Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
CONTENTS 1 SUMMARY 3 CHAPTER ONE INTRODUCTION Objective and Background, 3 Scope, 3 Study Approach, 3 4 CHAPTER TWO SYNTHESIS OF THE STATE OF THE PRACTICE Pipe Material Types, 4 Service Life, 5 Agency Policies, Systems, and Experiences, 6 General State of the Practice Survey Observations, 6 8 CHAPTER THREE DEGRADATION MECHANISMS Corrosion, 8 Abrasion, 11 Combined Effect of Corrosion and Abrasion, 13 Other Durability Factors, 14 19 CHAPTER FOUR PIPE MATERIALS Concrete Pipe, 19 Metal Pipe, 23 Thermoplastic Pipe, 30 Ductile Iron Pipe, 32 Vitrified Clay Pipe, 32 Material Service Life Calculation Examples, 33 34 CHAPTER FIVE PIPE PROTECTION, REPAIR, REHABILITATION, AND REPLACEMENT Coatings, Linings, and Paving, 34 Rehabilitation and Repair Practices, 35 39 CHAPTER SIX INSPECTION Inspection of Pipe Materials at Delivery, 39 Inspection During Construction, 39 Post-Installation Inspection, 40 Post-Installation Inspection Techniques, 40 AASHTO LRFD Bridge Construction Specifications, 41 Other Inspection Techniques, 41 Summary of Inspection Techniques, 41 Summary of Current Inspection Practices, 42 43 CHAPTER SEVEN LIFE-CYCLE COST ANALYSIS 44 CHAPTER EIGHT CONCLUSIONS Summary of Key Findings, 44 Summary of Knowledge Gaps, 46 Research Needs, 48
49 REFERENCES 53 APPENDIX A STATE OF THE PRACTICE SURVEY RESULTS 109 APPENDIX B SUMMARY OF SERVICE LIFE CALCULATION METHODS 124 APPENDIX C EXAMPLE SERVICE LIFE CALCULATIONS Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.
SUMMARY SERVICE LIFE OF CULVERTS The objective of this study was to update the 1998 NCHRP Synthesis 254: Service Life of Drainage Pipe, which in turn updated the 1978 NCHRP Synthesis 50: Durability of Drain- age Pipe. In the past 18 years, the culvert pipe industry and research community has made numerous developments in pipe materials, sophisticated analytical soil-structure interac- tion modeling techniques, greater use of in situ pipe rehabilitation, and the introduction of larger and more diverse structures. As such, the AASHTO subcommittees on culverts determined that a new synthesis study of the service life of culverts was needed. The study approach consisted of two primary thrusts. First, a survey of North American transporta- tion agencies was performed to determine the current state of practice. Second, a literature review was performed to assess both the state of practice and the state of the art with regard to the subject topic. Forty-one U.S. departments of transportation (DOTs) and seven agencies in Canada responded to the survey. The results showed a diverse range of pipe types in common usage, with concrete, corrugated galvanized steel, and high-density polyethylene (HDPE) pipes as the most common pipe types, followed by galvanized structural plate and polyvinyl chloride (PVC). Almost half of agencies gather site-specific environmental data on drain- age projects, indicating a broad appreciation of the importance of selecting the durability of materials to match site conditions. Less than a quarter of respondents indicated that they had developed or improved pipe durability prediction models. Those that have developed prediction models include DOTs that are subject to extremely variable or extreme envi- ronmental conditions. There was little consistency in definitions of end of service life, but there appears to be a trend toward using the results of pipe inspection rating systems to set threshold values that trigger maintenance, rehabilitation, or replacement. The majority of respondents indicated that quality of pipe installation has a significant influence on culvert pipe performance. HDPE and PVC were identified as the pipe types where the relationship between pipe performance and installation quality were strongest. Less than 40% of agen- cies had a formal culvert asset management system in place. In situ pipe rehabilitation is becoming routine, with only two agencies indicating that they have not used it. Sliplining was the most common technology in use. Agencies are developing methods for predict- ing the service life of culverts, but developments are generally concentrated within a core group of agencies where this topic is regarded as a high research priority. Within the past 15 years, much advancement has occurred in understanding the mecha- nisms of pipe degradation in service. Significant work has been done with respect to cor- rosion and the main factors that influence its development in concrete and metal pipes; that is, pH, resistivity, chloride, and sulfates. This work has led to studies about how to retard or prevent corrosion through the use of thicker walls, better materials, coatings, and liners. Advances have also been made in understanding abrasion and how it enhances the rate of degradation from corrosion and how its damaging effects can be mitigated. Effec- tive research has also been undertaken in understanding time-dependent changes in the
2 mechanical properties of thermoplastic pipe, particularly slow crack growth and oxidative/ chemical failure and how they can be controlled. Florida DOT and several other select agencies have sponsored significant research in the area of pipe degradation, and this research can form the basis for better service life predic- tion models in the future. The schematic degradation models for metal-reinforced concrete and thermoplastic pipe materials (Figure 7 in chapter two, Figure 11 in chapter three, and Figure 20 in chapter four) indicate the trend of an initial relatively stable condition followed by a more rapid deterioration. Little recent advancement has been made in refining pipe service prediction models, even for the more common pipe types. However, with research on degradation mechanisms and a better understanding of the progression of deterioration, combined with greater sources of pipe performance data from agency pipe inventories, more rapid future progress in improv- ing these models should be possible. Survey results indicate that, in practice, a majority of agencies predict service life using case studies, internal research results, or default estimated service life values holistically or categorized by local environmental conditions, rather than published models. This study has confirmed rapid growth in the use of in situ pipe rehabilitation or trench- less technologies for extending the life of culverts. This trend will continue as technologies improve and more contractors can offer the service. This trend will increase the demand from agencies for better methods for predicting pipe durability so that a broader range of pipe strategies can be evaluated and best value for money in delivering highway drainage systems can be achieved. This report provides an overview of the current state of knowledge with respect to deteri- oration mechanisms of various pipe types under a range of field conditions and applications. The current service prediction models are generally based on a selected end-of-service-life indicator and consider only one distress modeâtypically corrosionâto predict expected service life. Where there is combined abrasion and corrosion, the models no longer apply. The current deterioration models, while providing broad guidance on pipe type suit- ability, are not sufficiently developed to allow a meaningful comparison of alternatives. A further limitation is the inability to relate a defined end-of-service-life indicator to ultimate failure of the pipe system. Ideally, pipe deterioration models need to be able to model the progressive loss of pipe condition from installation to final failure. With this type of model, it would be possible to evaluate the cost-effectiveness of maintenance activities, rehabilita- tion options, and full pipe replacement and to assist in establishing when these interventions are needed.
3 most often on average daily traffic or functional classifica- tion of roadway. Material service life models developed for different pipe materials are inconsistent and do not relate to limit state (failure mode) or service distresses adversely affecting both structural and hydraulic performance, includ- ing cold-weather-induced distresses. Specifically, the following topics are addressed in this synthesis: ⢠Summary of the required service life for culverts in varying conditions. ⢠Summary of the bases for determining service life. ⢠Summary of any additional design parameters or main- tenance requirements based on service life, including considerations of maintenance. ⢠Summary of the conditions constituting the end of useful service life for various culvert installations (including pipe materials, soil and backfill properties, hydraulic performance, and appurtenances). ⢠The time for a particular material to reach the end of its useful service life. ⢠Information on how material service life and culvert failure limit states are correlated. STUDY APPROACH The study approach consisted of two primary thrusts. First, a survey of state transportation agencies was per- formed to determine the current state of practice. Second, a literature review of state, local, and international practice was performed. Key results of the state of practice survey are summa- rized in chapter two, with the full survey results presented in Appendix A. Results of the literature review are included primarily in chapters three and four. CHAPTER ONE INTRODUCTION OBJECTIVE AND BACKGROUND This study is an update of NCHRP Synthesis 254: Service Life of Drainage Pipe (1998), which itself was an update of NCHRP Synthesis 50: Durability of Drainage Pipe (1978). In the past 15 years, the culvert pipe industry and research community have made significant developments in plastic pipe, fiber-reinforced concrete pipe, polymeric-coated metal pipe, recycled materials, larger and more diverse structures, and sophisticated analytical soil-structure interaction mod- eling. As such, there is a growing need for a new study of the service life of culverts. For the purposes of this study, service life is defined as the time duration during which a culvert is expected to pro- vide the desired function with a specified level of mainte- nance established at the design or retrofit stage. SCOPE The selection of culvert materials for a particular site is based on the materialsâ ability to satisfy the requirements of five design criteria: ⢠Structural design ⢠Hydraulic design ⢠Environmental and site considerations ⢠Joint performance ⢠Service life (durability). Significant published works provide guidance for the first three criteria, and NCHRP Project 15-38 and AASHTO 20-07 Task 347 address joint performance. Service life cri- teria are the missing piece. No consensus exists among state DOTs on service life, and predictive models are often param- eterized to specific geographic and environmental consider- ations. Design service lives range from 15 to 100 years based
