Masonry Magazine February 1994 Page. 35
What about the performance of reinforced versus unreinforced masonry?
In an article by Dr. Arturo Schultz (Reference #3) of the National Institute of Standards and Technology "Performance of Masonry Structures During Extreme Lateral Loading Events," he pointed out the performance of unreinforced masonry versus reinforced masonry systems. The comparison was dramatic and very strongly in favor of grouted reinforced masonry walls. This was true for all types of masonry structures throughout North and South America.
Why partially grout walls?
Assuming the masonry walls are to be reinforced, there are several reasons to partially grout a wall. The first is economic, there is less grout to be used in the wall and thus less labor need be used in placing the limited amount of grout. This can be quite significant, in a comparison between a solidly grouted wall and a wall partially grouted with maximum spacing of steel, there would be an estimated saving of 70% of the grout required.
Another consideration is that a partially grouted wall will weigh less and the seismic forces on the wall will be significantly less, thus there will be less reinforcing required in the design and construction of the wall. For tall slender walls this could mean an additional 10 to 15% of increased height or a saving in the amount of reinforcing steel required for the height of wall required.
Are there any drawbacks to partially grouting walls?
There may be some drawbacks to partially grouted walls. For partially grouted walls the sound transmission characteristics (STC) will be reduced and thus more sound will be going through. This is not desirable in certain uses of masonry walls, i.e. bedrooms of motels, theaters, sound studios, etc. Retaining walls are not partially grouted but solid grouted to increase their weight and stability against overturning.
Partially grouted walls have a lower fire rating than solid grouted walls. An 8" solid grouted CMU wall has a fire rating of four hours while a partially grouted CMU wall of the same thickness would have a fire rating of one hour.
What about load carrying capability?
Well, the load carrying capability between a partially grouted wall and solid grouted wall is basically dependent upon the requirements. A solidly grouted wall will have a greater load carrying capability of the wall than a partially grouted wall because there is more load bearing cross-section area. It may not be necessary to have this extra capability because of the design or light loads, therefore why pay for it? This is also true about the lateral shear capability of the wall. A solidly grouted wall would have a greater lateral shear capability than a partially grouted wall but if it's not necessary why specify it and encounter the extra cost.
A partially grouted wall can be quite adequate for the needs of the building which is determined by the architect and engineer. We have discussed about grout in detail, its advantages and why use it and why not use it. But should we get down to the fundamental of what is grout?
It is a cementitious material that transfers the load and provides all of the benefits mentioned above. Coarse grout is made up of portland cement, sand and pea gravel, while fine grout consists of cement and sand only.
Grout is not mortar and grout is not concrete. It's somewhere in between. For a rapid visual concept of what grout is, let's call it "soupy concrete". Soupy concrete may give the proper connotation and understanding because it is made up of a cement/ water combination which is the paste that binds together the aggregate, which may be sand only or sand and gravel. These are the same ingredients that make up concrete: cement, water, sand and gravel. All these materials harden into a stone like mass. You might consider this concrete which is made of the same materials. However, because concrete usually has a limited slump and has a highly controlled water cement ratio, this