St. Louis County performed two HMA reconstructions on portions of County State Aid Highways during 2004 and 2005; CSAH 4 south of Biwabik, and CSAH 16 east of US Highway 53. The county saw differences in initial cracking performance and identified the two roads as potential research sections in 2005. Both projects were HMA reconstructions consisting of two 12-ft driving lanes with 6-ft shoulders. 24 in. of select granular modified (less than 7 percent passing the #200 sieve) was placed above the natural soil, followed by 6 in. of class 5 base material, and 5.5 in. of bituminous pavement. The bituminous pavement was constructed as 2.5 in. base lift, 1.5 in. binder lift, and 1.5 in. wear course lift. The recycled Asphalt Pavement (RAP) for the two projects all came from CSAH 16 millings. Bituminous mixtures were designed using Marshall MV criteria.
This study is a continuation of Report 2009-15, "Best Practices for RAP Use Based on Field Performance."
Micro-milling provides an innovative way to rehabilitate asphalt pavements. Micro-milling uses a milling drum with more teeth and a tighter lacing pattern to create a smoother surface than the traditional milling process (about 3 times the teeth than regular milling heads). The smoother surface provides a better surface for thin overlays, ultra-thin bonded wearing course (UTBWC), chip seals, and microsurfacing.
This is a project summary of the research that went into Report 2013-15, " Recycled Asphalt Pavement: Study of High-RAP Asphalt Mixtures on Minnesota County Roads."
The Minnesota Department of Transportation (MnDOT) is currently conducting a research project aimed at reducing longitudinal joint (L JT) deterioration in hot mixed asphalt (HMA) pavements through improved construction techniques, preventive maintenance practices, and repair treatments. Constructing durable HMA pavements, with adequate (L JT) performance, has been well documented and extensively researched, however preventive maintenance and repair treatments specific for (L JT) have received little attention in the literature.
The research work plan seeks to address the deterioration through improved construction, targeted preventive maintenance, and repair methods.
Warm mix asphalt (WMA) is a general term describing the use of any additive or technology that allows for lower asphalt plant mixing temperatures. Developed in Europe, WMA was brought to the United States in 2004 and has since gained widespread use around the country. Environmental benefits experienced with WMA include reduced emissions, fumes, and odors. With a cooler work environment enabled by WMA technology, reduced production temperatures add up to energy savings. The Minnesota Department of Transportation (MnDOT) saw the promise in this technology, especially the anticipated benefit of reduced low temperature and reflective cracking because of the reduced binder aging at the plant.
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.
Bituminous test cell 4, on the Mainline at MnROAD was constructed in October 2008 as a partnership between Mn/DOT and Road Science LLC. Cores were taken by Road Science staff soon after construction and then filled the holes with an open graded Hot Mix Asphalt (HMA). In the spring of 2010 significant heaving was noticed in the pavement surrounding the core hole areas. It was decided that a small scale forensic be conducted to determine what caused the heaving in these areas in conjunction of repairing the pavements.
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.
