Koubaa, Amir

The primary objective of this project was to provide Mn/DOT with assistance in validating the Mn/ROAD database. The research approach consisted of the following: - review the Mn/ROAD data acquisition systems and data collection procedures, - evaluate the performance of the online and offline dynamic sensors, - validate the online dynamic data collection and database - validate the online static sensors and database, - propose activities and procedures to ensure that future data are reliable.

This study was conducted with the aim of improving the state of knowledge on the behavior of joints in concrete pavements, and to explore the feasibility of developing a non-destructive testing technique based on frequency response of dynamically loaded joints. One of the objectives of this study was to numerically investigate the existence of a relationship between load transfer capacity of a joint in rigid pavements and its dynamic response. The approach adapted for the present study is based on a numerical model which accurately represents the mechanism of shear transfer in reinforced concrete members implemented it in a commercially available finite element code. That tool is then used for the analysis of two models which consisted of various joint conditions. One model represented an ideal condition of full load transfer across a joint, while the other model was used to simulate variable load transfer conditions. The results obtained are analyzed in the time and frequency domains. These results provided a comprehensive description of the joint response characteristics, and enabled the derivation of a clear relationship between the response frequencies and the joint's shear transfer capabilities. The results may be used as the starting point for the development of a precise/non-destructive testing method for a wide range of cases in which shear transfer across discontinuities in concrete systems is a principal load resisting mechanism. Specific conclusions and recommendations on future developments have been provided.

Study goals included: 1) identify mechanisms causing premature failure in Minnesota concrete pavements; 2) evaluate the accuracy of existing tests of aggregate freeze-thaw durability using Minnesota aggregate sources and pavement performance records; 3) develop a new methodology for quickly and reliably assessing aggregate freeze-thaw durability; and 4) evaluate techniques for mitigating D-cracking. Research results indicate that the poor durability performance of some Minnesota PCC pavement sections can often be attributed to aggregate freeze-thaw damage. However, secondary mineralization, embedded shale deposits, poor mix design and alkali-aggregate reactions were also identified as problems. Petrographic examination can help to differentiate between these failure mechanisms. A reliable and universal method for quickly identifying D-cracking aggregate particles was not identified. A test protocol was developed for improved aggregate durability evaluation. It includes several tests which are selected for use based on aggregate geological origin and composition and the results of previous tests. Further validation of the proposed test protocol is recommended. Several techniques appear to be effective in improving the freeze-thaw durability of concrete prepared using marginally durable aggregate: mix design modifications, reductions in aggregate top size, and the blending of durable and nondurable aggregates. Some chemical treatments showed promise, but may not be economical.