Civil Engineering Reference
In-Depth Information
2.
Latex.
A latex-bonding agent is added to the cement-
sand grout and is spread in accordance with the latex
manufacturer's direction.
3.
Epoxy.
An approved epoxy-bonding agent placed on
the base concrete, prepared in accordance with the
epoxy manufacturer's direction.
Joint sealing compound
Expansion
joint material
The bonding procedure should produce tensile bond
strength with the base concrete in excess of 1.0 MPa
(150 psi).
Grout is placed just a short distance ahead of the
overlay or top-course concrete (Fig. 11-25). This method
may also be applicable to horizontal joints in walls. The
grout should not be allowed to dry out prior to the overlay
placement; otherwise, the dry grout may act as a poor sur-
face for bonding. The surface of the base slab should have
been prepared by one of the methods discussed pre-
viously. Overlays are discussed further under “
Patching,
Cleaning, and Finishing
” later in this chapter.
Isolation Joint
Fig. 11-26. Isolation joints permit horizontal and vertical
movements between abutting faces of a slab and fixed
parts of a structure.
(
1
⁄
2
-in.) material is commonly used. Care should be taken
to ensure that all the edges for the full depth of the slab are
isolated from adjoining construction; otherwise cracking
can occur.
Columns on separate footings are isolated from the
floor slab either with a circular or square-shaped isolation
joint. The square shape should be rotated to align its cor-
ners with control and construction joints.
Contraction Joints
Contraction joints (Fig. 11-27) provide for movement in
the plane of a slab or wall and induce controlled cracking
caused by drying and thermal shrinkage at preselected
locations. Contraction joints (also sometimes called con-
Sawcut
Fig. 11-25. Application of a bonding grout just ahead of the
overlay concrete. The grout must not dry out before the
concrete is placed. (51995)
1
/
4
D min.
D
Induced crack
MAKING JOINTS IN FLOORS AND WALLS
Sawed contraction joint
The following three types of joints are common in concrete
construction: isolation joints, contraction joints, and con-
struction joints.
Plastic or hardboard
preformed strip
Isolation Joints
1
/
4
D min.
Isolation joints (Fig. 11-26) permit both horizontal and ver-
tical differential movements at adjoining parts of a struc-
ture. They are used, for example, around the perimeter of
a floor on ground, around columns, and around machine
foundations to separate the slab from the more rigid parts
of the structure.
Isolation-joint material (often called expansion-joint
material) can be as thin as 6 mm (
1
⁄
4
in.) or less, but 13-mm
D
Premolded insert contraction joint
Fig. 11-27. Contraction joints provide for horizontal
movement in the plane of a slab or wall and induce controlled
cracking caused by drying and thermal shrinkage.
