A system is being developed to monitor in-service deterioration of reinforced concrete (RC) in highway bridges. The system includes the monitoring of acoustic emission (AE). To develop a preliminary understanding of AE source mechanisms and their causes while also getting closer to the challenges of separating relevant AE from noise, a 6ft long RC test article was monitored in the outdoors environment of a New Jersey summer. There were indications of daily swings in the AE rate, coinciding with the daily swings in temperature. However this correlation was not consistent or reproducible. As the monitoring was extended into the winter and the test site was buried in snow, the AE rate dropped drastically. It was concluded that temperature changes were instrumental in stimulating AE from this damaged concrete. Implications for the formulation of AE evaluation criteria are discussed. Also, the summer swings provoked consideration of the underlying stress field, the fractal nature of the heterogeneous material and the stochastic AE phenomenon. An analysis of calm time distributions yielded results similar to those found by Abe and Suzuki for earthquake time distributions. Analysis of this kind may help to differentiate relevant AE from some kinds of noise.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.