Thin Hot Mix Asphalt Overlays PennDOT Research Findings Pennsylvania Asphalt Pavement Association 53rd Annual Asphalt Paving Conference Hershey, PA December 12, 2012

Thin Overlay Development Back Ground- NEPPP: Smooth Seal in Ohio, THMAO in NY PAPA Technical Sub Committee Created draft specification 6.3mm PG 76-22, Polymer Modified, 75 Gyration mix Research Project approved

Special Provision 6.3 mm – 100% passing 3/8 in. Dense –graded ( 6 sieve sizes) - SRL PG 76-22 polymer modified N design = 75 gyrations Design voids = 4.0% Min. VMA = 16.5 No RAP or RAS Greater than 50 F Optimum Rolling Pattern

Use Guidelines Only on structurally sound pavement Same as micro-surfacing For correcting surface distresses only Consider grinding PCC first

Tack Coat Specification SS – 1h or CSS – 1h RS – 1h or CRS – 1h 60% min residue Low pen (40-90) asphalt residue 0.05-0.06 gal/sy rate.

Mix Design – Hempt Bros. 6 trial blends to get minimum VMA Component materials -baghouse fines ( 1.9%) -Toland Conc sand Type A, SRL-E (39.4%) -Toland ¼ in. SRL-E - 4.0% passing #200 - 43% passing #8 - NuStar PG 76-22 binder (6.7%)

Mix Design (cont’d) Volumetrics - N design : 75 gyrations - design voids: 4.0% - VMA: 17.1% - VFA: 77% - TSR: 83% (without antistrip)

Placed at 1 inch thickness 6.3 mm NMAS Mix Placed at 1 inch thickness Aggregate: Sandstone, Skid Resistance Level (SRL): E Polymer Modified Binder: PG 76-22 Gyration Level: 75 Design Air Void: 4%, Design VMA: 17.1 Design Binder Content: 6.7% NO RAP

Construction All night work 1/3 mile of four lanes (612 tons) Including intersection and turn lane 1 in thick overlay on diamond ground PCC CSS-1h tack coat 0.06 gal/sy tack application rate

Performance Evaluation - HWTD Good Performance

Performance Evaluation – Overlay Tester Test Temperature: 25ºC # of load cycles: 1200 Or until load reduced to 93% of original Repeated loading (triangular form) under constant deformation Deformation magnitude per load cycle: 0.025 inches (0.6 mm) Duration of each load cycle: 10 seconds

Performance Evaluation – Overlay Tester Cycles to failure > 500 High variability in data Good Performance

Tack Coat Evaluation Notice Displacement of the Asphalt Layer

Tack Coat Evaluation Shear Strength = 44.5 psi (307 KPa) - Good Performance

Emulsion Tack Coat Application

Smooth Mat Right Behind The Paver

Mat Temperature Data is courtesy of Mr. Garry Hoffman

Core Densities

Friction Improvement Data: Courtesy of PennDOT BOMO

Ride Quality (Smoothness) Improvement Data: Courtesy of PennDOT BOMO

Summary/Findings Good Mix Lab Performance Permanent Deformation (SST) Rutting and Moisture Resistance (HWTD) Crack Resistance (Overly Test) Good Tack Shear Resistance Improved Ride and Friction In-Place Average Density: 92.2% (based on 9 cores) (Cores from Test Strip Only) Could be better if compaction finished at higher temperature? Mat Temperature After Placement: 280-315ºF Rapid Mat Cooling No Apparent Segregation Coring Not A Problem

Conclusions Thin Overlays for Pavement Preservation Improved Ride Quality Improved Friction Maintained Road Geometrics Reduced Noise Reduce Life Cycle Costs Provide Long Lasting Service Place before extensive rehab required according to use guidelines Expected performance 10 years on asphalt 6 or more on PCC Thin overlays for pavement preservation are popular due to a number of advantages that have been discussed throughout this presentation. Some of them include better smoothness, reduced surface distress, geometric considerations, noise reduction, lower life cycle cost, and long-lasting performance. It is best to apply a thin asphalt overlay before extensive rehabilitation is required. This will maximize the performance and minimize the cost. Thin asphalt overlays can be expected to perform 10 or more years on an existing asphalt pavement and from 6 to 10 years on an existing concrete pavement.

Thin HMA Overlays Thin HMA overlays are an added solution to pavement preservation. They are economical, long-lasting, and effective in treating a wide variety of surface distresses to restore ride quality, skid resistance, and overall performance.