Page 64 - Masonry and Concrete

Concrete Construction Techniques
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CONCRETE CONSTRUCTION TECHNIQUES

As the concrete is placed, use a hook or a claw hammer to lift wire
reinforcing mesh and make sure that concrete flows underneath to
completely embed it. Be careful not to displace reinforcing bars or
knock them off their supports.
The third rule in pouring concrete is to effectively compact or con-
solidate the fresh mix immediately after it is placed and before it
begins to stiffen. Concrete must be consolidated to eliminate air pock-
ets and voids and to get the concrete to flow around reinforcement and
anchorages. In very small applications, adequate consolidation can be
achieved by rodding or puddling by hand with shovels, metal rods, or
tampers, but mechanical vibration is preferred on most applications.
High-speed mechanical vibrators cause the mix to settle evenly down
into the forms and brings enough fine material and cement paste to the
surface to permit finishing operations when appropriate. Internal or
immersion type vibrators are most commonly used (Figure 3-22). They
are immersed to the bottom of the concrete
for a few seconds and withdrawn when it
levels itself like a liquid and a thin layer of
cement paste forms at the surface. Over-
consolidation will cause the ingredients to
segregate.

3.7 Concrete Finishing

The tops of concrete slabs, driveways,
patios, and sidewalks must be leveled and
finished to apply an appropriate surface
texture. Surface finishes may be simple
and utilitarian or more elaborate and
decorative.
3.7.1 Floating, Troweling, and
Brooming

The tops of footings and walls are left
unfinished after the concrete has been
vibrated, but flat concrete elements such
as slabs, driveways, sidewalks, and patios FIGURE 3-22
must be leveled on top and an appropriate Mechanical vibrator.

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