Frost resistance of fiber cement
Frost resistance of the fiber cement board is a capacity of the material water-saturated to withstand repeated freezings with the subsequent thawing without great strength reduction and visible signs of failure.
It seems clear that this property is one of the most important for construction materials used in our country. Nobody wants to receive something similar to photo below instead of a new beautiful wall in several winters.
Frost resistance directly depends on structure of material and degree of its hydrophility - binding force with water. Strong hydrophilic materials take up water, drops spread on a surface, water is soaked through bugholes and capillaries of hydrophilic materials (an example of hydrophilic material - a brick). Hydrophobic materials repel water (for example, bitumen).
It seems clear that the more vesicular structure of material and above its hydrophility, this material is less frost-resistant. Water is absorbed in capillaries, penetrating deep into surface and when freezing it destroys the material, changing the aggregate state and expanding almost by 10%, becoming ice. Such expansion destroys walls of some bugholles, and when thawing water gets even more deeply into material. Consecutive cycles of freezing and thawing gradually destroy the material more and more.
To decrease a porosity of LATONIT fiber cement boards they are pressed under high pressure (about 600-650 N/sq.cm) during production, and then they are sent to autoclaves. The autoclaving facilitates the cement crystallization process, increasing its durability and chemical resistance. Still more to increase a durability and moisture resistance of LATONIT fiber cement boards they are covered with water-repellent hidrophobic composition before painting.
Resistance of materials to a frost is determined by the tests which are carried out according to special rules of the State Standards.
In a few words, summery of test method is as follows:
- Material is saturated with water by immersing the samples within the fluid for 48 hours.
- Then the alternate freezing and thawing of the samples consisting of two phases for 4 hours are carried out:
✽ freezing at a temperature not exceeding minus 15 °C;
☼ thawing in water of a temperature which is not below plus 10 °C.
After carrying out the set number of cycles the tested samples are reviewed for segregations or other damages, comparing them with the control samples not frozen.
Important examination of the test sample is strength testing. Comparison is carried out with control samples of the same untested material. Both control and test materials are saturated with water within 48 hours, and then strength tests are carried out by bending (for boards)or by pressing (for brick).
For LATONIT fiber cement boards the number of cycles of alternate freezing and thawing comprises 150 times at the current of residual strength not less than 90%.
What's interesting is that freeze-thaw durability test of a facing brick (a facing brick and a clinker brick) is carried out by means of a similar test methods. Value of frost resistance of a clinker brick has to be not lower than 75, the facing products - not lower than 50.