Surface Cracks on Reinforcing Steel 2

[Nawabfarhan]

Dear All,

On the Project that uses uncoated black steel conforming to ASTM A 615 Grade 60, field inspections and third party testing are regular Quality Control activities.

In one such consignment of 32mm rebar, we found some surface cracks penetrating less than 2mm deep, width about 1mm. The samples were tested in third party lab and the results of mechanical tests (tensile, yield & elongation) were found to be successful.

The Independent Laboratory is unable to certify that these cracks does not pose any danger to the Quality of the steel even if the tensile properties are tested and found OK.

Please put your expert comments about these cracks. Why they occur and if the tensile properties are OK, are they still unfit for use?

Thanks

 

[Ron]

At the very least, you have a reduced cross sectional area. Keep in mind that the testing was done on prepared specimens, and represents the capability of the material, not the capability of the section. For a 32mm rebar with a crack depth of 2mm, you have a potential section loss of 12.5 percent. That's significant!

Now...more importantly...there should not be cracks in rebar to be placed in a structure...reject it.

 

[metengr]

Agree with Ron regarding rejection of the lot of rebar if there are visible surface cracks. Now the cause of the cracks could be anything from surface defects during manufacture of the rebar to poor surface quality. In other words, you would need to have the materials lab evaluate the crack morphology to determine a probable cause.

 

[Nawabfarhan]

Dear Sirs,

Let me elaborate the appearance of these cracks. They are longitudinal hair cracks, visible at some places (not all along the 12 meter rebar. The average dimensions are LT 1mm(width) x LT 2mm (depth, and LT also 1mm in some locations) x LT 5-8mm (length).

Are they vulnerable? Could you refer also to some specs documents on such cracks?

Thanks in advance.

LT - Less Than

 

[metengr]

Nawabfarhan;
If you stand any chance of using the above rebar, you must have a metallurgical lab conduct an analysis of the rebar to determine the cause and severity of the longitudinal indications. Without this proper metallurgical examination, you have no engineering justification to use this material. Most likely, this examination will require a sample of rebar removed containing the indications and one sample with no indications for comparison.

 

[Guest102023]

Sounds like something induced by improper processing (i.e., forming). I agree rebars with cracks should not go into service. Cracks never get shorter, they can only grow longer ...

 

[Ron]

nawabfarhan...do as metengr suggests...if you want to use this lot of rebar (hopefully you have heat number traceability), then you need to get it checked with proper metallurgical examination. You can't rationalize the use of substandard materials.