Polypropylene Fiber Concrete:10 useful tips you don’t know

Q1. How does polypropylene fiber work?

Polypropylene fiber is known for its strength and corrosion resistance. It only takes a small wisp to improve the intensity of concrete. It works like this.

Before cracking

Before the concrete is dry (we call it the plastic stage), the deformation degree of the fiber is similar to that of the mortar ready to harden. The pp fibers can increase the tensile strength of concrete. Therefore, it can effectively prevent early-stage cracks.

During cracking

When the concrete cracks, the pp fibers act as a bridge, bearing the braking force when the concrete cracks. Thousands of fibers converge together to synthesize. The original coarse cracks become fine cracks under the action of pp fiber tension.

After cracking

After the concrete cracks, polypropylene fiber can still bear a certain weight for a long time. PP fiber concrete never breaks immediately like ordinary concrete.

Q2. Polypropylene fiber application

Fiberego cooperates with many projects. It has become a fixed supplier of pp fiber for many large-scale projects in China. Yet, the applications of polypropylene fiber in water conservancy construction are immeasurable. The following are a few examples.

When Polypropylene fiber is added to reinforced concrete panels:

Baixi Reservoir

Fish diving reservoir

Hongjiadu Reservoir

When Polypropylene fiber addition to concrete pavement engineering:

Huancheng Expressway

Tianhuangpingchang District Water Construction Station Factory Road

Polypropylene fiber is also added to the basement interior and exterior walls of industrial and civil buildingsHydraulic engineering panel

Three Gorges Water Conservancy Project

Q3. What are the highlights of polypropylene fiber?

When added to the polypropylene fiber produced by Fiberego, the concrete can prevent the cracking problem. At the same time, it improved the deformation performance of concrete. Concrete is impermeable and impact-resistant. The toughness of concrete has been enhanced.

Polypropylene fiber plays an irreplaceable role in engineering. The Engineering Bureau decided to find out the mixing ratio of pp fiber reinforced concrete at the diversion tunnel.

Q4. How to choose the raw materials of polypropylene fiber concrete during the experiment?

1. Fly ash

Fly ash in Nanjing Thermal Power Plant

2. Cement

Class 42.5 ordinary silicate cement.

3. Sand

Artificial sand in the aggregate yard of a Pumped Storage Power Station.

4. Broken stone

Artificial gravel in the aggregate yard of a Pumped Storage Power Station

5. Modified polypropylene fiber

The polypropylene fiber selected in this experiment is TB-20C produced by Fiberego. The technical parameters that appear in the experiment can be higher than the parameter standards.

6. Additives

JM-II concrete pumping agent. The dosage is 0.8%.

Q5. Which process is the best for mixing polypropylene fiber?

Process A:

First mix the four raw materials (sand, stone, cement, fiber), and then add water to mix in wet conditions.

Process B:

Add water to the four raw materials (sand, stone, cement, fiber) and mix them directly.

Process C:

Mix the three raw materials (sand, stone, fiber) first, and then add cement to mix again. Finally, add water to mix in moisture conditions.

Comparison results

We call the three processes PA, PB and PC respectively.

The results show that the distribution in PA fibers is more even than that of PB fibers. In PC, the fiber is more distributed than in PA. However, more time will be needed in PC for stirring in practice. PC is not very practical.

Therefore, after the test, we decide to use the mixing method for construction in the actual project.

In the self-falling mixer stirred in PA, samples are taken from the tank mouth, tank, and tank tail. The pp fiber distribution experiment was carried out by washing with water. The deviation of the washed fiber content is less than 10%. The result meets the standards.

Q6. What is the appropriate amount of polypropylene fiber?

In the experiment, the dosage of three polypropylene fibers was compared. The specific results are as follows:
0.6 KG/cubic meters ; 0.9 KG/cubic meters; 1.2 KG/cubic meters

Q7. How do the variate indexes change after adding polypropylene fiber?

1. Tensile modulus and ultimate elongation

The tensile elastic modulus of pp fiber concrete is lower than that of ordinary concrete. The ultimate elongation rate is greater. And it goes up with the increase of fiber dosage.

When the doping amount of polypropylene fiber is 0.9kg/m, the limit elongation rate of 28d is 8.3% higher than that of ordinary concrete. The amount of doping is 1.2kg/m is increased by 15.7%.

The lower the tensile elastic modulus is, the higher the limit elongation is, the better the deformation ability of polypropylene concrete is. Thus, it is conducive to the crack resistance of concrete.

2. Equivalent bending tensile

The addition of pp fiber improved the equal bending tensile strength of the concrete.

When the fiber content is 0.9kg/m, equivalent bending tensile strength increased by 34.7%; at 1.2kg/m, it increased by 21.3%.

The higher the bending tensile strength is, the greater we can tackle the weakness of conventional concrete.

It can adapt to deformation under temperature stress and dynamic water load to prevent concrete cracks.

3. Frost resistance grade

The antifreeze grade of non-fiber-mixed concrete is F100. Concrete with a fiber content of 0.6kg/m has a frost resistance grade of F150. When the fiber content is greater than 0.9kg/m, the antifreeze level reaches F200.

The freeze-thaw failure of concrete is caused by micro-cracks in the interior of concrete.

When 0.9kg/m pp fiber is added, microcracks can be effectively suppressed. The frost resistance of concrete can be significantly improved.

4. Comprehensive analysis

To sum up, the strength of concrete with a fiber content of 1.2kg/m performs no better than that with 0.9kg/m.

Moreover, that of 1.2kg/m has a greater viscosity and an increase in water consumption.

If the concrete with 1.2kg/m’s pp fiber is to reach the same strength as ordinary concrete, the water-cement ratio should keep unchanged. More cement is required for each square of concrete.

Concrete with a fiber content of 0.6kg/m has low bending strength. So do ultimate tensile value, bending tensile strength, and poor frost resistance.

5. Conclusions on the dosage of Polypropylene Fiber

Combined with the durability and crack resistance of fiber concrete, considering economic costs, the group recommended they add 0.9 kg of polypropylene fiber to concrete.

Q8. Is there a specific mixing ratio for polypropylene fiber reinforced concrete?

Water-cement ratio

1. The strength requirements of the concrete profile must be met.

2. Must meet the durability of concrete.

3. Because the addition of polypropylene fiber reduces the strength of concrete, the water-cement ratio coefficient is determined in the final draft: 0.4/0.45/0.5

Gradation ratio of crushed stone

When the gravel grading ratio is 50:50, the density of gravel is the highest, so when mixing concrete, the gravel grading ratio is 1:1.

Sand ratio

The sand ratio is determined through experimental mixing.

Q9. What are the Properties of polypropylene fiber concrete?

Mixture properties: good concrete and ease of use.

Mechanical properties: The compressive strength of concrete 28d is greater than the configuration strength to meet the strength design needs of C30 concrete.

Q10. How does the durability work after the test?

Impermeability grade greater than W10

Antifreeze level meets F50 standard for bridges and vult