Monday, November 18, 2019

What is Rebarring? Why Rebarring is required?


What is Rebarring?

Fixing of new reinforcement steel to existing concrete structure with drilling in concrete 150mm or 10 times of Diameter whichever in maximum to 600mm deep as per depend on structural design with applying chemical to bar with testing as per the design standards requirement.



Why need to rebar?

 When some changes in design of structures or failure of the existing structure or existing steel reinforcement is found low in quality or cut or break of any bar in existing structure all those locations need to rebar as per standard norms are given by structural consultant or RCC designer.

Where & Why we can rebar?

We can rebar the steel reinforcement at the following locations.
Rebarring for Footing and Column: For Column Jacketing.
Rebarring for Beam: For Chajja/Projection.
Rebarring for Beam: New beam structure introduced by RCC designer.
Rebarring at Slab: Extension of Slab.
Rebarring in Column: Fixing of Lintel at door and windows and
Rebarring at Column, Beam, Slab, Lift Wall, Retaining Wall, etc: if any bar cut/break due to by mistake.



What is Current Practice of Rebarring?

Currently all the contractor, developers, and some engineers are doing wrong practice for doing rebarring because they are always doing rebarring at various location any levels due to forgotten to keep dowels, or keep wrong diameter steel dowels, etc. but all the time everyone is following the wrong practice to close his mistakes in concrete. Because no one can find any mistakes after concreting. And some contractors are using this practice normally with mutual understanding and discussion with the site engineer or project manager.
                Some builders, developers, contractors and engineers also don’t know the standard practice of Rebarring. But due to avoid the hurdles of breaking of the existing structure, and re-reinforcement of this structure, they are always thinking to save the cost of material, labour, and to save time. Some contractors are giving this benefit behind at builder, developer, project manager, etc.


This is the current process of rebarring which is using at everyone was.


1. Drilling in the existing structure. :

Sometimes the bore depth is not up to 10 times the diameter of the bar or 150mm, because there will be some obstructions of steel bars of existing steel in the existing structure. Also not proper care is taken when drilling like the diameter of the bar. Depth of drill, perpendicular to the existing structure to keep dowels in line. Spacing is not maintained properly due to obstructions of existing steel bars. Contractors are always using a small drill machine that is needed to use by a single hand and needs to operate manually. But due to that drills and the bore is not perpendicular to the existing structure.



2. Cleaning of Drills/bore:

No one is clean the bore properly and remove all the dust particles where can put the bar. Also, no one is using blower on any other tools to clean the drill or bore.

3. Fixing of Bar:

Some contractors are directly fixing the bar in the drill without using any chemicals. Some contractors are using GP2 cement to show the engineer and project manager. Also some contractors are using any diameter of bar as well as rusted, dirty, oily bars are used to rebarring without discussing with a technical person.


4. Immediate shuttering and concreting:

Contractors are always want to close the mistakes of steel reinforcements, shuttering, sizes, etc. at this time contractor is immediate complete rebarring, same day shuttering will fix and concrete work also complete, but no one can cross-check the quality of rebarring an all after concreting.


5. No rebarring test

When work is completed with the above procedure, no one can check the pull-out test of the bar.

What is Standard Rebarring Procedure?

Before Rebarring always keep one sentence in mind “Rebarring is 2nd option to rectify the Mistakes from someone like a structural designer, contractor, engineer, architect,  or permission changed, government rules changed, etc. to avoid losses of material, labour and time.

Following are the steps to show the standard procedure of rebarring.


1. Check the Drawing.

Check the drawing and compare the existing drawing and changed drawing, with the help of drawing we can easily cross-check the exact location of the drawing.

2. discuss with the project manager and RCC designer or structural consultant.

You need to discuss the details of the situation with RCC designer or structural consultant and project manager to given the decision on this situation. You can arrange the site visit of the structural consultant to understand the site condition.

 3. rebarring drawings from a consultant.

After the written direction given by a structural consultant or RCC designer, request to issue the revise drawing with rebarring details. They can give you all the details about the rebarring of steel as per load calculations as well as they will give you the diameter of the bar, the diameter of the drill, depth of bore. Which chemical should be used, what type of tests needs to do, etc.

4. Drilling of Bore:

Drilling of Bore from the standard agency which is certified by rebarring chemical manufacturers like Hilti, Fischer, Wurth, Fosroc, etc. those standards companies are giving you pull out tests at your site, with a quality report. Drilling should be 10 times dia. Or as per given by the structural designer.

5. Cleaning of bore:

When the drilling process is complete, there may be a lot of dust balance in the bore which is need to remove properly, for cleaning of bore you can use water pressure, or air blower. But all dust should be removed from the bore.



6. Application of Chemical:

Drilling the agency is certified from the standard chemicals, those agencies are expert in rebarring and application of rebarring chemicals. They are using chemical guns to fill full of chemicals in the bore as per the standard procedure. Generally, 60% to 75% of the bore will be fill by the chemical.



7. Fixing of Bar:

This agency will fix & press the cleaned and rust-free bar in this bore which is filled by the chemical. At the time of fixing and pressing the bar in bore some chemicals will come out near the bar, but don’t worry this is standard practice. After rebarring work complete wait for 4 to 5 hours to gain the strength. Some chemical companies are giving 30min time to set the chemical but you should wait for 3 to 4 hours to further process.



8. Pull-Out test:

After rebarring work completed wait for 48 to 72 hours to pull out tests.  
What is pull out a test of rebarring? We can check in the next blog.









Team
CBEC India

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