Cement, powdered hydraulic inorganic cementitious material. After adding water, it becomes a slurry, which can be hardened in air or hardened in water, and can firmly bind sand, stone and other materials together. So, what are the cement buying tips and cement precautions? Let's take a look with Xiaobian.
Cement Buying Tips Cement Considerations
First, the purchase of cement tips
1, look at the time, see the production date of cement. Cement performance beyond the valid period of 30 days has declined. After three months of storage, the strength of cement decreased by 10%-20%, decreased by 15%-30% after six months, and decreased by 25%-40% after one year. High-quality cement can be solidified in more than 6 hours. Cement that does not solidify for more than 12 hours is of poor quality.
2, look at the appearance, to see if the cement paper bag packaging is intact, the logo is complete. The labels on the paper bags are: factory name, production license number, cement name, registered trademark, variety (including variety code), label, packaging year, month, date and number.
3, look at the color, observe whether the color is dark gray or dark green, yellow color, white (yellow clinker shows raw material burning, white, indicating excessive slag content) cement strength is relatively low.
4, feel guilty, use your fingers to pick up the cement powder, feel a little fine, sand, powder feeling, indicating normal cement fineness.
5. “Smell†Mud Analysis Quality The smell here is not a smell. After all, it is unsafe for cement to smell to the consumer. The “smell†here is “hear†and listen to the introduction of the ingredients of cement, so as to infer the quality of cement. . At present, some small cement plants in China have used cement mixing materials in excess of cement standards in order to carry out low-priced sales, and have not strictly followed the national standards to match the raw materials. The performance of their products can be imagined. The regular manufacturers are very rigorous in the choice of raw materials for cement, generally choose the highest quality limestone as raw material, not only chemical composition is stable, but also the content of effective components is high, the cement produced has moderate setting time, high bonding strength, and durability. Good features. At the same time, in the production of raw materials are also strictly in accordance with national standards, through strict quality control system products fully consistent with ISO9000 standards, helium, radioactive materials, chloride ions, alkali and other four tests are better than national standards.
6. It is advisable to add the phrase “must conform to national standards†to the purchase contract, and at the same time it is best to leave a sample in the construction. Once the project is finished, it can be used as a judgment because of the indoor environment pollution caused by Daxin board quality problems. The basis of responsibility.
Second, cement matters needing attention
The cement factory quality certificate shall be stamped by the manufacturer's quality department; the test report shall have a test number in order to verify the verification with the relevant data of the laboratory, and shall have clear conclusions with complete signature and seal; the manufacturer's cement 28 The daily strength report form must not be missing; the use unit must carefully check the cement's validity period; for the expired cement, a re-test must be done and the test report must carefully check whether the measured values ​​meet the standard values ​​specified in the specification; for quality problems Cement, according to the test report data can be downgraded, but must be signed and approved by the relevant technical person in charge, and should indicate the name of the use of the project, the use of the site.
1, avoid moisture knot hard
Cement that is hardened by moisture will reduce or even lose its original strength. Therefore, the specification requires that cement that has been delivered for more than three months should be retested and used according to the test results. For cement that has been dampened into clusters or hardened, it must be used after sifting. The lumps that have been sieved are finely crushed or finely milled and are generally used as masonry mortar or plaster mortar for minor works. For one-touch or pinch-to-powder cement lumps, strength levels can be appropriately reduced.
2, avoid drying speed
If the concrete or plaster is exposed after the operation, its strength will be reduced or even completely lost with the rapid evaporation of moisture. Therefore, the construction must be strictly cleaned and fully wetted before the construction; the construction should be strictly covered and watered and maintained in accordance with the specifications.
3, avoid negative temperature and freezing
After the concrete or mortar is mixed, if it is frozen, the cement cannot be hydrated, and if the water icing expands, the concrete or mortar will be damaged by the powder and cracks that are gradually deepened from the surface to the inside. Therefore, the construction project should be strictly observed. Winter Construction Procedures (JGJ104-97) for construction.
4, avoid high temperature heat
After the solidified mortar layer or concrete component, if it is often under high temperature and hot conditions, there will be strength loss because of the decomposition of calcium hydroxide in the cement stone under high temperature conditions; in addition, some aggregates are also under high temperature conditions. Decomposition or volume expansion.
For long-term high temperature occasions, fireproof bricks can be used for isolation and protection of ordinary mortar or concrete. In case of higher temperatures, special heat-resistant concrete shall be used, and a certain amount of ground heat-resistant material may also be incorporated into the concrete.
5, avoid the grassroots dirty
The cement can be firmly bonded or gripped with a hard, clean base, but the bond grip strength is related to the smoothness of the base face. In the smooth construction of the grass-roots level, must be brushed nettle before brushing, in order to make the cement and the base layer firmly bonded.
The above- mentioned cement buying skills and cement precautions are briefly introduced here. I hope to help you. For more information, please visit this website. Stay tuned.
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