GB/T 750-2024 PDF English
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Test method for autoclave expansion of cement
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Autoclave method for soundness of portland cement
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Similar standards GB/T 50726 GB/T 750-2024: Test method for autoclave expansion of cement---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT750-2024
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 91.100.10
CCS Q 11
Replacing GB/T 750-1992
Test Method for Autoclave Expansion of Cement
Issued on: OCTOBER 26, 2024
Implemented on: MAY 1, 2025
Issued by. State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3
1 Scope... 6
2 Normative References... 6
3 Terms and Definitions... 6
4 Method Principle... 7
5 Instruments and Equipment... 7
6 Materials... 9
7 Test Conditions... 9
8 Molding and Curing of Specimens... 10
9 Measurement of Specimen Length... 11
10 Autoclave of Specimen... 11
11 Calculation and Evaluation of Results... 13
Appendix A (Normative) Test Method of 25mm×25mm×146mm specimen... 15
Appendix B (Normative) Safety Precautions... 19
Test Method for Autoclave Expansion of Cement
Warning. This test is dangerous. The autoclave shall be used safely during the test. Pay
attention to the direction of the exhaust port to avoid steam burns.
1 Scope
This Document gives the method and principle of cement autoclave stability test; and stipulates
the instruments, equipment, materials, test conditions, specimen molding and maintenance,
specimen length measurement, specimen autoclave and result calculation and evaluation.
This Document is applicable to the determination of autoclave stability of hardened cement
paste. Among them, the test method of 25 mm×25 mm×280 mm specimen is the reference
method; and the test method of 25 mm×25 mm×146 mm specimen is the substitute method.
2 Normative References
The provisions in following documents become the essential provisions of this Document
through reference in this Document. For the dated documents, only the versions with the dates
indicated are applicable to this Document; for the undated documents, only the latest version
(including all the amendments) is applicable to this Document.
GB/T 1346 Standard test method for water requirement for normal consistency, setting
time, and soundness of the portland cement
GB/T 6682 Water for analytical laboratory use - Specification and test methods
GB/T 17671 Test method of cement mortar strength (ISO method)
JC/T 603 Test method for dry shrinkage of cement mortar
JC/T 681 Mixer for mixing mortars
JC/T 723 Cement mortar vibration compaction equipment
JC/T 729 Mixer for cement paste
3 Terms and Definitions
For the purposes of this Document, the following terms and definitions apply.
3.1 Autoclave
The specimen is treated for a certain period of time in a closed environment with saturated
water vapor at 215.7°C and a corresponding pressure of 2.0 MPa.
4 Method Principle
Under saturated water vapor conditions, the temperature and pressure are increased to hydrate
most of the periclase and free calcium oxide in the cement in a short period of time. The linear
expansion rate of the specimen is used to determine the volume stability of the cement.
5 Instruments and Equipment
5.1 Cement mortar mixer
It shall meet the requirements of JC/T 681.
5.2 25 mm×25 mm×280 mm test mold
Triple or double, shall meet the requirements of the test mold in JC/T 603; and the size shall
meet the requirements of Figure 1.The end plate and partition board of the test mold are made
of 45# steel; the hardness shall be no less than HRC48; and the surface roughness Rα shall be
no greater than 1.6.
25 mm×25 mm×146 mm test mold can also be used. The test method of 25 mm×25 mm×146
mm specimen shall be carried out according to Appendix A.
Unit. mm
Key.
1 – partition board;
2 – end plate;
3 – tightening bolt;
4 – nail head.
Figure 1 – Schematic diagram of 25 mm×25 mm×280 mm test mold
5.3 Nail head
It shall meet the requirements of JC/T 603.
5.4 Tamping rod
It shall meet the requirements of JC/T 603; the bottom surface of the square tamping rod shall
be covered with a rubber layer.
5.5 Autoclave
5.5.1 The autoclave is a high-temperature and high-pressure steam container with a temperature
and pressure measurement system, including a safety valve, an exhaust valve, an electric heater,
a heat dissipation hole, an automatic pressure control device and a timing device. The safety
valve is activated when the pressure in the autoclave reaches 2.2 MPa.
5.5.2 The autoclave shall be equipped with an exhaust valve to discharge air in the early heating
stage and release the remaining steam pressure at the end of the later cooling stage.
5.5.3 The maximum range of the pressure gauge is 4.0 MPa, and the accuracy is no less than
Level-1.6.When the working pressure is 2.0 MPa, the error of the pressure gauge shall not
exceed ±0.06 MPa.
5.5.4 The autoclave shall be made of stainless steel, and the autoclave body and the autoclave
cover shall be sealed with ground metal. No steam shall be discharged during the constant
pressure process. The inner diameter of the autoclave is about 160 mm, and the volume of the
autoclave cavity is about 8.5 L. Under the condition of maximum test load (with specimen and
water in the autoclave), the electric heater can raise the steam pressure in the autoclave to 2.0
MPa within 65 min~95 min after closing the exhaust valve.
5.5.5 The automatic pressure control device shall be able to control the pressure in the autoclave
within the range of 2.0 MPa±0.1 MPa (equivalent to a temperature of 215.7 ℃±2.6 ℃) and
maintain it for more than 3 h.
5.5.6 After the autoclave stops heating, the heat dissipation holes can be opened manually or
automatically; and the pressure can be reduced from 2.0 MPa to below 0.1 MPa within 90 min.
The use of the autoclave shall comply with the provisions of Appendix B.
5.6 Temperature measuring device
The measuring range shall be no less than 250 ℃; and the graduation value shall be no greater
than 1 ℃.
5.7 Curing box
The temperature shall be maintained at 20 ℃ ±1 ℃; and the relative humidity shall be no less
than 90%.
5.8 Comparator
It shall meet the requirements of JC/T 603.Automatic measuring equipment that meets the
requirements may also be used. When in use, the comparator shall be consistent with the
laboratory temperature. It is made of a specific alloy steel with a small thermal expansion
coefficient, and both ends are processed into spherical surfaces of the same size as the
measuring nail head. The middle hand grip shall be wrapped with rubber or other insulation
materials and marked with vertical marks.
6 Materials
6.1 Cement sample
The cement sample shall pass through a 0.9 mm square hole sieve and be mixed evenly.
6.2 Mixing water
Drinking water shall be used, and Grade-3 water in accordance with GB/T 6682 shall be used
for acceptance tests or in case of disputes.
6.3 Water for autoclaving
Use Grade-3 water in accordance with GB/T 6682.
7 Test Conditions
7.1 Molding laboratory
The temperature of the laboratory shall be maintained at 20 ℃ ± 2 ℃, and the relative humidity
should be no less than 50%.
7.2 Autoclave laboratory
It shall be equipped with ventilation equipment and tap water source, and shall not be shared
with other tests.
7.3 Length measurement environment
The length measurement environment of the specimen shall be consistent with that of the
molding laboratory.
8 Molding and Curing of Specimens
8.1 Preparation of test mold
Before the test, apply a thin layer of engine oil to the inner cavity of the test mold; and install
the nail head into the round holes at both ends of the mold cavity. The exposed part of the nail
head shall not be stained with engine oil.
8.2 Preparation of cement paste
Weigh 800 g + 2 g of cement; and measure the mixing water according to the standard
consistency water volume determined by GB/T 1346.Stir according to the procedure specified
in GB/T 17671; lift the mixing pot appropriately; and stir the cement paste evenly after stopping
stirring for 90 s.
8.3 Molding of the test specimen
Wearing rubber gloves, mix the prepared cement paste thoroughly and evenly; and then load it
into the two cavities of the prepared test mold in two layers according to the following steps.
a) The first layer of paste is loaded to a height of about 3/5 height of the test mold. First, use
a table knife to compact the paste at a 45° angle to the horizontal direction to evenly fill
the mold cavity; then insert and scratch; insert several times on both sides of the nail
head to compact the cement paste near the nail head. Starting from the inside of the nail
head, between the tails of the two nail heads, compact the paste from one end to the other
end in sequence until a dense test specimen is obtained;
b) Load the second layer of paste; fill the test mold evenly; use a table knife to insert and
scratch; the insertion and scratch depth does not penetrate the compacted paste; and then
compact the paste from one end to the other end in sequence;
c) Regularize the paste to the upper part of the mold cavity and compact it; lift one end of
the test mold 30 mm~50 mm and let it fall freely on a hard plate to compact it 3 times;
and lift the other end in the same way to compact it 3 times;
d) Use a table knife to scrape off the excess slurry and smooth it, number it.
8.4 Curing and demolding
Put the formed specimen together with the test mold in a moisture curing box for curing for 24
h±30 min and demolding; counting from the time when the cement is mixed with water. After
measuring the initial length, place the specimen flat in 20 ℃ ±1 ℃ water for curing; and
complete the autoclave test within 2 days.
9 Measurement of Specimen Length
9.1 Dial indicator calibration
Before measuring, use the calibration rod to calibrate the base length reading of the comparator
dial indicator. After the measurement is completed, measure the calibration rod reading again.
If the change exceeds ±0.01 mm, recalibrate the dial indicator.
9.2 Length measurement
Use a comparator to measure the length of each specimen. Keep the specimen in the comparator
in the same position in each measurement. Rotate the specimen before reading. Read the result
when the dial indicator pointer is stable. The result is retained to 0.001 mm.
10 Autoclave of Specimen
10.1 Sealed autoclave
10.1.1 Place the specimen on the specimen holder of the autoclave at room temperature.
10.1.2 Add about 850 mL of Grade-3 water in accordance with GB/T 6682 into the autoclave.
10.1.3 Use fine cotton yarn to clean the sealing opening of the autoclave body and the sealing
groove of the autoclave cover. Put the autoclave cover vertically on the autoclave body through
the bolts and make close contact.
10.1.4 Put 10 nuts with washers on the autoclave cover bolts; and then use a torque wrench to
fix them one by one in the order of covering the diagonal lines of the bolts. As shown in Figure
2, first tighten 1 and 6, then 4 and 9, 2 and 7, 5 and 10, 3 and 8.Tighten all nuts repeatedly; and
finally check whether the torque force reaches 100 N·m one by one in the order of 1, 2, 3, 4,
5, 6, 7, 8, 9, 10.
10.2 Start the temperature measuring device
Insert the temperature measuring device (5.6) into the temperature measuring hole on the
autoclave cover.
Figure 2 -- Schematic diagram of relative position of the autoclave cover bolts
10.3 Autoclave operation steps
10.3.1 Open the exhaust valve, electric heater and pressure control system; and the hot air in
the autoclave cavity is discharged from the exhaust valve until continuous steam is released and
then close the exhaust valve.
10.3.2 Record the temperature and pressure increase process of the autoclave. After 65 min ~
95 min, the pressure in the autoclave reaches 2.0 MPa ± 0.1 MPa and is maintained at this
pressure for 3 h.
10.3.3 Turn off the electric heater; open the heat dissipation hole; and cool to the pressure in
the autoclave below 0.1 MPa within 90 min.
10.3.4 Open the exhaust valve to discharge the remaining steam in the autoclave.
10.3.5 During the autoclave experiment, observe the relationship between pressure and
temperature at any time (the temperature is 215.7 ℃ ± 2.6 ℃ when the gauge pressure is 2.0
MP ± 0.1 MPa). The corresponding relationship between temperature and saturated water vapor
pressure is shown in Table 1.If the temperature rises and the pressure drops, the power supply
shall be cut off immediately and the experiment shall be stopped. For cement types with added
steel slag, the pressure steaming time is 6 h.
Table 1 -- The corresponding relationship between saturated water vapor pressure and
temperature
10.4 Steps to open the autoclave
10.4.1 The order of opening the nuts of the autoclave cover is still. first tighten 1 and 6, then
tighten 4 and 9, 2 and 7, 5 and 10, 3 and 8.
10.4.2 Vertically extract the autoclave cover to separate the autoclave cover from the autoclave
body, and take out the specimen support.
10.4.3 After the autoclave body temperature drops, use a ruler to measure the height of the
remaining water and record it; and wipe the remaining water in the autoclave with a clean towel.
Use two wooden strips of about 20 mm×20 mm×200 mm to pad between the autoclave body
sealing port and the autoclave cover; and cover it with a dust cover.
10.5 Specimen cooling
After taking out the specimen, immediately place it in hot water above 90℃. The height of the
water tank shall be higher than 3 times the height of the specimen. Then pour cold water into
the hot water. Avoid pouring cold water directly onto the specimen surface. Reduce the water
temperature to 20℃±2℃ within 15 min. Keep the water temperature constant for at least 1 h
before measuring the specimen length.
10.6 Measure the length after autoclaving
Measure the length of the specimen after autoclaving (L1) according to the steps in Clause 9.
Record the phenomenon of specimen powdering, bending, cracking, bursting, and exceeding
the measuring range of the comparator.
11 Calculation and Evaluation of Results
11.1 Calculation of autoclave expansion rate
The autoclave expansion rate of the specimen is calculated according to Formula (1), and the
result is retained to 0.001%.
Pressure Pressure Temperature Temperature
Where.
LA - Expansion rate of the specimen after autoclaving;
L1 - Length of the specimen after autoclaving, in mm;
L0 - Initial length of the specimen, in mm;
L - Effective length of the specimen, in mm; generally, 250 mm.
11.2 Test results
The average value of the pressure expansion rate of two specimens in one group is taken as the
test result; and the result is retained to 0.01%.
When the difference in the pressure expansion rate of the two specimens is no greater than
0.05%, the average value of the pressure expansion rate of the two specimens is taken as the
test result. When the difference in the pressure expansion rate of the two specimens is greater
than 0.05%, and the pressure expansion rate of the two specimens differs from the average
value by no more than ±10%, the average value of the pressure expansion rate of the two
specimens is taken as the test result. When the difference in the pressure expansion rate of the
two specimens is greater than 0.05%, and the pressure expansion rate of the two specimens
differs from the average value by more than ±10%, this test is invalid and shall be retested.
11.3 Qualification assessment
11.3.1 If the specimen is powdered, bent, cracked, burst, or exceeds the measurement range of
the comparator, it is considered unqualified for pressure steam stability.
11.3.2 If the autoclave expansion rate of Portland cement is no more than 0.80%, it shall mean
the autoclave stability is qualified; otherwise, the autoclave stability is unqualified.
11.3.3 If the autoclave expansion rate of ordinary Portland cement, slag Portland cement,
pozzolanic Portland cement, fly ash Portland cement, composite Portland cement and other
cement varieties with mixed materials is no more than 0.50%, it shall mean the autoclave
stability is qualified; otherwise, the autoclave stability is unqualified.
Appendix A
(Normative)
Test Method of 25mm×25mm×146mm specimen
A.1 Instruments and equipment
A.1.1 25 mm×25 mm×146 mm test mold
The test mold is a two-piece type; and its dimensions shall meet the requirements of Figure A.1.
The end plate and partition board of the test mold are made of 45# steel, with a hardness no less
than HRC48 and a surface roughness Rα no greater than 1.6.
Key.
1 - base;
2 - positioning pin;
3 - nail head;
4 - fastening device;
5 - end plate;
6 – partition board.
Figure A.1 -- 25 mm×25 mm×146 mm pressure steaming two-piece test mold
Unit. mm
A.1.2 Nail head
It is made of stainless steel or copper; the dimensions shall meet the requirements of Figure A.2.
After the nail heads are fixed on the test mold, the distance between the inner sides of the nail
heads is 120 mm±2 mm; and the depth of the nail heads penetrating into the test mold is 7
mm±1 mm.
Figure A.2 – Nail head
A.1.3 Mold sleeve
The mold sleeve is made of steel and is used to block the material and fix the test mold during
forming. The size shall meet the requirements of Figure A.3.
Figure A.3 – Mold sleeve
Unit. mm
Unit. mm
A.1.4 Cement slurry mixer
It shall meet the requirements of JC/T 729.
A.1.5 Mortar vibrating table
It shall meet the requirements of JC/T 723.
A.1.6 Autoclave
It shall meet the requirements of 5.5.
A.1.7 160 mm comparator
The range of the dial indicator is 0 mm ~10 mm, and the minimum graduation value is 0.01
mm. The length of the correction rod is 160 mm; and the structure is shown in Figure A.4.
Key.
1 – dial indicator;
2 – bracket;
3 – correction rod.
Figure A.4 – 160mm comparator
A.2 Forming and curing of test specimens
Unit. mm
A.2.1 Preparation of test molds
Before the test, apply a thin layer of engine oil to the test mold and insert the nail heads (A.1.2)
into the round holes at both ends of the mold groove. The exposed part of the nail heads shall
not be contaminated with engine oil.
A.2.2 Preparation of cement paste
Weigh 500 g ± 1 g of cement and mix it with water of standard consistency according to the
procedure specified in GB/T 1346.
A.2.3 Molding of test specimen
Clamp the test mold with installed nail heads and the mold sleeve on the working position of
the mortar vibrating table (A.1.5); put the mixed cement paste of standard consistency into the
test mold at one time and flatten it with a table knife; start the mortar vibrating table and use a
knife to scratch back and forth along the length of the test mold to make the surface of the paste
flat and fill the edges and corners of the test mold. The scratching operation shall be completed
within 80 s after starting. After vibrating for 2 min, remove the mold sleeve and take off the test
mold, and remove the excess paste.
A.2.4 Curing and demolding
Put the molded test specimen and the test mold horizontally in the curing box (5.7) for curing
for 24 h ± 30 min and demolding. The counting starts from the time when the cement is mixed
with water.
A.3 Measurement of specimen length
Use 160 mm comparator (A.1.7) to measure the length.
A.4 Autoclave of specimen
Perform according to Clause 10.
A.5 Calculation and evaluation of results
Perform according to Clause 11, but the effective length (L) of the specimen is 120 mm.
Appendix B
(Normative)
Safety Precautions
B.1 During the autoclave test, the temperature and saturated steam pressure shall be measured
simultaneously. Because the temperature and saturated steam pressure have a certain
relationship, using them simultaneously can timely detect the failure of the pressure gauge or
the abnormal situation caused by the loss of water in the autoclave during the test.
B.2 The safety valve shall be adjusted to 10% higher than the working pressure of the autoclave
test, which is about 2.2 MPa. The safety valve shall be inspected at least once a year. During
the inspection, the pressure gauge can be used to inspect the equipment; or the pressure
automatic controller can be adjusted to make the autoclave reach 2.2 MPa. At this time, the
safety valve shall be opened immediately.
B.3 During the use of the autoclave, the following failures may occur at the same time. the
automatic controller fails; the safety valve is not sensitive; the pressure pointer suddenly
indicates zero, but it has actually exceeded the maximum scale and returned to zero from the
opposite direction. The pressure gauge needle returns to the initial position of the test; and the
autoclave may still maintain a certain pressure. If these situations are found, no matter how high
the pressure in the autoclave is, the test shall be stopped immediately, the power supply shall
be cut off, and safety measures shall be taken.
B.4 When the pressure steam test is completed and the air is released, the operator shall stand
away from the release valve. When opening the autoclave cover, asbestos gloves shall be worn
to avoid burns.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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