Roger C Olson

Rebirth of Chip Sealing in Minnesota

Chip sealing is a common form of pavement preservation used by most cities and counties and by the Minnesota Department of Transportation (MNDOT). MNDOT, working in partnership with the Minnesota Local Road Research Board, was able to rejuvenate the chip seal program in Minnesota. Efforts to improve the performance of chip sealing as a pavement preventive maintenance treatment are discussed. The discussion covers chip seal design, aggregate characteristics, and training efforts, and the successes of MNDOT, counties, and cities are documented.

Nine Steps to Constructing High-Quality Chip Seals

If chip seals are constructed properly, they are a cost-effective means of extending the useable life of hot-mix asphalt pavements. Over the years, chip seals have been criticized because they sometimes do not perform as expected. This paper discusses the steps necessary to build chip seals that perform well, including project selection, specifications, material quality, and construction methods.

Flexible Slurry-Microsurfacing System for Overlay Preparation: Construction and Seasonal Monitoring at Minnesota Road Research Project

Microsurfacing mixtures are made of high-quality aggregate and asphalt emulsion components. They are produced at the project site by a mobile microsurfacing machine that mixes and places the product. Normal micro-surface designs contain approximately 13.5% emulsion and include a performance grade (PG) 64-22 asphalt cement (AC). This study investigates the field performance of softer-AC flexible slurry surfacing mixtures used for preparation and surface courses. A PG 48-34 AC was chosen for flexible slurry–microsurfacing mixtures constructed on four test cells at the Minnesota Road Research Project low-volume road facility near Albertville, Minnesota, in September 2005. This AC was used to produce mixtures for both surface preparation and wear courses. The mixtures used a reduced emulsion percentage for rut filling and an increased emulsion percentage for normal leveling courses. A single surface course mixture with the increased emulsion level was placed over the entire project. Pre- and postconstruction evaluations of cracking, rutting, and smoothness were performed. These evaluations were repeated at 6 months, following one winter of service. At 6 months an overall 71% of transverse cracking had reflected through the microsurface. Reflected distress from longitudinal cracks and patched areas was negligible. The rutting condition at 7 months was found to be similar to that at postconstruction, in which an overall 20% decrease was attributed to microsurfacing. Smoothness was favorably affected by microsurfacing construction. International roughness index values were correlated to the amount of material placed in the surface preparation course.

Traffic Densification of Asphalt Concrete Pavements

A 5-year study of newly constructed pavements showed that a reduction in in situ air voids occurred both within and between wheelpaths for highways with an average daily traffic (ADT) load of less than 10,000 vehicles. Regardless of the level of voids immediately after construction, mixtures in the upper 65 mm (2.5 in.) within the wheelpath indicated a reduction in voids by 3 to 5 percent (e.g., from 10 to 6 percent voids), and by between 2 to 4 percent between the wheelpaths. Because only limited densification occurred below this depth for lower–traffic-volume facilities, reducing the mix design level of air voids from 4 percent to 2 percent for the lower lifts was suggested so that lower initial voids could be obtained during construction. An evaluation of older pavements indicated that moisture damage to the lower pavement layers was typical; thus, a change in mix design procedures might also help improve durability by increasing the film thickness. Pavements with high traffic volumes (>50,000 ADT) consistently indicated an increase in voids over time in the upper lift [40 mm (1.5 in.)], little change in the middle 65 mm (2.5 in.), and a decrease in the bottom 65 mm (2.5 in.). The hypothesis suggested to explain these findings was that a loss of material in the upper lifts was occurring, most probably due to moisture damage as the upper, more permeable wear course, commonly used in Minnesota, allowed water trapping at the wear and binder course (i.e., less permeable) interface. A further investigation of in situ void changes on an interstate indicated that for a pavement constructed with the same fine gradation in all lifts, traffic compacted the mixtures in a manner similar to that in low-volume roads. When the initial in situ voids increased from around 7 percent to nearly 10 percent, the influence of traffic on the densification was substantially increased.

CHARACTERISTICS OF TYPICAL MINNESOTA AGGREGATES

The consensus aggregate properties recommended in SUPERPAVE and selected mixture properties were evaluated for a wide range of Minnesota aggregate sources obtained from 16 construction projects completed in 1993. Measured aggregate properties included the sand equivalent (SE) and fine aggregate angularity for the fine aggregate fractions, and percentage of fractured faces and flat and elongated particles in the coarse aggregate fractions. Laboratory-compacted samples were prepared and tested to determine air voids, voids in mineral aggregate (VMA), tensile strengths, and an assessment of the moisture sensitivity of the mixtures. Only 3 of 29 SE values for individual stockpiles were less than 40 percent. These values were not significantly affected by changes in either the general mineralogy (i.e., igneous, limestone, mixed) or the percentage passing the 0.075-mm (No. 200) sieve. Single regression analyses indicated no significant relationship between SE and either mixture moisture sensitivity or VMA. While all 25 stockpiles tested had fine aggregate angularity values greater than 40, 9 stockpiles had values below 45. It was suggested that since Minnesota aggregate gradations commonly pass through the SUPERPAVE re-stricted zone (one purpose of which is to limit the use of rounded natural sands), the minimum fine aggregate angularity value be set at 45 for all mixtures to preclude the use of 100 percent natural sands. A significant number of Minnesota coarse aggregate stockpiles have a moderate to high content of flat particles (20 to 50 percent).

Thermoplastic Inlay Pavement Markings: Field Performance and Effect on Hot-Mix Asphalt

This report documents the study of the field performance of an inlay type of thermoplastic pavement marking material along with the 2-year-old bituminous pavement to which it was applied. Evaluation included physical performance of the product and the effect on overall durability of the pavement surface. The installation was performed in May 2006 on a bituminous test cell at the Minnesota Road Research Projects Low Volume Road. A total of 524 ft2 of inlaid thermoplastic pavement marking material was installed on a 4-in. surface of Superpave® hot-mix asphalt, including one segment installed along 100 ft of the left wheel path of a lane that received standard truck load configurations, and two crosswalks that received load configurations that varied by lane. From May 16, 2006, to August 1, 2007, the installations received 6,809 and 2,003 repetitions of the standard 80K and overloaded 102K truck configurations, respectively. The installation was a decorative treatment, not a retrofit of longitudinal lines on the existing pavement.