Control Joints for fuly grouted masonry

[JAE]

Concrete masonry - in our region of the world, we typically provide control joints in concrete block masonry walls at about 24 feet (7300 mm) spacing per a table I once got from a masonry publication. Not sure what NCMA recommends.

We have a one-story building that will be fully grouted with vertical bars in each cell and a bond beam a the top. (tornado shelter). We have heard from someone that if you fully grout all cells, you might get more overall shrinkage in the block walls than say a partially grouted wall (such as vertical bars at 32" o.c. (800 mm).

I can't see how individual grouted cells can add to overall global horizontal shrinkage.

Is there a concern here? Should I shorten up the spacing of CJ to something less?

 

[msquared48]

JAE:

On thinking further here, and I realize that is dangerous,
I think what the concern is here is the horizontal bond beams - the grout in those horizontal ties shrinking, loading up the bond beam steel. I still do not see how the grout in a single isolated cell could affect the whole structure.

As far as I am concerned, the vertical grouting does not enter into play here laterally, maybe vertically, but then you are generally dealing with 4 foot lifts and sequential curing, allowing the shrinkabe to happen gradually..

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[concretemasonry]

The important thing is that a wall is a structural element or an element in a structural if it just in-fill in a non-structural situation, but even there it effects the structure if it is tied in in some way. The block are about 95+% cured and the mortar is partially cured before the grout is even placed. The codes treat a masonry wall as an element and not a collection of pieces since everything is assembled on the site (generally except for panels).

It is like chasing wisps of smoke to try to differential the minor difference between ungrouted, partially grouted and fully grouted when the majority of the wall is composed by the CMUs (by weight or volume).

The location of control joints has been beat to death by many engineers and professionals for 40 years and a method to calculate the spacing not matter what software or assumptions are made. - That is the real reason for the current NCMA and ACI 530 recommendations. This is based on the performance of masonry for many years with all types of construction and aggregate types (which no one on the forum has bothered to think about or consider).

Next someone will start to worry about the temperature variations in different climates and the effects of carbonization of the cement/lime (free and added lime) portion of the wall and moisture over a long period of time, both of which have miniscual effects

Dick

 

[Ron]

JAE...as usual, your "gut feel" I think if correct. The most significant effect of grout shrinkage would be localized to the cell....not the wall.

Wetting the wall after laying the block is significantly not the same as laying wet block and letting it shrink. The effects are totally different.

 

[concretemasonry]

Just a quick correction. I used the term carbonization when I should have used carbonation, which is the term in most countries. This reflects the long term effects of concrete products in the presence of some moisture and carbon dioxide over time and is time-dependent.

Dick

 

[Ron]

Dick...right you are! Carbonation effects in masonry are miniscule....even in exposed concrete they are rarely a problem, except in fire exposure.