Environmental Benefits of Life Cycle Design of Concrete Bridges
Zoubir Lounis & Lyne DaigleUrban Infrastructure Research Program
3rd International Conference on Life Cycle ManagementAugust 27-29,2007 Zurich
Outline
• Introduction
• Life cycle design of concrete bridges
• Environmental and economic benefits of HPC bridges
• Case study
• Conclusions
Introduction
• Highway bridges: critical links in Canada’s transportation network– Enable personal mobility– Transport of goods– Support economy – Ensure high quality of life
• Design life = 50 -100 years requiring:– Inspections, maintenance– Rehabilitation– Replacement of components (deck, walls, bearings)– Replacement of superstructure– Replacement of substructure
Introduction
• State of highway bridges – Extensive deterioration– Reduced safety, serviceability, and functionality – Increased traffic disruption and user costs– Increased risk of fatalities/injuries– Increased maintenance
• Causes– Aging bridge network: average service life = 45 years– Increased traffic volume and load– Aggressive environment (snow, freeze-thaw, deicing salts)– Variations of environmental loads due to climate change– Inadequate funding for maintenance and renewal of bridges
Introduction
• Objectives : design long life bridges using high performance concrete– low maintenance costs
– minimized traffic disruption
– minimized environmental impacts
– optimized maintenance strategies
– sustainable bridges
Introduction
• Bridge Ponte Fabricio (or Ponte Quattro Capi)– oldest bridge in Rome (built in 62 BC) – 2 arches + central pillar– 62 m span; 5.5 m width – Built of Tufa, volcanic tuff and travertine
• Inca Rope Suspension Bridge in Peru (14th-15th century)– 67 m span; 37 m above the river – Built of woven grass for cables reinforced with branches– Cables are replaced every year by local villagers
Examples of Sustainable Bridges
Design Construction Use Deterioration
InspectionMaintenance
Rehabilitation
Replacement
Failure/Demolition
Deterioration
Recycling Deterioration
Road Sub-base Disposal Landfill
Materials & components manufacturing
Life Cycle Design of Concrete Bridges
Life Cycle of Highway Bridges
• Life cycle design of bridges = complex decision problem– Optimized designs for initial bridge and subsequent
maintenance, rehabilitations, and replacement stages– Need life cycle performance models to predict bridge
deterioration and service life– Need models to predict environmental impact– Multi-objective optimization problem
• Minimize cost• Maximize service life• Minimize environmental impact (GHG emissions, waste)
Life Cycle Design of Concrete Bridges
Time (years)
Limit state
Option #1: Conventional Bridge Design
Residual life
Life cycle
Perform
ance
Maintenance
Service life 1 Service life 2 Service life 3
Life Cycle Design of Concrete Bridges
Time (years)
Limit state
Life cycle
Perform
ance
Maintenance
Service life 1 Service life 2
Option #2: High Performance Concrete (HPC) Bridge Design
Environmental Loads on Bridges(snow, freeze-thaw cycles, deicing salts/chlorides,
wind, temperature gradients) + δHighway Bridges
Natural Environment
Bridge Loads on Natural Environment(GHG emissions, demolished elements/materials,…)
Life cycle performance
Life cycle environmental analysis
Corrosion, cracking, spalling, collapse
Global warming, ecological toxicity, etc.
Complex Interaction between highway bridges and natural environment
δ=variation in environmental loads due climate change
Life Cycle Design of Concrete Bridges
• Cement– Cement =critical component of concrete– World cement production= 2 billion tons in 2004; 7.5 billion tons in 2050 – Production of 1 ton cement leads to 0.8 -1.0 ton of CO2 emissions– World cement production accounts for 5% of world CO2 emissions– World cement production consumes 2% of world energy
Environmental & Economic Benefits of HPC Bridges
• Reinforced Concrete vs. Cement– Cement constitutes only 5% to 18% of concrete (by weight)– Aggregate (course and fine) make up 65%-70% of concrete– Concrete is made of readily available local materials (aggregate & water) – Enables to recycle industrial waste (fly ash, slag) – Low energy requirements for aggregate and water– Reinforcing steel is made from recycled steel
0
2
4
6
8
10
12
14
16
18
CementProduction
Iron & Steel Non-FerousMetals
Mining Pulp &Paper
Emis
sion
s of
CO
2 eq
(mill
ion
tons
)
Environmental & Economic Benefits of HPC Bridges
2005 Environment Canada Data
Units in kg/m3 of concrete
157
1110 (46%)
528 (22%)
132432 (18%)
30
6.5%5.5%
(2%)
Course aggregate
Cement
Fineaggregate
WaterFlyAsh
Silica Fume
Environmental & Economic Benefits of HPC Bridges
Mix design of high performance prestressed concrete bridge girders:
w/cm=0.27 f’c=69 MPa Chloride permeability=1010 coulombs
Coarse aggregate
1110
Cement
432
Fine aggregate
528
Water157
Fly Ash132
• Incorporate industrial waste having cementitious properties in concrete– Fly ash: by-product of thermal power generating stations– Slag: by-product of processing iron ore to iron & steel in blast furnace– Silica fume: by-product of silicon and ferro-silicon metal production
Environmental & Economic Benefits of HPC Bridges
• Benefits– Increased strength and reduced permeability– Reduced consumption of cement– Reduced GHG emissions– Reduced volume of land-filled materials– Reduced life cycle cost
Equal
reinforcement
(0.3%)
Top face
Bottom face
Concrete cover depth
60
Main reinforcement
200
Temperature & shrinkage reinforcement
Distribution reinforcement
Cast-in place reinforced concrete deck
S S
Detail of deck
Prestressed concrete girders
200 mm
12.35 m
Case Study: Life Cycle Design of Bridge Decks
Bridge length = 35 m
Case Study: Life Cycle Design of Bridge Decks
• Two bridge deck design options– Conventional deck using normal concrete– High performance concrete deck using fly ash, slag, silica fume– Life cycle =30 years; Discount rate = 3%
• Service life– Time to onset of corrosion
• Environmental impacts– CO2 emissions– Construction waste materials
• Costs– Owner costs (construction + maintenance)– User costs ( delay, accident, vehicle operation)
Case Study: Life Cycle Design of Bridge Decks
05
1015
202530354045
ConventionalDeck
HPC Deck
Serv
ice
life
(yea
rs)
Case Study: Life Cycle Design of Bridge Decks
• Conventional bridge deck–Service life = 15 years
–Requires• 4 detailed inspections;2 replacements of asphalt overlay + routine inspection every 2 years
• 4 patch repairs and 1 replacement at 15 years
• High performance bridge deck–Service life = 30 years
–Requires•2 patch repairs + routine inspection every 2 years
Life cycle = 30 years
Case Study: Life Cycle Design of Bridge Decks
140
49
0.2
114
151
53
0
20
40
60
80
100
120
140
160
NPC deck HPC deck
CO
2 em
issi
ons
(kg/
deck
m2 )
Cement production
Transportation
Car delay during MRR activities
Total
Conventional Bridge Deck HPC Bridge Deck
CO2 emissions over life cycles of bridge decks
Case Study: Life Cycle Design of Bridge Decks
Volume of waste materials produced over life cycles of bridge decks
-0.01
0.16 0.16
0.04 0.02
0.28
0.48
0.17
-0.2
0
0.2
0.4
0.6
0.8
NPC deck HPC deck
Land
fill u
se fo
r was
te m
ater
ial (
m3 / d
eck
m2 )
ConstructionAsphalt OverlayPatch RepairReplacementTotal
Conventional Bridge Deck HPC Bridge Deck
Case Study: Life Cycle Design of Bridge Decks
0100200300400500600700800900
1000
ConventionalDeck
HPC Deck
987
524584
Life Cycle Owner’s Costs of Bridge Decks ($/m2)
Case Study: Life Cycle Design of Bridge Decks
53.35
16.21
23.51
7.07
14.86
4.47
14.98
4.67
0
10
20
30
40
50
60
NPC deck HPC deck
Pres
ent V
alue
Use
r Cos
ts ($
/m2 ) Total User Costs
Delay Costs
Vehicle Operating Costs
Accident Costs
Life Cycle User Costs of Bridge Decks ($/m2)
Conventional Deck HPC Deck
Case Study: Life Cycle Design of Bridge Decks
• Service life– Conventional bridge deck = 15 years– HPC bridge deck = 30 years
• Life cycle CO2 emissions– Conventional bridge deck = 151 kg/m2
– HPC bridge deck = 53 kg/m2
• Life cycle production of waste materials– Conventional bridge deck = 0.48 m3/m2
– HPC bridge deck = 0.17 m3/m2
• Life cycle costs– Conventional bridge deck = $1040/m2
– HPC bridge deck = $560 /m2
Summary
Conclusions
• Life cycle design of highway bridges using HPC yields:
– long service life bridges
– low maintenance costs
– Reduced energy and materials consumption
– Reduced CO2 emissions
– Reduced volume of land-filled materials
– Recycling of industrial byproducts
– Reduced life cycle costs for owners and users of bridges