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Thin LIFT ASPHALT Pavement Construction

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Presentation on theme: "Thin LIFT ASPHALT Pavement Construction"— Presentation transcript:

1 Thin LIFT ASPHALT Pavement Construction
Department of Public Works 7/29/2018 Thin LIFT ASPHALT Pavement Construction Charlie Holland Asphalt Pavement Association of Indiana March 9, 2011 March 2011

2 Topics Project Selection Materials Selection and Mix Design
Construction and Quality Control Performance Cost Comparsions Conclusions This presentation will cover the following topics: How to select a project for a thin overlay The process for materials selection and mix design The construction and quality control considerations The expected performance of thin overlays and Finally, the conclusion. March 2011

3 Project Selection Avoid Projects Needing Structural Rehabilitation!!
Not every pavement project is suitable for a thin asphalt overlay. It is best to apply a thin overlay prior to the need for a more extensive pavement rehabilitation. March 2011

4 Thin Asphalt Overlays Thin asphalt overlays are a popular 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. March 2011

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6 Department of Public Works
7/29/2018 History HAE “Sand Mix” used extensively in Indiana in Early 1980’s as Wearing Course High skid resistance Interstates Method Spec. (Natural Sand, 10% LSS, 7.0% AC20) Moratorium due to poor performance with increased traffic volumes Not used again until recently Need for preservation tool and to reduce costs Improved technology & methods March 2011

7 Why Thin Asphalt Pavements?
Department of Public Works 7/29/2018 Why Thin Asphalt Pavements? Shift from new construction to renewal and preservation Functional improvements for safety and smoothness needed more than structural improvements – Perpetual Pavements Material improvements Binders – Superpave and Polymers Superpave mix design Warm Mix Reclaimed Asphalt Pavement (RAP) Roofing Shingles Thin asphalt overlays have become increasingly popular over the last several years, especially as the infrastructure emphasis in the U.S. has switched from the construction of new facilities to the renewal and preservation of existing roads. As a lot of agencies have discovered, many asphalt pavements do not require anything more to keep them in service other than a thin overlay to improve the smoothness and safety of the surface. These are usually thick, well-constructed asphalt pavements that would be classified as Perpetual Pavements. This approach to pavement preservation is largely possible due to improvements in asphalt binders, new types of surface mixtures such as stone matrix asphalt, open-graded friction courses, and improved dense-graded mixes, the advent of the Superpave mix design procedure, the development of warm mix asphalt, and the improvements to processes which allow more recycled materials to be introduced. March 2011

8 Benefits of Thin Asphalt Pavements
Department of Public Works 7/29/2018 Benefits of Thin Asphalt Pavements Long service, low life- cycle cost Maintain grade and slope Handles heavy traffic Smooth surface Seal the surface Minimize Traffic Delays High Public Acceptance Clean Pavement Surface – no surface stones Apply to existing HMA or Composite Pavements Mixture can contain up to 25% RAP or combination of RAP and Shingles Can Utilize Warm Mix Technology Can be Placed at Night during Off Peak Hours. Thin asphalt overlays have a number of advantages to recommend their usage. Most importantly they provide a long life and low life-cycle cost. Their application provides a means of maintaining the grade and slope of a pavement eliminating the need for deep excavation and unnecessary handwork. Thin asphalt overlays have been used in high traffic conditions. They have no loose stones and minimize dust after application unlike some other types of pavement preservation treatments. There is no need for a curing time prior to allowing traffic. Binder does not run off the pavement at the time of application or soon thereafter. They provide a quiet pavement surface. The asphalt mixture can be recycled at the end of its performance life. Thin overlays have been effectively used in stage construction. And, finally, they are easy to place and maintain with minimal traffic disruption. Thin asphalt overlays will also enhance the pavement’s appearance and helps to seal the pavement from oxidation and moisture. March 2011

9 Department of Public Works
7/29/2018 Basic Evaluation Visual Survey Structural Assessment No structural improvement required Drainage Evaluation What changes are needed Functional Evaluation Ride quality Skid resistance Discussion with Maintenance Personnel In deciding whether a thin overlay is applicable, the designer should conduct a visual survey to determine the extent and severity of existing distresses, a structural evaluation to validate that structural improvements are not needed, a drainage evaluation to ascertain if grade and slope need to be changed, a functional assessment of ride quality and skid resistance, and a consultation with pavement maintenance personnel. March 2011

10 Visual Survey Part of a good Pavement Management System.
Get good, current project- specific data Need to know: Type of distress Extent Severity Visit the site and validate data. A visual survey is usually included as part of a pavement management system, but it is important to ensure that current project-specific data exist. It should include the type of distress present in the pavement along with the extent and severity. It is important to visit the site and validate the data, but that can normally be done through a windshield survey by two personnel rather than the platoon of pavement raters shown here! March 2011

11 Department of Public Works
7/29/2018 Types of Distress Raveling Longitudinal Cracking (less than 3/8”) Transverse Cracking (less than 3/8”) Alligator Cracking Rutting & Flushing Polishing March 2011

12 Department of Public Works
7/29/2018 Raveling Raveling is readily fixed by a thin asphalt overlay, even if it is relatively severe. It is important to catch it before the extensive pavement deterioration. Raveling is recognizable as a loss of fine aggregate on the pavement surface, which can be followed by loss of the coarse aggregate. March 2011

13 Longitudinal Cracking (wheel path)
Department of Public Works 7/29/2018 Longitudinal Cracking (wheel path) If longitudinal cracking occurs within the wheelpath, it may signal the beginning of some fatigue cracking. While a thin overlay may help temporarily, it should be noted that most likely the crack will eventually propagate through the overlay, and the structural deterioration of the pavement will continue. Remember, a thin overlay does not cure structural problems. Temporary Fix for Minor Distress March 2011

14 Longitudinal Cracking (wheelpath)
Department of Public Works 7/29/2018 Longitudinal Cracking (wheelpath) If longitudinal cracking occurs within the wheelpath, it may signal the beginning of some fatigue cracking. While a thin overlay may help temporarily, it should be noted that most likely the crack will eventually propagate through the overlay, and the structural deterioration of the pavement will continue. Remember, a thin overlay does not cure structural problems. Temporary Fix for Minor Distress March 2011

15 Department of Public Works
7/29/2018 Transverse Cracking Pavements with low to medium transverse cracking may be suitable for a thin overlay, especially if the overlay is applied prior to severe cracking. If caught early enough, the existing pavement can be merely overlaid, or, if it has progressed beyond its initial stage, the crack can be milled to a depth below the crack and the thin overlay will have the opportunity to avoid or reduce reflective cracking. If milling is to be done, then it is desirable to mill the surface with transverse cracking just to reduce the crack width prior to overlay placement. March 2011

16 Alligator (Fatigue) Cracking
Department of Public Works 7/29/2018 Alligator (Fatigue) Cracking A thin asphalt overlay is not recommended for a fatigue cracked pavement. This requires a structural rehabilitation which includes fixing the failure prior to the placement of a structural overlay. Temporary Fix for Minor Distress March 2011

17 Department of Public Works
7/29/2018 Rutting or Shoving A thin overlay can be used on a rutted pavement so long as the rutting is not structural in nature and the in-place mixtures below the surface layer are properly designed and performing well. If it is structural, then the problems have origins fixed deep in the pavement structure, the rut is relatively broad, and the rehabilitation will have to begin with fixing the structural problem. This is shown in the left hand picture. If the distress is on the surface, then the wheelpaths will be very clearly defined as in the right hand picture. In this case, milling to remove the defective surface and replacement with a thin overlay should work very well. Surface Failure – Milling Required Severe Structural Failure March 2011

18 If a Thin Overlay is the Answer. . .
Department of Public Works 7/29/2018 If a Thin Overlay is the Answer. . . Select Surface Preparation Distresses Roughness Considerations for Curb Reveal and Drainage Materials Traffic Availability Climate Thickness NMAS Geometrics Once the determination has been made that a thin asphalt overlay is appropriate, then decisions must be made regarding surface preparation, materials, and overlay thickness. Surface preparation will be dependent upon the distresses present in the existing pavement, the need to correct roughness problems and geometric considerations. The types of materials used in the thin overlay will depend upon the level of traffic expected, availability, and the climate of the particular project. The thickness of the overlay will depend upon the nominal maximum aggregate size used in the overlay and geometrical demands of the pavement surface. March 2011

19 Department of Public Works
Mix Design 7/29/2018 Laboratory Compaction Volumetrics Void Requirements – Mixes are relatively impermeable VMA – caution about too high Asphalt Content – Should depend on Voids and VMA Gradation Laboratory compaction effort should be sufficient to obtain an interlocking between aggregate particles without fracturing them. In most applications for small NMAS mixes, this has usually translated to between 50 and 75 gyrations of the Superpave gyratory compactor. Volumetric requirements should generally follow standard practice for voids, VMA and asphalt content. It should be noted, however, that small NMAS mixes are relatively impermeable even with higher void contents. This will be discussed further in a couple of slides. A proposed TLAS specification will be presented later in this program March 2011

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21 March 2011

22 Superpave Design Guide reference for 4.75mm ASSHTO M323
Department of Public Works 7/29/2018 Superpave Design Guide reference for 4.75mm ASSHTO M323 GRADATION Sieve Size % Passing Range 12.5 mm 100 9.5 mm 95-100 4.75 mm 90-100 1.18 mm 30-60 0.075 mm 6-12 VMA Minimum 16.0 D/B ratio ( ) March 2011

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25 Materials Selection - RAP
Department of Public Works 7/29/2018 Materials Selection - RAP Small NMAS mixes should contain fine RAP RAP or shingles will help Stabilize cost by reducing added asphalt and added aggregate Prevent rutting Prevent scuffing Use maximum allowable while maintaining gradation The use of reclaimed asphalt pavement in a thin overlay should be encouraged if the RAP is sized appropriately. Small size RAP can be very beneficial to the performance and cost of the mix, especially since the fine RAP will contain a higher amount of asphalt than coarser RAP. The approach in mix design should be to use the maximum amount of RAP while maintaining the gradation of the aggregate. March 2011

26 March 2011

27 Superpave Design (Virgin)
Department of Public Works 4.75 mm Thin Lift Pavement St Joseph County, Indiana 2007 7/29/2018 Superpave Design (Virgin) Composition Limestone sand Natural sand Limestone -3/8” chips PG % Design data Air voids 4.0% VMA 17.9% D/B ratio 1.4 March 2011

28 Wasniak Road LaPorte County, IN 2009
Department of Public Works 7/29/2018 Wasniak Road LaPorte County, IN Composition Limestone sand Natural sand Limestone -3/8” chips RAP 15% PG % Design data Air voids 4.0% VMA 17.1% March 2011

29 Highway SR 227 Wayne County
Mix Design #12 Dolomite (34%) #24 Dolomite Sand (34%) Dolomite QA Sand (32%) PG (6.9%) No RAP March 2011

30 Highway US 27 Wayne County
85 lbs/sq.yd. = 3/4” depth 310 – 315 degrees 3.3% Air Voids 91.6% = Density average No RAP March 2011

31 Department of Public Works
7/29/2018 Ice Box Parking Lot South Bend, IN 2009 Composition Limestone sand Natural sand Limestone -3/8” chips RAP 30% PG % March 2011

32 Ice Box Parking Lot South Bend, IN 2009
Department of Public Works 7/29/2018 Ice Box Parking Lot South Bend, IN 2009 March 2011

33 Construction & Quality Control
Production Paving Quality Control Next, we will discuss the construction and quality control of thin asphalt overlays. March 2011

34 Quality Control - Plant
Aggregate Gradation Moisture Content Mix Volumetrics Air Voids VMA Asphalt Content Quality control at the plant should follow normal procedures by checking gradation and moisture content on the incoming aggregate, and normal mix volumetrics on the plant output including air voids, VMA, asphalt content, and gradation. March 2011

35 Best Practices – Paving Surface Preparation
Department of Public Works 7/29/2018 Best Practices – Paving Surface Preparation Milling Remove defects Roughen surface Improve smoothness Provide RAP Size machinery properly Tack Emulsion Polymer emulsion or unmodified Rate: 0.10 to 0.15 gal/sy (undiluted emulsion) Milling of the existing pavement is encouraged for a number of reasons. It removes defects that may otherwise reflect through the new overlay and provides an opportunity to improve the smoothness of the final pavement. It roughens the surface which improves the bond between the overlay and the old pavement, and some research has shown it may eliminate the need for a tack coat. It also provides RAP which can be used in future projects. However, it is important to properly size the milling equipment for the pavement structure. A milling machine which is too heavy may structurally damage the pavement. Tack coats may be either asphalt emulsions or hot applied tack. The advantage of an emulsion is that it may be applied at ambient or slightly elevated temperatures, where a hot asphalt tack must be applied at elevated temperatures. On the other hand, some practitioners feel that better bonding occurs with the hot applied tack. Some agencies specify the use of a polymer modified tack coat while others are satisfied with the performance of unmodified tack coats. Most specifications require an application rate of between 0.1 and 0.15 gal/sy for undiluted emulsion. March 2011

36 Highway SR 227 Wayne County
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37 Highway US 227 Wayne County
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38 March 2011

39 Highway SR 227 Wayne County
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40 Best Practices – Paving Placement and Compaction
Department of Public Works 7/29/2018 Best Practices – Paving Placement and Compaction Paving Best to move continuously MTV or windrow can help Cooling can be an issue 1” cools 2X faster than 1.5” Warm mix Compaction Seal voids & increase stability Low permeability No vibratory on < 1” In paving, the best strategy to obtain a smooth mat is to move the paver slow but continuously. If starting and stopping is necessary to deal with interrupted material flow, then it is best to start and stop the paver suddenly rather than gradually to maintain a constant mat thickness. A material transfer vehicle or windrow pickup device can be of help for the delivery and feeding of the asphalt mixture. However, an MTV is not necessary to prevent segregation since the mix is comprised mostly of fine aggregate. When dealing with polymer modified binders, it is also important to minimize the amount of handwork as the material may be very sticky and difficult to rake. Cooling of the mixture can be an issue for a thin overlay. Keep in mind that a 1 inch mat will cool twice as quickly as a 1.5 inch mat. Again, warm mix technology can help extend the time for compaction of the mix. Compaction of the mat should be done with the idea of sealing the surface to the penetration of water and air and maximizing the stability of the mix. As discussed earlier, permeability will be decreased with smaller NMAS mixtures even for higher air voids. This will improve the performance of the overlay by reducing the amount of access that air and water have to the mixture. Vibratory compaction should not be used on mats of less than one inch in thickness as this may damage the mat. As with any pavement construction, uniformity in all aspects of production, transportation, placement, and compaction is key to the success of the pavement. March 2011

41 SR 29 Clinton County March 2011

42 SR 29 Clinton County March 2011

43 Occasional dragging of clay balls in mix
Department of Public Works 7/29/2018 Occasional dragging of clay balls in mix Originally thought to be oversized contamination from stockpiles March 2011

44 Department of Public Works
7/29/2018 Clay balls from dryer March 2011

45 Pavement Life Location Traffic Underlying Pavement Performance, yrs.
Ohio High/Low Asphalt 16 Low Composite 11 High 7 North Carolina ---- Concrete 6 – 10 Ontario 8 Illinois 7 – 10 New York 5 – 8 Indiana 9 – 11 Georgia 10 The expected pavement life of a thin overlay will be determined by traffic loads, the type of underlying pavement and climate among other factors. These studies have documented thin overlay performance in a variety of locations. March 2011

46 Annual Cost, $/lane-mile
Economics Thin overlays on asphalt – almost always most cost effective Thin overlays on PCC – not as cost effective, but greater deterioration prior to overlay 2008 NAPA Survey of State Asphalt Associations Treatment Expected Life, yrs Range Cost, $/SY Annual Cost, $/lane-mile Chip Seal 4.08 2.06 0.50 – 4.25 3,554.51 Slurry Seal 3.25 2 - 4 1.78 1.00 – 2.20 3,855.75 Micro-surfacing 4.67 4 - 6 3.31 2.30 – 6.75 4,989.81 Thin Surfacing 10.69 7 - 14 4.52 2.40 – 6.75 2,976.69 In 2008, Chou and his colleagues found that in almost all cases, a thin asphalt overlay on an asphalt pavement was the most economical solution. He reported that thin overlays of concrete were not as cost effective, possibly due to increased deterioration of the underlying pavement. Also, in 2008, NAPA surveyed the state asphalt pavement associations concerning the cost and effectiveness of various pavement preservation treatments. Thin asphalt overlays had a longer expected life than the other treatments although the initial cost was higher. However, when that was divided over the expected life, the thin overlay option was the cheapest pavement preservation treatment as shown in the next graph. March 2011

47 Performance - Economics
Department of Public Works Performance - Economics 7/29/2018 APAM Information (Michigan) March 2011

48 Surface Treatments Cost
Cost per SYS Cost per Lane Mile 12 Ft Wide Life Lane Mile Cost (Life) Chip & Seal $ 1.31 $ 9,208 4 $ 2,302 Microsurface $ 2.80 $ 22,480 8 $ 2,810 UBWC $ 5.64 $ 38,446 $ 4,806 UTAS Overlay Milled surface $ 3.77 $ 26,574 $ 3,322 UTAS Overlay $ 3.02 $ 21,294 $ 2,662 1 ½” HMA Overlay Milled surface $ 5.23 $ 36,664 12 $ 3,055 1 ½” HMA Overlay $ 4.87 $ 34,169 $ 2,847 March 2011

49 Department of Public Works
Conclusions 7/29/2018 Thin Overlays for Pavement Preservation Improve Ride Quality Quiet – Low Tire Noise No Curing Time Maintain Road Geometrics ¾” Thickness Conserves Curb Height Volumetrically Controlled under current QC/QA HMA Specifications Provide Long Lasting driving surface Place before extensive rehab required Expected performance 10 years or more on asphalt ( when applied to stable underlying pavement) 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. March 2011

50 Department of Public Works
7/29/2018 NAPA BROCHURE March 2011

51 City of Centerville March 2011

52 City of Centerville March 2011

53 South Bend (Roosevelt)
March 2011

54 South Bend (Roosevelt)
March 2011


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