NB/T 20325.1-2014Prestressing technology specification for safety containment of PWR nuclear power plants - Part 1: Material (English PDF)

3.1 Anchorage

It refers to the permanent anchor devices for holding the tension of the prestressing strand and transmitting it to the concrete, including the bearing plates, anchor plates and clips.

3.2 Bearing plate

4.3 Steel pipe

It is suitable to use the ERW high frequency welded steel pipes with straight seams or seamless steel pipes, whose grades are between Q195 and Q345.

The steel pipes shall conform to GB/T 3091 or GB 8162. The elongation shall be greater than or equal to 15%.

The steel pipes shall be straight. The flexibility of overall length shall be less than 0.2% of the steel pipe's length. The diameter deviation shall be ± 1.5mm.

The wall thickness shall not be less than 2mm, with a deviation of -0.2mm or +0.4mm.

The steel pipes shall be applicable to the flaring and bending requirements. The inner and outer surfaces shall be smooth and without any overlaps and gas holes.

4.4 Anchorage

Anchorages shall conform to the requirements of GB/T 14370 and NB/T 20303.

The products requiring tunnel grouting shall be equipped with grout holes or exhaust holes. The hole sites and hole diameters of the grout holes shall comply with the requirements for grouting process. Furthermore, the grout holes shall be provided with the structures connected with the grout pipes.

4.5 Prestressing strand

USE the standard prestressing strands laid by seven steel wires. The tensile strength shall not be less than 1,770MPa.

During initial type inspection, the specifications, grades and chemical compositions of the raw materials shall comply with the following requirements.

a) Nominal diameter and deviation. 15.7mm ± 0.2mm.

b) Nominal area. 150 mm².

c) Nominal mass and deviation. 1.178 kg/m (1 ± 2%).

d) The increased range of the core steel wire's diameter shall not be less than 3%.

e) The total percentage elongation at maximum force (L0 >= 500mm) shall not be less than 3.5%.

f) Direction of lay. right-hand direction of lay. requirements of GB 175.

4.9 Mixing water (ice)

The chloride content shall not be greater than 0.025%. Other indicators shall comply with the requirements of JGJ 63.

4.10 Admixture

The water reducing agent shall use the product with stable properties and good adaptability with the cement in use. The water reducing rate shall not be less than 20%. Other indicators shall comply with the requirements of GB 8076. The retarder shall conform to GB 8076. The water reducing agent and retarder in use shall have good adaptability.

The expanding agent shall comply with the requirements of GB 23439. It is not allowed to use the expanding agent using aluminum powder as expansion source.

4.11 Cement paste

SEE NB/T 20325.2 for the test method.

4.11.1 Water cement ratio

The water cement ratio shall be within the range of 0.30 to 0.38.

4.11.2 Bleeding rate and expansion rate

The bleeding rate of 3h is not suitable to be greater than 2%, and shall not be greater than 3%. All of the bleeding shall be able to be absorbed by the paste within 24h.

The expansion rate of the expansive cement paste shall not exceed 6%, and shall be greater than the bleeding rate.

4.11.3 Setting time

Under the laboratory conditions, the retarding paste's initial setting time shall be less than 50h, and the final setting time at 5°C shall be less than 80h.

4.11.4 Fluidity

After stirring for 6h, the retarding cement paste's fluidity shall be less than 14s.

After stirring for 10h, the retarding cement paste's fluidity shall be less than 25s.

The ambient temperature is suitable to be within the range of 5°C to 35°C. The paste temperature is not suitable to be higher than 32°C.