TM 5-809-12/AFM 88-3, Chap. 15
(1) Width and' depth of weakened plane
concrete and dictate the depth of groove required.
groove. The width of the weakened plane groove
For example, concrete placed early in the day, when
will be a minimum of 1/8 inch and a maximum equal
the air temperature is rising, may experience
to the width of the sealant reservoir contained in (2)
expansion rather than contraction during the early
life of* the concrete with subsequent contraction
below. The depth of the weakened plane groove
must be great enough to cause the concrete to crack
occurring several hours later as the air temperature
under the tensile stresses resulting from the
drops. The concrete may have attained sufficient
shrinkage and contraction of the concrete as it
strength before the contraction occurs so that each
cures. Experience, supported by analyses, indicates
successive weakened plane does not result in
that this depth should be at Last one-fourth of the
fracturing of the concrete. As a result, excessive
slab thickness for floor slabs 12 inches or less, 3
opening may result where fracturing does occur. To
inches for pavements greater than 12 and less than
prevent this, the depth of the groove will be
18 inches in thickness, and one-sixth of the slab
increased to assure the fracturing and proper
thickness for floor slabs greater than 18 inches in
functions of each of the scheduled joints.
(2) Width and depth of sealant reservoir. The
thickness. In no case will the depth of the groove be
less than the maximum nominal size of aggregate
width and depth of the sealant reservoir for the
used. Sawcut contraction joints for steel-fiber
weakened plane groove will conform to dimensions
reinforced concrete should be cut a minimum of
shown in figure 5-8. The dimensions of the sealant
one-third of the slab thickness. Concrete placement
reservoir are critical to satisfactory performance of
conditions may influence the fracturing of the
the joint sealing materials.
5-14
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