Waste products as road materials

In support of a broader MnDOT effort to evaluate current practices, materials, and policies for pavement patching and repair for both asphalt and concrete pavements, the University of Minnesota Duluth Natural Resources Research Institute (NRRI) conducted additional evaluation, refinement, field testing, and performance monitoring of two taconite-related approaches to pavement repair that rely on mixes/techniques that contain (or are enhanced by) taconite mining byproducts and co-products. The first taconite-related approach to pavement repair uses a rigid pavement/pothole repair compound formulation developed and patented by NRRI that is fast-setting, taconite-based, and contains no petroleum or Portland cement. Depending on the formulation, the repair compound can be water-activated or activated by a chemical solution. A water-activated formulation referred to as Rapid Patch was the focus of the investigation. The second taconiterelated approach to pavement repair employs a high-power (50kW), vehicle-based (truck-mounted) microwave system for in-place pothole/pavement repair/recycling in which magnetite and/or magnetite-containing aggregate (taconite rock) can enhance microwave absorption and therefore the systems performance. The two repair alternatives evaluated during this project merit further development and consideration, as the field performance of both suggests they have long-term potential for more widespread use. Based on feedback from maintenance personnel who used and/or observed both repair alternatives during the project, both alternatives would benefit from operational modifications that would reduce the deployment time required to complete a repair and increase the number of repairs that can be accomplished during a single shift. Doing so would likely lead to greater acceptance and more widespread use.

Recycled Asphalt Shingles (RAS) include both manufacture waste scrap shingles (MWSS) and post-consumer tearoff scrap shingles (TOSS). It is estimated that Minnesota generates more than 200,000 tons of shingle waste each year. Recently, a portion of this waste has been incorporated into hot-mixed asphalt (HMA) pavement mixtures. The current technology limits the amount of RAS in HMA to no more than 5 percent by weight. This leaves a lot of underutilized shingle waste material throughout the state. This has prompted MnDOT to investigate other potential uses RAS. One potential use is to improve the performance of gravel surfacing and reduce dust by replacing common additives such as calcium chlorides with RAS. This is especially relevant as gravel sources in Minnesota have been depleted and/or have declined in quality, which has affected the performance of gravel surfacing. These poorer quality fines can increase the amount of dust generated and increase the difficulty of keeping the roadway smooth. Some agencies have used dust control additives to help the performance of these lower quality gravels. Successful implementation has the potential of removing valuable RAS materials from the waste stream to supplement the use of more expensive virgin materials and improve the performance of local roads.

Conservation and reuse of resources is a necessity in achieving sustainability across the globe. In recent years, construction and demolition debris including bricks has appeared in stockpiles around Minnesota. The objective of this research project was to investigate the possibility of putting the brick to beneficial use as aggregates for base courses in pavements. This would help to conserve natural stone aggregate and also recycle the brick instead of dumping it as waste in a landfill. In addition, contractors could save money by being able to reuse locally available material. MnDOT is already quite progressive in its use of recycled materials and allows the use of recycled concrete aggregates, recycled asphalt pavement, and recycled glass in base and surface courses. Based on current literature review, Minnesota may become a pioneer in the use of recycled brick aggregate as well. There are many different types of clay bricks including structural bricks (both commercial and residential), pavers, and refractory bricks. The structural bricks and pavers will also vary from region to region. The bricks used in Minnesota are of the highest quality available because they have to meet severe weathering requirements. Structural brick accounts for the largest amount of brick manufactured. In this project, samples of various types of bricks were tested. The main tests conducted were the Los Angeles Rattler to assess abrasion properties and the magnesium sulfate soundness to evaluate freeze-thaw durability. In addition, basic engineering properties such as specific gravity and absorption were determined.

Tire Derived Aggregate (TDA) is referred to in this report as rough shreds, shreds, and tire chips of various sizes. The potential uses discussed herein include TDA as lightweight fill, retaining wall backfill, insulation layer, drainage layer, and capillary moisture break. Other uses exist; however, they are beyond the scope of this report. This report summarizes the results of numerous studies regarding the environmental concerns of using TDA both above and below the ground water table. The summary provides general observations based on the literature review performed, comments on the current state of the practice regarding the use of TDA for highway applications, and information on additional resources.

This report summarizes lessons learned about the field performance of local roads containing Recycled Asphalt Pavement (RAP) and associated field and laboratory work with asphalt activation as well as the design and performance testing of high-RAP bituminous mixtures. Transverse cracking performance of Minnesota county highways averaging 20-26% RAP was improved when PG 52-34 binder was selected over PG 58-28 or other binder grades. Testing of the activation of RAP asphalt binder in plant and laboratory settings showed that coarse aggregates from plant mixing achieved a more uniform coating and were subjected to less abrasion than those from laboratory mixing. Low temperature testing of laboratory mixture designs containing up to 55% RAP, and new-to-total asphalt cement ratios as low as 43%, found that indirect tensile test (IDT) creep stiffness increased along with RAP content. IDT critical temperature results showed that the addition of RAP significantly increased the critical temperature, predicting less crack resistance. Semi-circular bend fracture testing showed that the addition of RAP lowered the fracture energy and increased the fracture toughness of the mixtures, and the highest RAP contents had the most reduced fracture performance.

This report summarizes lessons learned about the field and laboratory performance of the Recycled Asphalt Pavement (RAP) and Fractionated Recycled Asphalt Pavement (FRAP) test cells at the Minnesota Road Research Project (MnROAD) between 2008 and 2012. The project scope included: developing specifications for FRAP, construction of FRAP and RAP test cells at MnROAD, field performance evaluations, and laboratory testing of binders and mixtures. The project that monitored 11 test cells.

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.

The construction and maintenance of highways creates a demand for high quality paving aggregates, which are becoming scarce in many parts of the country. Taconite industry waste rock and tailings are a potential new source of virgin aggregates. Currently there is limited information available for implementing these products in construction specifications. The goal of this project was to assess available taconite aggregate resources that could supply a high quality, low cost aggregate for roadway use, especially in areas where aggregates are becoming scarce.

Rises in construction and asphalt binder costs, as well as the growing pressures on landfills, have contributed to the increased use of tear-off scrap shingles (TOSS) and manufacturer waste scrap shingles (MWSS) into hot-mixed asphalt (HMA) pavement mixtures. This research project was undertaken to address the responsible incorporation of recycled asphalt shingles (RAS) into HMA pavement mixtures to ensure environmental benefits are realized and pavement durability is retained or improved. The research consisted of a literature review, extensive laboratory testing and field evaluations of in service RAS/RAP HMA pavements. Binder testing established a strong correlation between the new asphalt binder to total asphalt binder ratio and the extracted high/low binder performance grade temperatures. Dynamic modulus testing on HMA mixtures proved to be an invaluable tool in comparing the effects of RAS and RAP on mixture properties across a wide range of temperatures. Field performance appeared to validate the laboratory findings in some instances.

Construction and maintenance of roads requires large volume of aggregates for use as base and subbase materials. Because of the cost of virgin aggregates, federal and state agencies are encouraging the recycling of waste materials including materials in old pavements. This study assessed the suitability of four recycled materials relative to virgin aggregates for use as base and subbase materials. The four recycled materials were the reclaimed asphalt pavement (RAP), fly ash (FA), reclaimed concrete material (RCM), and foundry sand (FS). Assessment of these materials was done in terms of their hydraulic, mechanical, and leaching properties when mixed in with various proportions of virgin aggregates. Except for slightly higher fine content in some RAP-aggregate mixtures, particle size distribution of all mixtures was within the Mn/DOT specification band for Class 5 materials. Water retention (pore size distribution), hydraulic conductivity, resilient modulus, and shear strength measurements were generally similar to that of 100% aggregates. Exception was the mixtures of FS. Heavy metal concentrations in the leachate were also generally less than the EPA drinking water standards. We concluded that FA, RAP, and RCM mixtures will be good substitutes of virgin aggregates as base and subbase materials.