Q: How long will a concrete pavement typically last?
A: It is common for concrete pavements to last 30 years or more1 before major rehabilitation. Even after the first major rehabilitation, many concrete pavements continue to remain in service for several more years2. In fact, the first concrete city street in Iowa was built in 1904 in LeMars (Eagle Street now First Ave NW), was not overlaid until the late 1960s, and is still in use today.
Concrete pavements allow great flexibility in design life by providing the designer with the broadest possible range. In the past, it was common to design concrete pavements for 30 years3. Today, concrete pavements are being designed for service lives of 30 to 50 years. The Iowa Department of Transportation (DOT), for example, has moved to a service life of 40 years4 while the Minnesota DOT uses 50 years5. The Statewide Urban Design and Specifications (SUDAS) also include a 50 year design life for concrete pavements6.
Concrete pavements allow great flexibility in design life by providing the designer with the broadest possible range. In the past, it was common to design concrete pavements for 30 years3. Today, concrete pavements are being designed for service lives of 30 to 50 years. The Iowa Department of Transportation (DOT), for example, has moved to a service life of 40 years4 while the Minnesota DOT uses 50 years5. The Statewide Urban Design and Specifications (SUDAS) also include a 50 year design life for concrete pavements6.
Q: How does the service life of concrete compare to that of asphalt?
A: Typical comparisons of service lives between asphalt and concrete show a ratio of about 2:1, with concrete having the higher of the two7. Iowa DOT, and others, use this ratio in their pavement type selection process8. A similar ratio is also reflected in the SUDAS pavement design guidance which uses a 50 year design for concrete and a 30 year design for asphalt9.
Iowa's primary highway system further demonstrates the greater longevity of concrete pavements10. Our primary system includes about 1,300 miles of concrete pavements over 30 years old that have never been overlaid. There are no asphalt pavements on today's primary system in Iowa that have made it over 30 years without overlay and only about 1% (25 miles) of Iowa's asphalt pavements have made it to 20 years without overlay.
Iowa's primary highway system further demonstrates the greater longevity of concrete pavements10. Our primary system includes about 1,300 miles of concrete pavements over 30 years old that have never been overlaid. There are no asphalt pavements on today's primary system in Iowa that have made it over 30 years without overlay and only about 1% (25 miles) of Iowa's asphalt pavements have made it to 20 years without overlay.
Q: How closely does concrete compare to asphalt on initial cost?
A: In Iowa, the cost to construct a concrete pavement is typically within 10% of the cost to construct an equivalently designed asphalt pavement11. We sometimes see comparisons that do not use equivalent designs and these should not be used as a true comparison of construction costs. For example, comparing the cost to construct an 8" asphalt pavement to the cost to construct an 8" concrete pavement would not give accurate results because 8" of concrete will carry far more load than 8" of asphalt12. This would be like comparing the cost to construct an 8" concrete pavement to the cost to construct a 10" concrete pavement.
Q: Which type of pavement costs less to maintain?
A: Studies conducted in the Midwest indicate that concrete pavements cost significantly less to maintain13. In support of these results, many agencies include relatively few maintenance activities for concrete in their pavement type selection processes14. Specifically, the only maintenance activity reflected in Iowa DOT's analysis is joint resealing.
Q: Which type of pavement costs less to own?
A: The Iowa Concrete Paving Association recommends using Life Cycle Cost Analysis (LCCA) as a means to evaluate the true cost of owning a pavement. 15LCCA takes into account the construction costs, maintenance costs, and the service life of the pavement. In its simplest form, LCCA would be the sum of the two costs divided by the number of years in the evaluation period. An accurate LCCA will include equivalently designed pavement sections and an evaluation period equal to the longest of the service lives for all pavement options. It is important to note that equivalently designed concrete and asphalt pavement sections will not perform equivalently. For example, Iowa DOT's pavement type selection process uses equivalent designs, but the asphalt pavement is projected to require major rehabilitation in half the time as the concrete pavement16.
Under long-term analysis like properly conducted LCCAs, concrete pavements are commonly found to be the most cost effective options. Studies across the country report significant savings (upwards of 72% in one Iowa study17) as a result of selecting concrete over asphalt18.
There is probably no agency in Iowa that has more experience with pavement construction and maintenance than the Iowa DOT. Each year, the Iowa DOT performs life cycle cost analysis for each of their upcoming paving projects. After performing LCCAs, the Iowa DOT selects concrete over 90% of the time19.
Under long-term analysis like properly conducted LCCAs, concrete pavements are commonly found to be the most cost effective options. Studies across the country report significant savings (upwards of 72% in one Iowa study17) as a result of selecting concrete over asphalt18.
There is probably no agency in Iowa that has more experience with pavement construction and maintenance than the Iowa DOT. Each year, the Iowa DOT performs life cycle cost analysis for each of their upcoming paving projects. After performing LCCAs, the Iowa DOT selects concrete over 90% of the time19.
1 City of West Des Moines, 2004 Street Management System Report and ERES Studies of:
Interstate 15 - Utah
Interstate 40 - Oklahoma
Interstate 40 - Tennessee
2 Quick Guide to Transportation System Facts
3 Iowa DOT's 30 Year Design Pavement Type Selection Process
4 Iowa DOT's 40 Year Design Pavement Type Selection Process
5 MnDOT's Pavement Selection Life Cycle Cost Analysis
6 Statewide Urban Design and Specifications (SUDAS)
7 ERES Studies and City of West Des Moines, 2004 Street Management System Report
8 Iowa DOT's 40 Year Design Pavement Type Selection Process and MnDOT's Pavement Selection Life Cycle Cost Analysis
9 SUDAS
10 Quick Guide to Transportation System Facts
11 Alternate Bidding – Bid Tabs
12 Equivalency Chart for Concrete and Asphalt Pavements
13 Impact of Pavement Type on County Road Systems and A Comparison of the Life-Cycle Costs of Asphalt Concrete and Portland Cement Concrete Pavements in Olmsted County, Minnesota
14 Iowa DOT's 40 Year Design Pavement Type Selection Process, MnDOT's Pavement Selection Life Cycle Cost Analysis, examples of maintenance projections from City of Cedar Falls and City of Carroll (pavement type selection processes)
15 Life Cycle Cost Analysis: A Guide for Comparing Alternate Pavement Designs
16 Iowa DOT's 40 Year Design Pavement Type Selection Process
17 Impact of Pavement Type on County Road Systems
18 Impact of Pavement Type on County Road Systems; A Comparison of the Life-Cycle Costs of Asphalt Concrete and Portland Cement Concrete Pavements in Olmsted County, Minnesota; ERES' studies from Utah, Oklahoma, and Tennessee
19 Iowa DOT Full-Depth Paving Projects by Pavement Type (2000-2004)