environmental benefits of life cycle design of concrete

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)


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


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


• 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

)


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


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


• 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


• 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)


05

1015

202530354045

ConventionalDeck

HPC Deck

Serv

ice

life

(yea

rs)


• 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


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


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


0100200300400500600700800900

1000

ConventionalDeck

HPC Deck

987

524584

Life Cycle Owner’s Costs of Bridge Decks ($/m2)


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


• 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

environmental benefits of life cycle design of concrete

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