Life-Cycle Cost Survey of Concrete Bridge Decks ΠA Benchmark for FRP Bridge Deck Replacement

Lopez-Anido, Roberto A

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• Langue: English

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January 7-11, 2001
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HELP EXITLife-Cycle Cost Survey of Concrete Bridge Decks– A Benchmark for FRP Bridge
Deck Replacement
Roberto Lopez-Anido
Assistant Professor
Department of Civil and Environmental Engineering
Advanced Engineered Wood Composites Center
University of Maine

ABSTRACT
A study on the life-cycle cost and performance of concrete bridge decks was conducted to establish a
benchmark for fiber-reinforced polymer (FRP) bridge decks. A survey was developed and distributed to
State Departments of Transportation engineers and the responses were analyzed. The survey facilitated
identifying and estimating the cost parameters associated to concrete bridge deck replacement, and
correlating cost with traffic volume, bridge span length, age and climate. The cost assessment included:
removal and disposal, construction, maintenance and overlay repair. The resulting life span of concrete
decks ranged from 36 to 54 years depending on the average daily traffic. The average cost to construct a
reinforced concrete deck was $29.50 per square foot during1997-1998. Although the first cost of a
replacement FRP bridge deck is typically higher than the corresponding one for a conventional concrete
deck, other cost advantages of FRP bridge decks may partially, or completely, compensate for the higher
initial cost. The data analyzed provides a baseline to evaluate economic and durability performance
requirements of FRP bridge decks.
INTRODUCTION
Of all elements in a bridge superstructure, bridge decks may perhaps require the maximum
maintenance, for reasons ranging from the deterioration of the wearing surface to the degradation of the
deck system itself. In addition, a large number of bridge decks are structurally deficient or functionally
obsolete due to higher load ratings (HS20 to HS25, for example) and increased number of lanes to
accommodate the ever-increasing traffic flow on major arteries (1). Based on the National Bridge Inventory
rating, deck geometry and deck condition are among the most prevalent items with respect to deficiency
percentages (1). Bridge deck deficiencies are related to physical deterioration due to environmental
conditions, maintenance policies, and unanticipated factors such us fatigue, high friction and dynamic
responses, among others. Beyond the costs and visible consequences associated with continuous retrofit
and repair of such structural components are the real consequences related to losses in productivity and
overall economies related to time and resources caused by delays and detours (2).
Replacing and/or upgrading these bridge decks to today’s design standards are more economical
alternatives to replacing the bridges themselves (3). One advantage of a deck replacement alternative
compared to entire bridge replacement is the timeliness in initiating the project, i.e., deck replacement
shortens the length of time the public has to suffer with a posted bridge. For example deck replacements
have a shorter lead-time because typically the work is technically simpler than the bridge replacement
alternative. Besides, deck replacements also have fewer environmental impacts than entire bridge
replacement.
Reasons such as those listed above provide significant impetus for the development of new bridge decks
out of materials that are durable, light and easy to install. Besides the potentially lower overall Life-Cycle
Costs (LCC) (4) (5) (6) (7), decks fabricated from fiber reinforced composites are significantly lighter,
thereby affecting savings in substructure costs, enabling the use of higher live load levels in the case of
replacement decks, and bringing forth the potential of longer unsupported spans and enhanced seismic
resistance (1). Fiber reinforced polymer (FRP) composites are relatively new construction materials that are
technically viable to replace conventional materials in bridge decks (3) (8) (9) (10) (11) (12). However, one
of the major obstacles against the use of FRP bridge decks is their high initial cost and the uncertainty on
the service life.
2 A practical discussion on the economy and evaluation criteria of bridge decks can be found in (14). To
justify the use of fiber-reinforced composites for bridge construction and replacements an economic
evaluation process between conventional concrete bridge deck and new FRP composite deck systems need
to be carried out. Life Cycle Cost Analysis is the most appropriate economic evaluation process for
emerging construction materials as it takes into consideration all costs from construction, maintenance of
the facility, replacement, and associated user impacts over the service life of all alternatives (5) (15) (16).
For example, a life-cycle benefit-cost model for composites in construction that does not require monetary
quantification of benefits for comparison of alternative materials was presented in (17). In particular, the
life-cycle cost of FRP bridge decks shall include (18): (1) Construction costs; (2) Maintenance cost (labor
and materials); (3) User’s delay costs (operation and maintenance); and (4) Traffic management costs
(during maintenance).
The value of economic analyses for evaluating FRP-reinforced concrete beams versus conventional
reinforced concrete beams was shown in (19). In order to establish a baseline comparison of FRP decks
with conventional concrete decks a survey was prepared and sent to select State Departments of
Transportation (DOTs) across the Nation. This study contributes to the understanding of the life-cycle cost
of reinforced concrete decks in order to establish benchmark cost and durability performance for FRP
bridge decks.
FRP BRIDGE DECKS
FRP composites have been used for decks, beams and superstructures of pedestrian and highway
bridges (2). Most recently, the focus on FRP composite bridge developments focused on decks supported
by concrete and steel girders (3) (8)(9) (10) (11) (12). Several FRP deck systems have been developed and
used in demonstration projects both for replacement of aged concrete or wood decks, as well as for new
construction. Examples of FRP composite deck systems that have been used for bridge construction are
presented in TABLE 1.
The first cost of a replacement FRP bridge deck is typically higher than the first cost of a replacement
concrete deck. However, other cost advantages of FRP bridge decks may partly, or fully, compensate for
the higher first cost (13). The proposed benchmark for FRP bridge decks is the life-cycle cost of
conventional reinforced concrete decks. Therefore, to assess the cost and durability performance of FRP
bridge decks, the benchmark parameters need to be correlated to bridge geometry, age, climate, and
average daily traffic. The following issues need to be properly addressed: What shall be the maximum
initial cost of FRP bridge decks? What installation method shall be adopted for FRP bridge decks? What
are the maintenance benefits that need to be realized? What shall be the durability requirements for FRP
bridge decks (e.g., 50 or 75 year life span)? What type of wearing surface shall be considered for FRP
bridge decks? What range of traffic volume has more benefits for FRP bridge decks? For what span range
FRP bridge decks are more competitive?
CONCRETE DECK REPLACEMENT SURVEY
To characterize benchmark parameters for FRP bridge decks, a survey on concrete bridge deck
replacement was conducted to evaluate the owner and user’s costs during the life cycle of a highway bridge
deck (6). The goal of the survey was to estimate the cost items associated to concrete bridge deck
replacement, to correlate cost with traffic volume, bridge span length, age and climate, and to identify what
are the main parameters that control the life-cycle cost. A questionnaire was developed and distributed to
State DOT engineers. The questionnaire asked for information on the life span of bridge decks, time span
for overlay repair, construction time and cost including deck, mobilization and traffic control, maintenance
practice and cost, and replacement and disposal costs. Responses were received in January 1998 from
twelve DOTs. The respondents were asked to correlate specific items with average daily traffic and with
bridge span length. The diversity in the geographic locations of the participating DOTs provided
representative data on life cycle of concrete decks, as shown in TABLE 2.
The following three span length ranges were assumed in the questionnaire:
(1) Short Span: less than 15.2m (50 ft.),
(2) Medium Span: from 15.2 to 45.7 m (50 to 150 ft.), and
(3) Long Span: more than 45.7 m (150 ft.).
3 The average daily traffic (ADT) was classified in four ranges in the questions related to the life span of
decks, as follows:
(1) Low Volume: less than 5000,
(2) Low to moderate volume: between 5000 to 20,000,
(3) Moderate to high volume: between 20000 to 40000, and
(4) High Volume: greater than 40000.
LIFE-CYCLE COST AND PERFORMANCE ASSESSMENT
The condition rating of highway bridges has been correlated with two factors (20): age and average