Yu, Jianhua

The objectives of this study were to document the performance of roads using full-depth reclamation (FDR) and stabilized FDR (SFDR) in Minnesota; help develop SFDR design parameters appropriate for Minnesota; provide information on FDR/SFDR design procedures and specifications from beyond Minnesota; share current Minnesota FDR practices; and catalog the characteristics of some FDR/SFDR roads. A comprehensive literature review of FDR/SFDR projects and case studies was conducted; and an online survey was distributed to Minnesota local road agencies to determine the stabilizing agents used for SFDR projects. Eighteen FDR/SFDR test sections from eight counties were then selected for a case study; and performance data and core samples were collected for the sections. Minnesota gravel equivalency (GE) analysis was performed to back-calculate the granular equivalent factor for FDR/SFDR layers based on the design equivalent single axle loads (ESALs) and R-values for subgrade soils. The back-calculated GE values indicate that designers have likely been using GE values for FDR/SFDR layers that are consistent with current recommendations. It is recommended that the current GE values be generally retained for FDR/SFDR design. However; when slower-moving vehicles are the critical design consideration; relatively robust performance of FDR/SFDR layers may be expected. Visual distress surveys indicated that the FDR/SFDR bases studied are performing well in terms of destroying crack patterns that are often reflected through traditional hot mix asphalt (HMA) overlays. Therefore; decision makers may want to consider the use of FDR/SFDR as a base for reasons other than structural capacity.

Minnesota's local highway agencies are tasked with maintaining their low-volume road networks with available financial resources, prompting increased interest in lower-cost pavement rehabilitation alternatives. In-place cold recycling technologies, such as cold in-place recycling (CIR) and full-depth reclamation (FDR), provide lower-cost opportunities to renew deteriorated roads than traditional rehabilitation methods, particularly if surfaced with a thin surface treatment such as a chip seal (seal coat) or microsurfacing rather than hot-mix asphalt. However, the resulting road surface may not meet some road users’ expectations. This study investigated the performance and economics of four pavement rehabilitation alternatives involving recycling technologies. The alternatives included CIR and FDR treatments with either an asphalt overlay or thin surface treatment. Fifteen case study sections in Minnesota and neighboring states were selected for performance evaluation and lifecycle cost analysis (LCCA). Pavement condition surveys were performed to evaluate the study sections’ pavement distresses and roughness. The results indicated satisfactory performance for fourteen sections, while a CIR section with a chip seal surface using quartzite as cover aggregate had extensive transverse cracking. The cause of the distress is not clear. The LCCA results indicate a 14% to 42% lower lifecycle cost for CIR and FDR treatments with chip seal surfaces. Costs savings may be achieved if asphalt overlay thicknesses are reduced, though chip seal surfaces may be rougher and nosier and require more maintenance than asphalt overlays. A decision tree was developed to aid local agencies during the treatment selection process.

Minnesota has a large network of aggregate roads. The majority of the system is maintained by counties and townships. Some of the aggregate roads need to be upgraded with a sealed surface for dust control or to provide a smoother driving experience, as well as for local economic development. Local road officials are often faced with the responsibility of upgrading the roads with a limited budget. Light surface treatments (LSTs) are considered an economical alternative to the conventional upgrade approaches using hot-mixasphalt (HMA) or concrete pavements. The currently used methods in Minnesota for the structural design of LSTs for aggregate roads were originally developed for structural design of flexible pavements. This research evaluated the design methods that can be used to design LSTs for aggregate roads. The methods evaluated include the MnDOT granular equivalent (GE) method and the MnDOT mechanistic-empirical method (MnPave design software), which are used in Minnesota, and the American Association of State Highway and Transportation Officials (AASHTO) flexible pavement design method and South Dakota aggregate road design method, which are practiced in other places in the United States. The results include a discussion of the applicable situations for each method. The research team also conducted a survey that was distributed to the county engineers in Minnesota to document their experiences with LSTs. Recommendations for improving the current design methods when applied to LSTs on aggregate roads are suggested based on the survey results.