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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. Management of Infrastructure.

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A Performance-based Strategy for Ensuring Sustainable Concrete Infrastructure W. John McCarter,

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  1. A Performance-based Strategy for Ensuring Sustainable Concrete Infrastructure W. John McCarter, Heriot-Watt University, Edinburgh, Scotland

  2. Management of Infrastructure • 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

  3. 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).

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

  5. Mis-management of Infrastructure Canada 2006 (Laval, Quebec): 5 people were killed in a bridge collapse caused by road-salt induced corrosion

  6. Sustainability in the context of concrete structures 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? Environment Social 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? Economy

  7. 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

  9. Durability and Cover to Reinforcement Corrosion protection of steel reinforcement depends on density, quality and thickness of concrete cover ……… .

  10. Deterioration Processes Concrete Cover Moisture gradient Temperature gradient Carbonation Chloride Ingress Sulphate attack Surface Micro Climate Wetting / Drying Air Temperature [CO2] [Cl- ] [SO4--] Transport Mechanisms: absorption, diffusion, permeability

  11. Environmental Conditions Meso-scale: local Macro-scale: Regional Micro-scale: surface

  12. 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.

  13. Deterioration Processes • 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)

  14. 25mm 4mm 4mm Capillary pores in the cement matrix

  15. Labcrete vs Sitecrete Cover-zone of poorer quality concrete due to: Freeze-thaw Specimens cast and cured under laboratory conditions do not represent the true quality of cover-zone concrete • segregation • compaction • curing • bleeding • finishing • microcracking

  16. 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. An approach to deliver sustainable infrastructure • 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 Inception Planning/Design Construction Ideal scenario Maintenance Decommissioning • End-of-life management • Alternative use? • Plan for decommissioning • Recycling/Reuse • Cost savings by resale • Minimising impact to society • Maintenance Management • Performance assessment/monitoring • Proactive maintenance • Repair/Retrofitting • Estimating residual service life • Whole Life Costing • Minimising impact to society

  18. Management of 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.

  19. Components of Service Life Degree of Deterioration Initiation period: Changes in concrete due to environmental action Propagation period: condition reached which defines the serviceability limit state Service life Monitor and Test

  20. The Case for In Situ Monitoring Intermittent Repair/maintenance 1 Performance in measurable terms 3 Minimum acceptable level 2 Duration of exposure (years) Service Life A key aim of sensor and NDT research has been to extend the service life of structures.

  21. Inter-relationship between transport processes • 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 = sA(dV/dx)

  22. Electrical Property Measurements Advancing water/chloride front Steel Water / Chlorides Electrodes placed at discrete points within the cover zone

  23. Performance Monitoring: Remote Interrogation Installed sensors ‘Interrogate structure from office = Monitoring unit Remote structure

  24. Kincardine Test Site

  25. 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=maphttp://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 Final position of monoliths (A876)

  26. Monoliths reinstated at Heriot Watt

  27. Dornoch Firth Exposure Site North Sea

  28. Road 3 Spray 2 4 5 1 Seaward 6 8 7 Pier stems 7-9 Spray Splash High-Water Pier stems 4-6 Splash Tidal Pier stems 1-3 Tidal Rip-Rap Low-Water Schematic showing positioning of pier stems

  29. Splash Spray

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

  31. Watertight housing for instrumentation

  32. Watertight housing Multiplexing Unit Connection to Controller

  33. Modem Controller / measurement unit Battery charger and connection to solar panel Battery

  34. Solar panel Wireless connection to mobile network

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

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

  37. Arrhenius relationship between Conductivity and Temperature (GGBS: XS2)

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

  39. As-measured conductivity and temperature

  40. Corrected conductivity and rainfall data

  41. 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.

  42. Thank You • Acknowledgments • Engineering and Physical Sciences Research Council, U.K. • Transport Scotland.

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