Crumbling bridges often get that way because steel reinforcement bars have rusted within the concrete. A Charlottesville, VA-based company called Virginia Technologies has devised a system of networked sensors that can be embedded in concrete, tell when the steel is corroding and report the information through a wireless link-avoiding the need to drill holes or install probes that must be checked individually.

The networked probes are tethered to the steel bars and wired together before concrete is poured (photo). Each sensor monitors electrochemical factors that indicate rusting, such as changes in salinity, moisture and conductivity. If any one instrument detects a relatively high corrosion rate, it can check with neighboring sensors to gauge how far the problem has spread. Sensor readings travel by wire to a communications module, from which the data can be accessed wirelessly. The company expects to bring the sensors to market early next year.