Instrumentation and Monitoring of Concrete Bridge Decks: Moisture, Temperature, and Electrical Conductivity.

Corrosion of reinforcing steel in concrete bridge decks is a leading concern among bridge engineers nationwide.  The rate and extent of steel corrosion are largely affected by the properties of the surrounding concrete.  In particular, higher moisture content, temperature, and chloride concentration are generally associated with higher corrosion rates.  While evidence of corrosion activity can be eventually observed as damage on affected decks, effective programming of cost-effective preventive maintenance treatments requires knowledge of internal deck conditions well before damage is manifest. 

In this research, the embedment of sensors in new concrete bridge decks is demonstrated as a technique for non-destructively monitoring internal deck conditions.  Concrete, like soil, is a porous medium that can exhibit variable moisture content, temperature, and electrical conductivity through time.  Sensors capable of measuring these three properties were installed in four concrete bridge decks constructed in 2011 along the Interstate 15 corridor in Orem, Utah.  Two decks were constructed using lightweight concrete, and two decks were constructed using conventional concrete.  The sensors were situated at the same level as the top mat of reinforcing steel on each deck. 

Data collected during the first several months of bridge life were analyzed to establish a baseline condition for long-term monitoring of each deck and to evaluate early trends in the concrete properties.  While temperatures and electrical conductivities for all the decks are similar, the data indicate consistently higher water contents in the lightweight decks than in the conventional decks, attributable to the much higher absorption of the expanded shale aggregate accounted for in the design of the lightweight concrete; this absorption water is released into the cement paste during concrete curing when the magnitude of suction within the paste exceeds that within the aggregate.  Continued monitoring is planned to evaluate long-term concrete properties and overall bridge deck performance.