Corrosion of reinforcing steel in concrete structures causes concrete cracking, steel diameter reduction and eventually loss of safety. In infrastructure this is mainly due to penetration of chloride ions from de-icing or marine salts. Conventional repair means heavy, labour intensive and costly work and economic pressures (time and money) work against the required quality level. Consequently, conventional repair is short lived in many cases in practice. Corrosion reappears quickly and the structure needs to be repaired again after a relatively short time, further increasing life-cycle cost. A completely different situation applies to cathodic protection (CP) of steel in concrete as a repair method. Cathodic protection of reinforcing steel has been applied successfully to concrete structures with corrosion damage for more than 25 years. This paper reports on past experience and presents a model for predicting life cycle costs for maintaining CP systems. Results will be presented from an inventory of CP systems in The Netherlands installed between 1987 and 2009 on about 150 structures, for which performance and maintenance data are reported. The large majority provides corrosion protection for a long time. Degradation of components and overall systems seems to occur in limited numbers. Failure of components and total systems as a function of age is quantified. On the average, the time until minor repairs of parts is necessary is about 15 years. Global failure of the anode, which necessitates near complete replacement of the system, is rare. Based on the statistical analysis of field data, the cost of maintaining a CP system is predicted using a life cycle cost model.
Water distribution networks (WDNs) are critical to provide safe, clean drinking water around the globe. However, they are susceptible to accidental or deliberate contamination, potentially resulting in poisoned water, many fatalities and large economic consequences. In order to protect against such intrusions, an efficient sensor network should be placed in a WDN. Finding the optimal placement for water quality sensors is a challenging problem. Several sensor placement strategies have been proposed, but the vast majority of these strategies rely on the assumption that the sensors are perfect. In this paper we provide evidence for the imperfection of water quality sensors, by conducting measurements in an operational environment. We investigate the imperfection of four types of water quality sensors being employed in actual WDNs for the purpose of contamination detection. We describe experiments conducted at the WaDi testbed, a realistic water distribution facility at the Singapore University of Technology and Design. Through these experiments we study the imperfection, sensitivity and degradation of the water quality sensors, under normal conditions (water flow without contaminants present) as well as under attack conditions. It is shown that several aspects of sensor imperfection do occur, including missing values, inexplicable jumps and drifting.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.