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The use of recycled materials promotes sustainability in roadway construction by reducing the consumption of energy and emission of greenhouse gases associated with mining and the production of virgin aggregate (VA). Recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA) have comparable characteristics to VA that have been used in roadway base course applications. This study develops a database for RAP and RCA material characteristics, including gradation, compaction, resilient modulus (Mᵣ), California bearing ratio (CBR), and saturated hydraulic conductivity (Kₛₐₜ). In addition, this study summarizes construction specifications provided by several departments of transportation (DOTs) regarding the use of recycled aggregates in pavement systems. The effects of the presence of RAP and RCA in aggregate matrices on the engineering and index properties of aggregates are investigated and some trends are observed. For example, the study finds a higher RAP content reveals a higher summary Mr (SMr), and a higher RCA content causes an increase in optimum moisture content (OMC) and a decrease in maximum dry unit weight (MDU). In addition, a series of AASHTOWare Pavement Mechanistic-Empirical (ME) Design (PMED) analyses are conducted for three traffic volumes [low (1,000 AADTT), medium (7,500 AADTT), and high (25,000 AADTT)] with the material inputs collected for the database to determine whether different values of different characteristics of RCA and RAP can be used in flexible/rigid pavement designs. Results show that Mr has a higher effect on pavement distress predictions compared to gradation and saturated hydraulic conductivity (Kₛₐₜ).

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.