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Notes on handling cement in daily life.

Update:03-07-2020
Summary:

1. Avoid moisture and hardening   Moisture and hardenin […]

1. Avoid moisture and hardening   Moisture and hardening cement will reduce or even lose the original strength, so the specification stipulates that the cement that has been shipped for more than 3 months should be reviewed and used according to the test results.

Cement that has been wetted into agglomerates or hardened must be sieved and used. The sieved agglomerates are generally used for masonry mortar or plastering mortar in secondary projects after being ground or milled. For one-touch or one-powder cement paste, the strength level can be reduced appropriately.

2. Avoid exposure to quick-drying   concrete or plaster if exposed after the operation, as the water quickly evaporates, its strength will be reduced, or even completely lost. Therefore, it is necessary to strictly clean and fully moisten the grassroots before construction; after construction, it should be strictly covered and watered according to the regulations.

3. After mixing the frozen concrete or mortar, if it is frozen, the cement cannot be hydrated, and the water freezes and expands, then the concrete or mortar will be damaged by the deepening of the surface and the inside. Therefore, the construction should be carried out in strict accordance with the "Construction Engineering Winter Construction Regulations" (JGJ104-97).

4. Avoid the mortar layer or concrete component after high temperature and extreme heat solidification, if it is often under high temperature and extreme heat conditions, there will be strength loss, this is because under high temperature conditions, calcium hydroxide in the cement stone will decompose; In addition, some aggregates It will also decompose or expand in volume under high temperature conditions.

For long-term high temperature applications, refractory bricks can be used to isolate and protect ordinary mortar or concrete. In case of higher temperature, special heat-resistant concrete should be used for pouring, and a certain amount of ground heat-resistant material can also be mixed into the concrete.

5. It is forbidden that the base is dirty and soft. Cement can be firmly bonded or gripped with the hard and clean base, but its bonding strength is related to the smoothness of the base. Construction on a smooth base must be pre-chirped and smashed in order to make the cement firmly adhere to the base.

Dust, greasy, acid and alkali substances on the base layer will play a role of isolation, and must be carefully removed and washed. Afterwards, first brush a plain cement slurry, then apply mortar or cast concrete.

Cement must shrink during the setting process, and in the process of dry, wet, cold and hot changes, it is very incompatible with the volume change of the loose and weak base, and hollowing or cracks are inevitably occurring, making it difficult to bond firmly. Therefore, wood, slag cushion and lime soil cushion cannot be firmly bonded with mortar or concrete.

6. Avoid impure aggregates. As gravel for concrete or cement mortar aggregates, if there is dust, clay or other organic impurities, China MALE PIPE Factory  will affect the bond strength between cement and sand and stone, which will eventually reduce the compressive strength. strength. Therefore, if the impurity content exceeds the standard, it must be washed before use.

7. Avoid water and heavy ash. People often ignore the impact of water consumption on the strength of concrete. In order to facilitate pouring during construction, sometimes the mix ratio is not carefully implemented, and the concrete is mixed very thinly. Since the water required for hydration is only about 20% of the weight of the cement, the excess water will leave a lot of pores in the concrete after evaporation, and these pores will reduce the strength of the concrete.

Therefore, under the premise of ensuring the compaction of the pouring, the mixing water should be minimized. Many people think that the more the amount of cement used for plastering, the stronger the plastering layer. In fact, the more the amount of cement, the thicker the mortar, the greater the volume shrinkage of the plaster layer, and the more cracks there are.

Generally, when plastering, you should first use 1: (3-5) coarse mortar to level the layer, and then use 1: (1.5-2.5) cement mortar to apply a very thin surface layer, and avoid using too much cement.

8. Avoid acid corrosion. Acidic substances and calcium hydroxide in cement will undergo a neutralization reaction. The volume of the product is loose and swollen. It is easily hydrolyzed and pulverized after encountering water. As a result, the concrete or plaster layer is gradually corroded and disintegrated, so the cement should not be corroded by acid. In the places or containers that are in contact with acid substances, acid-resistant mortar and acid-resistant concrete should be used.

Slag cement, pozzolan cement and fly ash cement all have good acid resistance. These three kinds of cements should be preferred to prepare acid-resistant mortar and concrete. Strict requirements for acid corrosion resistant projects are not allowed to use ordinary cement.

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