Bloom, Paul R.

Recycling part or all of the pavement materials in an existing road during reconstruction is an attractive construction alternative. When reconstructing roads surfaced with hot mix asphalt (HMA), the HMA, underlying base, and a portion of the existing subgrade often are pulverized to form a new base material referred to as recycled pavement material (RPM). Compacted RPM is overlain with a new HMA layer to create a reconstructed or rehabilitated pavement. This process is often referred to as full-depth reclamation. Similarly, when an unpaved road with a gravel surface is upgraded to a paved road, the existing road surface gravel (RSG) is blended and compacted to form a new base layer that is overlain with an HMA surface. Recycling pavement and road materials in this manner is both cost effective and environmentally friendly. However, recycled base materials may contain asphalt binder, fines, and/or other deleterious materials that can adversely affect strength and stiffness. To address this issue, chemical stabilizing agents can be blended with RPM or RSG. Use of industrial material resources for stabilization (e.g., cementitious coal fly ash) is particularly attractive in the context of sustainability. The purpose of this study was to develop a practical method to design local roadways using stabilized RPM or SRSG as the base layer and Class C fly ash as the stabilizing agent. The design method was developed in the context of the "gravel equivalency" (GE) design methodology employed for local roads in Minnesota.

Mn/DOT engineers are increasingly looking to recycled materials as readily available and cost-effective substitutes for natural aggregate and to fly ash as a material that can be used in the stabilization of sub-base soils. These recycled wastes have the potential to contain unacceptably high levels of some chemicals. This project produced chemical data on wastes, non-surface background soils, and natural aggregates for use in a due diligence screening tool in current service by Mn/DOT and developed by the Office of Environmental Services (OES). These data will be used by OES for their internal Mn/DOT due diligence determinations using their streamlined hazard evaluation process. A future Local Road Research Board project will transform the OES streamlined hazard evaluation process into a CD-based product for use by the larger transportation community. Data developed by this current project will be used to populate the future CD-based product electronic database. This project will maintain consistency with the current in use Office of Environmental Services (OES) streamlined hazard evaluation process for waste recycling in Mn/DOT infrastructure projects.

The properties of soft fine grained soils sometimes require enhancement to facilitate road construction and increase long term road durability. One option for roadbed stabilization is to treat the soil with fly ash, which possesses several beneficial engineering properties. However, the concentrations of elements in fly ash may potentially pose an unacceptable risk to human health. The Screening Tool provides straightforward assessments of this hazard. This tool is intended to be used as part of the assessment of due diligence of these risks. The Screening Tool does not give permission for the use of fly ash and the screening tool was not designed to predict the effects on surface waters, which are regulated by the Minnesota Department of Natural Resources (DNR) and Minnesota Pollution Control Agency (MPCA). This computer program provides guidance to users, but users must make sure the proposed project complies with all applicable and relevant rules and regulations that govern use of fly ash. Details of the calculation and further discussion of the importance of site-specific data is included in this document.