Noise Barrier Material Selection

Transcription

1 Paper No Noise Barrier Material Selection Susan M. Morgan, Ph.D., P.E. Southern Illinois University Edwardsville Department of Civil Engineering Campus Box 18 Edwardsville, IL Dianne H. Kay, P.E., C.P.C. Southern Illinois University Edwardsville Department of Construction Campus Box 183 Edwardsville, IL Duplication for publication or sale is strictly prohibited without prior permission of the Transportation Research Board Transportation Research Board 8 th Annual Meeting January 7 11, 21 Washington, DC

2 Morgan and Kay 1 Noise Barrier Material Selection ABSTRACT Due to the large capital expenditures required to construct or replace a noise barrier, it is important for designers to have information with which to make rational choices between the materials available. Designers, however, face difficulty due to a lack of information on both existing materials and designs as well as the many new products being introduced that are not typical in highway construction. Therefore, research was conducted to determine the service lives of the various noise barrier materials and products currently in use in Illinois and to develop a life cycle cost model for evaluation of alternative materials. Wood and metal products were estimated to have 25-year service lives, and earth berms, concrete, and fiberglass were estimated to have 5-year service lives. The results of the life cycle cost analyses (LCCA) indicated that earth berms represented the lowest cost alternative while metal barriers with absorptive panels were the most expensive. The life cycle costs of the other barrier materials modeled (including wood, concrete, and proprietary materials) were approximately twice the cost of earth berms. However, while LCCA can provide an additional piece of information in the selection process for noise barrier materials, it should not be used as the sole criterion due to the lack of reliable historical field data on the costs and frequency of maintenance and replacement of barriers. INTRODUCTION Over the past three decades, noise has been recognized as a problem affecting many Americans living close to highways. Federal legislation addressing the issue of highway noise culminated in the United States Code of Federal Regulations Part 772 (23 CFR 772), "Procedures for Abatement of Highway Traffic Noise and Construction Noise." This regulation and subsequent federal policies give the states latitude in determining the need for and type of highway noise abatement. However, most noise abatement projects nationwide have involved the construction of a physical barrier between the noise generator and noise receptors (1). The most recent data (1995) show that over 2,121 km (1,318 miles) of noise barriers have been built in the United States since the early 197s at a total cost of over $1.4 billion (1995 dollars) (2). In Illinois, the Illinois Department of Transportation (IDOT) and the Illinois State Toll Highway Authority (ISTHA) have constructed over 96 km (6 miles) of noise barriers on highways in their respective jurisdictions. The total cost of Illinois noise barriers is over $61.5 million (1995 dollars) (2), or slightly more than $.6 million per kilometer ($1 million per mile). Recent IDOT construction of new noise barriers has averaged over $1.3 million annually. Despite the high cost of noise barriers, the general trend nationally is increasing annual length constructed (Figures 1 and 2). Replacement of existing barriers, however, will become an increasingly important issue in the next decade. If each barrier's service life were 2 years, then 2% of U.S. noise barriers (425 km) would require replacement by 21; approximately 33% (687 km) would require replacement by 25, and nearly 5% (1,32 km) would require replacement by 28 (Figure 3). By 215, all the barrier length constructed through 1995 (2,121 km) would require replacement. However, if the barriers have a 5-year service life, replacement would not begin until 22 (.5%, or 1 km, of barrier). Similar results are obtained for both IDOT and ISTHA (Figures 4 and 5). Specifically for IDOT, if a 2-year service life is assumed, 2% of the barrier length (7.5 km) constructed as of 1993 will be 2 years old in 2. By 26, 53% (2.2 km) of barrier length would require replacement, and by 213, % of the length (38.3 km) would require replacement. For ISTHA, 36% of the barrier length will reach 2 years old (21.2 km) in 28, and % (58.6 km) will reach 2 years old in 216. Due to the aging of existing barriers and the large capital expenditures required to construct a noise barrier, it is important for designers to have information with which to make rational choices between the materials available. Designers, however, face difficulty due to a lack of available information on both existing materials and designs as well as the many new products being introduced that are not typical in highway construction, e.g., recycled materials and plastics. Therefore, IDOT requested that the Illinois Transportation Research Center (a cooperative research unit of IDOT and 12 public and private Illinois universities) oversee research to estimate the service lives of the various noise barrier materials and products currently in use in Illinois and to develop a life cycle cost model for evaluation of alternative materials. The research project was conducted in 1997 and 1998.

3 Morgan and Kay 2 FIGURE 1 Noise barrier length constructed annually in the U.S. (2). 25 Linear Length (km) FIGURE 2 Cumulative percent of noise barrier length constructed annually in the U.S. through 1995 (2). Cumulative Percent Length FIGURE 3 Cumulative percent of barrier length nationally requiring replacement for service lives of 2 to 5 years (2). a Cumulative Percent at Service Life years 3 years 4 years 5 years a All these estimates neglect 9 km of barrier, which is.42% of the length constructed as of 1995, because it cannot be assigned a construction year.

4 Morgan and Kay 3 FIGURE 4 IDOT cumulative percent of barrier length requiring replacement for service lives of 2 to 5 years. Cumulative Percent at Service Life years 3 years 4 years 5 years FIGURE 5 ISTHA cumulative percent of barrier length requiring replacement for service lives of 2 to 5 years. Cumulative Percent at Service Life years 3 years 4 years MATERIAL PERFORMANCE AND SERVICE LIFE The service life of a noise barrier can be defined as the period of trouble-free performance with no discernible change in barrier insertion loss or appearance. The 4 states having noise barriers (2) were surveyed regarding their experiences with noise barriers and noise barrier materials (3); 3 states (75%) completed the survey. Over half the states had repaired or replaced noise barriers or were considering barrier repair or replacement. However, nationally, less than 1% of noise barriers by length had been repaired or replaced or were being considered for repair or replacement according the survey results. Repairs and replacements generally appear to have been due to vehicle damage or poor performance structurally or aesthetically; only one state reported performing repairs or replacements due to normal aging. One-third of the states that had repaired or replaced walls (six of 18) changed construction specifications as a result of the repairs or replacements, and half (nine) changed design specifications. However, the majority of states (67%) did not have a formal design life policy for noise barrier walls. For those states with policies, over half used 2 years or less, which is less than the reported maintenance period of more than 2 years.

5 Morgan and Kay 4 Nationwide, concrete has been used for noise barriers more than any other single material (although this is not the case for IDOT) (Figure 6 and Table 1). However, despite this wide use of concrete, only 13% of the states had repaired or replaced concrete barriers or were considering repairing or replacing concrete barriers. On the other hand, metal, which made up only 3% of the length of barriers constructed, had been repaired or replaced or was being considered for repair or replacement by 2% of the states responding to the survey, and wood, which made up approximately 14% of the length of barriers constructed, had been repaired or replaced or was being considered for repair or replacement by 23% of the states. Precast concrete, cast-in-place concrete, block walls, and berms received generally favorable comments from the respondents regarding construction cost, maintenance costs, and field performance. Precast concrete received the most comments about positive acoustical and structural performance while berms received the most comments about positive economic and aesthetic performance. The main negative comment received about berms was the need for large amounts of right-of-way. Metal walls received the highest percentage of negative comments for maintenance costs and wood barriers (both hardwood and softwood) received the highest percentage of negative comments for acoustics. FIGURE 6 Percent of total noise barrier length nationally by material type 197 to 1992 (2). TABLE 1 Comparison of U.S. and Illinois Noise Barrier Material Types (1, IDOT and ISTHA unpublished data) Barrier Area (%) a Material U.S. ISTHA IDOT Concrete Block 28 Combination Wood Berm Only 3 9 Metal 3 3 Brick 1 a Percents to not add to because not all materials are included.

6 Morgan and Kay 5 For most of the survey respondents, the most important factors when choosing noise barrier materials were construction cost and durability followed closely by in-state experience, initial appearance, and noise reduction. Similarly, survey respondents ranked construction cost and structural performance as the most important factors considered when determining service life. Few respondents ranked acoustical performance or maintenance cost as the most important factor when determining service life. There was no consensus among survey respondents on the average service life of noise barriers, although 2 years was considered a minimum (Figure 7). Due to the limited data, regional differences and similarities cannot be determined; however, four of the six highest estimates were from northeastern states (Table 2). Despite a minimum service life estimate of 2 years, all the respondents reported being responsible for the walls for more than 2 years. Despite this responsibility, most of the respondents did not have a maintenance program for their walls. The activities of those states that had programs were generally related to aesthetics maintaining landscaping, cleaning, or coating. Only 17% of the respondents conducted structural or visual inspections of walls, and none of the respondents conducted acoustic testing as part of a maintenance program, despite the importance of durability and acoustical performance to the states when selecting noise barrier materials. In fact, half the respondents did not consider failure to meet insertion loss and/or noise level criteria to be reason to replace a barrier, although noise reduction is the ostensible purpose of the walls. Periodic inspections of a noise barrier's structural, acoustical, and aesthetic performance are the ideal method to determine the end of barrier service life. However, based on the authors findings, these types of inspections are not being performed, so data is lacking to calculate service lives accurately. Therefore, the authors used information obtained from the literature, the survey of state DOT noise personnel, a survey of IDOT maintenance personnel, field observations of barriers in several states, and engineering judgment to estimate the service lives of the materials and products in service in Illinois. Based on the findings, glue-laminated softwood and metal products were estimated to have 25-year service lives, and earth berms, concrete, and fiberglass reinforced polymer composite were estimated to have 5-year service lives (3). The estimated service life for fiberglass reinforced polymer composite was based only on vendor literature and is not verifiable due to the short in-service life in Illinois. These estimates were subsequently used in developing a life cycle cost model to evaluate alternative materials for noise barriers. FIGURE 7 Estimated average service life of barriers by survey respondents. a a Based on 24 responses. Percentages do not add to due to rounding.

7 Morgan and Kay 6 TABLE 2 Comparison by Region of Estimated Average Service Life by Survey Respondents Number Reporting Estimated Service Life (years) Region Midwest a Northwest b 1 Southwest c 4 1 Southeast d Northeast e a The midwest region surveyed included 1 states (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, Ohio, and Wisconsin). Eight of these states responded to the survey; five answered the question about service life. b The northwest region surveyed included two states (Oregon and Washington). One of these states responded to the survey and answered the question about service life. c The southwest surveyed region included eight states (Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas, and Utah). Six of these states responded to the survey; five answered the question about service life. d The southeast region surveyed included nine states (Arkansas, Florida, Georgia, Kentucky, Louisiana, North Carolina, South Carolina, Tennessee, and Virginia). Six of these states responded to the survey and answered the question about service life. e The northeast region surveyed included 11 states (Connecticut, Delaware, Maine, Massachusetts, Maryland, New Hampshire, New Jersey, New York, Pennsylvania, Vermont, and West Virginia). Nine of these states responded to the survey; seven answered the question about service life. LIFE CYCLE COST ANALYSIS The authors developed a life cycle cost model using assumptions based on the information collected during the course of the research project (3, 4, Table 3 footnote a ). Current materials used for and pre-approved for noise barrier walls in Illinois were analyzed with the model using Springfield, Illinois and year 2 as bases. Because the estimates include all costs required to construct each barrier (including such items as foundations, contractor's overhead, contingency, and profit) as well as costs to maintain and, if necessary, replace each barrier, these estimates vary significantly from the average barrier costs reported by FHWA (1996). However, they should be a better indication of the actual cost for each barrier. The results indicated that earth berms represented the lowest cost alternative at approximately $15 per square meter ($14 per square foot) while both steel and aluminum barriers with absorptive panels were the most expensive at 2.9 and 3.6 times the cost of berms, respectively. The life cycle costs of the other barrier materials modeled (wood, concrete, fiberglass reinforced polymer composite, and composite concrete sandwich panels covered with compressed cemented wood shavings) fell within a relatively narrow range near $32 per square meter ($3 per square foot), more than twice the cost of earth berms. A sensitivity analysis showed that the two most important variables in determining life cycle cost are the initial construction cost and the service life. The costs of maintenance activities were small compared to the cost of construction and replacement, so variations in assumptions regarding maintenance were relatively insignificant for all barrier materials. Changing service life assumptions had the greatest impact on barriers that were initially assumed to have 5-year lives (which were earth berms, concrete, and fiberglass reinforced polymer composite). For example, reducing the assumed service life of concrete barriers by 5 years or more increased the estimated life cycle cost by at least 34% while increasing the assumed service life of wood barriers by 5 years or more reduced the estimated life cycle cost by only 1 to 15%. Clearly, historical data on service lives of noise barrier materials is required to perform accurate LCCA. In addition, field data on replacement costs and frequency as well as maintenance costs and frequency are required. The cost and frequency estimates used in the model were not readily verifiable due to a lack of maintenance records and a lack of the breakdown of costs in those records that were available. In fact, this difficulty of obtaining historical field data is the primary reason why 7% of respondents to the survey of state DOT noise personnel did not use LCCA to select noise barrier materials.

8 Morgan and Kay 7 CONCLUSIONS Despite the obstacles to using LCCA to select noise barrier materials, it can serve as an additional tool to rank the cost effectiveness of alternative materials and designs. As can be seen in Table 3, life cycle costs can significantly impact the relative costs of noise barrier materials. However, it may not be practical to use LCCA as the sole criterion for selecting noise barrier materials. First, the lack of reliable historical field data on the costs and frequency of maintenance and replacement of noise barriers hinders the accuracy of the model. Few national noise barriers and no Illinois barriers have failed due to old age. In addition, most noise barriers are not subject to routine inspection and maintenance but are repaired in response to discrete events, such as vehicle impacts and public complaints. Therefore, there remains a lack of data to show clear differences in the maintenance requirements or the service lives of various products currently in use. Second, the performance of a highway noise barrier must be judged in at least three ways acoustically, structurally, and aesthetically. These performance criteria, in particular the involvement of the public in judging appearance, make highway noise barriers unique in the highway environment. Most highway elements are judged solely on structural performance, and criteria for determining minimum acceptable performance are well established, even though these criteria are often subjective and dependent on the evaluation of experienced observers (as in the determination of pavement distresses using the Condition Rating System (5)). Similar criteria and rating systems do not exist for determining the serviceability of noise barriers and, in fact, may be impossible to create. Whereas highway pavements are constructed of either of two basic materials, portland cement concrete or bituminous concrete, noise barriers can be constructed of any one of dozens of materials or proprietary products. In addition, assessment of the acoustical performance of miles of highway noise barrier cannot be accomplished as easily as the appearance of highway pavement can be videotaped from a specially equipped van. Finally, the assessment of the aesthetics of highway noise barriers is a matter of personal taste, not only of highway officials but the public at large. An aesthetic rating system representing such a diversity of personal opinions would be difficult to devise. Other factors that limit the usefulness of LCCA as a means of selecting noise barrier materials are the need for design flexibility to respond to engineering considerations (for example, weight limitations on structures or land availability) and the opportunity to use innovative technologies. While LCCA may in theory provide a more rational means of selecting noise barrier materials, it should be recognized that the best choice for a given situation might involve trade-offs between several of the considerations discussed. LCCA can provide an additional piece of information in the selection process but should not be used as the sole criterion for material selection. TABLE 3 Comparison of Ranking by Initial Construction Cost and Life Cycle Cost for Barriers in Illinois a Barrier Rank by Initial Rank by Life Change in Construction Cost Cycle Cost Ranking Earth berm 1 1 Timber post-and-panel Glue-laminated wood Precast/prestressed concrete stacked panels, steel posts b 4/5 2 +2/+3 Composite concrete sandwich panels covered with 4/5 9-4/-5 compressed cemented wood shavings Precast/prestressed concrete stacked panels, concrete posts b Fiberglass reinforced polymer composite Precast/prestressed cantilever Steel Precast concrete, full-height panels, monolithic posts Aluminum a Costs and, thus, rankings are based on assumptions outlined in detail in Reference 3. A standard barrier section 35 m ( ft) in length by 4.6 m (15 ft) in height was assumed for all barriers. Berms were assumed to be constructed of excess materials available at the site and to include 3 m ( ft) of right-of-way with no cost premium; however, calculations assuming land acquisition at $12,35/ha ($5,/ac) did not change the rankings. Drilled pier foundations 2.4 m (8 ft) deep were assumed for all barriers except the precast/prestressed concrete cantilever and earth berm. Drilled pier diameters and post spacing were assumed based on Illinois designs and vendor data; diameters ranged from cm (24 39 in), and post spacing was limited to m (28 3 ft). b Precast/prestressed concrete stacked panels are included for comparison although none have been built in Illinois.

9 Morgan and Kay 8 ACKNOWLEDGMENTS The authors wish to acknowledge the Illinois Transportation Research Center (ITRC) for funding the project on which this paper is based and the survey respondents for taking time to complete the surveys. This paper does not necessarily reflect the views of ITRC or the Illinois Department of Transportation. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. REFERENCES 1. FHWA. Unusual Features of Noise Barriers and Other (Non-Barrier) Abatement Measures Implemented by December 31, U.S. Department of Transportation, FHWA. Summary of Noise Barriers Constructed by December 31, U. S. Department of Transportation, Kay, D., S. M. Morgan, and S. N. Bodapati. Evaluation of Service Life of Noise Barrier Walls in Illinois. Report No. ITRC FR Illinois Transportation Research Center, Illinois Department of Transportation, Morgan, S. M., D. H. Kay, and S. N. Bodapati. A Study of Noise Barrier Life Cycle Costing. Journal of Transportation Engineering. Accepted for March 21 publication. 5. Buttlar, W.G., D. Bozkurt, and B.J. Dempsey. Evaluation of Reflective Crack Control Policy. Report No. ITRC-F Illinois Transportation Research Center Report, Illinois Department of Transportation, 1999.