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GB/T 750-1992 English PDF (GBT750-1992)

GB/T 750-1992 English PDF (GBT750-1992)

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GB/T 750-1992: Autoclave method for soundness of portland cement

This Standard specifies the instrument, operating method and result assessment, etc. of autoclave method for soundness of Portland cement.
GB/T 750-1992
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
UDC 669.94.012.1
Q 11
GB/T 750-92
Replacing GB 750-65
Autoclave Method for
Soundness of Portland Cement
ISSUED ON. SEPTEMBER 28, 1992
IMPLEMENTED ON. JUNE 01, 1993
Issued by. State Bureau of Technical Supervision;
Approved by. State Bureau of Technical Supervision, September 28, 1992. Table of Contents
1 Subject Contents and Applicable Scope ... 3
2 Normative References ... 3
3 Method Principle ... 3
4 Terminologies ... 4
5 Apparatus ... 4
6 Specimen ... 4
7 Test Conditions ... 5
8 Molding of Test Piece ... 5
9 Boiling of Test Piece ... 6
10 Autoclaving of Test Piece ... 6
11 Results Calculation and Evaluation ... 7
Appendix A Test Method for 25mm??25mm??146mm Test Piece (Supplement) 8
Appendix B Safety Precautions (Supplement) ... 12
Additional Information... 12
Autoclave Method for
Soundness of Portland Cement
1 Subject Contents and Applicable Scope
This Standard specifies the instrument, operating method and result assessment, etc. of autoclave method for soundness of Portland cement.
This Standard is applicable to determine the uneven volume changes of the following cements due to periclase hydration like Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, flyash Portland cement, etc.; it is also applicable to other cement products designated use of this Standard. 2 Normative References
GB 177 Test Method for Strength of Hydraulic Cement Mortar
GB 751 Test Method for Drying Shrinkage of Cement Mortar
GB 1346 Standard Test Method for Water Requirement for Normal Consistency Setting Time and Soundness of the Portland Cement
GB 3350.2 Apparatus for Physical Test of Cement ?€? Vibrator for Compacting Mortar Specimen
GB 3350.8 Apparatus for Physical Test of Cement ?€? Mixer for Cement Paste 3 Method Principle
Under the condition of saturated water vapor, improve the temperature and pressure to cause most of the periclase in the cement to hydrate in short period; use the test piece deformation to judge the volume soundness of cement slurry.
4 Terminologies
Autoclave method. it indicates the treatment process under the condition of saturated vapor with temperature greater than 100??C. In order to make the periclase in the cement hydrate in short period, use 215.7??C saturated vapor to treat 3h; its corresponding pressure is of 2.0MPa.
5 Apparatus
5.1 25mm??25mm??280mm test mode, nail head, tamper and length comparator
It shall meet the requirements of GB 751.
5.2 Mixer for cement paste
It shall meet the requirements of GB 3350.8.
5.3 Boiling box
It shall meet the requirements of 3.3 in GB 1346.
5.4 Autoclave
It is Installed automatic pressure controller, pressure gauge, safety valve, drain vale and electric heater for high-pressure steam container. The electric heater shall be able to make the steam pressure in the pot up to the gauge pressure of 2.0MPa within 45~75min under the maximum test load; try not to discharge the steam under the constant pressure. The automatic pressure controller shall be able to control the pressure in the pot at 2.0??0.05MPa (equivalent to 215.7??1.3??C) range; and maintain for 3h above. The autoclave can reduce the pressure from 2.0MPa to 0.1MPa or less within 90min after the heating is stopped. The drain valve is used to remove the air from the pot during the initial heating phase and to release the remaining water vapor from the pot at the end of the cooling period. The maximum range of pressure gauge is 4.0MPa; the minimum scale value shall be no greater than 0.05MPa. The autoclave cover shall also be equipped with temperature measuring hole, after inserting the thermometer into it, it can measure the temperature into the autoclave. 6 Specimen
6.1 The specimen shall pass through the 0.9mm square-mesh screen.
6.2 The specimen?€?s boiling soundness must be qualified. To reduce the impact of f- CaO on the autoclave results, the specimen is allowed to spread into the air and store for no more than 1 week prior to the molding of test piece.
7 Test Conditions
The molding laboratory, mixing water, moisture curing tank shall conform to the provisions of 3.1, 3.2 in GB 177. The specimen temperature shall be kept at 17~25??C before the molding of test piece. The autoclave laboratory shall not be shared with other laboratories; and be equipped with ventilated device and tap water source. 8 Molding of Test Piece
8.1 Preparation of test mold. apply a thin layer of engine oil within the test mold before the test; install the nail head into the round hole on two ends of the mold groove; pay attention that the exposed part of the nail head shall not be contaminated by the engine oil.
8.2 Preparation of cement standard consistency paste. each cement shall be molded two strips of test pieces; take 800g of cement, mix with standard consistency of water; its operating procedure shall be performed as per 6.4 in GB 1346.
8.3 Molding of test sample. divide the mixed uniform cement slurry into 2 layers and install them into the prepared test mold. The installing height of firstly-layer slurry shall be three fifths of the height of test mold; firstly, use knife to scratch; especially the two sides of the nail head shall be inserted for several times; then use 23mm??23mm tamper starting from the internal side of the nail head, namely, between the two nail head tails to ram from one end to the other end for 10 times; totally ram for 20 times back and forth; then use notch-tamper to ram for 2 times on each side of the nail head; install the second-layer of slurry, after the slurry is filled with the test mold, use knife to scratch evenly; the depth of knife scratch shall penetrate the first-layer mortar surface; then use tamper to ram for 12 times in order on the slurry; totally ram for 24 times back and forth. Each time ramming, the tamper shall touch the slurry surface; then ram fiercely. The ramming must be uniform rather than blowing. After the ramming, install the remained slurry onto the mold; wipe flat with knife; place into the moisture curing oven to cure for 3~5h; then remove the excessive slurry onto the mold; so that the slurry is flat with the edge of mold. Then mark the number, place into the moisture curing oven for curing till molding; then demolding within 24h.
NOTE. in the exit-factory inspection, the test mold and molding method in Appendix A (supplement) are allowed to be used for preparing the test piece; but when the result is in dispute, it shall be subject to the result of 25mm??25mm??280mm test piece. 9 Boiling of Test Piece
9.1 Measurement of initial length. after the test piece is demolded, measure its initial length. Use the adjustable stem to calibrate the zero reading of dial-gauge of length comparator before measurement; the zero reading shall also be checked after the measurement; if there is any change, the test piece shall be re-measured. Clean the nail head before measure the length of the test piece; in order to minimize the error, the upper and lower position of the test piece in the length comparator shall be consistent in each measurement; rotate left and right before reading; when the dial- gauge indicator needle indicates to a stable reading (L0), the result shall be recorded to 0.001mm.
9.2 Boiling test. horizontally place the test piece that have been measured length onto the test frame of boiling box; boil as per the system of boiling soundness test stipulated in GB 1346. If necessary, the length of test piece after boiling can be measured.
10 Autoclaving of Test Piece
10.1 After boiling, the test piece shall be finished autoclaving within 4 days. The test piece before autoclaving and after boiling shall be placed into 20??2??C water for curing. Place the test piece onto the test frame at the room temperature before autoclaving. Gaps shall be maintained between test pieces. In order to ensure the vapor pressure in the autoclave is always saturated during the autoclaving period, sufficient distilled water shall be added; the adding quantity is generally about 7%~10% of pot capacity; however, the test piece shall not touch the surface.
10.2 Open the drain valve in the initial heating period; discharge the air from the autoclave, and close till the vapor is seen release; improve the temperature in autoclave; so that the gauge pressure can reach 2.0??0.05MPa from heating to after 45~75min; maintain for 3h under such pressure, then cut off the power; cool off the autoclave, so that the pressure in the autoclave can reduce to 0.1MPa below within 90min. Then slightly open the drain valve to discharge the remained vapor from the autoclave.
The operating procedures of autoclave shall be performed in strict accordance wit...

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