Aggregates

This research investigated the effects of incorporating recycled concrete aggregate (RCA) at low replacement levels on the properties of concrete. Four different RCA sources were used, each with different aggregate properties. For each source, replacement levels of 5, 10, and 15% were tested and compared to a control group, which had no RCA. Of the four RCA sources investigated, three had similar levels of absorption capacity and percent fines, while one source had higher levels of both properties. RCA replaced virgin aggregate of a similar gradation and replacement was on the basis of volume. Fresh and hardened concrete properties were tested, including air content, super air meter (SAM) number, slump, workability via the box test, compressive strength, flexural strength, elastic modulus, Poisson’s ratio, coefficient of thermal expansion, surface resistivity, freeze-thaw durability, and unrestrained shrinkage. Digital image correlation was used to visualize strain fields during compression testing. A statistical analysis was conducted to determine if any observed differences in hardened properties between the test mixes and the control group were statistically significant. This research found that using up to 15% of an RCA with reasonable values of absorption capacity and percent fines would not negatively impact most concrete properties. It also provided an outline for future research to develop a specification to define what constitutes reasonable values of RCA properties for future use.

Full Depth Reclamation (FDR) is the process of pulverizing a roadway’s flexible pavement section and a portion of its underlying base, and crushing and blending the recovered material to create a uniform base material.

An Otta seal is an asphalt surface treatment constructed by placing a graded aggregate on top of a thick application of relatively soft bituminous binding agent. Minnesota has used emulsified asphalt exclusively (HFMS-2s). The binder works its way into the aggregate with rolling and traffic. In comparison to other surface treatments, material and construction specifications are not as strict. Local aggregates that would not meet the requirements for high quality paving aggregate are often used in Otta seals.

This is a Research in Progress summary for the project that was eventually published as Report 2010-024, "Use of Taconite Aggregates in Pavement Applications."

The objective of this study is to demonstrate the use of fine and coarse taconite aggregate materials in hot mix asphalt, Portland cement concrete, and other pavement applications for both its constructability and field performance over time. This would help create a greater comfort level for the use of taconite aggregate and help promote its use in the state and around the nation. The specific goal of Task F is to perform laboratory tests on taconite aggregates and on pavements made out of taconite aggregates to establish how these materials will be used in the most appropriate manner for long-lasting roadways. Mn/DOT has the laboratory equipment and expertise to do this required material testing.

Shoulders are critical roadway components. They provide repose for vehicles to stop during an emergency and a recovery area when vehicles depart the driving lane. Granular shoulder installation is inexpensive and therefore is a commonly found roadway section. However, they often result in a condition called shoulder drop-off. Shoulder drop‐offs become dangerous when errant drivers unexpectedly swerve off the paved roadway, which is sometimes inches from the drive lane, and attempt to quickly redirect their vehicle onto the road. The vertical edge created by the paved roadway prevents the vehicle from easily returning to the roadway. The driver is forced to over steer to compensate for the drop‐off and can lose control of the vehicle. Maintaining shoulders generally consists of replacing the lost aggregate material, regrading, and compacting. This is a temporary solution and needs to be repeated frequently. The money saved initially by constructing aggregate shoulders is often surpassed by on‐going maintenance costs.

An Otta seal is an asphalt surface treatment constructed by placing a graded aggregate on top of a thick application of relatively soft bituminous binding agent. Minnesota has used emulsified asphalt exclusively (HFMS-2s); it could be constructed with cutback asphalt if desired. The binder works its way into the aggregate with rolling and traffic. In comparison to other surface treatments, material and construction specifications are not as strict. Local aggregates that would not meet the requirements for high quality paving aggregate are often used in Otta seals.

The goal is to assess potentially suitable, available aggregate resources that could supply an abundant, high quality, low cost aggregate for roadway use. This effort will help pave the way to use this material in the near future, especially in areas that aggregates are becoming scarce. Currently this aggregate material from the Iron Range is considered "waste product" relating to their taconite production, but it has high potential for its use in our roadways which includes the use of fine to coarse taconite aggregate materials in hot mix asphalt, concrete mixes, and other pavement applications for both its constructability and field performance over time. This would help create a greater comfort level for the use of this aggregate and help promote its use in the state and the nation

Annual Minnesota Department of Transportation State Aid Office reports, cost estimates, and interviews were used to determine a typical county spending history for low volume roads. It was found large initial costs for bituminous roads (HMA), but the ongoing routine annual maintenance activity in later years was less costly than for gravel. The graph of cumulative maintenance costs verifies that annual maintenance costs/mile for a gravel road increase with traffic volume.

Unsafe conditions exist on aggregate surfaced shoulders when material erodes either from vehicular means or from erosion caused by wind, rain, and other forces. Most of the material is unrecoverable and therefore wasted. This adds to the labor, equipment, and additional costs of maintaining the shoulder. The following results are from a study sponsored by the Mn/DOT Maintenance Operations Research Fund and the Mn/DOT Office of Materials Based upon input from maintenance supervisors; the project monitored the field performance of several aggregates and stabilization treatments during a 2-year evaluation period. Materials were evaluated along straight sections, vertical, and horizontal curves where AADT conditions varied from 3,000 to 25,000. Aggregate gradation, shoulder drop-off, and erosion were monitored. Measurements also included shoulder cross slope and photo documentation of shoulder condition.