Title: Joint Design
1SESSION 7
2Objectives
- Identify types of joints
- Determine suitable joint spacings
- Determine load transfer requirements
- Develop joint reservoir designs
- Define tie bar requirements for longitudinal
joints
3Types of Joints
- Contraction joint
- Construction joint
- Expansion joint
4Joint Type?
Butt Joint
Construction Joint (transverse or longitudinal)
5Joint Type?
Initial Sawcut
Contraction Joint (transverse or longitudinal)
6Joint Type?
Expansion Joint with Filler Material
Expansion Joint
7Elements of Joint Design
- Transverse joints
- Joint spacing
- Load transfer design
- Sealant reservoir design
- Longitudinal joints
- Tie bar design
8JPCP Joint Spacing
- Short enough to prevent mid-slab cracking
- Intricately linked with
- Slab thickness
- Base support
- Climatic conditions
- Generally between 3.6 and 6.1 m (12 and 20 ft)
9Example JointSpacing Guidelines
10Uniformity of Joint Spacing
- Uniform joint spacing
- Joints spaced at fixed intervals
- Variable joint spacing
- 3 or 4 joint spacings in a repeating pattern,
e.g., 3.7 - 4.6 - 4.0 - 4.3 m (12 -15 - 13 - 14
ft) - Intended to reduce rhythmic response of vehicles
11Joint Orientation
- Perpendicular
- Joints perpendicular to centerline
- Skewed
- Joints placed at an angle to pavement centerline
(counterclockwise skew) - May be beneficial for nondoweled joints
- Limit skew to minimize corner breaks (maximum
110)
12Example Variable Spacing and Skewed Joints
4.3 m
4.0 m
3.6 m
(12 ft)
(15 ft)
(13 ft)
(14 ft)
13Skewed Joints
14LoadTransfer
- Ability of joint to convey wheel load from one
side to the next - Reduces deflections
- Reduces pumping, faulting
- Methods
- Dowels
- Aggregate interlock
15Load TransferIllustration
0 Load Transfer
Direction of Traffic
Leave Slab
Approach Slab
16Load TransferRecommendations
- Dowels recommended for most highway pavements
(slab thickness gt 200 mm 8 in) - Minimum 32 mm diameter (38 mm preferred)
- Corrosion inhibitor required
17Dowel Layout
Conventional Spacing
18Alternative Dowel Layout
Cluster Spacing
19Joint Sealing and Reservoir Design
- Purposes of joint sealing
- Reduce moisture infiltration
- Keep out incompressibles
- Cost-effectiveness of sealing?
20Consideration Factors
- New or rehabilitation design
- Climate
- Joint design
- Base and subgrade type and drainability
- Local experience
- Others?
21Joint Channel Design
- Unsealed joints
- Crack control sawcut (3 mm 1/8 in
22Joint Channel Design (continued)
- Sealed joints
- Crack control sawcut (3 mm 1/8 in)
- Joint reservoir sawcut (typ. 10 to 15 mm 0.4 to
0.6 in wide)
23Joint Reservoir Sawcut
Reservoir Widening Cut
Depth of Widening Cut (25 to 38 mm) (1 to 1.5 in)
Crack Control Sawcut
24Joint Reservoir Design
- Selection of sealant material
- Estimation of joint movements
- Determination of required joint width
25Sealant Materials
- Rubberized asphalt (ASTM D3405)
- Silicone
- Preformed compression seals
- Placed in state of compression
- Must be compressed 20 to 50 of normal width over
service life
26Joint Reservoir
Width
- 3 to 6 mm
- (1/8 to 1/4 in) Recess
Depth
Backer Rod
Joint Sealant
Shape Factor W / D
27Example Compression Seal Installation
Compressed Width
Reservoir Depth
Preformed Compression Seal
28Estimating Joint Movements
- ?L C L (? ?T ?)
- ?L Joint opening, in
- C Adj. factor (0.8 gran. base, 0.65 stab.)
- L Joint spacing, in
- ? Thermal coef. of expansion (3.8 to
- 6.6 x 10-6), in/in/oF
- ?T Temperature range, oF
- ? Drying shrinkage coefficient (2 to
- 8 x 10-4), in/in
29Required Joint Reservoir
- Hot-poured/silicone sealants
- Required joint width
- W ?L / S
- W Required joint width
- ?L Joint opening
- S Allowable sealant strain
- Required sealant depth
- Apply proper shape factors
30Required Joint Reservoir (continued)
- Compression seals
- Select uncompressed seal width
- USW gt ?L / (Cmax - Cmin)
- Cmax 0.5 (typ) Cmin 0.2 (typ)
- Determine width of sawcut
- W (1 - Pc) USW
- Pc of compression at installation
31Longitudinal Joint Design
- Contraction (sawed) joints
- Between lanes or between lane - shoulder
- Adequate sawing depth/timing
- Effective tie bar system
- Construction (butt) joint
- Commonly between lane and shoulder
- Effective tie bar system
32Longitudinal Contraction Joint
33Longitudinal Construction Joint
34Summary
- Joint types
- Joint spacing guidelines
- Load transfer recommendations
- Joint sealant system
- Longitudinal joint requirements