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Solution to the problem of moisture expansion and water absorption of fiber cement board

  • Categories:Blog
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  • Time of issue:2020-08-21 15:59
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(Summary description)

Solution to the problem of moisture expansion and water absorption of fiber cement board

(Summary description)

  • Categories:Blog
  • Author:
  • Origin:
  • Time of issue:2020-08-21 15:59
  • Views:
Information

The moisture expansion rate of the wall panel is high, the moisture absorption expansion of the board is affected by moisture, and the drying shrinkage is significant, which will cause the wall deformation, or even lead to the whole wall cracking. And high water absorption, the material will be more vulnerable to moisture erosion, in the joint treatment, the moisture in the joint material is quickly absorbed by the plate, thus affecting the final joint strength, easy to crack in wet season.

Because the water absorption rate of the board without waterproof treatment is high, it is not simple to consider the change rate of specimen length (i.e. humidity deformation) as specified in JC / T 396-2012 "non load bearing fiber reinforced cement board for external wall" when the relative humidity changes from 30% to 90%, the change rate of the board in the extreme state of saturated water absorption (i.e. moisture expansion rate) should be considered. The moisture expansion rate of autoclaved curing products is less than or equal to 0.25%, and the maximum wet expansion length is 6.1 mm when the applied length of plate is 2440 mm; however, in practical engineering, the joint width of non transparent curtain wall is generally 8-16 mm. Considering the effect of construction error, earthquake reservation and temperature deformation, it is difficult to meet the requirements of curtain wall engineering.

Therefore, it is necessary to limit the partition size and moisture expansion rate of fiber cement board for curtain wall in the design. Fiber cement board has a high water absorption rate, and the moisture on the back of the board exists for a long time after absorbing water. Due to the appearance of condensate water, the anti-corrosion requirements of the closed curtain wall system for foundation wall and curtain wall keel are greatly improved. Even if our plate has been coated with waterproof coating, it is difficult to maintain long-term surface waterproof effect like glass, metal plate and stone, so it should be given priority If the environment is suitable and the board is well protected, the closed type can also be adopted. In severe cold areas and cold areas, the temperature difference between autumn and winter is large. If there is accumulated rain and snow water vapor, it will melt in the daytime and freeze at night. In order to prevent the water in the slab joint from freezing and causing the brittle material panel to be damaged, the closed slab joint should be adopted, and the glue injection sealing joint should be preferred. If the open man-made panel curtain wall is adopted, full consideration shall be given to prevent the damage to the curtain wall caused by the frost heaving of ponding and ice accretion.

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