CONCRETE EMBEDMENT STRAIN SENSORS AT THE Mn/ROAD PROJECT: AS-BUILT ORIENTATION AND RETROFIT

Over 430 concrete embedment (CE) strain sensors were originally installed into the test cells of the Minnesota Road Research Project (Mn/ROAD). Due to traffic loading and extreme climate conditions, many of these sensors have ceased to function. A program of CE sensor removal and retrofit was put forth, providing valuable information on the as-built orientation of the original sensors, as well as the feasibility of retrofitting new strain sensors. The program consisted of the removal and retrofit of 24 pairs of stacked CE sensors. Removal by coring allowed sensor depth and angular orientation measurements to be taken. To further investigate sensor condition and bond quality, the cores were systematically sawed and chipped to reveal details. Observation of the core samples revealed rotational shifting and occasionally breakage of the sensors had occurred during construction. Laboratory testing showed rotational shifting of the sensors causes negligible differences in measured strain. Significant differences were found between the design and in-situ depths of the sensors. New CE sensors were retrofit into core holes using a standard Mn/DOT concrete patch mix. Load response testing of the retrofitted sensors showed balanced and linear responses between stacked sensors. Comparisons of measured to predicted strain were found to be highly variable for both original and retrofit sensors. Retrofit sensors installed in this study provided measurements with similar strain magnitude and behavior as sensors installed during the construction of Mn/ROAD concrete test cells. BURNHAM 1