3 rd International Conference on Life Cycle Management August 27-29,2007 Zurich Environmental Benefits of Life Cycle Design of Concrete Bridges Zoubir Lounis & Lyne Daigle Urban Infrastructure Research Program
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 Examples of Sustainable Bridges • 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 (14 th -15 th 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
Life Cycle Design of Concrete Bridges Life Cycle of Highway Bridges Materials & Design Construction Use Deterioration components manufacturing Maintenance Inspection Replacement Deterioration Rehabilitation Failure/ Recycling Deterioration Demolition Road Sub-base Disposal Landfill
Life Cycle Design of Concrete 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 Option #1: Conventional Bridge Design Maintenance Performance Limit state Service life 1 Service life 2 Service life 3 Residual life Life cycle Time (years) Option #2: High Performance Concrete (HPC) Bridge Design Maintenance Performance Limit state Service life 1 Service life 2 Life cycle Time (years)
Life Cycle Design of Concrete Bridges Bridge Loads on Natural Environment (GHG emissions, demolished elements/materials,…) Environmental Loads on Bridges Natural Highway (snow, freeze-thaw cycles, deicing salts/chlorides, Environment wind, temperature gradients) + δ Bridges Life cycle environmental Life cycle analysis δ =variation in environmental performance loads due climate change Global warming, Corrosion, cracking, ecological toxicity, etc. spalling, collapse Complex Interaction between highway bridges and natural environment
Environmental & Economic Benefits of HPC 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 CO 2 emissions – World cement production accounts for 5% of world CO 2 emissions – World cement production consumes 2% of world energy • 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
Environmental & Economic Benefits of HPC Bridges 2005 Environment Canada Data 18 Emissions of CO2 eq (million tons) 16 14 12 10 8 6 4 2 0 Cement Iron & Steel Non-Ferous Mining Pulp & Production Metals Paper
Environmental & Economic Benefits of HPC Bridges Mix design of high performance prestressed concrete bridge girders: Silica Fume 30 (2%) w/cm=0.27 Fly Fly Cement Ash Ash Water Water f’c=69 MPa Cement 132 157 132 157 5.5% Chloride permeability=1010 432 (18%) 432 6.5% coulombs Fine aggregate Fine aggregate 528 (22%) 528 Course aggregate Coarse aggregate 1110 (46%) 1110 Units in kg/m 3 of concrete
Environmental & Economic Benefits of HPC Bridges • 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 • Benefits – Increased strength and reduced permeability – Reduced consumption of cement – Reduced GHG emissions – Reduced volume of land-filled materials – Reduced life cycle cost
Case Study: Life Cycle Design of Bridge Decks Bridge length = 35 m Cast-in place reinforced concrete deck 200 mm Prestressed concrete girders S S Detail of deck 12.35 m Temperature & shrinkage reinforcement Main reinforcement Concrete cover depth Top face 60 Equal 200 reinforcement (0.3%) Bottom face Distribution reinforcement
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 – CO 2 emissions – Construction waste materials • Costs – Owner costs (construction + maintenance) – User costs ( delay, accident, vehicle operation)
Case Study: Life Cycle Design of Bridge Decks 45 40 Service life (years) 35 30 25 20 15 10 5 0 Conventional HPC Deck Deck
Case Study: Life Cycle Design of Bridge Decks Life cycle = 30 years • 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
Case Study: Life Cycle Design of Bridge Decks CO 2 emissions over life cycles of bridge decks 160 151 140 Cement production 140 Transportation CO 2 emissions (kg/deck m 2 ) 120 Car delay during MRR activities Total 100 80 60 53 49 40 20 11 4 0.2 0 NPC deck HPC deck Conventional Bridge Deck HPC Bridge Deck
Case Study: Life Cycle Design of Bridge Decks Volume of waste materials produced over life cycles of bridge decks 0.8 Construction Asphalt Overlay Landfill use for waste material (m 3 / deck m 2 ) 0.6 Patch Repair Replacement 0.48 Total 0.4 0.28 0.17 0.2 0.16 0.16 0.04 0.02 0 -0.01 Conventional Bridge Deck HPC Bridge Deck -0.2 NPC deck HPC deck
Case Study: Life Cycle Design of Bridge Decks Life Cycle Owner’s Costs of Bridge Decks ($/m 2 ) 987 1000 900 800 700 584 600 524 500 400 300 200 100 0 Conventional HPC Deck Deck
Case Study: Life Cycle Design of Bridge Decks Life Cycle User Costs of Bridge Decks ($/m 2 ) 60 53.35 50 Total User Costs Present Value User Costs ($/m 2 ) Delay Costs Vehicle Operating Costs 40 Accident Costs 30 23.51 20 16.21 14.86 14.98 10 7.07 4.67 4.47 0 NPC deck HPC deck Conventional Deck HPC Deck
Case Study: Life Cycle Design of Bridge Decks Summary • Service life – Conventional bridge deck = 15 years – HPC bridge deck = 30 years • Life cycle CO 2 emissions – Conventional bridge deck = 151 kg/m 2 – HPC bridge deck = 53 kg/m 2 • Life cycle production of waste materials – Conventional bridge deck = 0.48 m 3 /m 2 – HPC bridge deck = 0.17 m 3 /m 2 • Life cycle costs – Conventional bridge deck = $1040/m 2 – HPC bridge deck = $560 /m 2
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
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