Modern Countries with Aging Infrastructure:
Bridge collapses arising from quality control issues during construction and from aging of infrastructure causing reduction in load capacities are rare and unfortunate events. The figure 1 shows the failed De la Concorde overpass that collapsed in Laval Quebec in 2007. A summary of the conclusions from the commission into the failure clearly points to poor construction followed by inadequate condition assessment over time.
In Italy on Aug. 14, 2018, a major bridge collapse reminded engineers that responsibility lies in their hands to make sure infrastructure is properly designed and constructed, maintained and repaired, and decommissioned when appropriate. This could have happened anywhere in the world.
Just in the United States in 2016, 39% of 614,387 bridges are over 50 years old and an additional 15% are between the ages of 40 and 49. Most of these bridges were designed for a lifespan of 50 years. Major infrastructure elements in other developed countries have almost the same age condition. Based on a report on 2016, there is an average of 188 million trips across a structurally deficient bridge somewhere each day.
Quantified risk assessment analysis over time, based on measurements, is the only reliable way to prioritize maintenance or rehabilitation of deteriorated bridges, or to make decisions for replacement. Quantification of a structure’s health condition should be done through appropriate non-destructive testing methods. Transportation bridges are mostly reinforced concrete (RC) based or steel based, and corrosion of the steel is the main reason for deterioration. Detecting and quantifying the level of corrosion in steel infrastructure is therefore a preferred method to provide metrics that permit quantitative risk assessment over time.
Corrosion is a key aspect of infrastructure life span and maintenance; it affects everyday life and its effects are visible everywhere (Gardiner Expressway in Toronto – Beerjis and Panesar 2011). Generally, under challenging environmental conditions such as offshore, alpine, or industrial situations, reinforced concrete elements should exhibit higher performance levels compared to their performance in normal environmental conditions. Nevertheless, despite long-term durability and good performance of high quality materials, the majority of concrete structures fail because of reinforcing bar corrosion (Khan et al., 2010). Although there are guaranteed lifetimes for reinforced concretes, numerous factors can lead to the destruction of concrete and the exposure of bars (Abdulrahman et al., 2011). Corrosion appear to be the primary cause of reducing the durability and lifespan of reinforced concrete structures (Ahmad, 2003). Corrosion also affects concrete by expansion, and corrosion and expansion lead to de-bonding between concrete and rebar and cracks, allowing water and corrosive substances to seep more rapidly into the corroded site. Figure 2 shows the decrease in rebar’s yield strength (Fig. 2.a) and decrease in bonding strength between concrete and rebar (Fig. 2.b), based on corrosion percentage.
A developed technology at InspecTerra Inc. based on a passive magnetic inspection method is able to detect corrosion percentage of rebar by scanning concrete from the surface (Figure 3).
By combining interpreted corrosion percentage (reinforcement condition) from the corrosion detector device data, with ultrasonic data (concrete condition), quantified input has become available to assess the condition of the structure over time. Using software developed at InspecTerra Inc., the progress of corrosion of reinforcement and concrete cracks can be tracked quantitatively, helping to prioritize structures for their next inspection, maintenance, rehabilitation or decommissioning times.
1. Berjis, P. and Panesar, D.K. 2011. Another Perspective on Case Studies in Civil Engineering Design – The Gardiner Expressway. Downloaded from 3670 Article text 6572-1-10-20110806.pdf from ojs.library.queensu.ca
2. ASCE analysis of U.S. Department of Transportation, Federal Highway Administration. National Bridge Inventory ASCII files.
3. U.S. Department of Transportation, Federal Highway Administration. 2015 Status of the Nation’s Highways, Bridges and Transit: Conditions and Performance. January 2017.
4. U.S. Government Accountability Office. Report to Congressional Committees: Highway Bridges—Linking Funding to Conditions May Help Demonstrate Impact of Federal Investment. September 2016.
5. Khan., A. and Teja., T.S., 2010. An Experimental Study nn Prevention of Reinforcement Corrosion in Concrete Structures, Ijrras 5(2), November 2010.
6. Abdulrahman, A. S. Ismail, M., Hussain, M.S., 2011. Corrosion inhibitors for steel reinforcement in concrete a review, Scientific Research and Essays 6(20), 4152-4162.
Ahmad, S., 2003. Reinforcement corrosion in concrete structures, its monitoring and service life prediction-a review, Cement & Concrete Composites 25, 459–471.