a performance-based strategy for ensuring sustainable concrete infrastructure w. john mccarter,

A Performance-based Strategy for Ensuring

Sustainable Concrete Infrastructure

W. John McCarter,

Heriot-Watt University, Edinburgh, Scotland

In Europe, around 40-60% of the construction budget is

devoted to repair and maintenance of existing

structures with a high proportion of this expenditure on

concrete structures.

Inspection, maintenance and repair costs now

constitute a major part of the recurrent costs of the

infrastructure

Management of Infrastructure

• £550 million is spent on the maintenance and repair of

concrete structures each year in the UK alone.

• ‘Hidden costs’ include traffic delay costs due to inspection

and maintenance programmes and are estimated to be

between 15%-40% of the construction costs (economic costs

include fuel and time wasted; health impact from pollution).

Management of Infrastructure

‘Timely maintenance activities, which are well-planned and

carried out with minimal disruption to road users can present

substantial savings in terms of both time and money for both

bridge owners and road users …’

Management of Infrastructure

http://www.academon.com/Essay-Bridge-Management/63191 accessed 21.02.13

5

Canada 2006 (Laval, Quebec): 5 people were

killed in a bridge collapse caused by road-salt induced

corrosion

Mis-management of Infrastructure

6

Social Environment

Economy

Is this structure suitable for society needs?Does this structure add value to the society?What are the impacts on all sections of the society?Are the materials sourced locally?

What are the emissions/energy associated with this construction?Does the structure help to reduce the overall emissions?Does the design cater for the environment?How is the resource efficiency during construction and maintenance stage?What is the impact at the “end of life” scenario?What is the value for money proposition?

What is the affordability over its life time including maintenance?What are the economic impacts on the client and all sections of the society?

Sustainability in the context of concrete structures

De Sitter's Law of Fives !

A major repair can be expected to cost roughly five times

what routine maintenance would have cost. An all-out

replacement will cost five times what major repair would

have cost.

So …… the longer you defer your capital spending, the

bigger the bill when it is finally due!

8

The Achilles Heel of Concrete

•Ferrous reinforcement

•Concrete cover-zone

Corrosion protection of steel reinforcement

depends on density, quality and thickness

of concrete cover ……… .

Durability and Cover to Reinforcement

Deterioration Processes

Transport Mechanisms:absorption, diffusion, permeability

Surface Micro

Climate

Wetting / Drying

Air Temperature

[CO2]

[Cl- ]

[SO4--]

Concrete Cover

Moisture gradient

Temperature

gradient

Carbonation

Chloride Ingress

Sulphate attack

Macro-scale: Regional

Meso-scale: local

Micro-scale: surface

Environmental Conditions

Performance of Infrastructure

We need to consider each relevant deterioration

mechanism, the working life of the element or

structure, and the criteria that define the end of this

working life, in a quantitative way.

Deterioration Mechanism Class Designation

No risk of corrosion attack X0

Steel corrosion induced by carbonation

XC1, XC2, XC3, XC4

Steel corrosion induced by chlorides

XD1, XD2, XD3

Steel corrosion induced by chlorides from sea-water

XS1, XS2, XS3

Freeze/thaw attack on concrete

XF1, XF2, XF3, XF4

Chemical attack on concrete XA1, XA2, XA3

Transport mechanisms depend on:

Pore size, pore size distribution

Pore connectivity and tortuosity

Micro-cracks

Cement/aggregate interface transition zone

Hydration/pozzolanic reaction (means properties are time variant)

Deterioration Processes

25mm

4m

4m

Capillary pores in the cement matrix

Labcrete vs Sitecrete

CO2 Cl- SO4

Cover-zone of

poorer quality

Due to:

Segregation Compaction Curing Bleeding Finishing Microcracking

Frost

Moulded specimens made and cured

under standard conditions do not

represent the quality of the cover-

zone concrete

Specimens cast and cured under laboratory conditions do not

represent the true quality of cover-zone concrete

Freeze-thaw

Cover-zone of poorer quality

concrete due to:

segregationcompactioncuringbleedingfinishingmicrocrackin

g

Importance of the Concrete Cover

Service life depends, to a large extent, on the

penetrability of the cover concrete and on the

thickness of the cover – as achieved in the final

structure.

Measurements on the final structure quantify

the result of the contribution of all the players

in the concrete construction ‘chain’ (owners,

specifiers, materials suppliers, contractor, etc.)

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Inception

Planning/Design

Construction

MaintenanceDecommissioning

• Life Cycle Assessment• Service Life Scenarios• Whole Life Costing• Social Impacts

Performance-based specification•Quality Control Measures•Installation of Monitoring systems•Minimising impact to society

Maintenance Management•Performance assessment/monitoring•Proactive maintenance•Repair/Retrofitting•Estimating residual service life •Whole Life Costing•Minimising impact to society

End-of-life management •Alternative use?•Plan for decommissioning•Recycling/Reuse•Cost savings by resale•Minimising impact to society

Ideal scenario

An approach to deliver sustainable infrastructure

The development of integrated monitoring systems for new

(and existing) reinforced concrete structures could reduce

costs by allowing:

a rational approach to the assessment of repair

options;

scheduling of inspection and maintenance

interventions thereby minimising traffic delays

resulting from road closures;

continuous real-time monitoring of the performance

of the structure.

Management of Infrastructure

Components of Service LifeD

eg

ree o

f D

ete

riora

tion

Initiation period:

Changes in concrete due to environmental action

Service lifeMonitor and Test

Propagation period:

condition reached which defines the serviceability limit state

20

Duration of exposure (years)Duration of exposure (years)

Perf

orm

an

ce in

m

easu

rab

le t

erm

sPerf

orm

an

ce in

m

easu

rab

le t

erm

s

1

2

3

Minimum acceptable levelMinimum acceptable level

Service LifeService Life

Intermittent Repair/maintenanceIntermittent Repair/maintenance

The Case for In Situ MonitoringThe Case for In Situ Monitoring

A key aim of sensor and NDT research has been to extend the service life of structures.

Permeability

The rate of flow of water through concrete under a pressure gradient obtained from Darcy’s law:

Q = -kA(dP/dx)

Diffusion

The rate of flow of matter (ions, molecules etc.) which occurs under the influence of a concentration gradient obtained from Fick’s Law:

M = -DA(dC/dx)

Electrical Conduction

The rate of charge transfer through an electrical conductor under a potential gradient obtained from Ohm’s Law:

I = A(dV/dx)

Inter-relationship between transport processes

Water / Chloride

s

Electrodes placed at discrete points within the cover zone

Steel

Advancing water/chloride front

22

Electrical Property Measurements

Monitoring unit

Remote structure

Installed sensors

Performance Monitoring: Remote Interrogation

‘Interrogate structure from

office

=

Kincardine Test Site

24

Final position of monoliths (A876)

http://maps.google.co.uk/maps?f=d&t=h&utm_campaign=en_GB&utm_medium=ha&utm_source=en_GB-ha-emea-gb-sk-dd&utm_term=map

25

Monoliths reinstated at Heriot Watt

27

North Sea

Dornoch Firth Exposure Site

28

Low-Water

Schematic showing positioning of pier stems

High-Water

Tidal

Spray

Splash

1 Seaward

23

456

7 8

Road

Pier stems 7-9

Spray

Pier stems 4-6

Splash

Pier stems 1-3

Tidal

Rip-Rap

29

Splash

Spray

Installation of Remote Interrogation System at Marine Exposure site (Dornoch)

31

32

Watertight housing for instrumentation

Multiplexing Unit

Connection to Controller

Watertight housing

33

Modem

Controller / measurement

unit

Battery charger and connection to solar panelBattery

34

Wireless connection to

mobile network

Solar panel

35

36

1

2

3

4

5

6

0 25 50 75 100 125

10mm15mm20mm30mm40mm50mm

Nov 09

Time (days)

t (S

/m

10-3

)

As-measured conductivity within cover-zone (GGBS: XS2)

37

As-measured temperature within cover-zone (GGBS: XS2)

-5

0

5

10

15

0 25 50 75 100 125

10mm20mm30mm40mm

Nov 09

Time (days)

Cov

er T

empe

ratu

re ( C

)

38

2

3

4

5

6

3.50 3.55 3.60 3.65 3.70

10mm15mm20mm30mm40mm50mm

1000/T (K -1 )

(S

/m

10 -

3 )

Arrhenius relationship between Conductivity and Temperature (GGBS: XS2)

39

Conductivity ‘corrected’ to a reference temperature (25C) using activation energy obtained from measured

data.

0

2

4

6

8

10

0 25 50 75 100 125

10mm15mm20mm30mm40mm50mm

Nov 09

Time (days)

t (S

/m

10 -

3 )

0

0.005

0.010

0.015

0.020

0.025

0 10 20 30

5mm10mm50mm

OPC

Time (days)

(S

/m)

0

10

20

30

0 10 20 30

Temperature at 10mm

Time (days)

Tem

perature (C

)

As-measured conductivity and temperature

0

0.005

0.010

0.015

0.020

0 10 20 300

5

10

15

20

5mm10mm15mm20mm40mm50mm

Time (days)

(S

/m)

Rai

nfal

l (m

m)

Corrected conductivity and rainfall data

42

CONCLUDING COMMENTS

A detailed picture of the cover-zone response to the environment can be obtained.

Allow assessment of the 'integrated' quality of the cover-zone

Virtually continuous, real-time monitoring of the cover-zone is possible (if required).

Electrical property measurements could be exploited in quantifying cover-zone concrete performance.

The methodology could form part of a management and maintenance strategy.

43

Acknowledgments

•Engineering and Physical Sciences Research Council, U.K.

•Transport Scotland.

Thank You