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Strategies to improve and preserve flexible pavements at intersections

ProQuest Dissertations and Theses, 2011
Dissertation
Author: Imad N Abdallah
Abstract:
Many rural intersections originally constructed with thin untreated flexible base and hot mix or a two-course surface treatment experience severe pushing, shoving and rutting. These failures cause an extremely rough surface that can cause damage to small vehicles and potentially cause motorists to lose control of their vehicle. These distresses almost always result in complete failure of the existing pavement that must be repaired several times during the life of the roadway by maintenance forces. Pavement sections constructed with the same materials adjacent to the intersection perform adequately until the approach (approximately 150 ft in advance) of the intersection and in the intersection itself when the failures become apparent. The mechanisms of intersection pavement failures and the best practices to minimize the failures at existing intersection pavements are discussed in this study. The outcome of this study is an expert system that can be used to reduce the frequency of maintenance needed at rural intersections with consideration of the life-cycle cost analysis.

vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS...........................................................................................................iv ABSTRACT.....................................................................................................................................v TABLE OF CONTENTS.............................................................................................................. .vi LIST OF TABLES................................................................................................................. ..........x LIST OF FIGURES................................................................................................................ .......xi CHAPTER 1 - INTRODUCTION................................................................................................... 1 1.1 STATE OF PROBLEM ........................................................................................................ 1 1.2 OBJECTIVES .......................................................................................................................2 1.3 ORGANIZATION OF REPORT .......................................................................................... 3 CHAPTER 2 - REVIEW OF LITERATURE .................................................................................. 4 2.1 BACKGROUND ................................................................................................................. .4 2.2 COMMON TYPES OF DISTRESSE S ON ASPHALT PAVEMENTS ..............................5 2.2.1 Ruttin g.................................................................................................................. ......5 2.2.2 Shoving ....................................................................................................................10 2.2.3 Fatigue Cracking ......................................................................................................11 2.2.4 Other Distresses ....................................................................................................... 11 2.3 REMEDIATION STRATEGIES OF ASPHALT PAVEMENT AT INTERSECTIONS ..................................................................................................... 12 2.3.1 Current Txdot Specifications For Flexible Pavem ent Rehabilitation...................... 13 2.3.2 Asphalt Institute ....................................................................................................... 14

vii 2.3.3 Canada......................................................................................................................21 2.3.4 Colorado Department of Transportation (C dot)......................................................23 2.3.5 Australia ...................................................................................................................23 2.3.6 New Zealand ............................................................................................................25 2.3.7 Illinois Dot ...............................................................................................................26 2.3.8 Hot Mix Asphalt Mixtures For Nevada’s Intersections ...........................................28 2.3.9 National Center For Asphalt Technology ................................................................29 2.4 REMEDIATION STRATEGIES CONSI DERING SUBSURFACE LAYERS OF PAVEMENTS...................................................................30 2.4.1 Base Layer ...............................................................................................................30 2.4.2 Subgrade Layer ........................................................................................................36 2.5 MATRIX OF SOLUTIONS ...............................................................................................46 2.6 COST ANALYSIS..............................................................................................................47 2.6.1 Life-Cycle Cost A nalysis.........................................................................................49 CHAP TER 3 - UNDERSTANDING AND DOCUMENTING EXTENT OF PROBLEM AND SOLUTIONS IN TEXAS...................................................50 3.1 SURVEYING TXDOT DISTRI CTS..................................................................................50 CHAPTER 4 - METHODOLOGY ................................................................................................59 4.1 FRAMEWORK OF THE EXPERT SYSTEM ...................................................................62 4.2 INPUT DATA ......................................................................................................................63 4.3 PREDOMINANT DISTRESS .............................................................................................69 4.4 REMEDIATION ALTERNATIVES ...................................................................................70

viii CHAPTER 5 - TYPICAL FORENSIC EVALUATION...............................................................74 5.1 BACKGROUND ................................................................................................................74 5.2 CONDITION SURVEY .....................................................................................................76 5.3 DATA COLLECTION .......................................................................................................78 5.4 DATA ANAL YSIS.............................................................................................................79 5.4.1 Core Analysis ...........................................................................................................79 5.4.2 FW D Analysis..........................................................................................................82 5.4.3 GPR Analysis ...........................................................................................................84 5.5 CONCLUSIONS.................................................................................................................86 CHAPTER 6 - CASE STUDY TO I LLUSTRATE USE OF EXPERT SYSTEM.......................88 6.1 EXPERT SYSTEM FOR SELECTION

OF APPROPRIATE REMEDIATION STRATEGIES.......................................................88 6.1.1 INPUT MODUL ES.................................................................................................90 CHAPTER SEVEN - PRESENTATION OF RESULTS ............................................................101 7.1 SITE DESCRIPTION .......................................................................................................102 7.1.1 Atlanta District: Intersection of FM 149 & FM 355 ..............................................102 7.1.2 Atlanta District: Intersection of US 259 & SH 11 .................................................104 7.1.3 Austin District: Intersection of IH 35 & CRr210...................................................106 7.1.4 Austin District: Intersection of US 281 & SH 29 ..................................................107 7.1.5 El Paso District: Intersection Of US 90 East & 5th Ave, Intersections of US 90 East & SH118, and Intersection of US 90 West & 6th Ave...................108 7.1.6 Laredo District: Intersection of FM 1472 & Interam erica Blvd............................109

ix 7.1.7 Laredo District: Intersection of US 83 &IH 35.....................................................112 7.2 RESULTS OF STUDIES AT INTERSECTIONS ...........................................................115 7.2.1 Summary of Re mediation Strategies In Intersections............................................115 CHAPTER EIGHT – TESTING PROTOCOL AT INTERSECTIONS .....................................118 8.1 SPECIAL CONSIDERATIONS FOR STRUCTURAL REMEDIATION ......................124 8.1.1 Material Selection ..................................................................................................124 8.1.2 Design Considerations ...........................................................................................126 CHAPTER NINE – SUMMARY AND CONCLUSIONS .........................................................129 LIST OF REFERENCES .............................................................................................................132 APPENDIX A - QUEST IONNAIRE..........................................................................................140 APPENDIX B – SUMM ARY OF CAUSES OF DISTRESS AND............................................145 REMEDIATION STRATEGIES FOR EACH DISTRICT .........................................................145 APPENDIX C - QUEST IONNAIRE FOR THE DISTRCIT INTERVIEW...............................151 APPENDIX D - RESUL TS OF THE QUESTIONNAIRE FOR THE DISTRCIT INTERVIEW................................................................156 APPENDIX E - SUMMARY OF THE DISTRI CTS INTERVIEWS.........................................174 APPENDIX F - TOPSIS ..............................................................................................................200 APPENDIX G - SUMMARY OF T HE CORE RESULTS FROM SH 155 AND SH 49 INTERSECTION................................................204 CURRICULUM VITA ................................................................................................................218

x LIST OF TABLES

page Table 2.1 - Superpave Binder Selection Adjustments for Design E SALs and Loading Rate......................................................................... 17   Table 2.2 - Stabilization Methods for Diffe rent Soil Types (Terrel et al., 1979)......................... 32   Table 2.3 - Geotextile Specifications for construction Survivability in Low-Cost Low-Volume Roads (from Cicoff and Sprague, 1991)........................ 45   Table 4.1 - Summary of Distresses Utilized in Condition Survey at Intersections...................... 66   Table 4.2 - Index Parameters Based on FWD to Diagnose Possible Distressed Layer................ 68   Table 4.3 – Subgrade Modulus Ranges Used to Diagnose Quality of Subgrade Layer............... 68   Table 4.4 – Ratio of Base to Subgrade Modulus Used to Diagnose Quality of Base Layer........ 68   Table 4.5 - Index Parameters Based on FWD and Layer Thickness to Diagnose Possi ble Distressed Layer....................................69   Table 6.1 - Summary of Appropriate Rehabilitation Alternatives................................................98   Table 7.1 - Summary of intersection Location and Pavement Structure.................................... 101   Table 7.2 - Summary of Results Based on the Recommendation of Expert System.................. 116  

xi LIST OF FIGURES

page Figure 2.1 - Structural Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council, 2003)................ 6   Figure 2.2 - Surface Deformation Due to Base Deformation. (Fang, 2001)................................. 7   Figure 2.3 - Surface Deformation Due to Subgrade Deformation. (Fang, 2001).......................... 7   Figure 2.4 - Instability or Plastic Flow on Asphalt Pavements (Federation of Canadian Municipalities and Cana dian National Research Council 2003)............ 8   Figure 2.5 - Wear Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian Na tional Research Council 2003)................................. 9   Figure 2.6 - Shoving on Asphalt Pavements................................................................................. 10   Figure 2.7 - Fatigue or Alligator Cracking on Asphalt Pavements............................................... 11   Figure 2.8 - Flowchart of Activities for Mitigating Intersection Rutting..................................... 22   Figure 2.9 - TxDOT Flowchart for Base Treatment (TxDOT, 2005)........................................... 33   Figure 2.10 - Improving Pavement by Using Ge osynthetics (from Hopkins et al.., 2005)..........45   Figure 2.11 - Probable Appropriate Re mediation for Different Layers........................................ 47   Figure 3.1 - Results of Survey Responses to Di stricts Experiencing Distress at the Intersecti ons of Low Volume Roads................................................. 51   Figure 3.2 - Percent of Intersections Expe riencing Distress in the Districts................................ 52   Figure 3.3 - Distribution of Distri cts that Responded to Survey..................................................53   Figure 3.4 - Level of Dist ress at Intersections.............................................................................. 54   Figure 3.5 - Type of Distress at Intersections............................................................................... 55   Figure 3.6 - Causes of Distress for Each Type of Distress...........................................................56  

xii Figure 3.7 – Remediation Strategies f or Distresses at Intersections.............................................57   Figure 3.8 – Typical Performance Period for Selected Remediation Strategies...........................58   Figure 4.1 - Typical Expert System Components.........................................................................62   Figure 4.2 - Overall Schematic of the Guideline Tool for Selecting Alternative Remediation Strategies for Flexible Pavements at Intersections..............................64   Figure 4.3 – Severity Level Identification for Alligator Cracking...............................................67   Figure 4.4 – Sample of the Description Pavement Distress..........................................................67   Figure 4.5 – A Sample Matrix Relating Distress to Appropriate Remediation Alternatives.......72   Figure 4.6 - Summary Matrix Relating Distress to Appropriate Remediation Alternatives........73   Figure 5.1 – Aerial View of SH 155 and SH 49 Intersection.......................................................74   Figure 5.2 - Geometry of SH 155 and SH 49 Intersection............................................................75   Figure 5.3 - Cross-sectional Pavement Design for SH 155 and SH 49........................................75   Figure 5.4 - Views of the Conditions of SH 155 and SH 49 Intersection.....................................76   Figure 5.5 - Rut Depth Measurement on SH 155.........................................................................77   Figure 5.6 - Cracking Resulting in Potholes on SH 49.................................................................77   Figure 5.7 - Location of the Core Extractions..............................................................................78   Figure 5.8 - FWD Collection on SH 155 and SH 49 Images........................................................79   Figure 5.9 - Coring Process Images..............................................................................................80   Figure 5.10 - Core Average Thicknesses as Approaching the Intersection..................................81   Figure 5.11 - Core Average Modulus as Approaching the Intersection.......................................81   Figure 5.12 - Phenolphthalein Test for Lime on Base Material...................................................82   Figure 5.14 - FWD Deflection Results on Eastbound SH 49.......................................................83   Figure 5.16 - GPR, FWD and Cores on SH 155...........................................................................85  

xiii Figure 5.17 - GPR, FWD and Cores on SH 49.............................................................................86   Figure 6.1 - Restricted Online Expert System Login Screen........................................................89   Figure 6.2 - Section No. 1 with General Project Information.......................................................89   Figure 6.3 - Survey Tab of the Expert System..............................................................................92   Figure 6.4 - Configuration Tab of the Expert System..................................................................92   Figure 6.5 - Survey Tab of the Expert System Highlighting the NDT Input Section...................94   Figure 6.6 - Pavement Condition Tab of the Expert System........................................................94   Figure 6.7 - Remediation Alternatives Tab of the Expert System................................................96   Figure 6.8 – Sample of the Remediation Strategies provided by the Expert System...................99   Figure 6.9 - The Saving Feature in the Expert System...............................................................100   Figure 6.10 - Online Guideline for Strategies to Improve..........................................................100   and Preserve Flexible Pavements at Intersections......................................................................100   Figure 7.1 - Aerial View of SH315 and SH149 Intersection......................................................102   Figure 7.2 - Views of the Conditions of SH 315and SH149 Intersection...................................103   Figure 7.3 – Aerial Layout of US 259and SH 11 Intersection....................................................104   Figure7.4 - Views of Conditions of US 259and SH 11 Intersection..........................................105   Figure 7.5 - Conditions on IH 35 and CR 210 Intersection........................................................106   Figure 7.6 - Conditions of US 281 and SH 29 Intersection........................................................107   Figure 7.7 - Views of Conditions of Intersection at US 90 East & 5th Ave in El Paso District...............................................................109   Figure7.8 - Views of Conditions of Intersection at US 90 East & SH 118 in El Paso District................................................................110  

xiv Figure7.9 - Views of Conditions of Intersec tion at US 90 W est & 6 th Ave in El Paso District....................................................................................110   Figure7.10 – Aerial Layout of FM 1472 and InterAmerica Blvd. Intersection.......................... 111   Figure 7.11 - Views of Conditions of Intersec tion at FM 1472 in Laredo District.................... 112   Figure 7.12 – Layout of US 83 and I-35 Intersection................................................................. 113   Figure 7.13 – Views of Conditions of US 83 and I-35 Intersection........................................... 114   Figure 7.14 – Alligator cracking and Su rface Rutting along US 83 Underpass......................... 114   Figure 8.1 - Snapshot of the Condition Su rvey Module in the Expert System........................... 119   Figure 8.2 - Trench as part of a Forensic study to Identify St ructural Rutting........................... 123   Figure 8.3 - Coring operation for a Core Profile across a Pavement Section............................. 123   Figure 8.4 - Illustration of Instability Rutting............................................................................. 125   Figure 8.5 - Example of Dynamic Modulus Test Results a.k.a. Master Curve.......................... 126  

1 CHAPTER 1 - INTRODUCTION 1.1 STATE OF PROBLEM Rural intersections originally constructed with thin untreated flexible base and hot mix or a two-course surface treatment te nd to experience severe pushing, shoving and rutting. These failures cause an extremely rough surface that can cause damage to small vehicles and potentially cause motorists to lose control of their vehicles. These distresses almost always result in complete failure of the existing pavement that must be repaired several times during the life of the roadway by maintenance forces. In mo st cases, pavements constructed with the same materials and cross-sections adjacent to the intersection perform adequately. The sources of and solutions for failure of the intersections in urban areas are well researched and a number of solutions (such as full-depth concrete slab s, white topping, high quality hot mix asphalt) have been implemented. For example, the National Asphalt Pavement Association (NAPA) and the Amer ican Concrete Pavement Association (ACPA) have several documents and training materials available for th is purpose. Little attention has been focused toward the rural low-volume road intersections in the US. A vast body of knowledge is available from work done in other countries (e.g., Africa , Southeast Asia, Australia and New Zealand) where the majority of their highw ay networks are either unpaved or are covered with thin surface treatment. The primary motivation for reconstr uction or rehabilitation of the urban high-volume intersections is the speed of the operation to mi nimize the road closure, and the economy of the solution is of the secondary consideration. Howe ver, to develop implementable solutions for the rural intersections, the economy of th e solution plays a primary role.

2 The goal of this study is to understand the mechanis ms of intersection pavement failures and to determine the best practices to minimize the failures at existing intersections. The outcome of this study should help to reduce th e frequency of maintenance needed at rural intersections. This st udy would also determine how the m echanisms causing the failures at intersections can be mitigated through design and construction modifications. The outcome will also be used to provide solutions that can be readily and economi cally carried out considering the location of the project, the construction practices, and the type of potential or actual damage at the intersections.

1.2 OBJECTIVES The basic objective of this st udy is to accum ulate the back ground information necessary to develop a guide as a decision tool for pavement and maintenance engineers involved in the design, maintenance and rehabilitation of low- volume road intersections. Based on this background, the goals in this study ar e to achieve the following items: 1.

Document the types of distress that are present in the field throughout Texas through surveys and site visits. 2.

Categorize the sources and layers that c ontribute to the damage at intersections. 3.

Develop maintenance and rehabilitation guide lines for intersections with problems. 4.

Provide feasible design alternat ives and remediation strategi es to minimize cost without compromise performance. 5.

Develop an interactive program to guide user s through distress iden tification, remediation selection, and design procedures fo r low volume road intersections.

3 1.3 ORGANIZATION OF REPORT Chapter Two contains a literatu re review with work related to this project throughout the United States and the rest of the world. Charac teristics and mechanisms of the most common types of distresses of asphalt pavements and prom ising remediation strategies for such problems at different layers of th e structure are described. Chapter Three documents the extent of the pr oblem and solutions in Texas. The results of district survey conducted at the beginning of this study are analyzed. The most prevailing low-volume road intersection distresses and their causes are identified. The survey also collected the different remediation methods utilized by Texa s districts and their eff ectiveness. The input data for the design and met hodology are also presented. Chapter Four provides the methodology used in this project. The study explored the available approaches to preserve flexible paveme nt intersections and deve lop an expert system approach to allow for better and a more optimal preservation and reha bilitation strategies. Chapters Five and Six present a forensic evaluation of one of the intersections investigated in this project fo llowed by case study used to illustra te expert system tool. The intersection was examined usi ng both destructive and nondestru ctive testing (NDT) combined with a condition survey. The result from the site investigation is used to demonstrate the use of the online expert system to select cost-eff ective remediation strategies for improving and preserving flexible pavements at intersections. Chapter Seven provides the presentation of resu lts for the intersections at the sites that were investigated and the outcome of the expe rt system recommendations. Finally, Chapter Eight includes a summary of findings, conc lusions as the resu lts of this study.

4 CHAPTER 2 - REVIEW OF LITERATURE A substantial literature review that documente d strategies to preser ve and rehabilitate flexible pavement at intersections is incorporated in this report. The report is organized starting with a review that is focused on most common flexible pavement distresses at intersections. Next, a review of current TxDOT specifications for flexible pavement rehabilitation is documented. What is followed, is a set of summari es of the flexible pavement at intersection specifications adopted by several organizations and state agencies. Al so incorporated are previous studies by agencies and strategies to stabilize and remedi ate base and subgrade problems.

2.1 BACKGROUND A vast m ajority of the TxDOT hi ghway system consists of seconda ry roads that are constructed with thin pavement structures and thin hot mix asphalt surface or two-course surface treatment. This network of low-volume roads has served the public well, and for the most part, performs satisfactorily with periodic maintenance. One of the weakest links in this network is the performance of the pavement at the intersec tions. Severe permanent deformation (pushing, shoving and rutting 1 ) have been reported at intersections of some of these low-volume roads while pavement sections constructed with the sa me materials adjacent to the intersection perform adequately. These failures occur because of the higher severity of loads exerted to the pavement at the intersections.

1 In this document the term permanent deformation is used to imply to rutting as well as shoving and pushing.

5 2.2 COMMON TYPES OF DISTRESSE S ON ASPHALT PAVEM ENTS 2.2.1 Rutting Rutting is defined as the longitudinal perm anent deformation or plastic movement of the asphalt pavement under the action of repeated lo adings over the wheel path. Rutting is usually caused by the densification and shearing of the different pavement layers. It is visually identified by the depression in the pavement surface along the wheel paths. Even though visible on pavement surface rutting may o ccur on any of the layers. Rutting is a serious safety issue for drivers. When water accumulates in the ruts, there is a potential for hydroplaning. Th e hydroplaning phenomenon consists of the buildup of a thin layer of water between the pavement and the tire and results in the tire losing contact with the surface, with the consequent loss of steering control (Yoder and Witczak, 1975). Three main mechanisms lead to the following th ree types of rutting: Structural Rutting, Instability Rutting and Surface/Ware Rutting. It is important to differentiate between these three types of rutting and their potential causes. Different mechanisms lead to a variation in visual characteristics of rutting. According to Fang (2001), shapes of transverse surface profiles differ between failures in the HMA surface mixtures and failures in the underlying support layers. Structural Rutting The defor mation of one or more layers unde rlying the HMA layer results in structural rutting. Base and/or subgrade materials are unab le to sustain the load stresses resulting in depressions and lack of support to the superior layers, mani festing on surface rutting. A cross sectional diagram of structural rutting is shown in Figure 2.1. Structural rutting can be visually identified rather easily. Two main characteristics distinguish structural rutting

6

Figure 2.1 - Structural Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian Na tional Research Council, 2003).

from other modes of rutting. St ructural ruts are wide and do not have humps on their sides as compared with instability ru tting described later. The surface deformation is dependent on which of the layers is failing to support the load. The visual characteristics will be different when the subgrade is fail ing as compared to the base. . Figures 2.2 and 2.3 illustrate and compare th e difference between the surface deformation profiles due to base and subgrade failures. When the base is failing, a small hump will be visible at the surface in the middle of th e two wheel paths, while the defo rmation due to subgrade failure will have no humps at all with a wider wheel path depression (Fang, 2001).

7 Figure 2.2 - Surface Deformation Due to Base Deformation. (Fang, 2001)

Figure 2.3 - Surface Deformation Due to Subgrade Deformation. (Fang, 2001

Inadequate design, poor constr uction, and improper material specification in asphalt pavement systems generally cause structural rutti ng. Traffic conditions, weak substructure, or even poor drainage are essentia l parameters in pavement desi gn. Miss-estimation of these parameters leads to inadequate design and affect the pavement system which could induce structural rutting. Instability Rutting Instab ility rutting or plastic flow is the type of rutting that is due to inadequate HMA mix design rather than the structural design. Epps (1 999) reported that the shear deformation, rather than densification, is the pr imary rutting mechanism in HMA surface mixtures when the supporting layers are reasonably stiff. This kind of rutting is visually recognized by the humps formed on the sides of the rut as shown in Figure 2.4. This type of distress is more visible in slow trafficked area of the pavement such as intersections which represent a variance in the loading conditions applied to the pavement. Braking, accelerating, turning, st anding, and slow moving stre sses at intersections induce instability rutting. It may also be contributed to factors such as: •

High pavement temperatures. •

Improper materials. •

Rounded aggregates.

8

Figure 2.4 - Instability or Plastic Flow on Asphalt Pavements (Federation of Canadian Municipalities and Canadian Na tional Research Council 2003).

Too much binder and/or filler. •

Insufficient or too high air voids According to Colorado DOT Pavement De sign Guide (2009), during warm summer months the sun radiation and th e exhaust of the slow/standing vehicles raise the pavement temperature. At higher temperatures a reducti on in the HMA stiffness occurs, which may induce instability rutting in the HMA layer. Dripping engine oil and other ve hicle fluids are also concentrated at intersections and tend to soften the asphalt (CDOT, 2009). At intersections, stopped and slow moving traffic allow exhaust to elevate asphalt surface temperatures even higher. A properly designed mixture with a stiffe r asphalt binder and stro ng aggregate structure will resist plastic deformation of the hot mix asphalt pavement. Surface/Wear Rutting W ear rutting is the consolidation in the wheel paths of the HMA layer due to insufficient compaction effort which is usually reflected in not achieving the target density. Consequently

9 additional compaction to the aspha lt layer is generated by vehi cle loading without any base/ subbase yielding or the formation of HMA humps as seen in Figure 2.5. According to the Colorado Department of Transportation (2009) the following list of factors contributes to this type of rutting: •

Insufficient compacting effort within the lower base layers •

Not enough roller passes while paving •

HMA cooling before target density •

Asphalt moisture or dust •

Low asphalt content in the mix •

Lack of cohesion in the mix (tender mix, gradation problem) Wear rutting is also the result of chains and studded tires wearing away the pavement surface during winter season. This problem is not common in Texas.

Figure 2.5 - Wear Rutting on Asphalt Pavement s (Federation of Canadian Municipalities and Canadian National Research Council 2003).

10 2.2.2 Shoving Shoving of an asphalt concrete pavem ent is defined as the longitudinal surface displacement of the HMA. Shoving is usually cau sed by an unstable asphalt layer that is not strong enough to resist horizontal stresses. Acce leration and deceleration of vehicles represent a continuous load in the same direction that generally causes shoving as shown in Figure 2.6. Excess binder in the mix, mistakes on the gradation, and erroneous temperature during compaction are parameters that cause a weak asphalt mixture. These potential problems along with poor bonding between the HMA and the unde rlying layer decreas e the resistance to horizontal stresses leadin g to shoving. Shoving can be easily id entified by distortion of pavement markings, and vertical displacements (dips and bumps). In many cases shoving is manifested with a large “bow wave” in front of the braking section or areas where HM A abuts a rigid object such as utilities. Shoving affects ride quality and may represent a safety hazard.

Figure 2.6 - Shoving on Asphalt Pavements.

11 2.2.3 Fatigue Cracking Fatigue in asphalt pavem ent ma nifests itself in the form of cracking from repeated traffic loading (Suo et. al., 2007). Three main factors that affect the initiation and propagation of fatigue cracking are the mix design, pavement stru cture, and construction procedures. The main visual characteristics of fatigue cracking are the interconnection of cracks in a chicken wire/alligator pattern as seen on Figure 2.7.  

Figure 2.7 - Fatigue or Alligator Cr acking on Asphalt Pavements.

Fatigue cracking is an important mechanism in the deterioration of asphalt pavement because of the harmful effect this cracking ha s on the stiffness and strength of pavement. Cracking allows water to percolate to the under lying layers, weakening the support and therefore accelerating permanent deformati on of the pavement sections.

2.2.4 Other Distresses The dom inant distresses at intersections are rutting, shoving and fatigue cracking, however other distresses may manifest at th e intersections. The sources of the dominant

12 distresses can also generate additional distresses and the distresses themselves can represent a source of other distresses. Such is the case of moderate to high severity fatigue cracked areas, where the interconnected cracks form pieces that when moved while subjected to traffic leave a Pothole behind. Another surface defects such as bleed ing, raveling and polis hed aggregates are distresses present at intersections which according to the LTPP “Distress Identification Guide” (2005) are potential mixture related performance problems.

2.3 REMEDIATION STRATEGIE S OF ASPHALT PAVEMENT AT INTERSECTIONS An extens ive review of the literature indicates that the sources of and solutions for failure of the intersections in urban areas are well res earched and a number of solutions (e.g., full-depth concrete slabs, whitetopping, high quality HMA overlay etc.) have been implemented. For example, the National Asphalt Pavement Associ ation (NAPA) and the American Concrete Pavement Association (ACPA) ha ve several documents and traini ng materials available for this purpose. On the other hand, less attention has been focused intersecti on on the rural low-volume road in the US. In many count ries in Africa and Southeast Asia, and in Australia and New Zealand the majority of their highway networks are either unpa ved or are only covered with surface treatment. Much can be learned from thei r operations and incorporated into this study. In this section a review of international strate gies is presented. The strategies and operations from this collection of work will help pr ovide the initial framework for developing implementable solutions for the rural.

13 2.3.1 Current TxDOT Specifications for Fl ex ible Pavement Rehabilitation TxDOT’s Flexible Pavement Rehabilitation methods are listed in the TxDOT Pavement Design Guide (2006) found in http://onlinemanuals.txdot.gov/manuals/ . According to such guide developing a rehabilitati on design generally requires exte nsive investigation into the condition of the existing pavement structure, performance history, and laboratory testing of materials to establish suitability of existing and proposed material s for use in th e rehabilitation design. The field investigation will require a deflection surve y, drainage survey, and perhaps additional nondestructive testi ng (NDT) surveys such as ground penetrating radar (GPR), dynamic cone penetrometer (DCP), and seismic. Examination of multi-year Pavement Management Information System (PMIS) distress and ride data will show performance related issues. Once these preliminary surveys are conducted, locations for material sampling can be established. In addition, for proj ects where full-depth reclamation is being considered, samples of the structure should be taken at interval s not to exceed 0.5-mi. These samples will be evaluated in the lab to verify field survey conc lusions and establish basi c properties necessary to quantify moisture susceptibility, stabilizer co mpatibility, blending re quirements, etc. The preferred rehabilita tion strategy should: •

Full document contains 233 pages
Abstract: Many rural intersections originally constructed with thin untreated flexible base and hot mix or a two-course surface treatment experience severe pushing, shoving and rutting. These failures cause an extremely rough surface that can cause damage to small vehicles and potentially cause motorists to lose control of their vehicle. These distresses almost always result in complete failure of the existing pavement that must be repaired several times during the life of the roadway by maintenance forces. Pavement sections constructed with the same materials adjacent to the intersection perform adequately until the approach (approximately 150 ft in advance) of the intersection and in the intersection itself when the failures become apparent. The mechanisms of intersection pavement failures and the best practices to minimize the failures at existing intersection pavements are discussed in this study. The outcome of this study is an expert system that can be used to reduce the frequency of maintenance needed at rural intersections with consideration of the life-cycle cost analysis.