GB/T 33240-2016Zinc-aluminum alloy-epoxy duplex coated steel bars for the reinforcement of concrete (English PDF)

3.1 Duplex coating

On the clean metal surface, firstly perform continuous hot dipping zinc-aluminum alloy; then, coat a coating that is obtained from epoxy resin.

3.2 Fusion-bonded epoxy coating

Spray on a heated clean metal surface in powder form to form a continuous coating after curing. The coating contains a thermosetting epoxy resin, a curing agent, a pigment, and other additives.

4.1 Code

The duplex coating steel is coded as ZEDR (the first letters of the words of Zinc-aluminum, Epoxy, Duplex, Reinforcement).

4.2 Model and example

The model of the duplex coating steel consists of the code number, the steel grade and the nominal diameter of the steel, and the plating grade. Example:

For the duplex steel bar, of which the nominal diameter is 20 mm, the grade is HRB400 hot-rolled ribbed steel bar and the zinc-aluminum alloy coating, the level is level-B, its product model is "ZEDR·HRB400-20B".

6.1 Materials

6.1.1 Steel bar

The base material for making duplex coating steel bars shall meet the requirements of GB 1499.1 or GB 1499.2 or GB/T 32968 or other product standards that are proposed by the buyer. The surface of the base material of the steel bar shall not have burrs, sharp corners and other defects that affect the quality of the coating, and shall be free of oil, grease or paint.

6.1.2 Zinc-aluminum alloy ingot

Zinc-aluminum alloy ingots shall comply with the requirements of YS/T 310.

6.1.3 Zinc ingot

Zinc ingots shall comply with the provisions of GB/T 470.

6.1.4 Epoxy resin powder coating

The coating that is formed by epoxy resin powder shall meet the requirements of GB/T 25826.

6.1.5 Repair materials

The repair material of zinc-aluminum alloy coating shall comply with the provisions of GB/T 32968. The repair material of epoxy coating shall comply with the provisions of GB/T 25826.

6.2 Coating requirements

6.2.1 Appearance

The surface of the zinc-aluminum alloy coating shall be uniform and continuous, and there shall be no defects such as leakage plating, zinc tumor, zinc thorn and slagging. After the epoxy coating is cured, the surface shall be flat, uniform in color, free of bubbles, cracks, shrinkage cavities, and other visible defects.

6.2.2 Coating thickness

The thickness of the zinc-aluminum alloy coating shall meet the thickness requirements of grade-B or grade-C of GB/T 32968. The recorded value of the duplex coating thickness after curing shall have at least 95% of probability between 180 µm ~ 300 µm; the single recorded value must not be lower than 140 µm. The upper limit of the coating thickness is not applicable to the area where the damaged coating is repaired. For environments with higher requirements on corrosion resistance, the recorded value of the coating thickness after curing shall have at least 95% of probability between 220 µm ~ 400 µm; the single recorded value must not be lower than 180 µm.

Note: the above coating thickness requirements do not include areas that are repaired due to coating defects or breakage.

6.2.3 Coating continuity

The number of leaks per meter of the steel bar shall not exceed 3.

6.2.4 Coating flexibility

The steel bar shall be tested for coating flexibility. After the sample is bent, the coating on the outer surface of the bending portion of the sample shall be free of visible cracks or peeling.

6.2.5 Coating adhesion

The coating adhesion test of the steel bar shall be carried out by the cathodic dis-bonding test method. Before the test, the flexibility test shall be carried out in accordance with 6.2.4. When it is tested from the edge of the artificial defect hole, the average value of the maximum peeling distance of 95% of steel bars shall not exceed 7.5 mm.

6.3 Repair of coating damage

The coating area that is repaired per meter of the steel bar shall not exceed 0.5% of the total area (excluding the cut). The damaged or cut part of the coating shall be repaired with a zinc-rich paint first, and then it shall be coated with an epoxy repair paint. Prior to repair, all rusts and contaminants on the damaged area shall be removed by appropriate methods. The thickness of the zinc-rich coating after repair shall be not less than 40 µm; the total thickness of the duplex coating shall be not less than 180 µm. The repair material of the damaged coating shall comply with the provisions of 6.1.5.

6.4 Duplex coating steel site construction application guide

For the duplex coating steel site construction application guide, refer to GB/T 25826.

7.1 Inspection items

7.1.1 The inspection items, sampling method, sampling portion and test methods of each batch of steel bars shall comply with the requirements of Table 1.

Table 1 -- Inspection items, sampling method, sampling portion and test methods Serial No. Inspection items a Sampling quantity / piece Sampling portion Test method

7.1.2 For chemical resistance, cathodic dis-bonding, salt spray test, chloride permeability, bond strength, wear resistance and impact test, perform type inspection only, that is, perform inspection only when there are major changes in raw materials, production processes and equipment and when new products are produced and suspended products are resumed. The bond strength test shall be in accordance with the relevant provisions of GB 50152; the bond strength of the steel bar shall not be less than 85% of the bond strength of the uncoated steel bar. The cathodic dis-bonding test is carried out in accordance with Appendix A. Chemical resistance, salt spray test, chloride permeability, wear resistance and impact test are carried out in accordance with the provisions of GB/T 25826.

7.2 Appearance

Use corrected vision to visually inspect under normal lighting conditions.

7.2 a The mechanical properties, bending properties and anti-bending properties of the steel bars after plating shall meet the requirements of GB 1499.2 and GB 1499.1. These items shall be tested as necessary.

7.3 Thickness

Measure and record the total thickness of the duplex coating according to the method of GB/T 4956. Measurements shall be made on opposite sides of the steel bar. For each side, at least 5 measuring points shall be taken evenly over its full length; the coating thickness of each measuring point shall be the average value of thickness measurement values of any 3 points within ±3 cm of the measuring point position. For ribbed steel bars, the measuring point shall be taken between their ribs. It is as shown in Figure 1. in millimeters

Note: when it is necessary to separately measure the thickness of the zinc-aluminum alloy layer or the epoxy coating layer, the cross-section method or the like can be used for the measurement.

7.4 Coating continuity

Before delivery, use a wet-sponge DC leak detector with a voltage of not less than 67.5 V and a resistance of not less than 80 k ohm or equivalent methods to perform the detection according to the instructions of the leak detector.

7.5 Coating flexibility

The coating flexibility shall be checked by a bending tester. The test sample shall be in a thermal equilibrium state between 23°C ± 5°C. The mandrel of the bending machine shall be covered with a special nylon sleeve. The test shall be bent at a uniform rate of not less than 8 r/min. For ribbed bars, the two longitudinal ribs of the test sample shall be placed in a plane perpendicular to the mandrel radius of the bending tester. Mandrel diameter and bending angle shall be in accordance with Table 2. For the coating steel with higher requirements of the bending properties, it shall be negotiated between the supplier and the buyer.

a) ribbed steel bar coating thickness measurement b) plain bar coating thickness measurement Thickness of point A Thickness of point A Table 2 -- Coating flexibility test Nominal diameter d/mm Mandrel diameter / mm Bending angle / (°)

Ribbed bar d <= 20 6d 180 20 < d <= 36 8d 180 d > 36 8d 90 Plain bar 6 ~ 22 6d 180

7.6 Coating adhesion

The cathodic dis-bonding test is carried out in accordance with the provisions of Appendix A.

8.1 Inspection and acceptance

The inspection and acceptance of steel bars shall be carried out by the supplier's quality supervision department.

8.2 Batch rules

The steel bars shall be inspected and accepted in batches. Each batch shall consist of steel bars of the same heat number, the same grade, the same nominal diameter and the same plating grade. The weight of each batch is not more than 60 t.

8.3 Inspection items and sampling quantity

The inspection items and sampling quantity of the steel bars shall comply with the requirements of Table 1.

8.4 Re-inspection and determination

The re-inspection and determination of steel bars shall comply with the provisions of GB/T 2101.

8.5 Numerical rounding

The numerical rounding of the inspection and inspection result shall be in accordance with YB/T 081.

9.1 Packaging, marking and quality certificate

The packaging, marking and quality certificate of steel bars shall comply with the provisions of GB/T 2101.

9.2 Transport and storage of steel bars

9.2.1 Steel bars shall be handled carefully during the transport. Between the sling and the steel bar, there shall be a cushion; they must not be in direct contact. Between the bundled material and the steel bar, there shall be a cushion or a suitable method to prevent damage to the coating. Use multiple lifting points for lifting to prevent the steel bar from overhanging. It is strictly forbidden to drag and throw the steel bar.

9.2.2 If the coating is stored outdoors for more than 2 months, protective measures shall be taken to avoid exposure to sunlight, salt spray and the atmosphere. If the steel bars are stored in a corrosive environment, special protective measures shall be taken. If the steel bars are stored outdoors and there is no covering, the outdoor storage time shall be indicated on the bundle of steel bars. The steel bars shall be covered with opaque material or other suitable protective covers. For steel bar bundles which are stacked in layers, the covering material shall be tightly covered. The covering shall be securely fastened; the air around the steel bars shall be ventilated, to avoid condensation on the underlying cover.

9.2.3 The steel bars shall be stored off the ground and provided with a protective barrier.