Keywords

1 Introduction

PX combined pump room in HUALONG nuclear power plant is a special concrete structure with extremely complex shape. The concrete construction at the bottom and inner wall of the structure is extremely difficult, and the designed service life of the project is 50 years. It is a permanent concrete structure that is not repairable during the operation life of the nuclear power plant, which is directly related to nuclear safety [1,2,3].

In addition, because of the volute pump in water environment, the lining concrete structure to withstand erosion and corrosion of sea water for a long time, the presence of cracks or other defects in concrete structure will lead to corrosion of the internal reinforcement, significantly reduce the overall durability of the concrete structure, in turn, affects the safe operation of nuclear power unit [4,5,6].

Therefore, it is required that the construction concrete has excellent working performance, crack resistance, chloride ion penetration resistance and steel corrosion resistance, in order to ensure the high durability of the concrete structure in the seawater corrosion environment. According to the above reasons, the high-performance concrete with wonderful property resistance to harmful ion erosion was made by optimization design. The workability, mechanical property, long-term behavior and durability were test. Furthermore, the technical feasibility of the concrete was evaluated.

2 Experiment Design and Method

2.1 Raw Materials Selection

Fly ash: Grade I class fly ash, fineness shall not be more than 12% (45 μm hole sieve residue), firing loss shall not be more than 5%, water requirement ratio shall not be more than 95%, sulfur trioxide content shall not be more than 3%.

Silicon powder: The dosage is 5%–10% of the cementing material, the specific surface area is more than 15000 m2/kg, and the silica content is more than 85%. The dosage should be determined by test according to the degree of grinding and application requirements.

Cement: Ordinary Portland cement with strength grade of cement is 42.5 mpa. Do not mix different varieties or strength grades of cement. It is required to use cement with low hydration heat. The 3d hydration heat shall be no more than 251 kJ/Kg, and the 7d hydration heat shall be no more than 293 kJ/Kg. Cement fineness (specific surface area) should not exceed 350 m2/kg. And cement with relatively high dicalcium silicate content should be used.

Coarse aggregate: The maximum particle size of concrete stones should not be greater than 25 mm, the water absorption rate should not be greater than 1.5%. The alkali active aggregate shall not be used. The other requirements should comply with the provisions of JGJ 52-2006.

Fine aggregate: The medium sand should be used for concrete sand, and marine sand should not be used. Its requirements should meet the provisions of JGJ 52-2006.

Polypropylene fibers: The fiber must own the function of increasing anti-crack, anti-seepage and wear resistance. Its size is 6D. Density is 0.91 g/cm3 with length of 19 mm. Its elastic modulus is no less than 3900 MPa, tensile strength is no less than 550 MPa, and tensile limit is no less than 15%. In addition, its anti-crack efficiency should be grade one.

2.2 Design of Mix Proportion

In order to approve the workability, mechanical property, long-term behavior and durability, the following technical measures have been taken:

The co-mixing of low-alkali cement with silica fume, fly ash and expansion agent gives full play to the superposition effect of cementing materials. At the same time, the polypropylene fiber and composite amino alcohol reinforcement rust inhibitor are added to jointly realize the protection of reinforcement in concrete structures [7].

The co-mixing of silica fume, fly ash and anti-crack and water-proof agent can reduce the auto shrinkage of concrete to a certain extent, give full play to the advantages of the electric flux of concrete doped with silica fume significantly reduced and the early strength increased quickly, and better inhibit the early shrinkage crack of concrete after the addition of silica fume.

Silica fume, polypropylene fiber and polycarboxylates high performance water-reducing admixture used in combination, can give full play to reduce and restrain plastic stage sedimentation and shrinkage crack, and reduce the affection of the internal capillary porosity of concrete structure. The water reducing effect is used to maintain the good fluidity of concrete mixture, which is conducive to construction [8].

Based on above design conception, the main design parameters of the concrete mix proportion are determined: the water-binder ration is 0.36, the binder content is 478 kg/m3, the reasonable sand ratio is 37.5% and water content is 172 kg/m3. Polypropylene fibers content is 0.9 kg/m3. The binder consists of cement, 19.9% fly ash, 6.3% silica fume and 8.4% expansion agent. The rebar inhibitor admixture is 12 kg/m3.

2.3 Test Method

The slump of fresh concrete was tested according to GB/T 50080-2016. The compressive strength (3d, 7d, 28d and 60d) of concrete was tested in accordance with GB/T 50081-2019. Chloride permeability coefficient and shrinkage rate were test according to GB/T 50082-2009.

3 Results and Discussion

3.1 Workability

Based on the experimental results, Fig. 1 gives the line chart of the slump.

Fig. 1.
figure 1

Slump of the concrete

Full size image

From Fig. 1, the following observations can be made:

  1. i)

    The high-performance concrete for volute region of PX combined pump room has wonderful workability. The slump was both no less than 190 mm, and it can well meet the technical requirements for construction.

  2. ii)

    Large flowing ability of the concrete can significantly improve the efficiency of construction and reduce the probability of concrete quality defects.

  3. iii)

    Adding rebar rust inhibitor in the concrete can effectively improves the steel corrosion-resistance. And compared with concrete without rebar rust inhibitor, it also owns fine workability.

3.2 Compressive Strength

Based on the experimental results, Fig. 2 gives the line chart of the compressive strength (3d, 7d, 28d and 60d).

Fig. 2.
figure 2

Compressive strength of the concrete

Full size image

From Fig. 2, the following observations can be made:

  1. i)

    With increasing of the test age, the compressive strength shows growth trend. The 7d compressive strength can reach 74.5% of the design strength. But the 28d compressive strength below the design strength. Large percentage of the mineral admixture results in the compressive strength of early-age increases slowly [9]. It is recommended to check and accept according to 60d strength.

  2. ii)

    The compressive strength with 60d test age were both above 50 MPa, and the maximum strength can reach 124% of the design.

  3. iii)

    Compared with concrete without rebar rust inhibitor, adding rebar rust inhibitor don’t affect the compressive strength. And the 60d compressive strength is basically the same. Meanwhile, rebar rust inhibitor can significantly improve the rust resistance of rebar in concrete matrix.

3.3 Chloride Permeability Coefficient and Shrinkage Rate

Based on the experimental results, Fig. 3 gives the line chart of the chloride permeability coefficient. Figure 4 gives the line chart of the shrinkage rate.

Fig. 3.
figure 3

Chloride permeability coefficient of the concrete

Full size image
Fig. 4.
figure 4

Shrinkage rate of the concrete

Full size image

From Fig. 3 and Fig. 4, the following observations can be made:

  1. i)

    The high-performance concrete for volute region of PX combined pump room has wonderful resistance to chloride penetration. The 28d chloride permeability coefficient is both below 4.5 × 10−12 m2/s. It can well meet the requirements of design which is no more than 5 × 10−12 m2/s. It is because that the mineral admixture can effectively improve the capillary structure of concrete and increase the compactness [10].

  2. ii)

    The concrete without rebar rust inhibitor has more lower chloride permeability coefficient, and the minimum is only 3.6 × 10−12 m2/s. According to the GB/T 50476-2019, the high-performance concrete for volute region of PX combined pump room can meet the requirement of 100 years design working life.

  3. iii)

    The shrinkage rate (14d in water) of the concrete is both more than 0.02%, and the shrinkage rate (14d in water and 28d in air) of the concrete is both less than 0.02%. They are both meet the requirement of design that shrinkage rate (14d in water) is more than 0.015% and shrinkage rate (14d in water and 28d in air) is less than 0.03%.

3.4 Evaluation of Concrete Compressive Strength Design Organization

Based on the engineering application of concrete, Fig. 5 gives the compressive strength of hardened concrete. And Fig. 6 gives the normal distribution curve of compressive strength.

Fig. 5.
figure 5

Compressive strength of hardened concrete

Full size image
Fig. 6.
figure 6

Normal distribution curve of compressive strength

Full size image

From Fig. 5 and Fig. 6, the following observations can be made:

  1. i)

    The mean compressive strength of concrete is 58.24 MPa which is 116.8% of the designed strength. The standard deviation of strength is 1.63 that shows the strength fluctuation is relatively stable. Base on the results, mfcu > fcu,k + λ1 × Sfcu = 50 + 0.95 × 1.63 = 51.54 MPa, in line with the “concrete strength Inspection and Evaluation Standard” (GBT 50107-2010) related control requirements.

  2. ii)

    The number of samples located in [mfcu − Sfcu, mfcu + Sfcu] was 40, accounting for 65.6% of the total sample, and the number of samples located in [mfcu − 2Sfcu, mfcu + 2Sfcu] was 61, accounting for 100% of the total sample. The results show that the concrete mix design method for PX pump house volute area conforms to the design requirements of “Ordinary Concrete Mix Design Regulations” (JGJ55-2011), and the measured compressive strength is well in accordance with normal distribution.

4 Conclusions

  1. i)

    The high-performance concrete for volute region of PX combined pump room has wonderful workability. The slump was both no less than 190 mm, and it can well meet the technical requirements for construction.

  2. ii)

    The compressive strength with 60d test age were both above 50 MPa, and the maximum strength can reach 124% of the design. It conforms to the design requirements of the design organization.

  3. iii)

    The high-performance concrete for volute region of PX combined pump room has wonderful resistance to chloride penetration. And the minimum chloride permeability coefficient is only 3.6×10−12 m2/s that indicates meeting the requirement of 100 years design working life.

  4. iv)

    The shrinkage rate (14d in water) of the concrete is both more than 0.02%, and the shrinkage rate (14d in water and 28d in air) of the concrete is both less than 0.02%. It shows the concrete owns wonderfully volume stability.