4 Significance and Use
4.1 The break-off number determined by this test method may be used to assess the in-place strength of concrete, and to delineate zones, regions, or areas of varying quality or dete-riorated concrete in structures
4.2 Prior to using this test method for determining in-place strength, a correlation relationship between the break-off num-ber and the concrete strength should be established Since such
a correlation may vary with type and size of aggregates and method of specimen preparation, a relationship may be devel-oped to take these and other variables into account This
1
This test method is under the jurisdiction of ASTM Committee C-9 on Concrete
and Concrete Aggregatesand is the direct responsibility of Subcommittee C09.64on
Nondestructive Testing of Concrete.
Current edition approved May 10, 1996 Published July 1996 Originally
published as C 1150 – 90 Last previous edition C 1150 – 90 e 1
2
The break-off method is covered by a patent held by SINTEF, Norwegian
Institute of Technology, Trondheim, Norway Interested parties are invited to submit
information regarding the identification of acceptable alternatives to this patented
item to The Committee on Standards, ASTM Headquarters, 100 Barr Harbor Drive,
West Conshohocken, PA 19428 Your comments will receive careful consideration
at a meeting of the responsible technical committee which you may attend.
3
Annual Book of ASTM Standards, Vol 14.02.
4Annual Book of ASTM Standards, Vol 04.02.
FIG 1 Schematic of Break-Off Test
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
Contact ASTM International (www.astm.org) for the latest information.
Trang 2relationship must be established for each new combination of
concrete-making materials In developing such relationships,
care must be taken to ensure that the break-off specimens and
the strength test specimens undergo similar curing histories up
to the time of the test
N OTE 1—Published reports (1-8)5 by different researchers present their
experience in the use and evaluation of the break-off test equipment and
in establishing break-off strength correlation with compressive strength of
concrete.
4.3 The break-off test may be used to evaluate the in-place
concrete in order to:
4.3.1 Determine if formwork or reshoring can be removed,
4.3.2 Test if concrete meets break-off number specifications,
4.3.3 Determine when prestressing strands may be cut to
release the prestressing force,
4.3.4 Determine if concrete has sufficient strength to allow
post-tensioning to proceed,
4.3.5 Estimate efficiency of curing techniques, and
4.3.6 Evaluate the effects of exposure to environmental or
chemical attack
4.4 When planning the break-off test and analyzing test
results, consideration should be given to (1) the normally
expected decrease of concrete strength with increasing height
within a given concrete placement in a structural element (see
9-11), and (2) locations with less favorable curing conditions
prior to form removal
4.5 Break-off tests are not recommended for concrete with a
nominal maximum aggregate size greater than 25 mm The
within test variability of the break-off test has been found to
increase in concrete with larger aggregate size (see (6) and
(11)).
4.6 The cylindrical break-off specimens may be kept and
used for additional testing The break-off test shall not be
performed on concrete that is at a temperature of less
than −5°C Prior to starting a testing program the break-off
tester must be calibrated according to the manufacturer’s
procedure (using the calibrator force gage and calibration
diagram provided with the test unit) to ensure a consistent
relationship between the pressure gage reading and the force
applied by the loading mechanism
5 Apparatus
5.1 The apparatus consists of a loading mechanism, a load
generating device, a load measuring instrument, a tubular
sleeve and seating ring of the dimensions shown in Fig 2, a
tubular sleeve remover, and a gage for calibrating or adjusting
the loading system The tubular sleeve shall be of a material
that is resistant to chemical attack by concrete It shall be rigid
enough to maintain a reproducible size of test specimen It
shall be coated with a release agent that is not reactive with
concrete prior to inserting it in the concrete Plastic is an
acceptable sleeve material and automotive grease is a suitable
release agent
5.2 For applications where tests are to be performed in
already hardened concrete, a diamond tipped drill bit is used,
which produces a core with a circular counterbore at the surface with dimensions as shown in Fig 3
5.3 The loading mechanism shall consist of a tubular shaped fixture that fits into the counterbore, and a hydraulic piston which when actuated applies a force at the top of the core, perpendicular to the longitudinal axis of the core
N OTE 2—The loading mechanism may include both a high and low measuring range capability to permit strength test of concrete over a wider range A correlation relationship must be developed using the range setting that will be used during strength assessment.
5 The boldface numbers in parentheses refer to the list of references appended to
this test method.
FIG 2 Sleeve for Creating Test Specimen in Fresh Concrete
FIG 3 Dimensions of Test Specimen Created by Core Drill
Trang 35.4 The load generating device shall consist of a hydraulic
pump that is connected to the loading mechanism so that it is
possible to apply load (with smooth strokes of the pump) to the
core until it breaks off
5.5 The load measuring device shall consist of a pressure
gage to measure the hydraulic pressure applied to the loading
mechanism The pressure gage shall have a maximum value
indicator The pressure gage shall have a pressure range up to
15 MPa (150 bars) and a least dial division not greater than 0.2
MPa (2 bars)
6 Sampling
6.1 The break-off test locations shall be separated so that the
center to center distance between test specimens is at least 150
mm Clear spacing between the plastic inserts and the edges of
the concrete shall be at least 100 mm
6.2 When the break-off test results are used to assess the
in-place strength, in order to allow the start of critical
opera-tions such as form work removal or applicaopera-tions of post
tensioning, at least five individual break-off tests shall be
performed for a given placement for every 100 m3, or a fraction
thereof, or for every 500 m2, or fraction thereof, of the surface
area of one face in the case of slabs or walls Select test sites
that are critical in terms of exposure conditions and required
structural capacity
6.3 When the break-off test is used to evaluate concrete
strength in an existing structure, the number and locations of
tests shall be established by the investigator Practice C 823 can
be used to assist in planning such an evaluation
7 Procedure
7.1 Preparation of Cylindrical Specimens by Tubular
Sleeves:
7.1.1 At each test location, carefully insert the tubular
sleeve which has been thoroughly coated with a release agent
N OTE 3—Insertion of the sleeve may be aided by simultaneously
twisting and pushing the sleeve into the concrete until the top of the sleeve
is flush with the concrete surface For concrete with slump less than 75
mm, a slight depression may occur in the center of the sleeve, which
should be filled with concrete, tapped in by fingers, and the surface struck
off flush Sleeves are not recommended for no-slump concrete or when
deep surface texturing is to be used In such cases, test specimens should
be prepared by drilling.
7.1.2 Tap on the concrete surface adjacent to each sleeve to
reconsolidate the concrete and close any visible voids next to
the sleeve Clean off excess mortar from the tops of the sleeves
and allow specimens to cure within the concrete mass
7.1.3 At the time of test, remove the sleeve using the sleeve
removal tool Remove all loose concrete or other materials
from the cylindrical slit before testing
7.2 Preparation of Cylindrical Specimens by Coring:
7.2.1 Select test locations Set up drilling equipment (using
a vacuum plate or bolts to ensure rigidity) so that core drill is
perpendicular to the concrete surface Drill core into concrete
using a suitable diamond core drill to produce a test specimen
having the dimensions shown in Fig 3
7.3 Testing:
7.3.1 At each test location, place the loading mechanism
into the counterbore so that the ring of the loading mechanism
is uniformly seated in the counterbore Set the maximum pressure indicator on the pressure gage to its zero value Apply
a gradual force to the specimen by means of the hydraulic pump until the core breaks off Use a loading rate that causes
a break-off within 606 15 s from the start of loading On the
pressure gage dial, read the maximum pressure required to break off the core and record the maximum reading as the break-off number for the test specimen In reading the maxi-mum pressure, estimate to the nearest 0.1 MPa (1 bar) 7.3.2 Record the nature of the break at the base of the core Note whether the fracture surface includes the presence of large aggregate particles, reinforcing steel, and other abnor-malities, such as foreign inclusions, soft aggregate particles, or excessive air pockets (honeycombing) Measure the diameter (to the nearest 1 mm) at the base of the core in directions parallel and perpendicular to the loading direction Measure the approximate average height of the core to the nearest 5 mm
N OTE 4—If the presence of abnormalities is associated with a test result that appears to be an outlier compared with the average, the Dixon criteria
in Practice E 178 may be used to test whether the suspected result can be discarded Another test should be performed to replace the discarded test result.
8 Calculation
8.1 Calculate the average of the break-off test results (to the nearest 0.1 MPa (one bar) pressure) This value is the break-off number for the concrete
9 Report
9.1 Report the following information:
9.1.1 Location of each test, 9.1.2 Date and the time of the test, identification symbols, and name of the operator who performed the test,
9.1.3 Method of specimen preparation, either by sleeve insertion or core drilling,
9.1.4 Maximum aggregate size, 9.1.5 The load range setting (if the loading mechanism is equipped with high- and low-range settings),
9.1.6 Break-off number for each test specimen and the average break-off number,
9.1.7 Description of the nature of the break at the base of the ruptured test specimen, and whether the fracture surface shows the presence of reinforcement or other abnormalities, and 9.1.8 Approximate average height of each test specimen to the nearest 5 mm and the average diameter at the base of the specimen to the nearest 1 mm
10 Precision and Bias
10.1 Precision—Based on the data summarized in ACI
228.1R-95 (12), the average coefficient of variation for
break-off tests made on concrete with maximum aggregate size
of 19.0 mm (3⁄4in.) or 25.4 mm (1 in.) by a single operator using the same test device is 9 %.6 Therefore, the range of individual test results (see Note 5), expressed as a percentage
of the average, should not exceed the following:
6 This number represents the (1s %) limit as described in Practice C 670.
Trang 4Number of
tests
Acceptable range (percentage of average)
N OTE 5—If the range of test results exceeds the acceptable range,
further investigation should be carried out Abnormal test results could be
due to faulty test specimens, improper procedures, or equipment
malfunc-tion The user should investigate the potential causes of the outliers, and
disregard those tests for which reasons for the outlying results can be identified positively If there are no obvious causes of the extreme values,
it is probable that there are real differences in concrete strength at the different test locations These differences could be due to variations in mixture proportions, degree of consolidation, or curing conditions.
10.2 Bias—The bias of this test method cannot be
deter-mined because the break-off number can only be obtained by the use of this test method
REFERENCES
(1) Carlsson, M., Eeg, I R., and Jahner, P., “Field Experience in the Use
of the Break-off Tester,” ACI SP82-14, In Situ/Nondestructive Testing
of Concrete, V M Malhotra, Ed., American Concrete Institute, Detroit,
MI, 1984, pp 277–292.
(2) Dahl-Jorgenson, E., and Johansen, R.,“ General and Specialized Use of
the Break-off Concrete Strength Test Method,” ACI SP82-15, In
Situ/Nondestructive Testing of Concrete, V M Malhotra, Ed.,
Ameri-can Concrete Institute, Detroit, MI, 1984, pp 293–308.
(3) “Early Strength Measuring Test for Offshore Oil Platform,” Concrete
Products, September 1985.
(4) Naik, T R., Hassaballah, A A., and Salameh, Z., “The Break-off Test
Method,” Department of Civil Engineering, the University of
Wisconsin-Milwaukee, Milwaukee, WI, 1988.
(5) Yener, M., and Chen, W F., “Evaluation of In-Place Flexural Strength
of Concrete,” American Concrete Institute Journal, Vol 82, No 6,
Nov./Dec 1985, pp 788–796.
(6) Barker, M G., and Ramirez, J A., “Determimation of Concrete
Strength Using the Break-off Tester,” American Concrete Institute
Journal, Vol 85, No 4, July/Aug 1988, pp 221–228.
(7) Dahl-Jorgenson, E., “In Situ Strength of Concrete, Laboratory and
Field Test,” SINTEF Report No STF 65A82032, 1982-06-04, Norwe-gian Institute of Technology.
(8) American Concrete Institute Committee 228 Report, “In-Place
Meth-ods for Determination of Strength of Concrete,” ACI 228-IR-89, American Concrete Institute, Detroit, Michigan, 1989.
(9) Murphy, W E., “The Interpretation of Tests on the Strength of
Concrete in Structures,” ACI SP-82, In Situ/Nondestructive Testing of
Concrete, V M Malhotra, Ed., American Concrete Institute, Detroit,
MI, 1984, pp 377–392.
(10) Munday, J G L., and Dhir, R K., “Assessment of In Situ Concrete
Quality by Core Testing,” ACI SP-82, In Situ/Nondestructive Testing
of Concrete, V M Malhotra, Ed., American Concrete Institute,
Detroit, MI, 1984, pp 393–410.
(11) Haque, M N., Day, R L., and Langan, B W., “Realistic Strength of
Air-Entrained Concrete with and without Fly Ash,” American
Con-crete Institute Journal, Vol 85, No 4, July/Aug 1988, pp 241–247.
(12) ACI 228.1R-95, “In-Place Methods to Estimate Concrete Strength,”
Report of ACI Committee 228 on Nondestructive Testing, American Concrete Institute, Farmington Hills, MI.
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