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- 1 Rules for Joint Layout
- 2 Joint Layout Terminology
- 3 Intersection Joint Layout
- 4 Culs-de-sac Joint Layout
- 5 Roundabouts
- 6 Diverging Diamond Interchanges (DDI)
- 7 Related Pages
- 8 Related Resources and Materials
Basic rules for jointing concrete pavements do not cover some special applications. Intersections, culs-de-sac, and roundabouts provide designers with challenges that need extra rules and guidelines to create effective jointing plans. Effective joint plans can ease construction and reduce issues and complications. This page presents methods and guidelines for creating joint layouts for specialty applications.
Rules for Joint Layout
There are some basic joint layout rules that result in the best performance for intersections and roundabouts. While it may not always be possible to follow all of theses rules, they should be followed whenever possible to minimize the potential for random cracking and other potential issues.
Things to do:
- Match existing joints or cracks.
- Place joints to meet in-pavement structures.
- Be mindful of the maximum joint spacing.
- Place isolation joints where needed.
- Allow necessary adjustments to joint locations in the field.
- Be practical.
Things to avoid:
- Slabs < 2 ft (0.6 m) wide.
- Slabs > 15 ft (4.5 m) wide, unless local experience dictates otherwise.
- Angles < 60° (~90° is best); do this by dog-legging joints through curve radius points.
- Creating interior corners.
- Odd shapes (keep slabs near-square or pie-shaped).
Joint Layout Terminology
Doglegs: Construction block-outs at points where the pavement changes width. (See figure for details.)
Circumference-Return Line: A lightly drawn line 1.5-3.0 ft (0.5-1.0 m) from the face of the gutter along the curve between the edges of the intersecting roads. For obtuse angles, the line is 1/2 the nominal lane width from the gutter. Any joint that meets the circumference-return line is brought along the curve's radius to the back of the curb and gutter. Older publications use the term "off-set points" to refer to the points where joints return to the back of the curb.
Taper-Return Line: A lightly drawn line 1.5 ft (0.5 m) from the face of the gutter at the start of a turn lane taper. Any longitudinal joint that meets a taper-return line defines a location for a dogleg in the gutter.
Cross-Road Return Line: A lightly drawn line 1.5 ft (0.5 m) from the edge of a the mainline roadway at a skewed intersection. Any cross-road longitudinal joint will meet a transverse joint for the mainline roadway at the cross-road return line.
Intersection Box: The box formed by the edge of the mainline and intersecting paving lanes (including turning lanes).
Intersection Joint Layout
Designers and contractors should outline an intersection joint layout while developing project plans. The initial plan view of an intersection provides the best birds-eye view for seeing the entire intersection. During construction it is difficult to visualize an intersection because of construction staging.
A good jointing plan will ease construction by providing clear guidance. It is common practice for some designers to leave intersection joint layout to the field engineer and contractor. These designers often justify this practice by citing the many field adjustments that occur during construction, which they contend negates the usefulness of a jointing plan. However, it is not desirable to eliminate the jointing plan except for very simple intersections. A jointing plan and appropriate field adjustments are both necessary for more complex intersections, because islands, medians and turning lanes complicate joint layout and require some forethought before construction. The plan will also enable contractors to more accurately bid the project.
During construction it is likely that location changes will be necessary for some joints within an intersection. The primary reason is to ensure that joints pass through fixtures embedded in the pavement like manholes or drainage inlets. It is common for the actual location of these fixtures to vary from the location shown on the plans. As a result, it will be desirable for the construction crew to adjust the location of some joints so that they coincide with the actual location of a nearby manhole or inlet. The designer should consider placing a note on the plan to give the field engineer and contractor the latitude to make appropriate adjustments.
The transverse and longitudinal joints in concrete pavement are necessary primarily to control cracking. The desirable transverse joint spacing depends on the slab thickness and subbase, but is usually about 15 ft (4.5 m). On typical roadway pavements, longitudinal joints divide lanes of traffic and in most cases are no more than about 12 ft (4 m) apart. Because the transverse and longitudinal joint spacing are usually not identical, it is difficult to maintain an even spacing on either roadway through an intersection.
10-Step Method for Jointing Intersections
The ten-step method provides intersection joint layout fundamentals. The examples show a right-angle and a skewed T-intersection. The detail diagrams show preferable alternates, but there may be certain intersections with unique geometry that the methodology does not fully address. This publication does not address dowel and reinforcing requirements for joints.
A primary goal of this method is to minimize or eliminate joints that intersect another joint or the pavement edge at an acute angle. Experience shows that cracks often occur near acute angles, especially angles less than 60°. For most intersections it is possible to eliminate all angles less than 90° from the roadway slabs — there may be some acute angles in the curb and gutter. For skewed intersections it is likely that some joints will intersect at angles less than 90°. However, even for skewed intersections it is preferable to avoid angles less than 60°.
The method works equally well for integral curb and gutter, as well as for separate curb and gutter. The diagrams show how to place joints through curb and gutter and along curves between the intersecting roadways. The method also helps produce a plan that is easier to construct by avoiding width changes along the edge of the mainline or primary paving lane(s).
- Draw all pavement edge and back-of-curb lines on the plan view.
- Lightly draw the circumference-return, taper-return, and the cross-road-return line(s).
- Draw all lines that define lanes on the mainline and cross road. (Do not extend these lines past the circumference-return, taper-return or cross-road-return lines.)
- Define the mainline lanes for paving. Find all locations where the mainline lanes intersect circumference-return or taper-return lines. At these locations only, extend the mainline paving edge lines past the circumference-return or taper-return line(s). Any block-outs for doglegs at these locations are preferable in the gutter for the curb.
- Add transverse joints at all locations where the pavement changes width, extending the joints through the curb and gutter. Do not extend joints that intercept a circumference-return or cross-road-return line, except at the tangent points. The joint at the tangent point farthest from the mainline becomes an isolation joint in the cross road for T- and unsymmetrical intersections.
- Add transverse joint(s) between and beyond the joints you defined in Step 5, but do not add joints to the center of the intersection yet. Attempt to keep the distance between joints less than the maximum desirable length. Usually the maximum length is about 15 ft (4.5 m). (To calculate: ML = Dx24 for slabs on granular or unstabilized subbases; ML = Dx21 on stabilized subbases or existing asphalt or concrete pavements; ML=maximum length; D=slab thickness.)
- By extending the edge of pavement lines for the cross road and any turning lanes, define the intersection box. (Note: For skewed intersections do not extend the lines for the turning lanes. Instead, place a transverse joint normal to the cross road centerline starting from the corner of the intersection box that is nearest to the acute angle of the intersection.)
- Check the distances between the "intersection box" and the surrounding joints.
- If the distance is more than the maximum desirable joint spacing, then add transverse joint(s) at an equal spacing. Do not extend these joints past the circumference-return or cross-road-return lines.
- Lightly extend lines from the center of the curve(s) to the points defined by the "intersection box," any intermediate joints surrounding the "intersection box" and point(s) along any islands. Add joints along these radius lines. Finally, make slight adjustments to eliminate doglegs in mainline edges. (See dogleg details figure).
Skewed Intersection Layout Alternative
This alternative for a skewed intersection is useful for simple curve radii greater than 36 ft (11 m) and offset or compound radius curves. It can simplify field construction when the contractor builds the curve area in a single hand pour (indicated by the shaded area).
It is necessary to add an additional longitudinal joint near the center of the slabs that exceed 15 ft (5 m) wide. The additional joint should prevent the occurrence of a longitudinal crack. It is desirable to begin and end the additional longitudinal joint at a transverse joint, as shown in the diagram. Some agencies core a small 2-in. (50-mm) hole through the slab at the ends of this longitudinal joint to prevent sympathy cracking (see diagram). This is one method of handling a dead-end joint.
Handling Wide Medians and Dual-Left Turn Lanes
Large urban and suburban intersections that contain dual-left turn lanes, create joint alignment challenges. The medians in these large intersections are often up to 30 ft (9.2 m) wide. The diagram shows how to skew joints through the intersection box in order to maintain the joints along the lane lines for dual-left turn lanes. The ability to use this method will depend on construction staging; it is just one option to apply for complex intersections.
Adjusting Joints for Utility Fixtures
After developing the jointing plan, plot any catch basins, manholes or other fixtures that are within the intersection. Non-telescoping manholes will require a boxout or isolation to allow for vertical and horizontal slab movement. Consider using rounded boxouts or placing fillets on the corners of square boxouts to avoid crack-inducing corners. Also for square boxouts, wire-mesh or small-diameter reinforcing bars in the concrete around any interior corners will hold cracks tight should they develop. Telescoping manholes can be cast integrally within the concrete, and do not necessarily require a boxout. The two-piece casting does not inhibit vertical movement and is less likely to create cracks within the pavement.
Finally, when a joint is within 5 ft (1.5 m) of a fixture, it is desirable to adjust the joint so that it will pass through the fixture or the boxout surrounding the fixture. The diagram on the right shows several acceptable ways to skew or shift a joint to meet a fixture.
Culs-de-sac Joint Layout
Joint layout for culs-de-sac can also be accomplished following the rules for joint layout and the intersection 10-step method. A few examples are displayed in the figure to the right. It is important to note that these are only examples and if the width, radius, or geometric design change substantially then the joint layout will need to be altered. The simplest way to create a jointing plan for these is to begin with the lanes that can be paved through using a paver. This will help create the most effective jointing plan. Once this has been laid out, the 10 step method can help layout the rest of the cul-de-sac.
Roundabouts are an increasingly popular intersection type due to their traffic flow and safety characteristics. Concrete is well suited to withstand the turning motion of vehicles at roundabouts, but the joint layout requires forethought to avoid joint issues resulting from breaking the aforementioned rules. Adhering the the rules for joint layout along with the following six step method will ensure a successful joint layout. There are a few methods for jointing roundabouts but the two most commonly used methods are the isolated circle and the pave-through methods. The 6 step method is presented for these two methods.
The typical 10-step intersection method could be used for roundabouts, but the resulting joint layout would have joints that would intersect traffic at strange angles. This could create joint issues and pavement deterioration.
Two additional rules or recommendations for roundabouts are that the joints in the circular portion should radiate from the center. The other rule is that the joints in the legs should be normal or perpendicular to the circle.
6-Step Method for Jointing Roundabouts
The 6-step method for jointing roundabouts is presented for both the isolated circle and pave-through jointing methods.
- Draw all pavement edge and back-of-curb lines in the plan view. Draw locations of all manholes, drainage inlets, and valve covers so that joints can intersect these.
- Draw all lane lines on the legs and in the circular portion. If isolating the roundabout circle from the legs, do not extend these through the circle. If using the "pave-through" method, determine which roadway will be paved through. Make sure no distance is greater than the maximum recommended width (typically 15 ft [4.5 m]).
- In the circle, add "transverse" joints radiating out from the center of the circle. Make sure that the largest dimension of a pie-shaped slab is smaller than the maximum recommended slab width. Extend these joints through the back of the curb and gutter.
- On the legs, add transverse joints at all locations where a width change occurs (at bullnose of median islands, beginning and end of curves, tapers, tangents, curb returns, etc.). Extend these joints through the back of the curb and gutter.
- Add transverse joints beyond and between those added in Step 4. Space joints out evenly between other joints, making sure not to violate the maximum joint spacing.
- Make adjustments for in-pavement objects, fixtures, and to eliminate L shapes, small triangular slabs, etc. Ensure isolation joints are used surrounding all islands.
Diverging Diamond Interchanges (DDI)
Diverging diamond interchanges (DDI) have become increasingly popular in the 2010's, with the first DDI being installed in Springfield, Missouri in 2009 . DDIs are primarily used to help improve traffic flow while improving safety relative to conventional diamond interchanges. This is achieved through eliminating conflict points and eliminating left turns across opposing traffic.
Similarly to concrete intersections and roundabouts, joint layout for DDIs can be challenging due to cross-overs and sharp angles. An 11-step quadrant method has been developed for step-by-step joint layout plans for DDIs.
11-Step Quadrant Method for DDIs
- Draw all pavement edges and back-of-curb lines in plan view.
- Divide the interchange into four quadrants.
- Place a joint in each quadrant when the pavement width changes as you work your way out from the center. Make sure the joint is perpendicular to the direction of travel.
- Lightly draw the circumference-return and taper-return line(s) outside of the central portion defined in Step 3.
- Lightly draw cross road return lines on each side of the central bisecting joint.
- Define paving lanes on the mainline approaches. Do not cross the cross road return lines defined in Step 5.
- Place transverse joints on the mainline approaches.
- Lightly draw cross road return lines for each of the on/off ramps.
- Add longitudinal joints to the on/off ramps.
- Add transverse joints to the on/off ramps.
- Address doglegs and odd shaped panels as possible.
Related Resources and Materials
Webinars (On-Demand Education and Training):
- All About Concrete Pavement Jointing and Load Transfer - Overview and Design
- All About Concrete Pavement Jointing and Load Transfer - Layout
- Intersection Joint Layout (PRINTED) or (PDF)
- Concrete Pavement Field Reference: Pre-Paving (PRINTED)