Page 173 - Masonry and Concrete

Masonry Construction Techniques
172 CHAPTER FIVE

1
displacement of as little as 8 in. will destroy the bed joint bond, and
the work must be torn down and rebuilt. The joint rupture will cause
a permanent plane of weakness and cannot be repaired by simply
realigning the wall. Grout that is in contact with the masonry hardens
more rapidly than that in the center of the grout space so it is impor-
tant that consolidation or puddling of the grout take place immedi-
ately after the pour and before this hardening begins. Vibrators used in
masonry grouting are usually smaller than those used in concrete work
because the space they must fit into is smaller. In single-wythe, hol-
low-unit construction, walls may be built to a maximum 4-ft. height
before grout is pumped or poured into the cores. Grout is placed in the
cores and then consolidated by vibration to ensure complete filling
and solid embedment of steel.
High-lift grouting operations are not performed until the wall is
laid up to full story height. The cross webs of hollow units are fully
embedded in mortar about every 25 ft. to form grout barriers. This lim-
its the size of the pour to a manageable area and contains the grout
within the designated area. Cleanouts must be provided at the base of
the wall by leaving out every other unit in the bottom course of the sec-
tion being poured. In single-wythe, hollow-unit walls, cleanout open-
ings at least 3 4 in. are located at the bottom of every core containing
dowels or vertical reinforcement, and in at least every second core that
will be grouted, but has no steel. In solidly grouted, unreinforced sin-
gle-wythe walls, every other unit in the bottom course should be left
out. A high-pressure air blower is used to remove any debris which
may have fallen into the cores. Cleanout plugs are filled in after clean-
ing the cavity, but before the grouting begins. The mortar joints in a
wall should be allowed to cure for at least three days to gain strength
before grouting by the high-lift method. In cold, damp weather, or dur-
ing periods of heavy rain, curing should be extended to five days.
Grout should be placed in a continuous operation with no intermedi-
ate horizontal construction joints within a story height. Four-foot max-
imum lifts are recommended, with 30 to 60 minutes between pours to
allow for settlement, shrinkage, and absorption of excess water by the
units. In each lift, the top 12 to 18 in. should be reconsolidated before
or during placement of the next lift.
It is critical that the grout consistency be fluid, and that it be
mechanically vibrated into place. When the grout is stiff, it hangs up

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.