Masonry Magazine July 2002 Page. 34
continued from page 31
to get the grout to the top of the wall. "We use two different systems. In most cases, with high-lift grouting, we would pump it with a grout pump with a 2-inch line. Or we could use a grout hopper system, like Grout Hog. The concrete would be dumped into the pump, and then pumped into the core or be put into the hopper and dumped in with the forklift."
With high-lift, care must be taken to insure the cleanouts are properly replaced and braced. MIW says, "Face shell plugs or mortared units should be adequately braced to resist the fluid pressure of the grout. In hollow unit masonry, the mortar should be permitted to cure sufficient before grouting to prevent mortar joints from being blown out by pressure of the grout. When filling the cavity space between two wythes of masonry, a specified period of time is recommended to prevent 'blowouts."
And one final issue, the "cramped quarters syndrome." As Harwell indicates, "The problem we run into is that the architecture/structural engineer sees this 4-inch square core as a perfect concrete form. He takes two pieces of rebar that have to be lapped as they're installed in the block. So inside this 4- to 6-inch square you have two pieces of rebar sitting side by side, and then you have the little pieces of reinforcing wire, call them 'butterflies,' and that stuff can block up that hole. Add to that the mortar that is squeezed into the cavity-mortar snot-and that hole is getting smaller and smaller. The engineer still sees it as a perfect concrete form, but it never is."
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Going low
LOW-LIFT GROUTING, what MIW defines it as "when the grout is poured as the wall is being built," has many fans. Harwell has found that many engineers call for low-lift, as do architects and owners, for a variety of reasons. He recalls, "Wal-Mart requires all low-lift grouting, and I believe the Army Corps of Engineer requires it as well. They feel the inspectors can keep a better eye on what's happening with low-lift. It's easier to make sure that the cavities are clean and unobstructed when you're low-lifting. And you get better consolidation."
Some considerations when doing low-lift include being sure the collar joint is wide enough to provide proper steel clearance. It must be at least 3/4-inch wide. One tier may be carried up 6 feet before grouting, but the other must be laid up and grouted in lifts not higher than 5 feet or the wall might blow out. And the last grout pour of the day should stop about an inch to an inch and a half below the top of an unfinished wall. This provides a keyway in the cold joint.
Harwell expands on that idea, saying that contractors should be sure that the space provided is always adequate. "Structurally, what we want is to make sure that grout stays down about an inch and a half below the top of the face shell of the block. That will provide a good mechanical connection so that the