Project Study：5 Incredible Infrastructural Project Solutions

We hope you can gain immeasurable experience with these projects!

The use of polypropylene fiber is immeasurable! Still not in favor of the fact that polypropylene fiber has a solid place in every step of life? Let’s take a look at how it is used in these infrastructural projects solutions! Polypropylene fiber occurs everywhere from civil engineering, water conservancy protection, to tunnels and more.  How have polypropylene fiber products been involved in China’s practical infrastructure projects in recent years? Read this paragraph to get a deeper understanding of polypropylene fiber project solutions.

Project 1: The Yellow River water source project –Tackle the corrosion

The Yellow River Diversion Project is in the middle of Shanxi Province. The underground power plant of the pumping station has a large excavation span. After the excavation, its upper arch is exposed to the flowing groundwater. However, the marl under the arch is slightly softened by the groundwater. Gradually, a unstable cavern appears.
We must consider the risks into consideration. Here’s what they did.

1. During the excavation, the team has introduced steel fiber pumped concrete as the first support for personnel safety.

2. Addition of Admixtures is an important way to optimize the mix ratio of concrete and improve the durability of concrete. Hydraulic concrete should contain the proper amount of admixture. This additive can optimize the concrete and reduce water consumption. It can also save cement, reduce costs, and accelerate the progress of construction.

3. As an advantage of technology, steel fiber has become the fifth material needed for reinforced concrete. Other addicts include cement, coarse aggregates, and admixtures. Polypropylene fiber is also one of these ideal polypropylene fiber additive materials.

Project 2: Baixi Reservoir in Ningbo — Optimize every single step

Polypropylene fiber has been used in civil engineering construction for over 20 years. Yet, polypropylene fiber in hydraulic structures needs further test and demonstration. The Reservoir Construction Headquarters in Baixi commissioned the Chinese Academy of Sciences to conduct an indoor test study on the performance of polypropylene fibers in the concrete of the Reservoir dam.

The Chinese Academy of Sciences has revised the mixing ratio. At the same time, the engineering team indicated several problems of the tested block include time control, difficulties in pressing the surface, and process connection, etc. These experiences will help the team to find the optimum mixing ratio of polypropylene fiber and the concrete afterward.
A further test is conducted to determine how polypropylene’s doses affect the concrete quality and construction technology. Added another test block with a polypropylene dose of 1.2 kg/m3. (Contains 0.2 kg more pp fiber.) The results of the experiment are worth learning.

This is all the experience we have closed:

1. Details of disclosure. Before pouring the panel, technical details must be disclosed to the construction and management personnel above the team leader, so that the operators can know their jobs fairly well and avoid mistakes.

2. Select raw materials. Raw materials such as steel bars, cement, sand, and gravel are inspected before being used. The quality of all raw materials must meet the relevant standards.

3. Control the mixing materials as well as measurements. When manual feeding is adopted, all materials must be put in by special pe rsonnel to avoid erroneous feeding and to ensure accurate measurements.

4. A self-falling mixer must be used. The mixing time must be no less than 5 minutes to ensure the fiber and the cement are completely mixed.

5. Control the slump.

If the slump is too small, the fibers will stick to the chute, the concrete will slip in the chute, and it will not vibrate in the bearing.
If the slump is too large, the concrete will slip into the slide and separate them. After the mold is ejected, the concrete collapses and its surface becomes less flat. The concrete strength cannot reach the design value.

The best slump control range is 4 ~ 6 cm at the exit and 2 ~ 3 cm at the warehouse surface. In this way, the entire process of transportation, storage, shaking, formwork sliding, and plastering can be ensured.

6. Shipping time must be accurate. The slump loss in fiber reinforced concrete is as fast as 1/2 in 0.5 h. Therefore, when transporting fiber concrete by a motorized dump truck, it is necessary to shorten the off-site transportation time as much as possible, usually within 15 minutes. Otherwise, the concrete is not easy to vibrate.

7. Flood control and sun protection. To prevent the evaporation of water on the surface, it is necessary to double the amount of plastering work required compared to conventional concrete so that plastering work can be done smoothly.

8. Fiber concrete should be constructed at a temperature below 25 ℃.

Project 3: Nalan concrete sheet of the rock-fill dam: Why crack?

We analyzed the experiments of the crew working for Nalan. The project bought a light for us to prevent the formation of cracks in fiber-reinforced concrete.

Some reasons for cracks in the Nalan polypropylene fiber concrete panels are:

1. Temperature cracks
Temperature cracks due to heat of hydration of cement or sudden temperature drop under the cold weather. This leads to the large temperature difference between the two inner surfaces of the concrete, causing cracks in the surface.

2. Dry shrinkage cracks
Dry shrinkage cracks lead to root cracking due to outside air temperature and humidity conditions. Losing too much moisture is the root cause of the shrinkage cracks of concrete slabs. Concrete shrinkage is usually a step-by-step process that can slow down the process that can take a year or more to complete. A step-by-step process can slow down the process, but there is a lapse between temperature stress and dry shrinkage. We should prevent superficial cracks before the final set.

3. Structural cracks
Since the plate is long and thin, the dam body and dam foundation will deform. Nalan’s polypropylene hybrid fiber-reinforced concrete slab has been optimized. Ash and polypropylene fiber enhance the crack resistance and durability of the plate. The team implemented strict controls, careful maintenance, and other engineering measures. This project reduced the crack resistance of the external slab concrete.

The results show that the cracks disappeared after pouring the concrete of the Nalan slab. Through the practice of Nalan Hydro-power Station, a new experience has been accumulated. This will provide new instruction on the later building of the anti-cracking concrete sheet.

Project 4: A reinforced concrete dam in the alpine region –Under harsh nature condition

The freezing and thawing damages of a concrete slab are related to the harsh natural conditions in Chalong.
Under the combined pressure of expansive freezing pore water and the seepage, the macro fiber concrete slab in the water level fluctuation area is destroyed by freeze-thaw denudation from the inside out.
There are three main maintenance methods:

1. Anchorage form
Expansion bolts are replaced by some form of chemical anchor. It has nothing to do with polypropylene fiber technology, which cannot solve structural damage, so we have to solve the problem from the structure first.

2. Eliminate the protruding parts in the structure
The structure adopts a horizontal type, replaces angle steel with flat steel, and uses a flexible edge sealing agent to fill the groove near the nut.
Polypropylene or steel fiber reinforced concrete can solve the damaging and scraping problem at protruding parts of the structure. Suggested to further optimize the structure.

3. Sealing of components
We use a chemical anchoring agent to seal the gap between the screw and hole in the wall, and use soft agent light-collecting materials to seal the gap of flat steel, cover sheet, and screw. This measure is for tackling polypropylene/ steel fiber corroding and rusting.

Project 5: Taokou Sand Discharge Tunnel in Liujiaxia: comparing 3 different fiber reinforcement

Through this project, we learned different concrete additives on the durability of concrete. The mixing ratio of C50 pump impact concrete met engineering requirements.
Among them, the pp fiber supplier has chosen the products of Fiberego company after careful selection. Screening details are as follows:

They are two types of polypropylene fibers, Grace in the United States and Fibergo, both of which have a fiber length of 19 mm.

The performance indexes of the two fibers are close. By mixing the concrete, both can be well dispersed in the concrete. At the same water-binder ratio, the compressive strength of polypropylene fiber concrete is 342 mPa, compared to that of American Grace’s 319 mPa.

Since American Grace polypropylene fiber is an imported fiber, it is more expensive than domestic fiber. The dose is 0.3 kg/m3 lower than that of domestic fiber, but the unit price of each square concrete is still increased by 30 yuan.

Therefore, considering various factors, the concrete with polypropylene fiber produced by Fiberego is recommended as the experimental fiber for the study of Liujiaxia anti-impact and grinding concrete.

The dosage ratio and selection of steel fiber are stipulated as follows:

Two types of steel fibers are selected. The Fibergo has a length of 32m millpot fiber, and another Fiber company has a 50m long dumbbell-shaped cold drawn steel wire. The selection principle of steel fiber is as follows:

1. It must have a strong grip with concrete.

2. It is suitable for pumping construction.

3. The steel fiber should be properly “short, thick and hard”.

Through mixing, we found that among the two kinds of steel fibers, milled steel fiber in Fiberego is easier to disperse in concrete. There are no lumps, and the concrete is well treated, making it suitable for pump construction. However, the dispersion of another company’s dumbbell-shaped cold-drawn steel wire and steel fiber in concrete is poor. The 7-day compressive strength of Fiberego’s milled steel fiber concrete is higher than the dumbbell-shaped cold-drawn steel fiber concrete.

Therefore, considering the early compressive strength of concrete and the requirements of construction technology, Fiberego’s milling steel fiber is recommended as steel fiber for the concrete test.
Above, this paper analyzes the application of different types of polypropylene synthetic fibers in national practical applications. We compared practical difficulties encountered in the project. Through this article, you will also have a further understanding of various products of polypropylene fibers and how to solve related difficulties! See you next time!