The use of hot mix asphalt (HMA) overlays is common in Minnesota. However, while overlaying pavements with sealed cracks, bumps tend to form in the overlay resulting in decreased overlay smoothness and poorer ride quality. Hypotheses as to why (or how) these bumps are caused include:
Thermal expansion of sealant during overlay
Roller slip or slide as it rolls over sealed crack
Differential melting points of the sealant and
asphalt binder
Vertical compression of sealant under roller.
Prior research (LRRB Investigation 802) studied the thermal expansion hypothesis. Results showed that sealant materials may soften during overlay placement but not expand. It appears likely that the bumps may be formed during rolling operations; either by compression of the sealant or by slipping or sliding of the HMA material. This project conducted field testing to examine these issues, evaluate the probability of the occurrence of bumps, and look at ways of mitigating any bumps that do occur.
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.
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.
The purpose of this report is to document the field evaluation of a thermoplastic pavement marking material on a 2 year old asphalt pavement located on Cell 26 of MnROAD’s Low Volume Road. HMA pavement reconstruction occurred on the test cell in 2004, using 4 in. of Superpave HMA over a 12-in. Class 6-Special aggregate base. The structural design is based on 20-year ESAL’s of 110,000, according to the MnPAVE design software. The mixture design is identified by Mn/DOT designation SPWEB240B-R.
On May 16, 2006 a total 524 square feet of inlaid thermoplastic pavement marking material was installed on Cell 26. This area included two crosswalks placed across both traffic lanes and a 2 x 100-ft segment installed in the left wheel path of the 80K load lane. The project was part of a
partnership agreement between Mn/DOT and Decorative Pavement Marking, LLC of Plymouth, Mn. The purpose of the project was to evaluate the physical properties of the product, including friction resistance and the evaluation of the overall durability of the pavement surface. Integrated Paving
Concepts Inc. of Vancouver, B.C., supported the project and assisted DPM in the installation process. During the period between May 16, 2006 and August 1, 2007 Cell 26 received 6,809 and 2,003 repetitions of the 80K and 102K truck configurations respectively.
The flexible slurry system is a mixture of emulsified asphalt, high quality crushed aggregate, and water. Depending upon the design, flexible slurry can be used in place of a blade leveling course prior to bituminous overlay or as a wear course. Flexible slurry is constructed using a micro surfacing machine, but is less brittle than a usual micro surface mixture. Historically Minnesota has used one type of emulsified asphalt (PG 64-22); but recent experimentation with binder grades shows that enhanced rutting and cracking performance is possible. Low speed traffic can aid in the curing and consolidation of flexible slurries.
The purpose of this report is to document the installation process of a thermoplastic pavement marking material on a 2 year old asphalt pavement and to provide an overview of historical information relating to the condition of Cell 26 up to the time of installation.
