Edil, Tuncer B.

This report contains the appendices to report number 2009-27: Use of Fly Ash for Reconstruction of Bituminous Roads.

These appendices pertain to report NRRA202103, Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase.

Seasonal freeze-thaw weakening has a significant effect on pavement foundation performance. The seasonal freeze-thaw cycles cause extensive damage to the pavement from frost-related problems such as frost heave, frost boils, thaw weakening, total rutting, and degradation of mechanical properties. Changes in temperature of pavement foundation geomaterials during freeze-thaw cycles can significantly influence the performance of pavement foundation layers. It is crucial to monitor the changes in water content, temperature, and matric suction of aggregate base and subgrade soils to be able to predict the frost depth, freezing and thawing times, and number of freeze-thaw cycles. This project has two main goals: (1) develop a data-driven model to predict the maximum/minimum frozen soil depths and (2) freezing and thawing duration and numbers via use of standard climate data that includes precipitation, shortwave radiation, and air temperature. During this research, a model was developed and validated using the climate and environmental data collected from MnDOT. As a result of this research an Excel tool was developed that can predict frost depth, soil temperature, number of freeze-thaw cycles, and duration of freezing and thawing periods at a given soil depth via use of weather data. The required climate data include air temperature, relative humidity, wind speed, precipitation, and solar radiation.

Poor drainage of roadway base materials can lead to increased pore water pressure, reduction of strength and stiffness, and freeze-thaw damage. Drainability is dependent on soil/aggregate physical properties that affect water flow and retention in the porous matrix, notably including particle-size distribution, particle shape, fines content, and density or porosity. The objective of this project was to quantitatively assess permeability and water retention characteristics of soil and aggregates applicable to pavement applications and to evaluate and derive predictive equations for indirect estimation of these properties. Samples of 16 materials used in transportation geosystems were obtained and laboratory tests were conducted to determine grain size distribution, index properties, saturated hydraulic conductivity, and soil-water characteristic curves. Results were analyzed to examine applicability of estimation equations available in the literature and to develop dataset-specific equations for the specific suite of materials. Procedures were provided to qualitatively assess base course drainability as "excellent," "marginal," and "poor" from grain size properties, thereby offering rationale to reduce pavement life- cycle costs, improve safety, realize material cost savings, and reduce environmental impacts.

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).

This project was performed to evaluate the performance of recycled aggregates and large stones used in the aggregate base/subbase layers of pavement systems and provide recommendations regarding pavement design and material selection. As part of this project, eleven test cells were built at MnROAD to evaluate the impact of recycled aggregates and large stones on the long-term pavement performance via a series of laboratory [permeability, soil-water characteristic curve (SWCC), stereophotography (image analysis), gyratory compaction, and resilient modulus (MR) tests] and field tests [intelligent compaction (IC), falling weight deflectometer tests (FWD), rutting measurements, international roughness index (IRI) measurements, light weight deflectometer (LWD) tests, and dynamic cone penetrometer (DCP) tests]. In addition, a pavement mechanistic-empirical (ME) design approach was used to provide recommendations for designs of pavement systems containing recycled aggregate base (RAB) and large stone subbase (LSSB) layers. Overall, this project found that finer recycled concrete aggregate (RCA) material would be preferable to coarser RCA material and a blend of RCA and recycled asphalt pavement (RAP) materials would be preferable to natural aggregate for aggregate base layers. RCA materials provided better performance than the blend of RCA and RAP materials, indicating that RCA materials would be preferable to the blend. For LSSB layers, this project found that geosynthetics would be required to successfully construct thinner LSSB layers. Overall, thicker LSSB layers provided better structural support than thinner LSSB layers both in the short term and the long term.

The objective of this project was to characterize the properties of crushed recycled concrete (RCA) and asphalt pavement (RAP) as unbound base without being stabilized, to assess how RCA and RAP behave in the field and to determine how pavements can be designed using RCA and RAP. Issues to be considered include variability in material properties, purity of material, climatic effects, how to identify and control material quality, and leaching characteristics. This project included laboratory specimen and large-scale model tests and evaluation of field data from MnROAD test sections constructed using recycled materials. To identify the characteristics of RAP and RCA typically available in different parts of the country, samples were obtained from eight states: California, Colorado, Michigan, Minnesota, New Jersey, Ohio, Texas, and Wisconsin covering a geographically diverse area. A conventional base course was used as a control material. The extensive investigation undertaken on RCA and RAP indicate that these materials are generally suitable for unbound base course applications and they show equal or superior performance characteristics compared to natural aggregates in terms of stiffness, freeze-thaw and wet-dry durability, and toughness. Their typical compositional and mechanical properties and their variability are defined in this study providing a basis for design considerations. Their relative differences from natural aggregate such as temperature sensitivity, plastic deformations, and water absorption and retention characteristics are also well established. It is noted that some RAP may be sensitive to temperature change that may lead to rutting. This aspect needs to be considered in design.

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.

Two field projects are described where cementitious fly ashes (10% by dry weight) and water were mixed to stabilize recycled pavement materials and road-surface gravel to form a base during reconstruction of a city street in Waseca, MN, and construction of a flexible pavement in a segment of gravel country road, CR 53 in Chisago County, MN, respectively. Addition of fly ash improves the stiffness and strength of the base materials significantly. A resilient modulus of minimum 50 MPa appears safe to assume irrespective of the base material at the end of construction due to fly ash stabilization. However, moduli of 100 MPa or more can also be achieved. There is no evidence of frost-induced degradation in the field over a single season of winter. Chemical analysis of the draining leachate from the fly ash-stabilized layers showed that the concentrations of trace elements (with the exception of Mn) were below USEPA maximum contaminant levels and Minnesota health risk levels. Longer-term monitoring is needed to fully understand the potential for leaching of trace elements and frost action during the service life. These field cases show that fly ash stabilization provides an effective and economical means of providing a base for asphalt paving using existing roadway materials.

Pavements are constructed on compacted soils that are typically unsaturated. The negative pore-water pressure (soil suction) due to the ingress of water in between soil particles has a significant effect on pavement foundation stiffness and strength. The study characterized the effects of soil suction on shear strength and resilient modulus of four soils representing different regions of Minnesota. The deviator stress in shear strength measurements followed a power function relationship with soil suction. Resilient modulus also followed the power function relationship with suction but these relationships fell within a narrow range. We present models for incorporating suction effects in shear strength and resilient modulus measurements of highly compacted subgrade soils. We also briefly outline a framework for incorporating these models in the resistance factors of MnPAVE. Since soil water content and the resulting soil suction under the pavement varies with season, adjustments are needed to account for increased strength and stiffness of the material as a result of unsaturated soil conditions. These adjustments will not only reflect the more realistic field conditions but will result in more reliable performance predictions than the current pavement design method.