Thin and Ultra-Thin Overlays

1.List benefits of thin and ultra-thin HMA overlays 2. Describe recommended materials 3. Describe recommended construction procedures 4. List key quality control activities Learning Outcomes

5. Describe potential construction and performance problems 6. Identify troubleshooting solutions Learning Outcomes (continued)

Description: “Thin” overlays —t hickness between 19 and 38 mm (0.75 and 1.50 in) “Ultra-Thin” overlays —t hickness between 10 and 20 mm (0.4 and 0.8 in) Thin vs. Ultra-Thin Overlays

Benefits Improved ride quality Improved surface friction Corrected surface defects Enhanced appearance Sealed surface Reduced splash and spray Balancing the industry

Plant-mixed Three types (based on gradation) Dense-graded Open-graded friction course (OGFC) Stone matrix asphalt (SMA) Thin HMA Overlays Definition THIN

Thin HMA Overlays Advantages Long service life Smooth riding surface Low noise emissions No stone loss No curing time No binder run-off Placed as part of staged construction THIN

Ultra-Thin HMA Overlays Definition Single pass placement Polymer-modified asphalt emulsion tack coat Dense-graded or gap-graded HMA ULTRA- THIN

Ultra-Thin HMA Overlays Advantages Rapid application Excellent adhesion Short, concise construction zone Quick opening to traffic Minimal effects on curb reveal, utilities, and guardrails ULTRA- THIN

Introduction to HMA Materials

Tack coat Aggregates Asphalt binder Additives Thin HMA Overlays Materials THIN

Thin HMA Overlays Aggregate Gradations Dense-GradedOpen-Graded Gap-Graded THIN

Thin HMA Overlays Aggregate Requirements Clean, high quality materials Polish resistant Conventional specifications for dense-graded overlays OGFC and SMA overlays have more stringent requirements Thickness = 2 times maximum aggregate size THIN

Conventional mix design procedures Binder choice influenced by traffic and climate Typically same asphalt grade used in conventional HMA mixtures Thin HMA Overlays Mix Design—Dense-Graded Overlays THIN

Methods vary considerably between states FHWA draindown test Other draindown tests Viscosity-temperature charts Optimum asphalt binder content Thin HMA Overlays Mix Design—Open-Graded Friction Courses THIN

High percentage of mineral filler Stabilizing additives Design procedure available from NAPA Asphalt content > 6% Air void content > 4% Voids in mineral aggregate > 17% Thin HMA Overlays Mix Design—Stone Matrix Asphalt THIN

Polymer-modified asphalt tack coat Aggregates Gap- or dense-graded Thickness = 1.5 times maximum aggregate size Asphalt binder Ultra-Thin HMA Overlays Materials ULTRA- THIN

Binder selection based on: Climate Traffic speed Loading conditions Elastic recovery requirement Compatibility with asphalt emulsion tack coat Ultra-Thin HMA Overlays Mix Design ULTRA- THIN

Thin HMA Overlay Construction THIN

Thin HMA Overlay Construction Process 1.Pre-overlay repair 2.Surface preparation 3.Tack coat application 4.Overlay placement 5.Compaction THIN

Preoverlay Repair and Surface Preparation Repair weak areas Deteriorated cracks Localized distresses Potholes Pavements with extensive distress may not be good candidates Clean surface (airblasting) THIN

Promotes bonding Usually same as for conventional HMA overlays Applied immediately prior to the placement of the overlay Apply uniformly THIN Tack Coat Application

Overlay Placement Conventional HMA paving equipment Continuous paving operation Minimize starts and stops Use material transfer device Effective longitudinal and transverse paving joint construction necessary THIN

Placement Considerations: OGFC and SMA OGFC and SMA mixtures should not be placed in cold weather Use short haul times SMA mixtures may be harsh and sticky immediately behind paver THIN

Compaction Minimal time available for compaction Roll as close to laydown machine as possible Uniform rolling Avoid turning wheels on mat Turn off vibratory system at stop or change in direction THIN

Influencing Factors on Compaction Timing Wind Solar flux Mix temperature Air temperature Pavement temperature THIN

Compaction Timing: MultiCool 3.0 Software THIN

Compaction Timing: MultiCool 3.0 Software THIN

Compaction of OGFC and SMA Layers OGFC No density specifications for OGFC Two to three passes with steel wheeled roller required SMA Rolling immediately behind paver Two or three passes with steel wheeled roller commonly used THIN

Steel-Wheeled Roller THIN

Ultra-Thin HMA Overlay Construction ULTRA- THIN

Ultra-Thin HMA Overlay Construction Process 1.Pre-overlay repair 2.Surface preparation 3.Tack coat application and HMA placement 4.Compaction ULTRA- THIN

Preoverlay Repair and Surface Preparation Repair weak areas Deteriorated cracks Localized distresses Potholes Pavements with extensive distress may not be good candidates Clean surface ULTRA- THIN

Special paving equipment Tack coat and HMA overlay placed at same time Minimized starts and stops Application temperature range: 143 to 165 °C (290 to 330 °F) Tack Coat Application and HMA Placement ULTRA- THIN

Mix Hopper Distributor Screed Ultra-Thin HMA Overlay Paver ULTRA- THIN

Ultra-Thin HMA Overlay Paver Augers ULTRA- THIN

Ultra-Thin HMA Overlay Paver Tack Coat and HMA Application ULTRA- THIN HMA Tack Coat

Compaction Vibratory screed acts as breakdown roller Two passes of a 9-ton (10-T) steel double drum roller Roll immediately after application (static mode) ULTRA- THIN

Compaction ULTRA- THIN

Quality Control Aggregate gradation Asphalt content In-place density Thickness and spread rate of overlay Tack coat application rate (ultra-thin HMA overlay)

NJ’s Thin-Lift Requirements  New Jersey requirements  Thin-lift ≤ 25mm thick (Ideally) – Minimal change to existing infrastructure (bridge clearances, drainage, etc.)  Minimal Impact to Users (Coverage vs Unit Time)  Re-new and upgrade road surface – Ride Quality (Smoothness)  No “Cure-time” dependent materials (i.e. – cold applications) – Typical high ESAL’s limit use

High Performance Thin-Overlay  Focused Applications  Preventative Maintenance – NJDOT – Placed after signs of initial surface distress – Also potential use of “Shim” course on PCC prior to Wearing Course  Pavement Overlay – Locals/Municipalities – Place immediately on surface of pavements showing signs of surface distress with or without milling – Low severity wheelpath alligator cracking (base issues) – Surface cracking with minimal rutting

Cracking Potential Areas of Application Low Severity Wheelpath Low to Mod. Transverse Cracking

Direct Overlay – No Milling Existing Surface Existing Base HPTO

High Performance Thin-Overlay Job Mix Formula Requirements Sieve Size Percent Passing 3/8" 100 # # # # # # # Min. % FAA > 45% (AASHTO T304) Fine aggregate of stone sand (no natural sands) Sand Equivalency > 45% (AASHTO T176)

Asphalt Binder  Polymer-modified binder – PG76-22 (NJDOT Spec)  RTFO Elastic Recovery > 25 o C (AASHTO T301)  Separation Test < 4.5 o C after 4 hrs (ASTM D5976)  Performance Specification  Utilize the Asphalt Pavement Analyzer (AASHTO TP 63) for stability check High Performance Thin-Overlay

Asphalt Pavement Analyzer - AASHTO TP lb wheel load; 100 psi hose pressure - Tested at 64 o C for 8,000 loading cycles - Samples at 5 +/- 0.5% air voids - APA Rutting < 4 mm to PASS

Mixture properties relative to field performance  Permanent Deformation Stability – Asphalt Pavement Analyzer (AASHTO TP63) – Repeated Load Simple Performance (NCHRP Report 465)  Fatigue resistance – Flexural Beam Fatigue (AASHTO T321)  Resistance to PCC Slab Horizontal Movement – Overlay Tester  Dynamic Modulus (AASHTO TP62) – HMA stiffness at various temperature and loading speeds  Permeability – Flexible Wall Permeability (ASTM D5084) HPTO Lab Performance Evaluation

3.3. Rutting Stability – APA

Repeated Load Test – NCHRP Report 465 I4 HD from AC Expressway 54.4 o C 130 o F)

Fatigue Evaluation Flexural Beam Fatigue Device, AASHTO T-321  Tests mix’s ability to withstand repeated bending which causes fatigue failure  Data = number of loading cycles to failure (loss of stiffness)  Run at high level of tensile strain (1000 m-strain) to simulate excessive bending, similar to PCC joints

Fatigue Resistance I4HD from AC Expressway Expressway I-4 Mix =3,354 HPTO =51,636

Fatigue Resistance I5HD from Garden State Parkway I5 HD GSP = 1,390 HPTO = 51,636

Fatigue Resistance NJDOT 12H76 from Rt 31 & I95

Climatic Loading – Horizontal Movement Hot Mix Asphalt Overlaid on PCC PCC Horizontal Tensile Stress due to expansion/Contraction of PCC from Temperature Horizontal Stress/Strain is modeled using Overlay Tester

RUTGERS Time (s) Fixed plate Aluminum plates 150 mm (6 in) Samp le 38 mm (1.5 in) 2 mm (0.08 in) Ram direction Movable plate  Sample size: 6” long by 3” wide by 1.5” high  Loading: Continuously triangular displacement 5 sec loading and 5 sec unloading  Standard Test Conditions (TxDOT) – Opening displacement: in. – Two temperatures: 77 F (TxDOT) and 59 F  Definition of failure – Discontinuity in Load vs Displacement curve – Visible crack on surface RUTGER S Overlay Tester

■ For Mechanistic Design procedures, Dynamic Modulus (E*) is main material input parameter ■ Test method determines the modulus of HMA under various temperatures and loading frequencies Dynamic Modulus Testing

E E+0 Dynamic Modulus Testing HPTO has higher E* at higher temps HPTO has lower E* at lower temps

Flexible Wall Permeability Testing  For Pavement Preservation, important to “seal” pavement to limit moisture  Permeability on order of a silt/clay, required testing in “Flexible Wall” Permeability Set-up Samples cored from 6-inch diameter gyratory sample

Typical Permeability Values nse Graded 3. 15

Thin and Ultra-Thin Overlays QUESTIONS?