Every year, several bridges nationwide have their structural integrity compromised, and in some cases ruined, by bleed water in the conduits housing their structural strands. A non-destructive technique for identifying the presence and amount of water in the conduit is desperately needed. The proposed technique uses gamma ray spectroscopy to determine the amount of water trapped in a mass of concrete or masonry. For example, in finding water, the search would focus on hydrogen, the main constituent of H20. The process uses a particular nuclear reaction in which a thermal neutron is captured by the nucleus of a hydrogen atom, converting it into deuterium. This reaction is commonly shown symbolically as H(n,()D, meaning a neutron reacts with an H atom generating deuterium and a gamma ray. The gamma ray comes from an excited state of deuterium that has a known energy. A gamma-ray spectrometer is used to measure the intensity of the gamma ray, which is proportional to the amount of H (water) present in the concrete and should differentiate between bleed water and intrinsic water.
In calendar year 2004, the Florida Department of Transportation (FDOT) spent $26,000,000 repairing two bridges the Sunshine Skyway Bridge and the Mid Bay Bridge - that had been affected by this condition and the problem has been reported by several other state highway agencies. The source of the water is the grout used to secure the structural steel strands inside a sheet metal or polyurethane conduit. As the grout hardens, water separates and rises to the highest elevation within the conduit. This gathering of water can range in volume from six ounces to as much as 13 liters and, according to FDOT Corrosion Engineers, can severely damage a bridge within 30 days of the water contacting the steel. The current method of locating the water is to use the construction plans to identify the most probable location and knock a hole in the bridge at that point to search for the water. Use of this destructive method causes significant and lasting damage to the very infrastructure that the process aims to help. The research team will use the University of Florida Nuclear Reactor to generate the neutrons necessary to perform the gamma-ray spectroscopy needed to locate and identify water in civil structures in a totally non-destructive manner. Though the initial application is bridges, the success of this research will mean that water and other harmful substances can be nondestructively identified and located in all manner of civil infrastructure such as bridges, dams, and buildings.
