كتاب المفاصل

CHAPTER 7
PAVEMENT JOINTS
EM 1110-3-132
9 Apr 84
7-1 . Joint types and usages . Joints are required in rigid pavements
to permit expansion and contraction of concrete due to temperature and
moisture changes, to relieve warping and curling stresses which result
from temperature and moisture gradients within the slab, to minimize
uncontrolled cracking caused by frost action, and as a construction
expedient to separate the areas of concrete placed at different times .
There are three general types of joints used in rigid pavements : (a)
contraction, (b) construction, and (c) expansion . Guidance relative to
the requirements for these joints is given in the following
subparagraphs .
a . Contraction joints . Contraction joints are provided to control
contraction cracking from temperature changes and from the initial
shrinkage of the concrete . The minimum depth of the groove for
contraction joints generally should be one-sixth of the pavement
thickness, but not less than the maximum nominal size of the aggregate
used . However, where this depth has been found to be insufficient to
produce the desired cracking at the groove, the depth of the groove
should be increased to one-fourth of the pavement thickness . The size
of the groove should conform to the dimensions shown on Standard
Mobilization Drawing No . XEC-006 .
(1) For transverse contraction joints in nonreinforced rigid
pavements, sufficient load transfer can be developed from the aggregate
interlock along the fractured face of the joint so that no other
provision for load transfer is required in Classes D and E pavements .
For reinforced rigid pavements, the longer slab lengths will result in
larger openings at the transverse contraction joints and for all such
pavements the transverse contraction joints should be doweled . Dowels
are also required for Class B nonreinforced pavements .
(2) Longitudinal contraction joints are required along the
centerline of nonreinforced rigid pavement lanes having a width equal
to or greater than the maximum spacing indicated in paragraph 7-3, for
transverse contraction joints for various pavement thicknesses . Where
such longitudinal joints are required, tie bars should be used to
prevent cumulative opening of the joint and excessive separation of the
adjacent lanes . The tie bars should be No . 5 deformed steel bars, 30
inches in length . Spacing of the tie bars should be 30 inches, center
to center .
(3) For reinforced rigid pavements where two traffic lanes are
placed as a single paving lane, a longitudinal dummy groove joint
should be provided at the centerline of the paving lane to control
cracking during concrete placement . In these joints, the reinforcing
steel is carried through the joint, and tie bars are not required .
EM 1110-3-132
9 Apr 84
(4) Longitudinal contraction joints at the centerline of
reinforced rigid pavements are required only when the width of the
pavement exceeds the allowable length of slab, L, for the percentage of
steel reinforcement being used . When such joints are required, the
steel reinforcement should be broken at the joint, and tie bars similar
to those described above should be used .
b . Construction joints . Construction joints are provided to
separate the areas of concrete placed at different times, and may be
either longitudinal or transverse, as required .
(1) The spacing of longitudinal construction joints will depend
largely on the paving equipment . With most present-day equipment,
paving lanes 24 feet or more in width are possible and may be used .
Determination of the width of paving lane to be used, that is, whether
a 24-foot-wide road or street should be paved in a single lane or in
two 12-foot-wide lanes, is left to the judgment of the designer .
(2) When a longitudinal construction joint is used at the center
of two-lane pavements, a keyed joint with tie bars similar to those
required for longitudinal contraction joints, or threaded split
5/8-inch tie bolt, should be used . When a longitudinal construction
joint is used at the center of pavements having four or more paving
lanes, a doweled joint should be used .
(3) Transverse construction joints should be installed at the
end of each day's paving operation, and at other points within a paving
lane where the placing of concrete is discontinued a sufficient length
of time for the concrete to start to set . All transverse construction
joints in nonreinforced rigid pavements should be of the doweled type,
and should be located in place of other regularly spaced transverse
joints . When paving is resumed, the regular transverse joint
construction should be used, beginning with the first regularly
scheduled transverse joint . When a transverse construction joint is
required within a slab in a reinforced rigid pavement, the reinforcing
steel should be carried through the joint and tie bars added .
c . Expansion joints . Expansion joints are provided for the relief
of forces resulting from thermal expansion of the pavement, and to
permit unrestrained differential horizontal movement of adjoining
pavements and/or structures . There are two types of expansion joints,
doweled and thickened-edge, both of which should be provided with a
nonextruding type filler ****l . Usually a preformed filler 3/4-inch
thick will be adequate . The expansion joint should be so designed as
to provide a complete and uniform separation between the rigid
pavements or between the rigid pavement and the structure concerned .
(1) Doweled expansion joints should be used for all transverse
expansion joints within rigid pavements except at the intersections of
rigid pavements with structures or with other rigid pavements . The
7-2
EM 1110-3-132
9 Apr 84
designer is cautioned that expansion joints within rigid pavements are
difficult to construct and maintain, and often contribute to pavement
failures . For these reasons, their use should be kept to the absolute
minimum necessary to prevent excessive stresses or distortion in the
pavement . Internal expansion joints should be omitted in all rigid
pavements 8 inches or more in thickness, and also in pavements less
than 8 inches thick when the concrete is placed during warm weather .
(2) At the intersection of two rigid pavements it is necessary
to provide for some differential horizontal movement in joints of this
type to prevent the expansion of one pavement from distorting the other
pavement . In such cases, the transverse expansion joints should be
designed as thickened-edge, slip-type joints . Similarly, the
thickened-edge, slip-type expansion joint normally will be the most
suitable for use where expansion joints are installed to surround or to
separate from the pavement any structure that projects through, into,
or against the pavement . Typical examples include the approaches to
buildings or around drainage inlets .
(3) Should it be necessary to construct a longitudinal expansion
joint within a rigid pavement, again a thickened-edge, slip-type
expansion joint should be used . Expansion joints are not required
between new and existing rigid pavements when the existing pavement is
being widened or extended with paving lanes parallel to the
longitudinal axis of the existing pavement .
7-2 . Joint design . Typical details for the design of expansion,
contraction, and construction joints are shown on Standard Mobilization
Drawing No . XEC-006 for nonreinforced and reinforced rigid pavements .
a . Doweled joints . The primary function of dowels in rigid
pavements is that of a load-transfer device . As such, the dowels
effect a reduction in the critical edge stress that is directly
proportional to the degree of load transfer achieved at the joint . A
secondary function of the dowels is to maintain the vertical alinement
of adjacent slabs, thereby preventing faulting at the joint . Dowels
should be required for the following types of joints : (a) transverse
contraction joints in Class B nonreinforced rigid pavements, (b)
transverse contraction joints in all reinforced rigid pavements, (c)
transverse construction joints in all nonreinforced rigid pavements,
(d) center longitudinal construction joints in rigid pavements four or
more lanes in width, and (e) transverse expansion joints in all rigid
pavements . Dowel diameter, length, and spacing should be in accordance
with the criteria presented in table 7-1 . Where dowels larger than
1-inch diameter are required, extra-strength pipe may be used as an
alternate for solid bars . When extra-strength steel pipe is used for
dowels, however, the pipe should be filled with a stiff mixture of
either sand-asphalt or cement mortar, or plugged at the ends of the
pipe . If the ends of the pipe are plugged, the plug should fit inside
the pipe and be cut off flush with the end of the pipe so that there
7-3
EM 1110-3-132
9 Apr 84
will be no protruding material to bond with the concrete and prevent
free movement of the pavement . Normally, dowels should be located at
the middepth of the pavement slab . However, a tolerance of one-half of
the dowel diameter, above or below the middepth of the slab, may be
allowed in locating the dowels in contraction or construction joints
where the allowance of such a tolerance will expedite construction .
For doweled expansion joints, the dowels should be placed at the
middepth of the slab with no tolerance allowed in positioning the
dowels . All dowels should be straight, smooth, and free from burrs at
the ends . One-half of each dowel should be painted and oiled or
greased thoroughly to prevent bonding with the concrete . Dowels used
at expansion joints should be capped at one end to permit unrestrained
movement of the dowels when the expansion joints close .
Table 7-1 . Doweled Joint Design Requirements
b . Keyed joints . As with dowels, keyed joints are constructed to
provide load transfer at the joint . The structural adequacy of keyed
construction joints in rigid pavements, however, can be impaired
seriously by such factors as : (a) small changes in the dimensions of
the key, and (b) positioning the key other than at the middepth of the
slab . Exceeding the design values for the key dimensions produces an
oversize key which can result in failure of either the top or bottom
edge of the female side of the joint . Similarly, construction of an
undersize key can result in shearing off the key . Keyed joints should
not be used in rigid pavements 8 inches or less in thickness except
where tie bars are used . Details of the required dimensions for keyed
joints are shown on Standard Mobilization Drawing No . XEC-006 . It
should be noted that the vertical and horizontal dimensions of the key
are expressed as a function of the slab thickness . Consequently, the
7-4
Pavement Thickness (inches)
Dowel Diameter and Type
Maximum Dowel Spacing
(inches) :
Less than 8
3/4-inch bar
8 to 11
1-inch bar
12 to 15
1-1/4-inch bar
Expansion Joints 9 10 12
Contraction Joints
Reinforced Pavement 11 12 14
Nonreinforced Pavement 18 20 24
Construction Joints 12 13 15
Minimum Dowel Length
(inches) 15 16 18
correct dimensions for the key must be determined for each thickness of
pavement . For all thicknesses of pavement where keyed joints may be
used, however, the center of the key should be located at the middepth
of the slab .
c . Thickened-edge joints . Thickened-edge type joints may be used
for all types of expansion joints with the exception of transverse
expansion joints within rigid pavements . When thickened-edge joints
are used, the amount of increased thickness at the edge should be
approximately one-fourth of the design thickness of the main portion of
the pavement . The thickening should start at a distance of not less
than 3 feet from the joint and taper uniformly to the full required
thickness at the joint .
7-3 . Joint spacing . For improved pavement performance and lower
maintenance costs, it is desirable to keep the number of joints to a
minimum by using the maximum joint spacings that will satisfactorily
control cracking . Under certain conditions where temperature changes
are moderate and high humidity prevails, joint spacings greater than
those indicated herein may be satisfactory .
a . Nonreinforced pavements . Transverse contraction joints should
be constructed across each paving lane, at intervals not less than
12-1/2 feet nor more than 25 feet . The joint pattern should be made
uniform throughout any major paved area . Each joint should be straight
and continuous from edge to edge of the paving lane, and extend across
all paving lanes for the full width of the paved area . The staggering
of joints in adjacent paving lanes should not be permitted . The
maximum spacing of transverse joints that will effectively control
contraction cracking will vary appreciably depending on pavement
thickness, climatic conditions, effective subgrade restraint,
coefficients of thermal expansion of the concrete, and other
characteristics of the aggregate, cement, etc . The joint spacings
shown in the following tabulation have given satisfactory control of
contraction cracking in most instances and should be used as a guide
subject to modification based on available information regarding local
conditions . Experience has shown that under traffic, oblong slabs tend
to crack into smaller slabs of nearly equal dimensions . This is
particularly true for thin pavements . Therefore, it is desirable to
keep the ratio of slab length to width as near unity as practicable .
In no case should the slab length exceed the width by more than 25
percent .
7- 5
EM 1110-3-132
9 Apr 84
Pavement
Thickness, inches
Spacing of
Cont raction Joints, feet
Less than 9 12 .5 to 15
9 to 11 15 to 20
More than 11 20 to 25
EM 1110-3-132
9 Apr 84
b . Reinforced pavements . Transverse contraction joints in
reinforced rigid pavements should be constructed across each paving
lane, perpendicular to the pavement centerline, and at intervals of not
less than 25 feet nor more than 75 feet . Allowable slab widths or
lengths can be determined directly from figure 6-1 for yield strengths
of either 56,000 or 60,000 lb/in 2 . Each joint should be straight and
continuous from edge to edge of the paving lane and should extend
across all paving lanes for the full width of the paved area .
7-4 . Joint sealing . All joints in rigid pavements should be sealed
with a sealing compound to prevent infiltration of surface water and
solid materials into the joint openings . In areas of heavy spillage of
diesel fuel or lubricants, a jet-fuel-resistant sealant will be used .
In some climates, joint sealing may not be required . Local sources of
information, such as state highway departments, should be investigated .

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