1, the sampling
Bulk cement should be sampled from the cement carrier prior to feeding into the barrel silo. For bagged cement, a sampler should be used to sample not less than 10 bags of cement. When sampling, the cement should be visually tested for moisture agglutination. For bags of cement, 10 bags should be randomly selected to weigh and calculate the average weight at each arrival.
2. Test conditions
The laboratory temperature is 20±2℃, the relative humidity should not be less than 50%; The temperature of cement samples, mixing water, instruments and appliances should be consistent with that of the laboratory;
The temperature of the moisture curing box is 20±1℃, and the relative humidity is not less than 90%.
3. Determination of water consumption for standard consistency GB/T1346-2001
3.1 Instruments and equipment: cement paste mixer, vica instrument
3.2 Wet the instrument and equipment with wet cloth, weigh 500g of cement, pour it into water within 5 ~ 10s, start the mixer, low speed mixing 120s, stop for 15s, and then high speed mixing 120s stop.
3.3 Measurement steps:
After mixing, immediately mix the good cement net slurry into the test mold has been placed on the glass bottom plate, insert and pound with a knife, gently vibrate several times, scrape off the excess net slurry; After leveling, the test mold and the bottom plate are moved to the veka instrument, and its center is fixed under the test bar, and the test bar is lowered until it contacts the surface of the cement net slurry. After tightening the screws for 1s ~ 2s, it is suddenly relaxed, so that the test bar sinks vertically and freely into the cement net slurry. Record the distance between the test lever and the bottom plate when the test lever stops sinking or releases the test lever for 30 seconds. The whole operation should be completed within 1.5 minutes. The standard consistency of the cement slurry is the cement slurry which is sunk into the test rod and 6±1mm away from the bottom plate. The amount of water used for mixing is the standard consistency of the cement (P), calculated as a percentage of the cement mass.
4. Determination of setting time GB/T1346-2001
Preparation of the sample: the standard consistency net slurry made of water with standard consistency was filled with the test mold at one time, scraped after several times of vibration, and immediately put into the moisture curing box. Record the time when cement is added to water as the start time of setting time.
Determination of initial setting time: specimens were cured in the moisture curing box until 30min after adding water for the first time. When the test needle sinks to the bottom 4±1mm, the cement reaches the initial setting state; The time from adding cement into water to reaching the initial setting state is the initial setting time of cement, expressed in “min”.
Determination of final setting time: after the determination of initial setting time, immediately remove the sample with slurry from the glass plate by translation, and turn it 180°. Diameter of big end up, small end on the glass plate, add moisture curing box to maintenance, near final setting time determination once every 15 min, when try needles into the body of 0.5 mm, namely ring attachment began to cannot leave a mark on try body, reach final set status of cement, the cement add water until the state of the final set time of the final setting time of cement, The value is min.
Attention should be paid to the determination, in the initial determination of the operation should gently support the metal column, so that it slowly down, to prevent the test needle collision bending, but the result is free fall shall prevail; During the whole test process, the position of the needle sinking should be at least 10mm away from the inner wall of the mold. When the initial setting is near, it should be measured every 5min, and when the final setting time is near, it should be measured every 15min. When the initial setting or final setting is reached, it should be measured again immediately. When the two conclusions are the same, it can be determined as reaching the initial setting or final setting state. Each test can not let the needle fall into the original pinhole, the whole test process to prevent the vibration of the mold.
5. Determination of stability GB/T1346-2001
Specimen molding: put the prepared Reisler’s clip on the slightly oiling glass plate, and immediately fill the prepared standard consistency clean slurry with the Reisler once, insert and tamp it several times with a knife about 10mm wide, then wipe it flat, cover the slightly oiling glass plate, and immediately move the specimen to the moisture curing box for 24±2h.
Remove the glass plate and take off the specimen. First measure the distance between the pointer tips of the Reefer’s clamp (A), accurate to 0.5mm. Put the two specimens on A test rack in boiling water with the pointer facing up, and then heat them to boiling in 30±5min and keep boiling for 180±5min.
Result discrimination: After the boiling, let the water in the box, after the box cooled to room temperature, take out the specimen for measurement, the distance of pointer tip (C), accurate to 0.5mm. When the average value of the increased distance (C-A) between the two specimens is not more than 5.0mm, it is considered that the cement stability is qualified. When the difference of the value of (C-A) between the two specimens is more than 4.0mm, the same sample shall be immediately retested. In this case, the cement stability is considered unqualified.
6, cement mortar strength test method GB/T17671-1999
6.1 mixture ratio
The quality mix of mortar should be one part cement, three parts standard sand and half part water (water cement ratio 0.5). Concrete cement 450g, 1350g standard sand, water 225 g. The accuracy of the balance should be ±1g.
6.2 stir
Each pot of glue sand is mechanically stirred by a blender. Put the mixer in working condition first, then follow the following procedure: add water to the pot, then add cement, put the pot on the holder, rise to the fixed position. Then start the machine, low speed mixing 30s, the second 30s began at the same time to evenly add sand, turn the machine to high speed mixing 30s, stop mixing 90s, and then high speed mixing 60s, a total of 240s.
6.3 Preparation of specimens
The specimen size should be 40mm×40mm×160mm prism.
Forming with vibrating table
Immediately after the preparation of mortar molding, with an appropriate spoon directly from the stirring pot will be divided into two layers of mortar into the test mold, the first layer, each tank about 300g mortar, with a large feeder vertical frame on the top of the mold cover along the top of the test mold along each groove back and forth once the material layer is seeded flat, then vibration 60 times. Then load the second layer of mortar, sow flat with a small feeder, and vibrate 60 times. With a metal ruler to approximately 90° Angle frame at the top of the test mold, and then along the length direction of the test mold with transverse sawing action slowly to the other end of the movement, a more than the test mold part of the sand scraping, and with the same ruler to nearly level the surface of the test body.
6.4 Curing of specimens
The marked test mold will be put into the cement standard curing box, demold between 20-24h. The marked specimen is immediately placed horizontally or vertically in water at 20℃±1℃ for maintenance, and the scraping plane should be upward when placed horizontally.
6.5 Strength testing and evaluation
Bending strength test:
The flexural strength was measured by center loading method with flexural strength testing machine. The compressive test was carried out on the broken prism by putting it on the compressive strength tester. The compressive surface was two sides of the test body when it was formed, with an area of 40mm×40mm. (Reading recorded to 0.1mpa)
The flexural strength is the direct reading on the test machine, unit (MPa)
Compressive strength Rc (accurate to 0.1mpa) Rc = FC/A
Maximum load at failure of Fc—-,
A—- Compression area, mm2 (40mm×40mm=1600mm2)
Flexural strength assessment:
The average value of the flexural resistance of a group of three prisms is taken as the experimental result. When the three strength values exceed the average value of ±10%, the average value should be removed as the flexural strength test result.
Compressive strength evaluation: the arithmetical evaluation value of six compressive strength values obtained on a set of three prisms is the test result. If one of the six measured values exceeds ±10% of the six mean values, the result should be eliminated and the remaining five mean values taken. If more of the five measured values exceed their mean ±10%, the set of results will be invalidated.
7, fineness test method (80μm sieve analysis method) GB1345-2005
7.1 Instrument: 80μm test screen, negative pressure screen analysis instrument, balance (the dividing value is not more than 0.05g)
7.2 Test procedure: weigh 25g cement, put it into the negative pressure sieve, cover the sieve cover, put it on the sieve base, adjust the negative pressure to the range of 4000 ~ 6000Pa. When screening analysis, if there is attached to the screen cover, you can gently knock, so that the sample falls, after screening, use a balance to weigh the remainder of the screen.
7.3 Result Calculation The residual percentage of cement sample sieve is calculated as follows:
F is RS/W times 100
Where: F — sieve residual percentage of cement sample, %;
RS — Mass of cement screen residue, G;
W — mass of cement sample, G.
The result is calculated to 0.1%.
Each sample shall be weighed and two samples shall be screened separately, and the average value of the remaining samples shall be taken as the screening analysis result. If the absolute error of the two screening results is greater than 0.5% (if the screening residual value is greater than 5.0%, it can be put to 1.0%), another test should be done, and the arithmetic mean of the two similar results should be taken as the final result.
8, the whiteness of white cement
When sampling, cement whiteness and color should be visually measured and compared with the sample whiteness.
Post time: Dec-06-2021