SESSION 7SESSION 7SESSION 7SESSION 7

Joint Design

ObjectivesObjectivesObjectivesObjectives

Identify types of joints

Determine suitable joint spacings

Determine load transfer requirements

Develop joint reservoir designs

Define tie bar requirements for longitudinal joints

Types of JointsTypes of JointsTypes of JointsTypes of Joints

Contraction joint

Construction joint

Expansion joint

Joint Type?Joint Type?Joint Type?Joint Type?

Construction Joint (transverse or longitudinal)

Butt Joint

SlabThickness

Dowel or Tie Bar

Joint Type?Joint Type?Joint Type?Joint Type?

Contraction Joint (transverse or longitudinal)

SlabThickness

Dowel Baror Tie Bar

InitialSawcut

Joint Type?Joint Type?Joint Type?Joint Type?

Expansion Joint

Expansion Joint with Filler Material

SlabThickness

Dowel Bar

Elements of Joint Elements of Joint DesignDesignElements of Joint Elements of Joint DesignDesign

Transverse joints

Joint spacing

Load transfer design

Sealant reservoir design

Longitudinal joints

Tie bar design

JPCP Joint SpacingJPCP Joint SpacingJPCP Joint SpacingJPCP 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)

Example JointExample JointSpacing GuidelinesSpacing GuidelinesExample JointExample JointSpacing GuidelinesSpacing Guidelines

Wet-Freeze/Dry Freeze

12

14

16

18

20

10 11 12 13 14 15 16Slab Thickness, in

Ma

x.

Jo

int

Sp

aci

ng

, ft

k = 75 psi/in k = 150 psi/in k = 300 psi/in

Uniformity of Joint Uniformity of Joint SpacingSpacingUniformity of Joint Uniformity of Joint SpacingSpacing

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

Joint OrientationJoint OrientationJoint OrientationJoint 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 1:10)

4.6 m 4.3 m4.0 m3.6 m

Traffic

Traffic

1

10

(12 ft) (15 ft) (13 ft) (14 ft)

Example Variable Example Variable Spacing and Skewed Spacing and Skewed JointsJoints

Example Variable Example Variable Spacing and Skewed Spacing and Skewed JointsJoints

Skewed JointsSkewed JointsSkewed JointsSkewed Joints

LoadLoadTransferTransferLoadLoadTransferTransfer

Ability of joint to convey wheel load from one side to the next

Reduces deflections

Reduces pumping, faulting

Methods

Dowels

Aggregate interlock

WheelLoad

0% Load Transfer

Direction of Traffic

Approach Slab Leave Slab

100% Load Transfer

Approach Slab

Wheel

LoadDirection of Traffic

Leave Slab

Load TransferLoad TransferIllustrationIllustrationLoad TransferLoad TransferIllustrationIllustration

UnloadedLT =

Loaded

Load TransferLoad TransferRecommendationsRecommendationsLoad TransferLoad TransferRecommendationsRecommendations

Dowels recommended for most highway pavements (slab thickness > 200 mm [8 in])

Minimum 32 mm diameter (38 mm preferred)

Corrosion inhibitor required

Dowel LayoutDowel LayoutDowel LayoutDowel Layout

Outer Traffic LaneInner Traffic Lane

12 dowels @ 0.3 m (1 ft) center to center

12 dowels @ 0.3 m (1 ft) center to center

Conventional Spacing

TrafficTraffic

Alternative Dowel Alternative Dowel LayoutLayoutAlternative Dowel Alternative Dowel LayoutLayout

Cluster Spacing

Outer Traffic LaneInner Traffic Lane

5 dowels @ 0.3 m(1 ft) center to center

4 dowels @ 0.3 m(1 ft) center to center

TrafficTraffic

Joint Sealing and Joint Sealing and Reservoir DesignReservoir DesignJoint Sealing and Joint Sealing and Reservoir DesignReservoir Design

Purposes of joint sealing

Reduce moisture infiltration

Keep out incompressibles

Cost-effectiveness of sealing?

Consideration FactorsConsideration FactorsConsideration FactorsConsideration Factors

New or rehabilitation design

Climate

Joint design

Base and subgrade type and drainability

Local experience

Others?

Joint Channel DesignJoint Channel DesignJoint Channel DesignJoint Channel Design

Unsealed joints

Crack control sawcut (3 mm [1/8 in]

Joint Channel Design Joint Channel Design (continued)(continued)Joint Channel Design Joint Channel Design (continued)(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)

ReservoirWidening Cut

Joint Reservoir Joint Reservoir SawcutSawcutJoint Reservoir Joint Reservoir SawcutSawcut

Crack Control Sawcut

Depth of Widening Cut (25 to 38 mm)

(1 to 1.5 in)

Joint Reservoir DesignJoint Reservoir DesignJoint Reservoir DesignJoint Reservoir Design

Selection of sealant material

Estimation of joint movements

Determination of required joint width

Sealant MaterialsSealant MaterialsSealant MaterialsSealant 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

3 to 6 mm(1/8 to 1/4 in) Recess

Width

Backer

Rod

Depth

Joint ReservoirJoint ReservoirJoint ReservoirJoint Reservoir

Shape Factor = W / D

Joint Sealant

Compressed Width

Reservoir Depth

Example Example Compression Seal Compression Seal InstallationInstallation

Example Example Compression Seal Compression Seal InstallationInstallation

Preformed Compression

Seal

Estimating Joint Estimating Joint MovementsMovementsEstimating Joint Estimating Joint MovementsMovements

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

Required Joint ReservoirRequired Joint ReservoirRequired Joint ReservoirRequired 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

Required Joint Reservoir Required Joint Reservoir (continued)(continued)Required Joint Reservoir Required Joint Reservoir (continued)(continued)

Compression seals

Select uncompressed seal width

USW > L / (Cmax - Cmin)

Cmax = 0.5 (typ); Cmin = 0.2 (typ)

Determine width of sawcut

W = (1 - Pc) * USW

Pc = % of compression at installation

Longitudinal Joint Longitudinal Joint DesignDesignLongitudinal Joint Longitudinal Joint DesignDesign

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

Longitudinal Longitudinal Contraction JointContraction JointLongitudinal Longitudinal Contraction JointContraction Joint

D/3 Joint Formed by Sawing

DD/2

Deformed Tie Bar(Minimum No. 5 Bar)

Mainline Pavement

Mainline Pavement or PCC Shoulder

Longitudinal Longitudinal Construction JointConstruction JointLongitudinal Longitudinal Construction JointConstruction Joint

D

D/2

Deformed Tie Bar(Minimum No. 5 Bar)

Butt Joint

Possible Key Way

PCC Shoulder

Mainline Pavement

SummarySummarySummarySummary

Joint types Joint spacing guidelines Load transfer recommendations Joint sealant system Longitudinal joint requirements