This Paper reviews available techniques for monitoring steel corrosion in reinforced concrete. Electrochemical techniques are by far the most suitable for this purpose, and meet most of the requirements. me responses of direct and alternating current corrosion monitoring methods for steel–concrete systems are compared under two extreme conditions, i.e. steel being corroded in the active state and in the passive state. Most practical situations will belong to one of these or be intermediate to them. Results of polarization resistance measurements (taken by applying a potential step, a current step and small-amplitude cyclovoltammetry), a coulostatic method and electrochemical impedance spectroscopy are reported. It is shown that metal polarization resistance in particular, and electrochemical methods in general, can provide fast and reliable information on the corrosion rate of steel in concrete, suflciently accurate to distinguish between acceptable and unacceptable conditions in most scientific and technical applications.
Summary
Objectives
To evaluate the effectiveness of a personal digital assistant (PDA)-based system for collecting tuberculosis test results and to compare this new system to the previous paper-based system. The PDA- and paper-based systems were evaluated based on processing times, frequency of errors, and number of work-hours expended by data collectors.
Methods
We conducted a cluster randomized controlled trial in 93 health establishments in Peru. Baseline data were collected for 19 months. Districts (n = 4) were then randomly assigned to intervention (PDA) or control (paper) groups, and further data were collected for 6 months. Comparisons were made between intervention and control districts and within-districts before and after the introduction of the intervention.
Results
The PDA-based system had a significant effect on processing times (p < 0.001) and errors (p = 0.005). In the between-districts comparison, the median processing time for cultures was reduced from 23 to 8 days and for smears was reduced from 25 to 12 days. In that comparison, the proportion of cultures with delays >90 days was reduced from 9.2% to 0.1% and the number of errors was decreased by 57.1%. The intervention reduced the work-hours necessary to process results by 70% and was preferred by all users.
Conclusions
A well-designed PDA-based system to collect data from institutions over a large, resource-poor area can significantly reduce delays, errors, and person-hours spent processing data.
The role of chlorides as an initiating factor for corrosion in the steel/concrete system, their mechanism of action, the critical threshold level above which the risk of corrosion of reinforcements in the active state is especially high, the corrosion rates observed under a variety of circumstances and their implications on the durability of reinforced concrete structures are analysed.
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