No abstract

In regions of the United States where pavements are constructed in freeze-thaw environments, springtime load restrictions are used to reduce distress caused by truck loads. During the spring, the pavement layers can be saturated and weakened because of partial thaw conditions and trapped water. Knowledge of the timing of freeze-thaw events is crucial to a successful load restriction strategy. Several studies in Minnesota are being done to evaluate criteria used to predict when to place and remove springtime load restrictions. The objectives are to evaluate current load restriction procedures, investigate pavement strength changes in relation to freeze-thaw events, and suggest improvements to current procedures. Data collected from eight Minnesota Road Research Project (Mn/ROAD) flexible pavement test sections, including falling weight deflectometer, response, and environmental data, were used to assess the effects on pavement strength. In conjunction with the Mn/ROAD work, the Minnesota Department of Transportation is conducting a statewide study using resistivity probes to monitor frost depth beneath various roads around the state. It was found that the existing procedure works well in predicting the thaw if the warming trend is uniform. In addition, over the past four springs the predicted thaw duration was greater than field observations. The date of maximum deflection occurs about 1 to 3 weeks after thawing is complete; the rate of strength recovery is quicker in sections constructed on higher quality base materials with low fines content. On the basis of the results a new criteria and equation for predicting the beginning and duration of the thaw are proposed.

Results of a blind test evaluation of various nondestructive testing techniques, including well-established methods such as chain dragging, rod sounding, and ground-penetrating radar, compared with an emerging ultrasonic array technology for determining the extent of concrete joint deterioration, are presented. Nondestructive testing at two concrete pavement joints at the Minnesota Road Research Facility was performed, and the results were independently evaluated and submitted to the Minnesota Department of Transportation. Significant discrepancies in subsurface deterioration assessments were observed between these techniques. Forensic evaluation (trenching and coring) was used to resolve the discrepancies in test results. It was concluded that the ultrasound array analysis was the only method that could accurately determine the horizontal extent of the deterioration otherwise undetected by the other available nondestructive evaluation methods. Additionally, ultrasonic tomography analysis was able to determine the depth of the deterioration. These results make this emerging technology an attractive alternative to traditional nondestructive testing methods for assessment of concrete pavement joints.