Introduction to Thin Maintenance Overlays What are thin maintenance overlays ? Why use thin maintenance overlays ? When to use thin maintenance overlays ? Where to use thin maintenance overlays ?
What Are Thin Maintenance Overlays? Defined as thin treatment using a hot mix system Non-structural layer Applied as a maintenance treatment (corrective or preventive) Thickness: Caltrans: 1.2 in (30 mm) Nationally: less than 1½ in (37.5mm)
a) Dense Gradedb) Gap Gradedc) Open Graded What Are Thin Maintenance Overlays?
Restores the surface conditions (smoothness, noise, and skid) Improves the appearance of the roadway Extends the life of the pavement Why Use Thin Overlays?
When to Use? Structurally sound pavement Rut depth < 1/2” Minor cracking cracking Minor to moderate bleeding Raveled surface I-77 Columbia, SC Dry, Oxidized, Slightly Rutted Pavement, 60,000 ADT
High Severity Alligator Cracking When NOT to use! Poor Candidates High Severity Block Cracking Rutting >1/2” High Severity “D” Cracking
Where to Use? As a surface treatment over asphalt concrete pavements and on portland cement concrete pavements Over structurally sound pavements Oxidation Reduction: Successfully used as a protection layer to prevent asphalt aging in the main structural layers. Mitigation of Cracking: Thin Overlays can be used to mitigate cracking. Dense-graded overlays required a SAMI or fabric interlayer. Skid Resistance: Use in sections with poor frictional properties. A skid test should be conducted to determine the existing coefficient of friction of the pavement surface (CT 342).
Where to Use? Open- and Gap-Graded Overlays Wet Weather Accidents: Use in sections with high frequency of wet weather accidents or when recommended to minimize wet weather accident occurrences.
End Overview Begin Project Design, Materials & Specifications
Factors to Consider When Choosing a Maintenance Treatment Will the treatment address the distresses present? (i.e., Will it work?) Can the required preparation for the treatment be carried out? Is the treatment affordable and cost effective? Will the treatment be performed before the situation being addressed changes?
Three Basic Steps In The Selection Process 1. Assess the existing conditions. 2. Determine the feasible treatment options. 3. Analyze and compare the feasible options with each other.
Initial Site Assessment – Distress Identification Types of Distresses and Definitions Definitions from Caltrans Pavement condition survey manual or the FHWA“DISTRESS IDENTIFICATION MANUAL for the Long-Term Pavement Performance Program” PUBLICATION NO. FHWA-RD JUNE 2003
Caltrans Maintenance Treatment Matrix MTAG Chapter 3 Figure 3-3 Rutting Treatment Raveling Oxidation Bleeding <1/2" >1/2" Urban Rural Slurry Seals Type II (Note 1) FGNNNGG Type III GNFNGG Chip Seal PME - Med. Fine GGNFNPG PME - Medium GGNFNPG PMA -Medium (Note 3.) GGNFNPG PMA - Coarse (Note 3.) GGNFNPG AR - Medium GGNFNPG AR - Coarse GGNFNPG
Distress Types and Levels that can be addressed by Thin Overlays Perform Visual Site Inspection. Identify types, quantity and levels of distress For example on a 2 lane highway (Route xxx from PM 0.0 to PM 10.8)with <30,000 ADT: 10% Alligator B Cracking Minor Transverse Cracking An area of isolated base failure 1000 ft x 4 ft Heavy raveling and oxidation Rutting < ½”
DISTRESS AND APPLICATION CONSIDERATIONS TMO is a viable application for treating structurally sound, worn pavements Cracking Patching/ Potholes Surface Deformation Surface Defects 1.Longitudinal & Transverse (Medium) 2.Block (Moderate) 3.Edge (Moderate) Patches: Moderate Potholes: Moderate Rutting: <0.5 in (12.5 mm) Shoving: No Bleeding Moderate Polished Agg: OK Raveling: Severe
Other Application Considerations Traffic Control Safety Night Work Returns/Hand Work Turn Pockets Milling Job Quantities Prep Work Required Quick return to traffic- Reduced Work Zone Time (Workers’ Safety) Noise Reduction- Open/Gap Graded Mix Night Work- Min Temp 45º F (More working days) Reduced Backspray- Open/Gap Graded Mix High Volume Roadways- Faster Paving Process (Get In- Get Out)
Mobilization Typical Asphalt Paving Rubberized Asphalt Binder will require additional equipment for its production On-site Staging Required – Area for Tanker and Distributor exchange
Typical Materials Items Asphalt Concrete Tons Use maximum lbs/SY for selected aggregate size 3/8” PMA OG or GG (9.5mm) = 85 lbs/SY ½” PMA OG or GG (12.5mm) = 100 lbs/SY 3/8” AR OG of GG (9.5mm) = 85 lbs/SY Emulsion Tons Use 0.2 gallons/SY for emulsion application
Quantity Calculations Lane Mile (LM) (Centerline to Fog Line) 5280 ft x 12 ft = 63,360 SF = 7040 SY When calculating quantities, application should extend beyond fog line Shoulder quantities need to be calculated independently Shoulder application may vary from mainline application Typical Shoulder calculation: 3 ft wide x 5280 ft length = 15,840 SF = 1760 SY Typical 2 Lane Roadway Calculation (2 x 7040) + (2 x 1760) = 17,600 SY
When calculating quantities for each application use highest application rate per SY for estimate purposes Example: Specification Spreading of screenings for chip seal application. Range is lb per SY. Use 20 lb for estimating quantities Quantity Calculations
Production Rates and Paving Days Production Rate Mainline Paving tons per hour Returns/Turnpockets tons per hour (# of Paving Days) Minimum 5 days to make cost effective
Roadway Geometry and Widths Urban Milling contour edge grind required to match curb and gutter and existing pavement Drainage Minimal water trapped against curb due to emulsion filling void structure and thin lift Less water intrusion to pavement interface due to emulsion membrane Rural Cross-slopes Shoulder Generally best used for Travel Lane with 1 foot beyond fog line For Grade differential greater than 2% from Mainline to Shoulder, the shoulder must be paved separately in order to maintain the grade Edge drop-off will be less than ¾” (consider bicycle traffic material can not be feather down lower then top size agg.) Varying Width Typical Paving machine width 8-14 feet variable
Traffic Control Typical release to traffic minutes behind paver Multi-lane highways, consider moving lane closure Two-lane roadways ½ to ¾ mile closure Thinner lift allows faster production
Miscellaneous Items Edge grinding Crack seal hot applied min one month prior Patching - hot mix only, cold mix continues to rut Utilities – Adjustments most likely necessary Loops may need to be replaced if doing edge grinding Dig Outs – Prior to paving Signing and Striping
PG Grade Specs Binder Climatic Region Conventional AsphaltRubberized Asphalt Open Graded Gap Graded Open Graded PGPBA (1) PG South Coast Central Coast Inland Valleys a North Coast64-16 Low Mountain South Mountain High Mountain High Desert Desert70-106a (mod)64-16
Polymer Modified Binders Maintenance Technical Advisory Guide Chapter 8 Page 2 Binder Grade General Climatic RegionCriteria GGB1 (PG ) Desert or Hot Valley Areas and Coastal Areas Areas below 1,050 m (3,445 ft) elevation with average 7-day maximum and 1-day minimum pavement temperatures between 70 C and -22 C (158 F and -8 F), respectively. GGB2 (PG ) Coastal Areas Areas below 1,050 m (3,445 ft) elevation with average 7-day maximum and 1-day minimum pavement temperatures between 64 C and -22 C (147 F and -8 F), respectively. GGB3 (PG ) Cool Coastal or Mountain Areas Areas below 1,500 m (4,920 ft) and above 1,050 m (3,445 ft) elevation with average 7-day maximum and 1-day minimum pavement temperatures between 64 C and -28 C (147 F and - 18 F), respectively. GGB4 (PG ) Mountain Areas Areas above 1,500 m (4,920 ft) elevation with average 7-day maximum and 1-day minimum pavement temperatures between 58 C and -34 C (136 F and -29 F), respectively.
Polymer Modified Binder Testing Specification DesignationTest Method GGB Grades 1234 Flash Point, Cleveland Open Cup, ˚C, min., original binder AASHTO T48230 Brookfield Viscosity, max. 2.0 Pa s test temperature, ˚CASTM D Elastic Recovery after RTFO test % minAASHTO T Mass Loss after RTFO test, % maxAASHTO T Dynamic Shear, G*/sin˚, min. 2.2 kPa RTFO aged residue, test temperature at 10 rad/sec, ˚C California Test 381 Part Residue from PAV, test temperature, ˚CAASHTO TP Creep Stiffness, 300 MPa, Max. and M-value, 0.30, Min. residue from PAV, test temperature ˚C AASHTO TP Report Only Dynamic Shear, SSD > 30 x (0.6 + SSV)3 original binder, ˚C California Test 381 Part 1 25 Dynamic Shear, SSD > -115 x (SSV) On PAV aged residue, from AASHTO PP1, ˚C California Test 381 Part 1 25 Maintenance Technical Advisory Guide Chapter 8 Page 3
Rubberized Binders A paving asphalt blended with a crumb rubber modifier Shall conform to : SSP (Type G) SSP (Type D-MD) SSP (Type G-MB) SSP (Type D) SSP (Type O)
Aggregate Gradations with PMA Aggregate Gradations Dense Graded: ¾” Maximum, Coarse and Medium ½” Maximum, Coarse and Medium 3/8” Maximum No. 4 Maximum Open Graded ½” Maximum 3/8” Maximum
Aggregate Gradations with PMA Aggregate Gradations Gap Graded: ¾” Maximum ½” Maximum
¾” Gradation Table for Gap Graded Overlays Aggregate Grading Requirements Percentage Passing, ¾ inch Maximum Sieve Sizes Limits of Proposed Gradation Operating Range Contract Compliance 1” (25 mm)—100 ¾” (19 mm)— 90 ‑ ½” (12.5 mm)83-87 X5X5X7X7 3/8” (9.5 mm)65-70 X5X5X7X7 No 4 (4.75 mm)33-37 X5X5X7X7 No 8 (2.36 mm)18-22 X4X4X5X5 No 30 (600 µm)8-12 X4X4X5X5 No 200 (75 µm)—2-70-8
Aggregate Physical Properties Polymer Modified Asphalt Test California Test Asphalt Concrete Type Open Graded Asphalt Concrete AB Percentage of Crushed Particles: Coarse Aggregate (Min.) Fine Aggregate Passing No 4, Retained on No 8 (Min) % 70% 25% 20% 90% Los Angeles Rattler: Loss at 100 Rev. (Max) Loss at 500 Rev. (Max) % 45% - 50% 10% 40% Sand Equivalent: Contract Compliance (Min) Operating Range (Min) Film stripping (Max) % K c Factor (Max) K f Factor (Max)
Aggregate for use with Rubberized Asphalt Concrete The aggregate for rubberized asphalt concrete (Type O) shall conform to the 9.5 mm maximum grading conforming to the provisions in Section 39 ‑ 2.02, "Aggregate," of the Standard Specifications. The aggregate for rubberized asphalt concrete (Type O) shall be lime treated in conformance with the specifications.
Gap Graded AR Aggregate Grading Requirements PERCENTAGE PASSING, ½” (12.5 MM) MAXIMUM Sieve Size Limits of Proposed Gradation Operating Range Contract Compliance 19 ‑ mm — ‑ mm — ‑ mm 83-87X±5X± ‑ mm 33-37X±5X± ‑ mm 18-22X±4X±5 600 ‑ µm 8-12X±4X±5 75 ‑ µm —2-70-8
AGGREGATE The aggregate for Type G rubberized asphalt concrete shall conform to the following grading and shall meet the quality provisions specified for Type A asphalt concrete in Section 39 ‑ 2.02, "Aggregate," of the Standard Specifications, except as follows: A. California Test 211, Los Angeles Rattler loss at 500 revolutions shall be 40 percent maximum. B.California Test 205, Section D, definition of a crushed particle is revised as follows: "A particle having 2 or more fresh mechanically fractured faces shall be considered a crushed particle." C.The swell and moisture vapor susceptibility requirements shall not apply. The symbol "X" in the following table is the gradation which the Contractor proposes to furnish for the specific sieve. Aggregate Physical Properties For Rubberized Gap Graded Mix
Open Graded Aggregate Gradations with AR or PMA Ref: Caltrans Standard Specifications 2006 Section 39 Page 282 Gradation, Maximum 12.5 mm (½ inch) PERCENTAGE PASSING, 12.5 MM MAXIMUM Sieve Sizes Limits of Proposed Gradation Operating Range Contract Compliance ¾” (19 mm)—100 ½” (12.5 mm)— 95 ‑ /8” (9.5 mm)78-89 X4X4X7X7 No. 4 (4.75 mm) 28 ‑ 37 X4X4X7X7 No. 8 (2.36 mm)7-18 X4X4X5X5 No. 16 (1.18 mm)— No. 200 (75 µm)—0-30-4
Open Graded Aggregate Gradations with AR or PMA Gradation, Maximum 9.5 mm ( 3 / 8 inch) (1) PERCENTAGE PASSING, 9.5 MM MAXIMUM Sieve SizesLimits of Proposed Gradation Operating Range Contract Compliance ½” (12.5 mm)—100 3/8” (9.5 mm)— 90 ‑ No. 4 (4.75 mm) 29 ‑ 36 X4X4X7X7 No. 8 (2.36 mm)7-18 X4X4X5X5 No. 16 (1.18 mm)— No. 200 (75 µm)— Ref: Caltrans Standard Specifications 2006 Section 39 Page 282
Mix Design for Polymer Modified HMA The performance of a bonded wearing course depends on the quality of the materials and how they interact during application, rolling and after opening to traffic. The amount of polymer modified asphalt binder to be mixed with the aggregate for gap-graded polymer modified asphalt concrete shall be determined by the Contractor using Asphalt Institute MS 2 Table 6.1.
Rubberized Type O Mix Design The amount of asphalt ‑ rubber binder to be mixed with the aggregate for rubberized asphalt concrete (Type O) shall be determined by California Test 368 with the following exceptions: The aggregate shall be mixed with PG paving asphalt and the optimum bitumen content shall be determined in conformance with the test procedure. The optimum binder content for rubberized asphalt concrete Type O shall then be determined using the following formula: OBC2 = (OBC1) x 1.20 where: OBC1 = Optimum bitumen content using Pg paving asphalt OBC2 = Optimum bitumen content using asphalt ‑ rubber binder
Rubberized Gap -Graded Mix Design SCOTT METCALF TO SUPPLY!!!!!
End Project Design, Materials & Specifications Begin Construction Inspection
Construction and Inspection From… Maintenance Technical Advisory Guide (MTAG) Module 10-2
Topics to be covered Understand/Review Specifications Safety and Traffic Control SWPPP Surface Preparation Equipment Requirements Calibrations Approved Mix design Sampling and Testing Binder Mix Emulsion Mix Production and Handling Required Application Conditions Application of Materials Production Rates Roadway Geometry and Paving Widths Application Problems and Solutions
Understand/Review Specifications Review Construction Manual Chapter 4 Section 94 emulsion (emulsion membrane) Section 39 Asphalt Concrete (mix and placement) Review RE file notes Project special provisions
Safety and Traffic Control Traffic control is required both for the safety of the traveling public and the personnel performing the work. It is also used to ensure the new surface is compacted and allowed to cool to below 70°C (158°F) prior to reopening the surface to traffic. Traffic control includes placing construction signs, construction cones and/or barricades, flag personnel, and pilot cars required to direct traffic clear of the maintenance operation.
Traffic Control Typical release to traffic minutes behind paver Multi-lane highways, consider moving lane closure Two-lane roadways ½ to ¾ mile closure Thinner lift allows faster production Emulsion Membrane eliminates need for Tack Coat
OPENING TO TRAFFIC Traffic can be allowed onto the new surface once rolling is completed and the mix temperature has fallen below 70°C (158°F). Typically, no post sweeping is required unless the mix begins to ravel.
SWPPP Review the storm water requirements for the project. Any questions should be directed to the construction storm water coordinator.
Surface Preparation Cracks greater than 6 mm wide (1/4 in) should be filled or sealed prior to application The use of over-banding methods of crack sealing is not recommended for this treatment Manhole covers, drains, grates, catch basins, and other utility services must be covered prior to application with roofing paper or equivalent Any surface irregularities deeper than 25 mm (1 in) should be filled with dense graded hot mix before applying the mix. Prior to application, the pavement should be swept with a rotary broom equipped with metal or nylon broom stock.
CRACK PREPARATION & MATERIAL APPLICATION PROCESS Sterilize Weeds 3 weeks prior Remove Weeds Grind out weeds Blow out Cracks (If moisture exists) Heat Lance cracks to remove moisture Material Application Apply sealer in cracks
Preparation Milled Joints Beware of Quarter Crown Issues transverse cuts should be 2X paving depth Consider hot-mix tapers
Construction Entrance Not Swept Prior to Mix Application
Miscellaneous Items Edge grinding Crack seal hot applied min one month prior Patching - hot mix only, cold mix continues to rut Utilities – Adjustments Loops Dig Outs – Prior to paving Signing and Striping
Equipment Requirements The most significant requirement is that the binder application and hot mix spreading function are combined into a single unit. HMA Membrane
Spray Paver Calibration Procedure 1. Once proper nozzles sizes have been selected, make sure all nozzles are clean and working. 2. Measure pad width and length to the nearest 0.1 of an inch and record. 3. Weigh calibration pads to the nearest 0.1g and record. 4. Place plastic container on balance. Either record the weight of the plastic container or zero out the weight of the plastic container. 5. Place calibration pads a minimum of 5 feet in front of the emulsion spray bar in the direction of travel. Use two calibration pads to get an average representative distribution. Place the second pad a minimum of 1 foot behind the first pad. 6. Make sure the emulsion pump and bar pressure is set to optimal manufactures operating range.
Spray Paver Calibration Procedure (Cont.) 7. Engage the paver in automatic mode and allow the paver to come up to full paving speed before passing over the calibration pads. 8. Once the spray bars has passed over the calibration pads, carefully fold the edges of the calibration pads towards the center and roll the pad up so no emulsion will be lost when picked up. 9. Bring the plastic container to the calibration pad and place the pad in the container. 10. Record weight of the calibration pads. 11. It will be necessary to clean the plastic container before the second calibration pad is weighed or the weight of the plastic container will have to be re-zeroed as emulsion from the first pad will increase the weight of the container.
Spray Bar Calculation Procedure
Spray Bar Calculation Sheet for Spray Paver
Spray Bar Shot Rate Calculation
Approved Mix Design
Sampling and Testing Required California Test 125 July 2002 METHODS FOR SAMPLING HIGHWAY MATERIALS AND PRODUCTS USED IN THE ROADWAY STRUCTURAL SECTIONS ASPHALT CONCRETE Aggregates... Part 1, Sections 1-2 Asphalt..... Part 6, Sections 1-3 Modified Asphalt Concrete.... Part 7, Section 4 BITUMINOUS SEAL Polymer Modified Asphalt Emulsion. Part 6, Section 4
Required Application Conditions May be applied on damp, but not wet, surfaces. Minimum air and pavement temperature requirements are 7°C (45°F) and rising, although it is recommended that the surface temperature be above 15°C (59°F). No freezing conditions are allowed in the first 24 hours, the emulsion-based tack coat requires about one day to fully cure.
Construction Trimming necessary. No overlap during construction due to emulsion membrane. Rolling operation showing traffic control.
Application A minimum of one steel drum tandem roller is required for compacting the mix. Rollers must be operated in static mode only. Usually two passes using a 12 to 15 ton roller is sufficient to properly seat the aggregates. Rolling must be carried out before the temperature, at mid layer of the mix, falls below 90°C (194°F).
Production Rates and Paving Days Production Rate Mainline Paving tons per hour Returns/Turnpockets tons per hour
Roadway Geometry and Widths Urban Milling ¾ - 1” contour edge grind required to match curb and gutter and existing pavement Drainage Minimal water trapped against curb due to emulsion filling void structure and thin lift Less water intrusion to pavement interface due to emulsion membrane Rural Cross-slopes Shoulder Generally best used for Travel Lane with 1 foot beyond fog line For Grade differential greater than 2% from Mainline to Shoulder, the shoulder must be paved separately in order to maintain the grade Edge drop-off will be less than ¾” (consider bicycle traffic material cant not be feather down lower then top size agg.) Varying Width Typical Paving machine width 8-14 feet variable
Application Problems and Solutions PROBLEMSOLUTIONS Surface Waves Ensure the head of material in front of the paver screed is at the correct height and does not fluctuate (i.e., rise and fall). Ensure the screed is not worn or set incorrectly. Ensure the mix is not too stiff or has not fallen below 275 F (135 C). Ensure the dump trucks do not bump the paving unit as this can cause long frequency waves resulting in increased pavement roughness. Ensure grade control equipment (if in use) is functioning properly Wash Boarding Slow roller down.
Application Problems and Solutions Tearing Ensure the paving unit is being operated correctly. Ensure the mix is not too cold (i.e., below 275 F (135 C)) or too stiff. May be fixed by adjusting the degree of crown and ensuring mix temperature is correct. Ensure application is not too thin Non Uniform Texture- Segregation Ensure the mixture is not separating in the hopper or during transportation. Ensure the paving unit is set up properly. Ensure the mix temperature is at least 275 F (135 C). Check the mix design for poor grading. Adjust if necessary.
Application Problems and Solutions Screed Marks Ensure the paving unit is set up correctly and that the screed in not worn or dirty. Ensure the mix temperature is at least 275 F (135 C). Check the mix design for poor grading. Adjust if necessary. Ensure mix is in specification. Roller Checking & Marks Ensure the roller does not cause a wave in the mat in front of the roller (i.e., mix too hot). Wait until the mix cools further. Check the mix design for too much asphalt in the mix, or too much middle size sand in the gradation. Adjust design if necessary.
Application Problems and Solutions Bleeding & Fat Spots Ensure the mix temperature is not too hot (greater than 351 F (177 C). Check the mix design for too much asphalt or for too coarse an aggregate grading. Adjust design if necessary. Ensure there is no moisture in the mix or on the pavement. Ensure the tack coat application rate is not too high for the surface to which it is applied. Tight, smooth surface require less tack coat than do more open surfaces. Reduce application rate on existing surfaces that exhibit bleeding. Ensure spray bar equipment is operating properly. Ensure aggregates are dry before mixing with asphalt in the hot mix plant, that pavement is not bleeding, that pavement is dry, and that mix is correctly designed for traffic and aggregate. Delamination Ensure adequate tack coat is applied. Ensure the mix is above minimum application temperature (275 F (135 C)). Ensure the mix is not below the minimum compaction temperature (194 F (90 C)). Ensure the existing pavement surface temperature is above the minimum (i.e., 45 F (7 C)) before paving. Ensure the surface is cleaned immediately before paving. Ensure roller drums are not dirty and have working spray systems.
Application Problems and Solutions Poor Transverse Joints Ensure butt joints are properly constructed. Poor Longitudinal Joints Ensure proper joint construction practices are followed, especially when compacting thin layers. Excessive Ravel Ensure the mix design meets project specifications, particularly that the mix contains sufficient binder. Ensure compaction is carried out above the minimum temperature (i.e., 194 F (90 C)).