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.)
17
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