operations end for the day or where one structural
element is cast against previously placed concrete.
These joints allow some load to be transferred from
one structural element to another through the use of
keys or (for some slabs and pavement) dowels. Note
that the construction joint extends entirely through
the concrete element.
LEARNING OBJECTIVE: Upon completing
this section, you should be able to determine
proper occasions for using the concrete saw.
THE CONCRETE SAW
The concrete saw is used to cut longitudinal and
transverse joints in finished concrete pavements. The
saw is small and can be operated by one person
(figure 7-40). Once the cut has been started, the
machine provides its own tractive power. A water
spray is used to flush the saw cuttings from the
cutting area and to cool the cutting blade.
Several types of blades are available. The most
common blades have either diamond or Carborundum
cutting surfaces. The diamond blade is used for
cutting hard or old concrete; the Carborundum blade
is used for cutting green concrete (under 30 hours
old). Lets take a closer look at these two blades.
Diamond blades have segments made from a
sintered mixture of industrial diamonds and metal
powders, which are brazed to a steel disk. They are
generally used to cut old concrete, asphalt, and green
concrete containing the harder aggregates. Diamond
blades must always be used wet. Many grades of
diamond blades are available to suit the conditions of
Twelve-inch-diameter diamond blades are the
most popular size. This size makes a cut about 3 1/4-
inches deep. Larger-size blades are used for deeper
Low-cost, abrasive blades are now widely used to
cut green concrete made with soft aggregates, such as
limestone, dolomite, coral, or slag. These blades are
made from a mixture of silicon carbide grains and a
resin bond. This mixture is pressed and baked. In
Figure 7-40.-Concrete saw.
and baked. In many cases, some of the medium-hard
aggregates can be cut if the step-cutting method is
used. This method uses two or more saws to cut the
same joint, each cutting only a part of the total depth.
This principle is also used on the longitudinal saw,
which has two individually adjustable cutting heads.
When a total depth of 2 1/2 inches is to be cut, the
leading blade cuts the first inch and the trailing
blade, which is slightly narrower, cuts the remaining
Abrasive blades come in 14- and 18-inch
diameters. They are made in various thicknesses to
cut joints from 1/4-inch to 1/2-inch wide.
When to Use
When is the best time to saw green concrete? In
the case of abrasive blades, there is only one
answeras soon as the concrete can support the
equipment and the joint can be cut with a minimum
of chipping. In the case of diamond blades, two factors
must be considered. In the interest of blade life,
sawing should be delayed, but control of random
cracking requires sawing at the transverse joints as
early as possible. Where transverse joints are closely
spaced, every second or third joint can be cut initially
and the rest cut later. Sawing longitudinal joints can
be delayed for 7 days or longer.
For proper operation and maintenance of the
concrete saw, follow the manufacturers manual.