Crack resistance refers to the ability of concrete to resist dry shrinkage deformation or temperature deformation. When the tensile stress caused by these deformations exceeds the ultimate tensile strength of concrete, cracks will occur. That is to say, when these deformations exceed the ultimate tensile strain value of concrete (generally referred to as the ultimate tensile value), the concrete cracks. Therefore, the greater the ultimate tensile value or ultimate tensile strength of concrete is, the higher its crack resistance is.
In order to improve the ultimate tensile value or tensile strength of concrete, the following measures can be generally adopted:
1) When the tensile strength is high or the elastic modulus is low, the ultimate tensile value is larger, and the elastic modulus increases with the increase of strength (in fact, the growth rate of concrete strength is much higher than that of its elastic modulus), so the ultimate tensile rate of concrete increases with the increase of strength. Therefore, when the strength of concrete is increased, its crack resistance can also be improved.
2) Under the condition of constant water cement ratio of concrete, the ultimate tensile value is larger when the content of cement slurry and mortar is more. Therefore, the ultimate tensile strength can be improved by using the stone with smaller maximum particle size because of the high content of cement slurry and mortar.
3) The results show that the ultimate tensile value of concrete made of crushed stone is about 30% higher than that of ordinary pebble; the ultimate tensile value of lightweight concrete made of light tuff or ceramsite is 2-3 times higher than that of ordinary concrete.
4) In the early stage, the content of calcium in aluminate cement is higher and the content of calcium in aluminate cement is higher than that in the later stage. The results show that the ultimate tensile value can be doubled by adding air entraining agent and about 50% by mixing with waste water reducing agent of pulp (reed pulp or wood pulp).
5) Sufficient moisture curing or water curing can improve the ultimate tensile strength of concrete and improve the crack resistance accordingly.
6)According to the situation, add appropriate amount of anti crack reinforced fiber ,like Polypropylene fiber, glass fiber, Steel fiber ,etc .
6)According to the situation, add appropriate amount of anti crack reinforced fiber ,like Polypropylene fiber, glass fiber, Steel fiber ,etc .
