Project study NO.2: Excellent Fiber Reinforced Concrete Performance

Previously we reported Project study NO.1  5 incredible project solutions where we mentioned fiber

reinforced concrete. We will discuss more about it today.

We are exploring how to mix fiber reinforced concrete most economically and give full play to its function. Concrete additives include admixtures, coarse aggregate varieties, fly ash, silica fume, polypropylene fiber, and steel fiber.

Well added, they can enhance the physical and mechanical properties of concrete. The physical and mechanical properties include compressive strength, modulus of elasticity, ultimate tensile strength, dry shrinkage, and wet expansion. These characteristics can enhance the durability of polymeric fiber concrete.

In this artical, our  main focus is on why and how to us C50 to pump erosion resistance concrete?

The total length of the sand discharge tunnel at Taohe Estuary in Liujiaxia is 1480.8m. It is composed of 7 sections.

● Yanzhai blasting section,

● Yunnel section in front of the inlet sluice chamber,

● Inlet accident maintenance gate chamber section

● Exit working gate chamber section,

● Pressureless tunnel section,

● Drainage channel section

● Flow regulating nose sill section.

The sand discharge tunnel on the left bank of the Taohe estuary has a high water head, high flow velocity, and high sediment content. After the rock plug is blasted, some gravel may also be discharged downstream through the sand discharge tunnel, which will cause serious wear on the tunnel coagulation. Therefore, C50 pumping anti-abrasion concrete is required.

This experiment carried out design and performance research on C50 pumping anti-abrasion concrete from the aspects of raw material selection, concrete workability, concrete mix design, and so on.

1. Raw materials for fiber reinforced concrete

Raw materials include cement, ash, fumed silica, polypropylene fiber, and steel fiber. The detailed ingredients of each raw material are as follows.

The type of cement is hot Portland cement. All indicators meet the national standards.We adopt the first grade ash from a thermal power plant in Gansu, with a density of 2.44g/cm, a fineness of 3.5%, a water demand ratio of 90.2%, and a loss on ignition of 3.2%.

Various performance indicators have reached the “Hydraulic Concrete Mixed-Use Grade I ash standard” specified in “Technical Specification for Fly Ash” (DL/T5055-1996).

The silicon fume is produced by a company in Qinghai, with a content of 87%, a density of 2.22g/cm, and a pozzolan activity index of 109%. The fine aggregate Hongliutai natural sand has a high mud content of 58%. After washing, the mud content of the sand is reduced to 1.3%. The fineness modulus is 2.22. After flushing, all indexes meet the specification requirements.

Coarse aggregate is selected from the Hongliutai bins. Natural pebbles with a diameter of 5-20mm and 20-40mm, made by crushing gravel larger than 80mm. It is best to choose the shape of coarse aggregate to be treated with a hammer crusher or impact crusher. The quality of aggregate directly affects the weary resistance of concrete. To ensure that the aggregate has a better shape, the pebbles in this test adopt a two-stage crushing method, in which the first stage is a collimator crusher, and the second stage is a hammer crusher.

As the site has not yet formed a concrete aggregate yard. Due to site conditions, the broken gravel material contains some pebbles after testing, and the content of pebbles is not high. It shows that the use of this gravel to mix concrete is still representative. The performance indexes of Hongliutai natural pebbles and crushed stones all meet the requirements of the “Hydraulic Concrete Construction Specification” for the quality of sand and gravel. There are four preliminary selections of admixture water-reducing agents. The optimization principle of the admixture is good adaptability to cement, a high water reduction rate, and high-cost performance.

Experiments have proved that the water reduction rate of the four admixtures has little difference.

2. Fiber Reinforced Concrete Workability

when using concrete SP and SX1, polypropylene fiber and steel fiber (see product)behave more viscously in concrete. The concrete slump is small so pumping construction is difficult. DHG is an air-entraining water-reducing agent. When the mixing amount is 1.0, the air content of concrete is only 10%, and the air-entraining effect is poor.  SX1 has better workability to two kinds of fibers, and the price is moderate.

Among the unilateral admixtures, SP is the highest,while DHG is the lowest. SX1 is close to the unilateral price of DHG, the cost is higher.

Therefore, based on the above-mentioned various comparison factors, SX1 is recommended as the admixture variety for concrete testing.

There are two types of polypropylene fibers, namely the anti-cracking from fiber U.S. and Fiberego’s polypropylene fiber, with fiber length both 19mm. The performance indicators of the two fibers are close, and the dispersibility of the two fibers in the coagulation system is better. Under the same water-binder ratio, the strength of Fiberego fiber concrete is 34.2 MPa, and the compressive strength of U.S. polypropylene fiber concrete is 31.9 MPa. U.S. polypropylene fiber is an imported fiber, and its price is higher than that of domestic fiber. Although the blending amount is 0.3kg/m lower than that of domestic fiber, the unit price of each cubic meter of concrete still increases by 30 yuan.

Based on various factors, Fiberego polypropylene fiber is recommended as the experimental fiber for the research of Liujiaxia’s impact-resistant and wear-resistant concrete.
Steel fiber pumping concrete steel fiber selection principles are

● Strong bond with concrete,

● Suitable for pumping construction,

● Steel fiber is appropriately short, thick, and hard.

3. Concrete mix ratio

●The mixed strength of C50 anti-abrasion concrete is 564MPa

●The optimal gradation ratio of silica fume content aggregate is 45:55.

●High-quality fly ash content can reduce water and reduce the temperature rise of concrete hydration heat. In this test, two blending amounts of 10% and 20% were selected for fly ash, and the blending method was internal blending.

Fiber Content: Polypropylene fiber content is 0.9kg/m, and steel fiber content is 0.75~1.3% of the volume ratio of steel fiber.

Concrete slump and air content control the concrete slump is controlled at 15cm~18cm and the air content is controlled at about 3%.

4. Experimental result

The experimental results of Fiberego’s polypropylene fiber products show that the compressive strength of fiber reinforced concrete is affected by the following factors:

●Aggregate varieties

Under the same other conditions, the 28-day compressive strength of pebble polypropylene fiber reinforced concrete is lower than the compressive strength of crushed polypropylene fiber concrete, indicating that the binding force of crushed stone and mortar is stronger than that of the pebble.

●Fiber varieties

Under the same conditions, the 28-day compressive strength of steel fiber reinforced concrete tends to be higher than the compressive strength of polypropylene fiber reinforced concrete, indicating that steel fiber has a greater effect on the reinforcement of concrete than polypropylene fiber.

●Steel fiber volume rate

Under the same conditions of other factors, there is little difference in compressive strength between steel fiber reinforced concrete with a volume rate of 1.3% and a volume rate of 0.75% after 28 days. The amount is not economical.

●Silicon powder content

For the polypropylene fiber reinforced concrete in crushed rock, the effect of 10% silica fume content on the compressive strength of concrete is more obvious than that of 6% silica fume content. For crushed stone steel fiber reinforced concrete, the effect of two types of silica fume content on the concrete compressive strength difference is not big.

●Fly ash content

Pebble, gravel polypropylene fiber reinforced concrete, and crushed stone steel fiber concrete, with 10% and 20% fly ash content, have little response to the 28-day compressive strength of the concrete.