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5. Blasting with copper slag and/or silica carbide reduces
as possible, either tooled while the slab is still plastic or by
the fracturing and is recommended and practiced by
saw cutting within 8 to 24 hours, but should be cut as soon
Shaw & Sons.
as possible. Delaying saw cutting operations increases the
6. Exposed aggregate retarder finish retards the surface setting
likelihood of random slab cracking. The ideal contraction
time only of the cement, enabling the concrete matrix to set
joint spacing is between 8 to 12 feet o.c.e.w. for a 4-inch
up enough for the top surface to be pressure washed the
reinforced slab. Cut all contraction joints at least 1/4 the
same day, or up to 24 hours after finishing. (Note: After con-
depth of the slab.
crete has leached free lime and other mineral deposit, sur-
2. Construction joint (often called cold joint or doweled
face must be acid and pressure washed clean approx. 3
construction joint) is the most commonly used method for
weeks after project completion.) Depth of retarders can be
A/B pours or checkerboard alternate pours. Construction
adjusted to light, medium, and heavy etch degrees.
joints are placed to define the extent of a given slab pour,
7. Hard trowel finish is not recommended for exterior hard-
e.g. end of day pour, paving type break or delays in concrete
scape due to a less than adequate slip co-efficient. However,
placement (hardened concrete), and usually conforms to a
hard troweling can develop a deeper contrast on walls if
predefined joint layout. Const ruction joints should always
forms are stripped and “faced.” Also applicable to wall tops,
use steel dowels with Speed DowelTM tubes to help distrib-
fountains, etc.
ute the load between adjacent slab sections and prevent
8. Form finish can be utilized primarily for cast-in-place walls.
vertical slab displacement.ACI recommended joint spacing is
9. Form liners attach to forms and are typically pre-formed.
16-foot by 16-foot modules (modules should not exceed 20
10. Sacked finish applies to cast-in-place concrete and
feet by 20 feet).
requires rubbing the finished concrete surface with raw
3. Isolation joint (often called expansion joint) used to permit
cement. Sacking is typical of exposed structural concrete
movement between vertical and horizontal surfaces, e.g.
construction.
horizontal slabs against walls, columns, foundations, footings
or other points of restraint such as drains, manholes, utility
covers, and steps. Isolation joints are normally installed first
with a pre-molded joint filler, backer rod and caulking.
RULE 10
CURING
All concrete should be properly cured. Curing consists of maintaining a satisfactory moisture content and temperature in concrete
during its early stages so that desired strengths may result without
excessive fracturing and breakage.
RULE 9
JOINTING
Architectural concrete must always be jointed. Concrete jointing
serves two basic purposes: it controls the location of anticipated
random slab cracking and it aids in the esthetic appearance of
architectural concrete. There are 3 basic paving joint types recognized by the ACI:
1. Contraction joint (often called control joint, hand-tooled
1. Begin curing slabs immediately after finishing because slabs
can lose moisture and change temperature very quickly. This
can lead to surface cracks.
2. Concrete should be kept continuously moist for at least
seven days.
3. There are several ways to cure concrete:
A. Water ponding.
B. Sprinkling or fogging with water.
joint, crack control joint, is a decorative saw cut or tooled
C. Virgin mill carpet (keep damp).
joint used to avoid random cracks or provide an esthetic
D. Wet burlap or synthetic blankets.
score line pattern. Contraction joints are installed as soon
E. Waterproof paper.
F. Curing compounds.
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