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GB/T 17671-2021 PDF in English


GB/T 17671-2021 (GB/T17671-2021, GBT 17671-2021, GBT17671-2021)
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GB/T 17671-2021: PDF in English (GBT 17671-2021)

GB/T 17671-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 91.100.10
CCS Q 11
Replacing GB/T 17671-1999
Test method of cement mortar strength (ISO method)
(ISO 679:2009, Cement - Test methods - Determination of strength,
MOD)
ISSUED ON: DECEMBER 31, 2021
IMPLEMENTED ON: JULY 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 4
1 Scope ... 8
2 Normative references ... 8
3 Terms and definitions ... 9
4 Method summary ... 9
5 Laboratory and equipment ... 9
5.1 Laboratory ... 9
5.2 Curing box ... 9
5.3 Maintenance pool ... 10
5.4 Test cement, Chinese ISO standard sand and water ... 10
5.5 Wire mesh test sieve ... 10
5.6 Equipment ... 10
6 Composition of mortar ... 18
6.1 Sand ... 18
6.2 Cement ... 19
6.3 Water ... 19
7 Preparation of mortar ... 19
7.1 Mix ratio ... 19
7.2 Stirring ... 19
8 Preparation of specimen ... 20
8.1 Size and shape ... 20
8.2 Molding ... 20
9 Maintenance of specimen ... 21
9.1 Treatment and maintenance before demolding ... 21
9.2 Demolding ... 21
9.3 Curing in water ... 21
9.4 Age of strength test specimen ... 22
10 Test procedure ... 22
10.1 Determination of flexural strength ... 22
10.2 Determination of compressive strength ... 23
11 Test results ... 24
11.1 Flexural strength ... 24
11.2 Compressive strength ... 24
12 Acceptance inspection of Chinese ISO standard sand and substitute equipment .. 25
12.1 General ... 26
12.2 Acceptance test of Chinese ISO standard sand ... 26
12.3 Acceptance test of alternative molding equipment ... 30
Test method of cement mortar strength (ISO method)
1 Scope
This document specifies the summary of the method for testing the strength of cement
mortar (ISO method), laboratory and equipment, mortar composition, mortar
preparation, specimen preparation, specimen maintenance, test procedures, test results,
acceptance inspection of Chinese ISO standard sand and substitute equipment.
This document is applicable to the flexural and compressive strength testing of general
Portland cement and limestone Portland cement mortar. Other cements and materials
may refer to this document. This document may not be applicable to strength testing of
some types of cement mortar, such as cement with a very short initial setting time.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 6003.1, Test sieves - Technical requirements and testing - Part 1: Test sieves
of metal wire cloth (GB/T 6003.1-2012, ISO 3310-1:2000, MOD)
GB/T 6682, Water for analytical laboratory use -- Specification and test methods
(GB/T 6682-2008, ISO 3696:1987, MOD)
JC/T 681, Planetary cement mortar mixer
JC/T 682, Cement mortar specimen forming vibrator
JC/T 683, 40mm x 40mm Jig for cement compressive strength test machine
JC/T 723, Cement mortar vibration compaction equipment
JC/T 724, Electrically driven flexure testing device for strength of cement mortar
JC/T 726, Mould for cement mortars
JC/T 959, Curing box for cement mortar specimens
JC/T 960, Cement mortar strength automatic pressure testing machine
3 Terms and definitions
There are no terms or definitions to be defined in this document.
4 Method summary
This method is for the determination of the compressive strength and flexural strength
of cement mortar of 40mm×40mm×160mm prism.
The specimen is made of a set of plastic mortar mixed with one part of cement, three
parts of Chinese ISO standard sand and half of water (water-cement ratio w/c is 0.50)
by mass. It has been demonstrated that the cement strength results obtained using the
Chinese ISO standard sand are not significantly different from those obtained using the
ISO reference sand (Chapter 12).
In the benchmark test step, the mortar is mixed with a planetary mixer and formed on a
vibrator. Alternative equipment and procedures may be used, provided it is
demonstrated that the cement strength test results obtained using them are not
significantly different from those obtained using the reference vibrator and procedures
(Chapter 12).
When in dispute, only reference equipment and operating procedures may be used.
The specimen together with the test mold are cured in moisture for 24 h. After
demolding, cure in water until strength test.
When the test age is reached, the specimens are taken out of the water. First use an anti-
folding machine to conduct a flexural strength test. After breaking, conduct a
compressive strength test on each section.
5 Laboratory and equipment
5.1 Laboratory
The temperature of the laboratory shall be maintained at 20℃±2℃. Relative humidity
shall not be less than 50%.
Laboratory temperature and relative humidity are recorded at least once a day during
work.
5.2 Curing box
The temperature of the mold curing specimen curing box shall be maintained at
8 Preparation of specimen
8.1 Size and shape
The specimen is a prism of 40mm×40mm×160mm.
8.2 Molding
8.2.1 Molding by vibrator
Molding is carried out immediately after the mortar is prepared. Fix the empty test mold
and mold sleeve on the vibrator. Use a spoon to clean the mortar on the wall of the pot
into the pot and turn it over to stir the mortar to make it more even. During molding,
put the mortar into the test mold in two layers. When installing the first layer,
approximately 300 g of mortar is placed in each slot. First use a spoon to draw the sand
along the length of the trial mold to cover the mold grooves. Then use a large distributor
(see Figure 3) to stand vertically on the top of the mold sleeve and move it back and
forth along each mold slot to spread the material layer evenly. Then tap 60 times. Then
add the second layer of mortar. Use a spoon to draw the rubber sand along the length of
the test mold to cover the mold groove, but do not touch the vibrated rubber sand. Then
use a small cloth maker (see Figure 3) to smooth the cloth. Tap 60 times. During each
vibration, a piece of cotton gauze that has been wetted with water and wrung out and
slightly larger than the size of the mold cover can be covered on the mold cover to
prevent the mortar from splashing during vibration.
Remove the mold sleeve. Remove the test mold from the vibrator. Use a metal straight-
edge ruler (see Figure 3) to rest on one end of the top of the test mold at an angle of
approximately 90° (but slightly inclined toward the scraping direction). Then slowly
move to the other end in a transverse sawing motion along the length of the test mold
(see Figure 2). Scrape off the mortar that exceeds the part of the test mold. The amount
of sawing action and the angle of the ruler depend on the consistency of the mortar.
Thicker mortar requires multiple sawing operations. The sawing action shall be slow to
prevent pulling of the vibrated mortar. Use a wrung wet towel to wipe clean the mortar
on the top of the test mold end plate. Then use the same straight edge to smooth the
surface of the specimen at a nearly horizontal angle. The number of times of smoothing
shall be minimized. The total number of times shall not exceed 3 times. Finally, wipe
off the mortar around the test mold.
Use a brush or other method to number the specimens. For specimens of more than two
ages, the three specimens in the same test mold shall be divided into two or more ages
when numbering.
8.2.2 Molding with vibration compaction equipment
While stirring the mortar, clamp the test mold and the unloading funnel in the center of
the vibration compaction equipment. Evenly put all the mixed mortar into the discharge
funnel. Start the vibration compaction equipment. The mortar flows into the test mold
through a funnel. Vibrate for 120±5 s and then stop vibrating. After the vibration is
completed, remove the test mold. Use a scraper to scrape off the mortar that is higher
than the test mold using the scraping technique specified in 8.2.1, smooth it, and number
it.
9 Maintenance of specimen
9.1 Treatment and maintenance before demolding
Cover the trial mold with a glass plate. Steel plates of similar dimensions or plates made
of a material that is impermeable and non-reactive to cement may also be used. The
cover plate shall not come into contact with cement mortar. The distance between the
cover plate and the test mold shall be controlled between 2mm~3mm. For safety reasons,
glass panels shall have ground edges.
Immediately place the marked test mold on a horizontal shelf in a curing room or wet
box for curing. Moist air shall be able to contact all sides of the test mold. Test molds
shall not be placed on other test molds during maintenance. Keep curing until the
specified demolding time and take out the demolding.
9.2 Demolding
Demolding shall be done very carefully. You can use a rubber mallet or ejector to
remove the mold.
For 24 h age, the mold shall be demolded within 20 min before the breakage test. For
those aged over 24 h, they shall be demolded between 20 h~24 h after molding.
If after 24 h of curing, the strength will be damaged due to demolding, demolding can
be delayed until after 24 h, but this shall be stated in the test report.
The demolded specimens that have been determined to be used for the 24 h age test (or
other direct tests without entering the water) shall be covered with a damp cloth until
the test is carried out.
For comparison of mortar mixing or vibrator, it is recommended to weigh the total
number of specimens in each model.
9.3 Curing in water
Immediately place the marked specimen horizontally or vertically in 20℃±1℃ water
11 Test results
11.1 Flexural strength
11.1.1 Calculation and presentation of results
The average value of the bending resistance results of a set of three prisms is used as
the test result. When one of the three strength values exceeds ±10% of the average value,
it shall be eliminated and then the average value shall be taken as the flexural strength
test result. When two of the three strength values exceed the average value by ±10%,
the remaining one is used as the flexural strength result.
Individual flexural strength results are accurate to 0.1 MPa. The arithmetic mean is
accurate to 0.1 MPa.
11.1.2 Reporting of results
Report all individual flexural strength results as well as the flexural strength results
excluded as specified in 11.1.1, and the calculated average.
11.2 Compressive strength
11.2.1 Calculation and presentation of results
The test result is the average of six compressive strength measurements obtained on a
set of three prisms. When one of the six measured values exceeds ±10% of the six
average values, this result is eliminated, and the average value of the remaining five is
used as the result. When any of the five measured values exceeds ±10% of their average
value, the results of this set will be invalid. When two or more of the six measured
values exceed ±10% of the average value at the same time, the results of this set will be
invalid.
Individual compressive strength results are accurate to 0.1 MPa. The arithmetic mean
is accurate to 0.1 MPa.
11.2.2 Reporting of results
Report all individual compressive strength results as well as compressive strength
results excluded as specified in 11.2.1, and the calculated average.
11.2.3 Accuracy of compressive strength method
11.2.3.1 Short-term repeatability
Short-term repeatability refers to the degree of consistency of test results obtained in a
short period of time using the same Chinese ISO standard sand sample and cement
sample, in the same laboratory, using the same equipment, and under the same operating
conditions by the same personnel.
For the compressive strength at 28 d of age, under the above conditions, the short-term
repeatability of the "general laboratory", expressed as the coefficient of variation, shall
be less than 2%.
NOTE: Practice shows that more skilled laboratories can achieve 1%.
When used for acceptance testing of Chinese ISO standard sand and substitute
equipment, short-term repeatability can be used to measure the accuracy of the test
method.
11.2.3.2 Long-term repeatability
Long-term repeatability refers to the consistency of test results obtained over a longer
period of time using the same homogenized cement sample and the same Chinese ISO
standard sand sample, in the same laboratory, using different equipment and different
personnel operating conditions. degree.
For the 28 d age compressive strength, under the above conditions, the long-term
repeatability of the "general laboratory", expressed as the coefficient of variation, shall
be less than 3.5%.
NOTE: Practice shows that more skilled laboratories can achieve 2.5%.
Long-term repeatability can be used to measure the accuracy of Chinese ISO standard
sand monthly inspections and long-term laboratory test methods.
11.2.3.3 Reproducibility
The reproducibility of the compressive strength method gives the degree of consistency
of the test results obtained by different operators in different laboratories at different
times, using standard sand from different sources and different equipment for the same
cement sample.
For the determination of 28 d compressive strength, the reproducibility between
"general laboratories", expressed as the coefficient of variation, may be required to not
exceed 4%.
NOTE: Practice shows that more skilled laboratories can achieve 3%.
Reproducibility can be used to evaluate the accuracy of cement or Chinese ISO standard
sand homogeneity test methods.
12 Acceptance inspection of Chinese ISO standard sand and
verification testing (12.2.5.1). For this reason, the sample shall be reduced into several
small samples for verification test.
Three different varieties of universal Portland cement with different strength levels are
used. Use the method described in 12.2.3. Each of the three samples shall be tested
against the ISO reference sand. Acceptance tests are carried out by designated
laboratories.
When the results of the three sand samples processed according to 12.2.3.2 meet the
requirements of 12.2.3.3, the Chinese ISO standard sand passes the acceptance.
12.2.2.2 Annual consistency test
Continuous acceptance of Chinese ISO standard sand is carried out through the
following activities:
a) If the requirements of 6.1.3 and 12.2.5.3 are met, check the verification test
according to 12.2.4;
b) Use the method described in 12.2.3 to compare random sand samples with the
ISO reference sand using universal Portland cement of strength class 42.5 or 52.5.
Acceptance tests are carried out by designated laboratories.
Sand samples shall be taken randomly at the delivery point. According to the method
specified in 12.2.3.1 and the verification test method specified in 12.2.5.1 for at least
one year, the sampling quantity shall be calculated and ensured to be sufficient. For this
reason, the sample shall be reduced into several small samples for verification test.
Chinese ISO standard sand passes acceptance when the following conditions are met:
- Verify that the test results comply with the provisions of 6.1.3 and 12.2.5.3;
- The annual consistency inspection results comply with the provisions of 12.2.3.3.
12.2.3 Acceptance test method
12.2.3.1 Procedure
Prepare 20 pairs of mortar specimens using the selected cement samples (12.2.2.1 and
12.2.2.2). The Chinese ISO standard sand and ISO reference sand to be accepted are
prepared in pairs one by one. Prepare each pair of mortar in random order. The two sets
of tests are interspersed.
Determine the compressive strength of the prism for 28 d and record all individual
results.
12.2.3.2 Calculation and presentation of results
For each pair of mortar specimens, calculations and expressions are made according to
the provisions of 11.2.1. Report in accordance with 11.2.2. represents the result
of the sand to be accepted, and represents the result of the ISO benchmark sand.
Calculate the coefficient of variation of each set of two sets of results and check whether
it meets the short-term repeatability requirements specified in 11.2.3.1. If both sets of
results do not meet the requirements, all results will be invalidated and the entire test
will be rerun. If only one set of results does not meet the requirements, proceed as
follows:
a) Calculate the average of 20 results, or ;
b) Calculate the standard deviation of 20 results, S1;
c) Calculate the algebraic difference between each individual result and the mean,
regardless of whether it is positive or negative;
d) When one of the differences exceeds 3 times S1, the corresponding result is
eliminated and the average of the remaining 19 results is recalculated. When there
are two or more differences greater than 3 times S1, all results will be invalidated
and the entire test will be rerun. When there is no difference greater than 3 times
S1, these 20 results are retained.
12.2.3.3 Acceptance requirements
According to the initial qualification test procedure, when each of the relative
deviations (expressed as D1 values) between the compressive strength of the sand to be
accepted and the compressive strength of the ISO benchmark sand is less than 5.00%,
the Chinese ISO standard sand to be accepted passes the acceptance. When one or more
D1 values are greater than or equal to 5.00%, the Chinese ISO standard sand cannot
pass acceptance.
According to the annual consistency acceptance test procedure, when the D1 value is
less than 5.00%, the Chinese ISO standard sand passes the acceptance. When the D1
value is greater than or equal to 5.00%, the Chinese ISO standard sand cannot pass
acceptance. The cause shall be found and initial identification tests shall be carried out
before acceptance.
12.2.4 Verification test method for Chinese ISO standard sand
In order to prove that Chinese ISO standard sand is consistent with international
standards, standard sand producers shall carry out continuous self-control tests
including the following:
a) Daily particle size distribution and moisture content tests according to 6.1.3;
12.2.6 Report
When requested by the purchaser, the standard sand producer shall provide a report,
which shall include:
a) Date of report issuance;
b) Producer's name and registered address;
c) Date of initial qualification test of Chinese ISO standard sand;
d) Date of most recent annual conformance test;
e) Name and registered address of the designated laboratory;
f) Chinese ISO standard sand meets the requirements of this document and test
certification materials that prove the quality of Chinese ISO standard sand.
12.3 Acceptance test of alternative molding equipment
12.3.1 General
When it is necessary to conduct an acceptance test of alternative molding equipment,
the designated laboratory shall select three sets of equipment that can be purchased on
the market, so as to compare and accept them with the reference vibrator that meets the
requirements of 5.6.4.
Equipment to be accepted shall provide the following documents:
a) Detailed description of the molding steps;
b) Detailed description of the molding equipment (design and construction);
c) Maintenance instructions, including test items to ensure correct operation.
The designated laboratory shall carefully compare the technical performance of the
equipment with the technical specifications provided. When it is proven that they are
consistent with each other, the designated laboratory will conduct three sets of
comparative tests using different cements in accordance with the provisions of 12.3.2
to accept each piece of equipment. For this purpose, three different strength classes of
cement are selected.
When each of the three sets of comparison test results meets the requirements of
12.3.2.3, the alternative vibration equipment passes acceptance. The results of the
acceptance tests shall be archived and retained until the equipment is no longer used.
See 5.6.4.2 for a description of a substitute vibration compaction equipment. See 8.2.2
for a description of the molding operation.
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.