Environmental Benefits of Life Cycle Design of Concrete Bridges - - PowerPoint PPT Presentation

Environmental Benefits of Life Cycle Design of Concrete Bridges

Zoubir Lounis & Lyne Daigle Urban Infrastructure Research Program

3rd International Conference on Life Cycle Management August 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 Inspection Maintenance 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 Performance Maintenance Service life 1 Service life 2 Service life 3

Life Cycle Design of Concrete Bridges

Time (years) Limit state Life cycle Performance 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) + δ

Highway 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

2 4 6 8 10 12 14 16 18

Cement Production Iron & Steel Non-Ferous Metals Mining Pulp & Paper

Emissions of CO2 eq (million tons)

Environmental & Economic Benefits of HPC Bridges

2005 Environment Canada Data

Units in kg/m3 of concrete

157 1110 (46%) 528 (22%)

132

432 (18%) 30

6.5% 5.5% (2%)

Course aggregate Cement Fine aggregate Water

Fly Ash 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

Water 157 Fly Ash 132

• 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

5 10 15 20 25 30 35 40 45 Conventional Deck HPC Deck

Service life (years)

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 11 4 151 53 20 40 60 80 100 120 140 160 NPC deck HPC deck CO2 emissions (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

0.2 0.4 0.6 0.8 NPC deck HPC deck Landfill use for waste material (m3/ deck m2) Construction Asphalt Overlay Patch Repair Replacement Total

Conventional Bridge Deck HPC Bridge Deck

Case Study: Life Cycle Design of Bridge Decks

100 200 300 400 500 600 700 800 900 1000 Conventional Deck HPC Deck

987 524 584

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 10 20 30 40 50 60 NPC deck HPC deck Present Value User Costs ($/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