Institute for Transportation

About the research

Geotextiles and geogrids are the most used geosynthetics in transportation/pavement applications. Geotextiles can reduce layer intermixing, facilitate moisture reduction, and provide confinement and stabilization to subgrade and base materials. Geogrids provide mechanical stabilization by giving strength to base and full depth reclamation material through lateral restraint and improved load bearing capacity in pavement systems. The main objective of the study is to produce a current best practices design guide for road designers detailing when to use and what types of geotextiles and geogrids to use for given soil, pavement designs, and traffic conditions. Having a guide will aid designers in utilizing these products to better predict pavement outcomes and to extend pavement life. The project tasks include (i) evaluating current MnDOT practice related to the beneficial and cost-effective use of geosynthetics; (ii) reviewing research and state of the practice on geosynthetics applications, available products, design methods, and specifications; and (iii) proposing recommendations for geosynthetic solutions in pavements to modernize MnDOT’s practices and manuals. The study will highlight current best practices and produce a synthesis report and a Technical Guide for using geotextiles and geogrids based upon soil type, pavement structure, and traffic loads, etc. This will include quantification of these benefits based upon the functions of the geotextile, i.e., separation, filtration, drainage, and stiffening or stabilization, and for geogrids, stabilization of aggregate cover over soft subgrade in unpaved roads and paved road unbound aggregate layer stabilization that will include the strength gain of the base or full depth reclamation material.

About the research

The limited availability of high-quality aggregates and rising transportation costs present ongoing challenges for pavement construction and maintenance in Minnesota. To address this, local agencies are increasingly exploring the use of lower-quality, locally available materials in pavement foundation layers. This study evaluates the performance and cost-effectiveness of aggregate base and subbase layers with varying material qualities and thicknesses to develop optimized pavement designs. A comprehensive aggregate index property (AIP) database is updated to include more than 1,100 aggregate sources and used to develop predictive models for resilient modulus and shear strength using both multiple linear regression analyses and artificial neural networks. Aggregates are categorized into low-, medium-, and high-quality categories and incorporated into MnPAVE simulations under a range of traffic levels, asphalt layer thicknesses, subgrade stiffnesses, and climatic conditions. In parallel, cost-benefit analyses based on historical MnDOT bid data are conducted to identify optimal-quality thickness combinations. A flowchart-based design framework is also introduced to iteratively determine the required aggregate base and subbase thicknesses corresponding to aggregate quality levels that meet fatigue and rutting life targets. The findings offer practical guidance for the efficient use of regional materials, supporting the development of resilient and economically optimized pavement infrastructure across Minnesota.

About the research

Changes in pavement foundation moisture levels, driven by environmental factors such as heavy rainfall, freeze-thaw cycles, and fluctuations in the groundwater table, can significantly affect the performance of Minnesota’s pavements in both the short and long term. Ground-penetrating radar (GPR) offers a non-invasive, portable, and cost-effective solution for rapidly assessing large road segments and detecting subsurface moisture levels, especially when compared to traditional methods such as in-place sensors or indirect techniques like the falling weight deflectometer (FWD). The advantages of GPR technology are particularly beneficial for local road authorities, who often face financial constraints and limited staff, by enabling prompt assessment of moisture conditions in critical pavement areas. The objective of this study is to enhance the validation and implementation of GPR-based pavement moisture assessments on actual low-volume roads. Specifically, this involves evaluating the ability of GPR to efficiently survey large pavement areas, monitor moisture, and identify sections potentially impacted by drainage issues. These objectives will be accomplished through GPR surveys on test sections of low-volume roads equipped with in-situ moisture sensors. The data collected will be analyzed and compared. An automatic detection algorithm will be developed to evaluate moisture variation in ground material within unbound pavement layers. This algorithm will be validated and implemented as software, featuring modularized, optimized code, a graphical user interface (GUI), and an accompanying user manual. The successful outcomes of this study will provide a set of implementation recommendations aimed at improving decision support tools and technical guidelines for assessing moisture fluctuations in Minnesota’s low-volume roads.

About the research

Incorporating recycled asphalt materials (RAM), including recycled asphalt pavements (RAP) and recycled asphalt shingles (RAS) in asphalt mixes is becoming a common practice in many states. There is a multitude of research that has addressed different aspects of RAP, including its impact on mixture properties. The use of recycled asphalt is primarily driven by economic and environmental reasons. Using RAM to replace virgin materials can lead to significant cost savings and a reduction in greenhouse gas emissions, which inspires the need to incorporate more RAM into asphalt mixes. However, concerns have arisen regarding using RAM with high virgin binder replacement contents due to instances of premature failure in some cases.

The goal of the project is to demonstrate the benefit of applying binder availability factors (BAFs), or other recycled binder availability approaches, to mixes containing RAM, based on field performance. This work is important to provide field validation of the findings from previous lab studies on recycled binder availability, and to further refine the concept of recycled binder availability in the design of high-RAM mixes based on the findings from the field studies, considering the effect of production variables, such as production temperature and silo storage.

About the research

Minnesota road users experience two standards of pavement marking retroreflectivity on the same roadway. Contractors for new construction must use high-performing glass beads to meet retroreflectivity requirements. In contrast, Minnesota Department of Transportation (MnDOT) crews use standard Type I glass beads, which are lower in cost but provide less retroreflectivity. This project aims to improve pavement marking visibility by demonstrating and selecting higher-performing glass beads for use by MnDOT crews statewide.

About the research

Base stabilization is crucial for enhancing the structural integrity of roads by improving the strength and stiffness of the base layer, which is vital for mitigating issues with vulnerable soils and increasing the longevity and performance of road foundations. Despite progress in pavement base stabilization using proprietary additives, there is a critical need for further research to fill knowledge gaps and enhance the use of these additives for more sustainable and cost-effective road infrastructure. The existing body of research mainly focuses on non-proprietary stabilizers, with limited exploration of the performance and economic viability of proprietary options.

A study sponsored by the Minnesota Local Road Research Board (LRRB) on entitled, “Base Stabilization Additives – Effect on Granular Equivalency (GE)” evaluated the advantages of proprietary additives in treating full-depth reclaimed (FDR) materials by the estimated GE factors, but it also identified areas needing more investigation. The study’s life cycle cost analysis (LCCA), based on assumed maintenance scenarios, and GE factors, and
derived from two years of data, call for further validation and long-term performance assessment. To address these issues and build on the current findings, a Phase 2 study aims to evaluate the long-term performance and durability of stabilized pavement sections with proprietary additives, validate GE factors through extended field monitoring, and assess the economic feasibility of these additives. This subsequent research seeks to advance the understanding of base stabilization practices and develop guidelines for selecting and optimizing proprietary additives, ensuring structural and cost-saving benefits for pavement design.

About the research

This project will evaluate the performance of a mineral-blended polymeric microsphere powder used to construct concrete pavement test sections at MnRoad. The microsphere concrete mixtures will also be compared with a reference mixture that contains conventional air entrainment and existing mixtures evaluated at MnRoad. Performance will be monitored over a three-year period. The three-fold objectives for evaluating the microsphere mixtures are as follows:

1. Determine the reductions in cement content that can be achieved with typical pavement concrete mixtures in which air-entraining agents are replaced with the microsphere-powder blend.
2. Develop test data on strength and freeze-thaw durability for selected concrete mixtures to support application of the microsphere concrete mixtures in pavement construction.
3. Quantify the sustainability benefits of use of microsphere concrete in lieu of conventional air- entrained concrete mixtures

Laboratory testing on specimens cast during pavement construction will be performed to evaluate strength, modulus of elasticity, resistivity, and freeze-thaw durability. Field data collection will include surface distress surveys, falling weight deflectometer (FWD) testing, ride quality measurements, joint faulting and movement, embedded strain sensor data, ultrasonic tomography (MIRA) testing, curling and warping measurements, and examination of core samples. Results from this project will demonstrate the effectiveness of the mineral-blended polymeric microsphere powder to be used in concrete mixtures to support reductions in cementitious materials content while also supporting freeze-thaw durability. The feasibility of using mineral-blended polymeric microsphere powder in large-scale pavement applications will be evaluated, as well as the impact of use of this material to support both durability performance and reduced environmental impact of concrete. Findings of this work may also support use of mineral-blended polymeric microsphere powder in applications where supplementary cementitious material (SCM) characteristics may cause issues with conventional air-entraining admixtures (e.g., higher carbon fly ash), thus allowing marginal SCMs to be more readily used in concrete.

About the research

Limited local availability often constrains the growing demand for high-quality aggregate materials in road construction. To address this challenge, recycled waste materials, including plastics, are being explored as sustainable alternatives. This study investigates the feasibility of incorporating recycled plastics into asphalt and concrete pavements to enhance sustainability and reduce landfill waste. Comprehensive laboratory testing was conducted to evaluate the performance of plastic-modified asphalt and concrete. Asphalt mixtures were produced using the wet process method and assessed for binder performance, cracking resistance, and moisture susceptibility. Concrete mixtures incorporating recycled plastics as aggregate replacements were analyzed for workability, mechanical strength, and durability. The test results on plastic-modified asphalt indicated a reduced cracking resistance of the mixture when Post-Consumer Recycled (PCR) plastic was added to the binder using a wet process as compared to the same mixture with the same binder without plastic. In concrete mixtures, incorporating plastic materials either maintained statistically similar mechanical and durability properties (when used as plastic sand) or enhanced them (when used as plastic fiber). Integrating recycled plastics into road construction offers a sustainable solution for reducing landfill waste, lowering carbon emissions and promoting a circular economy.

About the research

Pedestrian assets, particularly sidewalks, are highly susceptible to aging, adverse weather conditions, and suboptimal construction practices, often leading to rapid deterioration. This deterioration is often ignored due to the widespread misconception that pedestrian assets are low risk, resulting in many deteriorated sidewalks being left untreated or inadequately maintained. A comprehensive deterioration modeling framework that integrates advanced spatial and temporal data sources, advanced data analytics, and predictive modeling would enable infrastructure managers to predict the aging process of pedestrian assets and ultimately prioritize investments, plan maintenance schedules, and allocate budgets efficiently.

This project developed assessment frameworks and deterioration models for pedestrian assets that support reliable and informed decision-making regarding funding needs and asset design and maintenance. Various data sources and modeling and analysis procedures were explored, and a pedestrian asset assessment methodology was developed and evaluated. The research demonstrated a scalable and cost-effective approach to assessing sidewalk conditions, providing actionable insights for proactive maintenance. The quantifiable benefits, including construction savings, improved life-cycle costs, reduced risk, and safety enhancements, position this methodology as a valuable tool for sustainable infrastructure management.

About the research

Fleet managers are continuously challenged with determining the optimal equipment replacement time based on increasing operation costs and decreasing economic value. In addition, they are challenged with determining if a lease or purchase provides the greatest value. Compounding upon these challenges, new equipment purchases and leases can create a negative perception among the general public. This first phase of this research—which consists of a literature review, survey to Minnesota Local Road Research Board (LRRB) members, and follow–up case studies—is strategically designed to understand existing decision support models and methods, quantitative data, and constraints that agencies have when determining the optimal equipment replacement. The second phase of this research—which consists of tool development, validation, and training—is intended to meet the identified challenges and support life–cycle cost analysis (LCCA). This tool will provide quantifiable support for the decision–making process, enabling agencies to make defensible decisions.