Condition Monitoring System for Reinforced Concrete Structures

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TECHNOLOGY SOLVES:

Patent pending concrete condition monitoring system providing ‘real-time’ information on temperature, hydration and water and ionic movement within in the concrete cover-zone which are of relevance in the performance/durability of concrete exposed to different environmental actions.

TECHNOLOGY

The performance of the surface zone of concrete (i.e. the cover) is acknowledged as a major factor governing the rate of deterioration of reinforced concrete structures as it provides the

only barrier to the ingress of water containing dissolved ionic species such as chlorides. Since concrete is a porous material, with time, chlorides will permeate through the concrete and, ultimately, initiate corrosion of the steel reinforcement and eventual spalling of the concrete (see Figure below).

The protective qualities of cover-zone concrete are thus of considerable interest to engineers as the service life of a structure depends, to a large extent, on the permeation properties of the cover-zone. Factors such as pore-size, pore-size distribution, pore continuity, pore connectivity and pore tortuosity, which influence the penetrability of the cover-zone, assume an even greater significance than strength alone. Further, the ability to monitor hydration during the post-curing period, and the continuously evolving pore structure within cover-zone concrete, could be of considerable practical value as it is the properties of the ‘as-placed’ concrete which will play an important role in ensuring adequate protection of the reinforcing steel. This is particularly relevant as ‘slower reacting’ supplementary cementitious materials such as fly-ash and blast-furnace slag are now routinely specified.

In-situ monitoring of cover-zone concrete (i.e. surface 50mm or so) is therefore critical in attempting to make realistic predictions as to

OVERVIEW

The premature deterioration of concrete structures due to corrosion of the steel reinforcement is a world-wide problem, particularly highway structures subjected to de-icing salt used on roads for winter maintenance purposes. In most developed countries, including the UK, around 50% of the construction budget is devoted to repair and maintenance of structures with over 30% of this expenditure on concrete structures. In addition, our infrastructure has now reached an age

where capital costs have decreased, but inspection and maintenance costs have grown, constituting a major part of the recurrent costs of the infrastructure. Traffic delay costs due to inspection and maintenance programmes are already estimated to be between 15%-40% of the construction costs.

The ability to monitor water and ionic ingress through the concrete cover-zone would provide an early warning of incipient problems enabling the planning and scheduling of maintenance programmes, hence

minimising traffic delays resulting from road/lane closures. The development of integrated monitoring systems for new reinforced concrete structures could also reduce costs by allowing a more rational approach to the assessment of repair options; and, co-ordination and scheduling of inspection and maintenance programmes.

This system provides such data over the lifetime of the structure allowing informed (and timely) preventative maintenance decisions to be with greater confidence. The system can be interrogated remotely.

Distinctly Ambitiouswww.hw.ac.uk

Robert GoodfellowTechnology Transfer ManagerHeriot-Watt University

t: +44 [0] 131 451 3616e: Technology-Licensing@hw.ac.uk

Professor W. John McCartert: 0131 451 3318 e: w.j.mccarter@hw.ac.uk

www.hw.ac.uk/licensing

the in-service performance of the structure. To this end, the remote interrogation sensor system from Heriot-Watt will allow continuous real-time monitoring of the cover-zone concrete from an office environment.

Although water repellent coatings (e.g. silane) can minimise water/ionic ingress, these will deteriorate with time. Using a self-powered data-link accessing a network of strategically placed embedded sensors within the concrete cover-zone the Heriot-Watt system could, for example, inform preventative maintenance schedules on the condition of the waterproofing coating on a daily, weekly or monthly basis (see Figure below).

BENEFITS & APPLICATIONS:

• Informs preventative maintenance schedules:

Quality and performance of waterproofing systems

Tracking moisture/ionic ingress

The requirement for remedial action

• Real time measurement of water/ionic ingress; temperature changes within the cover-zone can also be monitored

• Low cost embedded system capable of remote operation via wireless technology

• Robust sensors – no moving parts/

zero operator intervention required

POTENTIAL MARKET APPLICATIONS

The main application is “Whole Life” condition monitoring and the preventative maintenance of reinforced concrete structures such as bridge piers, wingwalls and abutments etc. exposed to moisture and/ or salt spray

Proof of Concept has been demonstrated and data from the on-going trials at the University marine exposure test-facility located on the Dornoch Firth (Northern Scotland) are available•.

The University seeks commercial partners with an interest in utilising this patent pending technology within major civil engineering projects or in supporting further technology development.

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