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How can I keep the cement sculpture from cracking?

Update:28-04-2020
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How can we keep the cement sculpture from cracking? Thi […]

How can we keep the cement sculpture from cracking? This is a question worth considering. Cement sculptures usually exist in gardens or roadside buildings, and will withstand wind and rain. So it is easy to form dry cracks. The following are methods to prevent cracks in cement sculptures:

In the process of making cement sculptures: add a large amount of acrylic acid to make the cement dense, impermeable, and more difficult to weather. But if you want to solve the cracks caused by the shrinkage of cement during the production process, you can only use other methods, such as: you can reduce the thickness of the cement and make it hollow when making the round sculpture. Or add an expansion agent (the simplest is to add a certain proportion of gypsum)

Operation notes:
(1) Avoid hardening with moisture and hardening The cement with moisture and hardening will reduce or even lose the original strength, so the specification stipulates that the cement that has been out of the factory 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 agglomerates, the strength level can be reduced appropriately.

(2) After mixing the frozen concrete or mortar with temperature, 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, construction should be carried out in strict accordance with the "Construction Regulations for Winter Construction" (JGJ104-97).

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(3) Avoid exposure to quick-drying concrete or plaster if exposed after operation. With the rapid evaporation of water, its strength will be reduced or even completely lost. Therefore, the base must be strictly cleaned and fully moistened before construction; after construction, it should be strictly covered and watered according to the regulations.

(4) Avoid dirty and soft base. Cement can be firmly bonded or wrapped together with a hard, 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.

(5) Avoid acid corrosion Acidic substances and calcium hydroxide in cement will undergo a neutralization reaction, and the product volume is loose and swelled, and it is easily hydrolyzed and pulverized after encountering water. The concrete or plaster layer is gradually corroded and disintegrated, so the cement is not corroded by acid. Where acidic substances or containers are used, 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.

(6) Avoid the mortar layer or concrete component after high temperature and extreme heat setting, if it is often under high temperature and extreme heat conditions, there will be strength loss, because the calcium hydroxide in the cement stone will decompose under high temperature conditions; The material 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. Dust, greasy, acid and alkali substances on the base layer will play a role of isolation, must be carefully cleaned, and then brushed with a plain cement slurry, and then mortar or pouring concrete.

Cement must shrink during the setting process, and it does not adapt to the volume change of the loose and weak base during the dry, wet, cold and hot changes. It will inevitably cause hollowing or cracks, which makes it difficult to bond firmly. Therefore, wood, slag cushion and lime soil cushion cannot be firmly bonded with mortar or concrete.

(7) Avoid impure aggregates. As gravel for concrete or cement mortar aggregates, if there is dust, clay or other organic impurities, it will affect the bond strength between cement and sand and stone, which will eventually reduce the resistance Compressive strength. Therefore, if the impurity content exceeds the standard, it must be washed before use.

(8) 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. Under normal circumstances, use 1: (3-5) coarse mortar to level the layer first, then use 1: (1.5-2.5) cement mortar to apply a very thin surface layer, and avoid using too much cement.

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