Principal Investigator(s):
Joseph Labuz, Professor, Civil, Environmental and Geo-Engineering
Co-Investigators:
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Bojan Guzina, Professor, Civil, Environmental and Geo-Engineering
Project summary:
This project supplemented MnDOT's preparation to implement a mechanistic-empirical pavement design procedure using the MnPAVE software system for flexible pavements in conjunction with the Design Guide developed by the National Cooperative Highway Research Program project 1-37A. The primary objective of this study was to quantify engineering properties, such as resilient modulus and shear strength of the recycled bituminous and concrete as well as shredded tire subgrades for mechanistic-empirical pavement design implementation. In mechanistic-empirical pavement design, mechanical properties are the required inputs for pavement design. At the time of the study, a set of resilient modulus values of the traditional MnDOT aggregate bases (Class 3, 4, 5, 6 and 7) had been estimated using statewide data. However, the use of recycled materials for aggregate base in the districts, counties and cities is increasingly in demand (for example, more cold-in-place recycling, reclaimed bituminous mixtures and rubblized concrete being used in projects and shredded tires used in subgrades). The rising popularity of and demand for these practices motivated this research. After a survey of other states? specifications and implementation guidelines, Minnesota recycling projects were selected based on the availability of laboratory resilient modulus (MR) tests and field measurements from FWD. The projects were County State Aid Highway 3, Trunk Highway 23 and Trunk Highway 200. Based on the results of a parametric study, it was found that traditional peak-based analysis of FWD data could lead to significant errors in elastostatic backcalculation. A procedure for extracting the static response of the pavement was formulated and implemented in a software package called GopherCalc. Laboratory resilient modulus measurements were compared with moduli backcalculated from the FWD data, and the FWD data was analyzed using conventional (peak-based) and modified (FRF-based) elastostatic backcalculation (Evercalc) as well as a simplified mechanistic empirical model called Yonapave. Laboratory values from sequences in the MR protocol that produced a similar state-of-stress were used. Additionally, a seasonal analysis of FWD test data revealed a significant increase in stiffness when the pavement is in the frozen state.