Thin Overlays for Pavement Preservation and Functional Rehabilitation

Transcription

1 Thin Overlays for Pavement Preservation and Functional Rehabilitation Gary L. Fitts, P.E. Shell Sulphur Solutions Garden Ridge, Texas Shell Sulphur Solutions

2 What is a Thin Overlay? An HMA application not intended to strengthen the pavement structure Used to address functional problems or for preventive maintenance Surface replacement Mill and fill Defined here as less than 1½ inch compacted thickness Same definition used during SHRP Maintenance Effectiveness Study

3 Applications for Thin HMA Layers Preventive Maintenance Seal, preserve existing pavement structure Functional Rehabilitation Provide optimal functional qualities (smoothness, safety) Interlayer Reduce/delay reflection cracking Leveling course

4 Treatment Performance: There was consensus among all four regional ETG s that the thin overlay treatments have performed best after 5 years

5 Limitations Thin overlay performance depends largely on the condition of the existing pavement Construction quality has a significant effect on performance Smoothness, compaction, bonding

6 Mixture Types Dense-graded Continuous gradation, 2-4% air voids Smaller NMS versions of conventional HMA types #4 (4.75 mm), 3/8 (12.5 mm) NMS Gap-graded SMA Novachip Open-graded OGFC/PFC

7 Mixture Design Criteria, Thin HMA Overlays Little or no truck traffic N des = 50, %G N ini 91.5% Collectors, light arterials N des = 75, %G N ini 90.5% Arterials, most highways in or near urban areas N des = 75, %G N ini 89.0%

8 Ohio DOT, Section 424 Fine Graded Polymer Asphalt Concrete 24.htm

9 A.K.A Smoothseal Ohio DOT, Section 424 Fine Graded Polymer Modified Asphalt Concrete Formulated specifically for preventive maintenance/ thin overlay application, placed 3/4 to 1 inch thick, Two mixture types: Type A, for medium traffic and urban applications P b = 8.5%, PG 76-22M Type B, for any and all applications including heavy traffic VMA > 15.0% P b > 6.4% P a = 4.0% Aggregates must be at least 50% SiO 2

10 Smoothseal-Advantages Advantages of Smoothseal as a preservation treatment: Protection from damage due to climate and wear (esp. snowplows) Correct minor surface defects Improve ride quality and appearance Can improve cross slope and drainage Provide longer more cost effective service life Not a proprietary product

11 Smoothseal-Candidate Pavements Only superficial distress Dry looking or bony surfaces that may be permeable Raveled Polished aggregate surface Shrinkage/block cracking too fine for crack sealing (< ¼ inch wide)

12 Smoothseal-Construction Conventional production, paving equipment Surface needs to be clean and dry 60 degree min air temp At 60 degrees, less than 10 minutes available to compact Static rolling ONLY Either butt joints or hot longitudinal joints Avoid handwork Consider conventional mixes for drives and approaches

13 TxDOT Crack Attenuating Mixture (CAM) Initially developed as an interlayer to delay reflection cracking Primarily for overlays of concrete pavement in the Houston area Observed excellent performance over extended periods before a new surface was placed I-45, Galveston Interest in using CAM in a similar way as Ohio s Smoothseal Industry/TxDOT tour of Ohio in summer 2007 Used in at least 13 TxDOT Districts Statewide Special Specification 3165 effective January 2009

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15 CAM Gradation Requirements High VMA/high asphalt content required Other mixture criteria depend on whether it is used as a surface course or as an interlayer

16 CAM Mixture Design Requirements

17 FHWA/TX-08/

18 Novachip = Thin Overlay w/ Glue Seals existing pavement Glues thin lift Seals low severity Cracks -< ¼ Courtesy, Chris Abadie

19 Thin Bonded Wearing Course US 281, San Antonio-11 years old

20 Overspray protection Courtesy, Chris Abadie

21 Ultrathin Wearing Course Improvement in Ride Quality IRI Before IRI After Avg IRI Before = 143 (fair) Avg IRI after = 88 (good) Courtesy, Chris Abadie

22 Ultrathin Wearing Course Average Smoothness Improvement Actual IRI reduction % Improvement Avg reduction in IRI = 55 in/mi Avg % reduction = 37% Courtesy, Chris Abadie

23 Predicted Condition of Highways with Thin Overlay Preservation Investment of $175 million / year POOR TO V.P FAIR GOOD EXCELLENT Courtesy, Chris Abadie

24 Other Thin Overlay Applications OGFC/PFC Particularly effective where wet-weather accidents and traffic noise are problems Improvements in materials (polymer-modified asphalts, better placement techniques, more open gradations) have improved the life and effectiveness Widespread use in Alabama, Georgia, Texas Harris County Toll Road Authority (HCTRA) to upgrade 4 miles of rough, noisy CRCP on Sam Houston Toll Road this spring! The future-warm Mix Asphalt Technologies Made to order for thin lift overlays

25 Obrigado!