What is the National Standard TCVN 8877:2011 on Cement – Test method for autoclave expansion in Vietnam?
What is the National Standard TCVN 8877:2011 on Cement – Test method for autoclave expansion in Vietnam?
National Standard TCVN 8877:2011 is developed based on the reference of ASTM C151-09, Standard Test Method for Autoclave Expansion of Hydraulic Cement.
National Standard TCVN 8877:2011 is compiled by the Institute of Building Materials - Ministry of Construction, proposed by the Ministry of Construction, and published by the General Department of Quality Measurement and Standards - Ministry of Science and Technology.
National Standard TCVN 8877:2011 specifies the method for determining the autoclave expansion of cement by testing samples made from cement paste.
What is the National Standard TCVN 8877:2011 on Cement – Test method for autoclave expansion in Vietnam? (Image from the Internet)
What are the regulations on the autoclave equipment in Vietnam?
According to sub-section 4.5 of Section 4 of the National Standard TCVN 8877:2011, the requirements for the autoclave equipment are as follows:
(1) Technical requirements for autoclave equipment:
The autoclave equipment consists of a high-pressure steam chamber, a pressure gauge, a thermometer, a safety valve, and an exhaust valve. The pressure gauge has a diameter of 115 mm, with a scale ranging from 0 MPa to 4 MPa, and each division not exceeding 0.03 MPa. The accuracy of the pressure gauge should not exceed 0.02 MPa at a working pressure of 2 MPa. The heating rate of the equipment should ensure that the pressure reaches 2 MPa within a time frame of 45 minutes to 75 minutes from the start of heating.
The autoclave equipment is automatically shut off when the pressure exceeds (2.4 ± 0.12) MPa. The automatic control system must maintain the pressure at (2 ± 0.07) MPa for at least 3 hours. The pressure indicated on the pressure gauge at (2 ± 0.07) MPa corresponds to a temperature of (216 ± 2) oC. The autoclave equipment must be designed to reduce the pressure from 2 MPa to less than 0.07 MPa within 1 hour and 30 minutes from the time the heat supply is turned off.
(2) Safety considerations:
This standard aims to address all safety concerns, if any, in conjunction with the use of related safety issues. It is the responsibility of the user of this standard to establish appropriate safety measures, conduct inspections, and determine the application of any limiting provisions before use. Some specific safety issues are as follows:
- The pressure gauge has a measurement limit of 4 MPa, and using a measurement limit that is too small or too large can be dangerous for the operator.
- Check the pressure gauge by using a thermometer to detect any damage to the pressure gauge during operation.
- The automatic control system should be continuously maintained throughout the working period.
- The safety valve is set at a pressure value of 2.3 MPa. The safety valve should be tested twice a year, following the manufacturer's instructions or as needed, to ensure the equipment operates stably and safely for the user.
- When opening the lid of the equipment at the end of the test, the tester must wear heat-resistant gloves and direct the flow of hot air forward to avoid burns.
- Note: For the pressure gauge of the equipment, after it stops operating, the pressure gauge needle does not necessarily have to indicate "0" because there may still be significant pressure remaining in the equipment, which can be dangerous.
Cách tiến hành xác định độ nở autoclave được thực hiện ra sao?
Pursuant to Clause 7 of National Standard TCVN 8877:2011, the procedure for determining autoclave expansion is carried out as follows:
- Preparation of molds:
Prepare the molds according to National Standard TCVN 6068:2004.
- Determination of standard water:
Weigh 650g of cement, accurate to 1g. Measure 162ml of water using a measuring cylinder and pour it into the mixing bowl. Carefully pour the cement into the water to prevent water or cement loss, and let it soak for about 30 seconds.
Mix the sample at a low speed (140 ± 5) r/min for 30 seconds. Stop mixing the sample for 15 seconds to scrape the sides and bottom of the bowl into the mixing area using a trowel. Restart the machine and run it at a high speed (285 ± 10) r/min for 60 seconds. Then, shape the sample into a spherical form by hand and toss it from one hand to the other 6 times with a distance of about 150mm between the hands.
Place the sample in the mold, remove the excess, and flatten the surface of the sample.
Attach the Vicat needle to the Vicat apparatus, lower the needle to touch the top surface of the mold, and adjust the needle to the "0" mark above the graduation scale. Lift the needle and prepare for operation. After leveling the surface of the mold, move the mold and base to the Vicat apparatus at the center position under the needle. Slowly lower the needle until it contacts the surface of the mold. Keep it in this position for 1 to 2 seconds to avoid the acceleration of the moving part.
Then release the moving part quickly to allow the needle to sink straight into the center of the mold. Read the number on the graduation scale when the needle stops sinking or read it at 30 seconds after releasing the needle, whichever occurs earlier..
Record the reading, which indicates the distance between the needle tip and the free surface of the mold. Also record the water content of the mold as a percentage of the cement mass. Clean the needle after each penetration test.
Repeat the test with molds containing different amounts of water until the needle penetrates into the mold by (10 ± 1) mm. Record the water content of this mold with an accuracy of 0.5% and consider it as the standard water content of the mold.
The cement paste with the determined standard water content is used to make test samples.
- Preparation and maintenance of samples:
+ Number of test specimens:
Make at least one test specimen.
+ Preparation of test specimens:
known) or after determining the standard water content, pour the cement paste into the mold in two equal layers, each layer being compacted by pressing the thumb or index finger into the paste at the corners, around the measuring head, and along the mold surface until the sample reaches uniformity. The second layer is performed similarly, remove the excess with a thin spatula and level the surface. The laboratory technician must wear rubber gloves during the sample preparation process.
+ Maintenance of samples:
After making the samples, place the mold with the samples in a moist curing room for at least 20 hours. If the mold is removed before 24 hours, the test specimens are kept in the moist curing room for a total of 24 hours ± 30 minutes.
- Procedure:
+ At the time of 24 hours ± 30 minutes, remove the samples from the moist curing room and measure the length difference of the test specimens according to TCVN 6068:2004, record this value (Δlo). After determining (Δlo), place the test specimens in the autoclave device at room temperature on the support so that all surfaces of the specimens are in contact with saturated steam.
The autoclave device must contain enough water at an initial temperature ranging from 20°C to 28°C. To maintain a saturated steam environment throughout the pressure curing time, the amount of water poured into the device usually accounts for about 7% to 10% of the volume of the container.
+ Open the air release valve of the autoclave device during the heating process until the steam starts to escape. Close the valve and heat the autoclave device at a rate that reaches 2 MPa within 45 minutes to 75 minutes from the start of heating. Maintain a pressure of (2 ± 0.07) MPa for 3 hours.
After this time, turn off the heating and cool the device to reduce the pressure below 0.07 MPa within 1 hour and 30 minutes. Gradually reduce the internal pressure of the device by partially opening the air release valve until the pressure reaches approximately atmospheric pressure. Open the lid of the autoclave device, remove the samples, and immerse them in water with a temperature higher than 90°C.
Use cold water to cool the water surrounding the testsamples until the temperature drops to about 40°C. Then, remove the samples from the water and measure the length difference again according to TCVN 6068:2004, record this value (Δl1).
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