Kim, Sunghwan

The Midwest region of the United States, including Minnesota, has been experiencing an increase in the number of heavy precipitation events. Historical precipitation data confirmed an increasing trend of heavy precipitation in Minnesota in the 21st century. This study focused on assessing the impact of heavy-precipitation events on moisture levels and stiffness of pavement foundation layers at the MnROAD facility. A two-step approach was adopted for predicting changes in saturation and for estimating corresponding resilient modulus values using the resilient modulus prediction equation employed in AASHTOWare Pavement Mechanistic-Empirical (ME) design. PLAXIS 3D, a finite element analysis tool, was used to simulate the movement of moisture within the pavement layer under varying heavy rainfall scenarios. Multiple linear regression models were developed from rainfall simulation data of the PLAXIS 3D model to predict base layer saturation based on rainfall characteristics and hydraulic conductivity of the material. ArcGIS Pro was then used to develop a framework to generate a preliminary vulnerability map showing changes in the resilient modulus of the pavement base layer from rain events. Four regression models were developed and used in ArcGIS Pro to predict changes in resilient modulus for distinct aggregate types under heavy rainfall events, revealing significant reductions in the base layer's resilient modulus. Recycled aggregate (a mix of recycled concrete aggregate and recycled asphalt pavement) emerged as more susceptible, with initial reductions in modulus values higher under heavy rainfall.

An increase in freeze-thaw events will result in detrimental impacts on pavement systems. However, the impacts of recent climate changes on freeze-thaw cycles have not been well studied, although they are of interest to a broad number of transportation agencies. In this study, the number of freeze-thaw events at typical air temperature sensor level (e.g., 6 feet above the earth’s surface) as well as at different pavement layers and critical sub-pavement locations such as saturated subgrade within the active zone were quantified. In response to global warming, current work resulted in rigorously quantified freeze-thaw events rooted in climate data from 1941 to 2020. Results indicated that in the recent 40 years (i.e., 1981-2020), Minnesota winters have become warmer by 1-2 °F daytime and 2-5 °F nighttime temperatures. With a decrease in freezing temperatures, the yearly number of freeze-thaw cycles tended to decrease at shallow pavement depths (< 6 inches), whereas remained sporadic at deeper pavement layers. The decreases in freeze-thaw events at shallower depths were significant during the early and late winter months. However, the annual freeze-thaw events at the air temperature sensor level were randomly distributed throughout the analysis period.

Concrete grinding residue (CGR) is a slurry waste consisting of water and concrete fines generated from diamond grinding operations that is used to smooth a concrete pavement surface. During this process; CGRs are mostly disposed along the roadside; which can influence soils and plant communities along the roadways. To understand the effects of CGR on soil physical and chemical properties and plant growth; a controlled field site at the Kelly Farm in Iowa was used with CGR application rates of 0; 10; 20; and 40 dry ton/acre to test properties of soils and plants before the application and one month; six months and one year after the CGR application. Two roadsides along Interstate 90 in Minnesota where CGR material was applied in the past were investigated as well. Laboratory and field experiments were conducted to measure plant biomass; bulk density; hydraulic conductivity; infiltration; pH; electrical conductivity (EC); alkalinity; metals; cation exchange capacity (CEC); exchangeable sodium percentage (ESP); and percentage base saturation (PBS) of soil samples collected from the test sites. Statistical analyses were conducted to correlate the CGR additions to the properties of soils and plants. The results of statistical analyses from the Kelly Farm indicated that CGR material did not significantly affect soil physical properties and plant biomass but impacted the chemical properties of soil. Changes in some soil properties such as pH and percent base saturation (PBS) due to CGR did not persist after one year. The results from two Minnesota roadsides indicated that the areas receiving CGR applications in the past did not negatively affect soil quality and plant growth.

The effects of farm equipment on the structural behavior of flexible and rigid pavements were investigated in this study. The project quantified the difference in pavement behavior caused by heavy farm equipment as compared to a typical 5-axle, 80 kip semi-truck. This research was conducted on full scale pavement test sections designed and constructed at the Minnesota Road Research facility (MnROAD). The testing was conducted in the spring and fall seasons to capture responses when the pavement is at its weakest state and when agricultural vehicles operate at a higher frequency, respectively. The flexible pavement sections were heavily instrumented with strain gauges and earth pressure cells to measure essential pavement responses under heavy agricultural vehicles, whereas the rigid pavement sections were instrumented with strain gauges and linear variable differential transducers (LVDTs). The full scale testing data collected in this study were used to validate and calibrate analytical models used to predict relative damage to pavements. The developed procedure uses various inputs (including axle weight, tire footprint, pavement structure, material characteristics, and climatic information) to determine the critical pavement responses (strains and deflections). An analysis was performed to determine the damage caused by various types of vehicles to the roadway when there is a need to move large amounts agricultural product.