Steel is considered to be one of the vital construction materials. The process of construction involves the bending of steel to a particular form. Consequently, it is important to check the ductility of the steel, which is the ability to deform under applied pressure.

Bend and Rebend Test

This test procedure is used to check the ductility of the steel bar under applied pressure. During the construction of reinforced cement concrete (RCC) structures, bending and re-bending the steel during the process of construction is inevitable.

To ensure that the material is safe to deform without fracture, a bend test is performed at two different angles (90⁰and 180⁰). Moreover, strain ageing may take place which may result in a reduction in ductility, as well as an increase in the ultimate yield stress of the steel bar. Reduction in ductility can be checked by the re-bend test.

Use and Significance

Bending test can ensure that the rebars are deformable without any fracture while bending the rebar into different shapes.

Re-bend test ensures that the load-carrying capacity is not affected; in other words, the ductility of the material is not reduced (ultimate yield strength of the material is not increased due to strain ageing) by retesting the rebar, which has already tested and entered into its inelastic range.

Reference:

IS 1786: High Strength Steel Bars & Wires For Concrete Reinforcement – Specification

IS 1599: Method For Bend Test

Required Apparatus

Rebar bending test fixtures (clamps and mandrels)

Sampling

Bend and re-bend test is done for as per frequency shown in the following table.

Nominal Size	Quantity
	For Casts/Heats below 100 tonnes	For Casts/Heats of 100 tonnes or More
For all sizes	2 percent	3 percent

Bend Test Procedure

1. Based on the diameter of the chosen steel specimen, the mandrel is selected per Table 1.

2. Apply continuous bending pressure, and continue bending until the two straight sides of the specimen become parallel.

3. Then inspect the bent portion for cracks or rupture. If no cracks are observed during the bend test, the specimen has passed the test, otherwise, it has failed.

Table 1 (Bend Test – Mandrel Diameter)
	Diameter of a mandrel for different grades (d=Nominal Dia. of Test Piece)
Steel Rebar Nominal Size	Fe 415	Fe 415D & Fe 415S	Fe 500	Fe 500D & Fe 500S	Fe 550	Fe 550D	Fe 600	Fe 650	Fe 700
Upto and including  20 mm	3d	2d	4d	3d	5d	4d	5d	6d	7d
Above 20 mm	4d	3d	5d	4d	6d	5d	6d	7d	8d

Rebend Test Procedure

1. The mandrel is selected per Table 2.

2. One end of the test specimen is clamped, and the other end of the test specimen is bent to 135⁰.

3. Now, the specimen is placed in boiling water at a temperature of 100⁰C for a period of 30 minutes.

4. The test specimen is removed from the boiling water and allowed to cool at room temperature.

5. The test specimen is fixed in the appropriate mandrel and bent back to 157.5⁰. The bent portion is examined for cracks.

6. If no cracks are observed during the re-bend test, the specimen has passed the test; else it has failed.

Table 2 (Re-Bend Test – Mandrel Diameter)
	Diameter of a mandrel for different grades (d=Nominal Dia. of Test Piece)
Steel Rebar Nominal Size	Fe 415 & Fe 500	Fe 415D / Fe 415S / Fe 500D / Fe 500S	Fe 550 & Fe 600	Fe 550D	Fe 650 & Fe 700
Up to & including 10 mm	5d	4d	7d	6d	7d
Above 10 mm	7d	6d	8d	7d	9d

Report

• Bend test – Passed/Failed

• Re-bend test – Passed/Failed