INDOT Thin Concrete Overlay Initiatives. Tommy E. Nantung INDOT Division of Research and Development

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1 INDOT Thin Concrete Overlay Initiatives Tommy E. Nantung INDOT Division of Research and Development

2 System of Concrete Overlays Thinner Concrete Overlays Thicker Bonded Overlay System Unbonded Overlay System Bonded Concrete Overlay of Concrete Pavements Bonded Concrete Overlay of Asphalt Pavements Bonded Concrete Overlay of Composite Pavements Unbonded Concrete Overlay of Concrete Pavements Unbonded Concrete Overlay of Asphalt Pavements Unbonded Concrete Overlay of Composite Pavements Bond is integral to design Old pavement is base

3 Overlay Solutions for Rehabilitation and Maintenance

4 Uses and Advantages- Bonded Overlay of Asphalt or Composite Pavements 2 5 thickness Use when existing pavement is in fair or better structural condition with surface distress. Use to eliminate any surface defects; increase structural capacity; and improve surface friction, noise, and ride. Where increased traffic requires more structural capacity. Where vertical clearances are needed.

5 Pavement Candidates

6 Bonded Concrete Overlay of Asphalt Pavements Spots of distress that aren t visible can be determined through evaluation such as the stiffness of the asphalt pavement and subgrade support conditions. Localized areas of weakness can be strengthen through patching. Milling can remove a number of asphalt surface distresses. CONCRETE RESURFACING OF ASPHALT PAVEMENTS

7 Bonded over Asphalt/Composite Keys to Success Bonding is critical Small square panels reduce curling, warping, & shear stresses in bond (1.5 times thickness). Mill if necessary to correct crown, remove surface distresses, improve bonding. Be sure to leave 3 of HMA after milling. HMA surface temperature below 120 F before paving. Transverse joints must be sawed D/3 Joints in the overlay should not be placed in wheel paths, if possible Application of curing compound or curing methods must be timely and thorough

8 Milling The three main objectives of milling: to remove significant surface distortions that contain soft asphalt material; to reduce high spots to help ensure minimum resurfacing depth and reduce the quantity of concrete needed to fill low spots; to roughen a portion of the surface to enhance bond development between the new concrete overlay and the existing asphalt. (don t leave a thin lift)

9 Milling Direct placement without milling is recommended when rutting in the existing asphalt pavement does not exceed 2. Any ruts in the existing pavement are filled with concrete, resulting in a thicker concrete overlay above the ruts. A minimum of 3" 4" of asphalt should be left after milling because of the reliance on the asphalt pavement to carry a portion of the load. Page 15

10 Design of Thin Concrete Overlay Pavement Evaluation Structural Design Joint Design Pavement Type Reinforcement Design Mix Design Drainage

11 Pavement Evaluation Condition survey Deflection testing Coring

12 Thin Concrete Overlay Thin slabs 4 to 6 inches Short joint spacing 4 to 6 feet Bonded to existing HMA to increase loadcarrying capacity

13 Effect of Joint Spacing on UTW and BCOA 2 ft 2 ft 2 ft 9 ft Stresses Short Joint Spacing (slabs vertically deflect under loading) Stresses Conventional Joint Spacing (slabs bend under loading)

14 Structural Design Interim procedure available for determining load-carrying capacity Accounts for bonding of PCC to HMA Inputs: Traffic (ESALs) Post milling thickness PCC strength and Modulus Composite k-value (Modulus of Subgrade Reaction) % slab cracked Joint spacing

15 BCOA-ME Software

16 Illinois Thickness Inputs

17 Illinois DOT Thickness Catalog

18 INDOT Design Principle Jurisprudence from AASHTO 1993

19 INDOT Design Principle SNeff (after milling 3 inches) = x 0.3 = 4.78 Layer Coefficient of old HMA = 0.3

20 INDOT Design Concrete Overlay Thickness Effective Structural Number (From FWD) < 1 million ESALs 1 to 3 million ESALs 3 to 5 million ESALs 5 to 10 million ESALs * >

21 Joint Design Generally follows conventional PCC pavement jointing practices Joint spacing 4 x 4 feet or 6 x 6 feet Load transfer JPCP: Dowel if > 4-5 million ESALs

22 Joint Design

23 Preoverlay Repairs Localized repair of failed areas Repair/Filling of potholes Milling for bonding purposes and removal of rutting Repair of severe alligator cracking if poor support would otherwise result Goal: Uniform support

24 Preoverlay Repair?

25 Thermal Cracking

26 Surface Preparation Purpose Address distortions Correct surface profile Three common methods: Milling, maintain 3 to 4 inches of asphalt layer Don t be too close to the stripped layer

27 Thickened Edge Transition Traffic h Existing HMA Pavement PCC Overlay 2 m h + 75 mm Existing HMA Pavement Base or Subgrade

28 Example Transition Section Existing HMA pavement PCC overlay Transition length 300 feet typical Milled existing HMA pavement Reconstruction section with increased thickness to account for reduced support

29 Performance Good to excellent performance Extensive use in Illinois, Michigan, Nebraska, Utah, Nevada, California, Texas Some partial bonding occurs which may contribute to performance Uniform support and effective joint design required