Design and Jointing of Concrete Roundabouts 2009 PCCP Workshop & Expo January 27, 2009 Robert Rodden Director of Technical Services Why a Roundabout? According to FHWA: Up to 90% reduction in fatalities 76% reduction in injury crashes 30-40% reduction in pedestrian crashes 75% fewer conflict points than 4-way intersections 30-50% increase in traffic capacity No signal equipment to install/maintain No left-turn lane and reduced need for storage lanes Design of Concrete Roundabouts Thickness Design Joint Design Layout Locations Allow Adjustment in the Field Construction Design and Jointing of Concrete Roundabouts WHY CONCRETE? Why Concrete Roundabouts? Let’s ask a couple questions… 1. Where do we historically use concrete pavement? (situations, traffic conditions, applications, etc.) 2. What performance characteristics of concrete pavement make it the best choice for roundabouts? Where are Concrete Pavements Historically Used? Answers: High traffic areas Areas with lots of turning movements Situations where we need a “long-term fix” Situations where future maintenance must be kept to an absolute minimum Areas where future disruption to traffic must be kept to a minimum Areas where safety is a priority Why Concrete for Roundabouts? Answers: Long service life Minimal maintenance requirements Resistance to surface deformation Doesn’t rut or shove Maintains surface/drainage characteristics No future overlays required (grade issues) Ease of construction (constructability) Roundabouts typically hand placed but some have been constructed with slipform paving machines Why Concrete (cont.) Answers: Superior safety aspects Drainage Skid resistance Lighting More aesthetically pleasing Faster construction Economical over long-term (LCC) Why Concrete Roundabouts? Concrete is the perfect material for roundabout applications. Design and Jointing of Concrete Roundabouts THICKNESS DESIGN Pavement Thickness Design AASHTO 1993 Pavement Design Guide Most commonly used by state DOTs New Mechanistic-Empirical Pavement Design Guide Under calibration/implementation in many states ACPA (PCA) StreetPave software: http://www.pavement.com/streetpave/ MUST CONSIDER CUMULATIVE TRAFFIC!! Concrete Intersections: Thickness Physical Area Functional Area Concrete Intersections: Thickness Physical Area Functional Area Physical Area Roadway 1 Roadway 2 Thickness Low ADTT (T1) Low ADTT (T2) T2 Low ADTT (T1) High ADTT (T3) T3 High ADTT (T3) High ADTT (T3) T3 + 0.5 to 1 in. T3>T2>T1 Design and Jointing of Concrete Roundabouts JOINTING ROUNDABOUTS Jointing Decide on joint layout philosophy Like normal intersection Isolate circle from legs Pave-through, isolate two legs Other philosophy, based on experience Follow 6-step method Joints in circular portion radiate from center Joints in legs are normal (perpendicular) Layout Joints as Normal Good for small roundabouts or traffic circles? Proper Jointing of Roundabouts Concrete Roundabout Jointing Develop a jointing plan Bird’s eye view Remember rules Follow the steps Be practical! Rules for Joint Layout Things to Do Match existing joints or cracks – location AND type! Cut joints at the proper time Place joints to meet in-pavement structures Remember maximum joint spacing Place isolation joints where needed Understand that joint locations can be adjusted in the field! Be Practical Location Type Rules for Joint Layout Things to Avoid: Slabs < 2 ft wide Slabs > 15 ft wide Angles < 60º (90º is best) Dog-leg joints through curve radius points Creating interior corners Odd Shapes (keep slabs near- square or pie-shaped) Recommended Maximum Joint Spacing ML = T x Cs ML = Maximum length between joints (in.) T = Slab thickness (in.) Cs = Support constant Use 24 for subgrades or unstabilized [granular] subbases; Use 21 for stabilized subbases (ATB, CTB, lean concrete) or existing concrete or asphalt pavement; Use 12 to 15 for thin bonded overlays on asphalt Joint Spacing Recommendations For Streets, Roads, and Highways: Use ML = T x Cs Keep ratio of transverse to longitudinal spacing at less than 1.5 Keep maximum spacing of transverse joints to 15 ft for plain concrete unless local history shows longer panels work What About Load Transfer? Aggregate Interlock Maximum aggregate size is important Mechanical connection Dowel bars Tiebars Subbase support Dowel Bar Recommendations Pavement Thickness Dowel Diameter Less than 7.0 in. None 7.0 – 7.9 in. 1 in. 8.0 – 9.9 in. 1-1/4 in. Greater than 10.0 in. 1-1/2 in. Design and Jointing of Concrete Roundabouts 6-STEP METHOD FOR JOINTING ROUNDABOUTS Jointing a Roundabout Step 1: Draw all pavement edges and back-of-curb lines in plan view. Jointing a Roundabout Step 2: Draw all lane lines on the legs and in the circular portion, accounting for roundabout type. Jointing a Roundabout Step 3: Add “transverse” joints in the circle, being mindful of the maximum joint spacing. Jointing a Roundabout Step 4: On the legs, add transverse joints where width changes occur. Jointing a Roundabout Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing. Doglegs Layout Joints as Normal Good for small roundabouts or traffic circles? Jointing a Roundabout Step 5: Add transverse joints between those added in Step 4, minding the maximum joint spacing. Jointing a Roundabout Step 6: Make adjustments for in-pavement objects, fixtures, and to eliminate odd shaped slabs. …And Box Out Fixtures Properly! If You DO Box Out Properly… If You DON’T Box Out Properly… Good Practice… What If I Have to Dead-end a Joint? What If I Have to Dead-end a Joint? What If I Have to Dead-end a Joint? Design and Jointing of Concrete Roundabouts EXAMPLE IN KANSAS 110th Street & Lamar Avenue Overland Park, Kansas 110th Street & Lamar Avenue Overland Park, Kansas 110th Street & Lamar Avenue Overland Park, Kansas Properly Jointed Roundabout Properly Jointed Roundabout Rough Grading Grading of Subgrade Subbase & Curb Const. Curb Placement – Widened Gutter Field Joint Layout Plan Inner Pavement Ring Formed Inner Pavement Ring Formed Dowel Basket Placement Start Concrete Placement Hand Placement with Roller Screed Hand Finishing Half Way Done! Outer Ring… Outer Ring… Outer Ring… Outer Ring… 1 inch Isolation Joint Approach Lanes… Approach Lane Sequence Finishing Approach Lanes Open to Traffic! Another Kansas Example… More Information? “Concrete Pavement Field Reference,” EB237P, ACPA, 2007. “Concrete Roundabouts: Rigid Pavement Well-Suited to Increasingly Popular Intersection Type, “ R&T Update #6.03, ACPA, June 2005. “Roundabouts: An Informational Guide,” FHWA-RD-00-068, FHWA, March 2000. “Kansas Roundabout Guide”: http://www.ksdot.org/burTrafficEng/Roundabouts/Roundabout_Gui de/RoundaboutGuide.asp Various agency standards…KS, WI, IA, OH, etc… Questions? Robert Rodden [email protected].