Joint Placement

Concrete Placement Slabs/PavementsOhio Concrete
Ohio Concrete Contractor Seminar
Let’s Start Here…
If you don’t have proper compaction of the subgrade, out
of joint cracking will occur and no saw cut will stop it.
At a minimum proof roll.
Inadequate compaction results in a pavement with
decreased stiffness, reduced fatigue life, accelerated
aging/decreased durability, rutting, raveling, and
moisture susceptibility (Hughes, 1984; Hughes, 1989)
Ensure you have proper drainage.
Why Joint?
Control the location, width, and appearance of expected cracks (ex: drying shrinkage)
Facilitate construction
Minimize performance implications of any random (unexpected) cracks
Four Basic Slab Types
3. Reinforced to prevent cracking
4. Structural
Remains un-cracked between joints when loaded
and restraint to volumetric changes
Relatively close spacing of joints to control
shrinkage effects
Dowels are not reinforcement
Contraction/Construction Joints
Tied Joints
Tie Bars…
Can be used to only tie the first longitudinal joint
from the pavement edge to keep the outside slab
from separating from the pavement
Transverse Joints Typically run perpendicular to traffic at right
angles to longitudinal joint
Higher truck volume, channelized traffic
Provide load transfer between slab
Allows horizontal movement – not vertical
Types of Joints
and by effects of loads and warping and curling
• Load transfer achieved by aggregate interlock
The extent of cracking due to key
influences is somewhat predictable;
Recommended Spacing
joint spacing due to load transfer considerations.
Joint Spacing
Spacing: Recommended: 2 times the depth (feet) or
24-36 times the thickness (inches) with max @ 15 ft
Example: 5” thickness = 10 ft
Example: 8” thickness = max 15 ft
Panel shall be kept as square as possible 1.25 : 1.00 (length to width ratio)
Example: Maximum 10 ft x 12.5 ft
Avoid tee-intersections, create “sympathy cracks”
Width Typically 1/8 in, if sealed typically min. 1/4 in
Depth*: Minimum: 1/4 of the depth: 8” thick = 2” deep
Recommended: 1/3 of depth
Early Entry may apply
Conventional Saw
• Larger Diameter
• Typically 4-12 hours after finishing
Early Entry Saw (Green Saw)
• Smaller Diameter
• Slotted plate in contact with pavement to prevent damage
• Depth of contraction joint D/6 to D/5 (Min. 1”)
• Typically 1-4 hours after finishing
Time
• Sawing should begin as soon as the concrete can support the sawing
equipment and prevent raveling.
• No standardized test; contractors often use a nail or knife to scratch the
pavement surface to determine whether it spalls or ravels.
• There are guides using aggregate geometry, hardness, cement content and
saw rating to determine when to cut.
Timing of Cuts
Depth
Sympathy
Cracks
placements, try and use planned existing control joint
locations.
Thickened edges are commonly used to provide additional edge support.
Thickened Edges
Concrete at construction joints that will support wheel loads should be thickened to provide extra support.
Approximately
dowel bars
Now being used in some parking areas / industrial pavements
Accommodate some differential movement longitudinally along the joint (random traffic pattern)
Greater concrete bearing area, less stress
Can be effectively used in thinner slabs than round dowels
Efficient use of steel
Trapezoidal shapes in baskets for control joints
Construction joints using diamond dowel system
Tied Construction Joints
edges, curves, single longitudinal joint)
• Maybe not needed for roads with
tied curb & gutter, integral curb
• Placed at mid-depth of the pavement.
Keyways
D
0.1D
0.2D
No longer recommended for light traffic pavements!
…are sometimes called expansion joints but should generally not be used to provide for expansion. They provide no load transfer and should not be used as regularly spaced joints in a joint layout. Their proper use is to isolate fixed objects, providing for slight differential settlement without damaging the slab/pavement.
Types of Joints-Isolation Joints
Isolation W/ Thickened Edge
Isolation joints that will support wheel loads should be thickened to provide extra support.
Approximately
for movement
some cases
Common details for isolation of fixtures
Diagonal
None
Examples - Isolation Joints
Examples – Isolation Joints
Examples - Isolation Joints
Joint Layout Guidelines
Turn the joint about 1 foot away from the grate and turn it to meet the corner.
Thickened Edge
support is specified
gravel pavement (entrances/exits)
Joints in curbs
are constructed
Odd-Shaped Panels
(plunge cut or core hole)
Joint Layout Guidelines
Joint Layout Guidelines
Things to Do
Jointing plan drawn by designer of record, or submitted by
contractor & approved by designer
Cut at the proper location, depth, and time
Place joints to meet in-pavement structures
Adjust spacing to avoid small panels or angles
Intersect curves and edges perpendicular
Keep panels square
Joint Layout Guidelines
Things to Avoid
Slabs < 1 ft. wide
Slabs > 15 ft. wide
Creating interior corners
Offset (staggered) joints
Square Panels
Distributed Steel Reinforcement
PLACEMENT OF MESH SHALL BE IN TOP 1/3 OF PAVEMENT SECTION
Distributed Steel Reinforcement
Placed Too Low
Distributed Steel Reinforcement
Placed Too Low
Manufacturers recommended
dosage rate
1.5” to 2” typically
Added throughout the concrete
design must be effective
Factors to consider in whether or not to
seal joints:
Traffic level
JOINT FILLING AND SEALING
pavement design assistance.
and bidding purposes.
OC recommendations are not signed nor sealed and must be reviewed by an EOR prior to construction
ESC – Engineering Service Center
Sustainability References