Frequently asked questions in polypropylene fiber applications
I. Can polypropylene fiber be used as a waterproof material?
There are three principles of structural waterproofing of concrete:
(i)Expansion compensation type;
(ii)Water-reducing compact type;
(iii)Crack resistant and waterproof type.
This kind of polypropylene fiber is through the physical reinforcement effect to reduce concrete cracking, avoid the formation of capillary pores and greatly improve the waterproof ability of concrete, is the ideal material for rigid self-waterproof concrete structure.
II.What role does polypropylene fiber play in concrete?
(i)The shrinkage cracks of concrete can be reduced and the impermeability and durability of concrete can be improved.
(ii)Ensure the homogeneity of concrete.
(iii)Reduce brittleness of concrete.
(iv)Improve the fire resistance of concrete.
III.Is it necessary to use a special mixer to mix fiber concrete? Can fiber be added to commercial concrete?
No special equipment is required. Fiber reinforced concrete can be prepared by the forced concrete mixer commonly used in construction sites. In order to ensure that the fiber is evenly mixed in the concrete, the time can be extended appropriately. One approach is to make concrete by conventional mixing, and then without stopping, the fiber has been weighed into the concrete, continue to stir for 3mins, so that the fiber becomes a root of monofilaments evenly distributed in the concrete mix. In the actual project, the more used method is to directly put the fiber and sand material into the mixer to stir, and the effect is better.
Commercial concrete mixed with fiber can be prepared in concrete mixing station. The weighed fiber can be manually fed directly from the feed port on the feed platform of the mixing equipment. Although the density of the fiber is only 0.91g/m3, the actual operation shows that there is no flying phenomenon when feeding. The slump of the fiber added to the concrete is slightly reduced, but it does not affect the workability of the concrete, nor does it affect the temporal change of the concrete slump (the temporal change of the concrete slump mainly depends on the water-reducing agent used).
IV .how much is the appropriate amount of polypropylene fiber in concrete?
Polypropylene fiber can play its role in concrete, to a large extent depends on the number of fiber monofilaments in the concrete and its uniform distribution. Because the surface of the fiber is covered with a special film layer, tens of millions of monofilament fibers can be distributed very evenly in the concrete. For this reason, under normal circumstances, the amount of fiber in concrete need not be too high, and 0.6-1.2kg can be added to 1m3. Set the fiber content of 1m3 concrete to add 0.kg, the number of monofilament fibers (length specification 12mm) in 1m3 concrete can reach nearly 200 million.
V.What is the difference between the effect of polypropylene fiber and expansion agent?
The purpose of anti-cracking and anti-seepage can be achieved by adding expansion agent and fiber in concrete. But there are some differences in the principle and effect of action.
Principle: The expansion agent generates ettringite or calcium hydroxide crystals through chemical reaction, so that the concrete expands to compensate for its shrinkage, thereby reducing or preventing the generation of cracks in the concrete. Fibers act physically to reduce cracks in concrete.
Efficacy: The expansion agent can only obtain better anti-crack and anti-seepage effect in a humid environment. If in a dry environment, it may not be effective or even counterproductive; The fiber, whether in wet or dry environment can obtain a good crack and seepage resistance.
Construction conditions: The expansion agent is very harsh on the maintenance conditions, requiring water storage and maintenance for more than 14 days, and the fiber has no special requirements for maintenance.
VI. polypropylene fiber in the mixing process will not form a group?
No. In the mixing process, the fiber treated by the special process can be automatically dispersed in the alkaline cement slurry environment by mechanical mixing and aggregate impact, and can be evenly distributed in a three-dimensional manner without clumping.
VII.The use of polypropylene fiber need to change the mix of concrete or mortar?
No need. Polypropylene fiber is a completely physical reinforcement action, the ratio of concrete does not need to be adjusted.
VIII.Can polypropylene fiber reduce concrete cracking?
Fiber can effectively reduce plastic cracking and early shrinkage cracking of concrete, and the experimental results show that fiber can reduce the cracking by more than 90%.
IX.What are the precautions for using polypropylene fiber?
(i)The role of the fiber is a "secondary reinforcement", which cannot replace the structural reinforcement material or reduce the main structural size.
(ii)It can not be used alone to solve the settlement, mass concrete hydration heat and strong external impact occasions.
(iii)The construction quality management requirements can not be reduced because of the use of fiber, and the construction and maintenance should still be carried out in accordance with the relevant national technical specifications.
