Admixtures for concrete masonry grout

[charliealphabravo]

I am looking for a resource that considers the use of superplasticizer admixtures for masonry grout.

I am working on repair recommendations for a cmu lintel that was damaged by a loader. The lintel is 24 inches high and is constructed with stack bond masonry units and U-block units along the bottom (16' span over a roll up door). I see at least one 1-inch bar at the bottom of the lintel in stirrups. The original plans show 2 bars.

At this point I plan to leave the existing reinforcement in place, once the existing damaged grout and shell is removed, so as not to involve lapping and anchoring replacement bars. The owners want to do a masonry repair for cosmetic conformity rather than a cast in place repair so my concern is with filling the spaces around the existing reinforcement once the new units are in place.

In new construction I would require the grout to be vibrated in addition to the slump requirements but I'm wondering if I should take more precautions to ensure bonding since the grout will probably be poured into two or three ports rather than along the full length of the lintel.

Thanks in advance.

 

[concretemasonry]

Use the same grout that should have been used in the original. It is not a question of grout strength, but filling completely and bonding the rebar and the faces shells together to act as a beam.

The ASTM specs for grout require an 8" to 11" slump and the maximum aggregate size is determined the the minimum dimensions of the grout space.

The excess water is used in hydration and absorbed by the masonry units as it cures and consolidates.

For along shallow space, you should have several places to place grout and add some later as it consolidates, just as it is done in new construction.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

Agree with Dick. For placement, make the access hole in the course above the U-block and fill till it runs out the other hole if possible. Try to know where your grout goes though.

One, 1-inch bar? What kind of loads are on this lintel? A 1-inch bar and U-block are an odd combination.

 

[charliealphabravo]

Here's a pic...

 

[charliealphabravo]

Thanks all for the help.

The gravity loads are pretty small. The roof bar joists are parallel to the wall.

I believe that the second 1" bar may be above the first bar inside the stirrup. The u-blocks are 16 inches high. There are also (2) no. 5 bars at the top of the lintel.