Use of rebar to reinforce existing concrete block wall

[Frank1sav]

Has anyone thought about using steel rebar on the inside of a concrete basement block wall to reinforce it and prevent further bowing and cracking?

What I am suggesting is cutting vertical v-shaped grooves in the inside face of the block wall, floor to ceiling at regular intervals maybe every 2 1/2 to 3 feet. Each groove would be wide and deep enough to accommodate a #4 or #5 length of steel rebar. The rebar would be bedded in a continuous bead of epoxy or other suitable adhesive and would be flush with the inside surface of the block.

If feasible, this method would provide a number of benefits:
-Significantly lower cost than using carbon fiber straps
-It would serve to lock the courses of block together. This might be very beneficial if there were significant stair-step cracking of mortar joints.
-It would be minimally invasive
-The homeowner could install this system with an angle grinder and a few diamond cutting blades.
-It would require less cutting/grinding than with carbon fiber straps

If additional anchoring were needed, the top of the rebar could be bent and inserted into a hole drilled into the top block, or is could be attached with some kind of bracket and lag-bolted to the sill or a floor joist. The bottom could be inserted into a hole drilled in the floor slab.

What are your thoughts on this idea?

Frank W.

 

[Ron]

This is common! Usually the rebar is grouted in, not epoxied in. The cut in the masonry is usually to the margins of the cells, not a V-groove. It is then formed and grouted with an appropriate strength grout.


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[oldestguy]

A few photos and perhaps we can suggest some other things, such as work outside. Is frost action possibly involved? It's commonly involved when block walls move in.
While it may look different than grouted rebar, applying some tension to interior reinforcing may do more good. There have been other postings here dealing with that method.

 

[Frank1sav]

Hi and thanks for the input.

I considered using a portland cement-based grout to attach the rebar, but thought an epoxy-based cement might provide a stronger and more flexible adhesive bond between the rebar and the concrete block. This would be kind of a hybrid between traditional technology and more modern approaches such as using carbon fiber straps epoxied to the interior of the wall.

I realize that one traditional solution to a cracking and bowing wall would be to install rebar inside every 3rd or 4th block core and then fill the cores with concrete. That is a fairly big project.

The basement wall in question is 60+ feet long and entirely below ground. The main culprit for the external pressure against the wall appears to be expansive clay soil.

The interior of the wall has been braced with 7 foot long vertical steel U-channels through-bolted to exterior earth anchors every 4 feet along its length. Unfortunately there are still lots of cracks in the mortar joints....both horizontal, stair step, etc.. Although the u-channels are resisting the inward pressure on the wall, I would feel better if I could lock the blocks together and restore some of the wall's original integrity. In thinking about using the technique suggested, I'm searching for a less invasive and time/cost intensive solution.

 

[BridgeSmith]

It would seem that whether you notch it or cut out the face shell of the block, it's still 2 cuts. Cutting out the face shell and grouting the entire cell is more grout and needs a larger piece of plywood to form it up, but you can put several bars in the cell, but only one per notch. I would think opening up the cells would be the more cost-effective way to go.

 

[oldestguy]

If you are sure about expansive clay, you may be up against a continuing push,not satisfied with any bracing such as discussed. Replacing some of that exterior clay with sand may well be worth the effort. So then, while things are open, replace the wall with reinforced concrete and be done with it. To check the clay see if a local Soil Conservation person US Dept Agriculture can advise.

 

[Frank1sav]

We decided to use 1/2 inch rebar and embed it in a 3/4" - 1" wide X approx 1/2 " deep vertical channel cut floor to ceiling into the face of the block. I will probably use about 30 bars over about 90 feet of wall.

We cut the grooves with an angle grinder fitted with a diamond saw blade. We made 3 vertical cuts for each groove and then chipped it out using a rotary hammer. We used a cement-based mortar to grout the bars in place. I'll try to post some photos.

 

[Ron247]

The bigger question appears to be the epoxy used and if it can perform as intended. What epoxy will bond the rebar to the masonry block with sufficient strength to grip the bar in a similar manner as a proper grout mix that is completely around a rebar and pressed against the block cell? It has to create the composite member to work successfully. Grout is under some pressure when poured due to the height of the lift and this slight pressure forces it into the small block voids. Your epoxy will not have this similar pressure to force it into the masonry block voids. You may have to hand work it in.

What about clear cover distance requirements? Yours will be zero. I am not sure about how clear cover works with epoxy.

I would test it. Build 2 beams, one with no epoxy on the bar and one with epoxy. See if you get enough load resistance. If the numbers calc out, you should be good.

Lastly, are you stamping this?