Since the cement concrete has been used, the crack problem has not been completely solved, and it has become a hot spot of great concern. There are two basic technical routes to solve the problem of concrete cracks in China: one is to add expansion agent to make expanded concrete, and the other is to add synthetic fiber to make synthetic fiber concrete. Many projects using expander concrete have successfully solved the cracking problem of concrete, but some projects have not been successfully solved, mainly because the expander concrete has a certain application range and use conditions, and requires strict maintenance measures, otherwise Not only can it not crack, but it can cause cracks in concrete. For the second method, its research and engineering practice are relatively lagging, but in recent years, it has developed rapidly, and it has been applied more and more in engineering. There are many successful examples. Of course, some people have proposed its cracking resistance. question.

At present, the international consensus is that fiber concrete is an effective method to improve the crack resistance and toughness of concrete. Especially, polypropylene staple fiber has a unique role in solving the early plastic cracking of concrete and reducing the dry shrinkage deformation of concrete. There are tens of millions of polypropylene staple fibers distributed in each cubic concrete to form a three-dimensional powerful space support system, which improves the intrinsic quality of concrete and makes concrete impermeability, crack resistance, toughness, impact resistance and fatigue resistance. The properties such as abrasion resistance are significantly improved, and the service life of the structure is prolonged.

From this, the following conclusions can be drawn:

(1) Polypropylene staple fiber can significantly improve the crack resistance of cement mortar, and the larger the fiber content, the better the crack resistance effect.

(2) Long fiber (19mm) is more effective than short fiber (12mm) for the crack resistance of cement mortar.

(3) Polypropylene staple fiber and expansion agent are mixed together into cement mortar, and under suitable conditions, the superposition effect is better.