NCAT Conference Highlights Pavement Preservation Group Study

During the 2018 NCAT Test Track Conference that ran from March 27-29 in Auburn, Alabama, following the conclusion of NCAT’s sixth testing cycle, attendees learned about the history and current findings of the Pavement Preservation Group (PG) Study.

Assistant research professor Adriana Vargas provides NCAT Test Track Conference attendees information on preservations studies.

NCAT Assistant Research Professor Adriana Vargas first provided attendees an overview of the PG Study, which was initiated at NCAT during the fifth testing cycle in 2012 to quantify the life extending and condition improving benefits of the treatments in the study. 

During the summer and fall of that year, treatments were placed on Lee Road 159, a local low volume road with a high concentration of truck traffic dead ending into a rock quarry and asphalt plant which both agreed to provide load data to NCAT.   Twenty-five 100-foot sections were installed, including two control sections, one demonstration section, and 22 sections with individual or combination treatments. All emulsified asphalt based treatments were installed by ISSA member contractor Vance Brothers, Inc with the exception of the Fibermat sections which were installed by ISSA member Colas, Inc. In the spring of 2014, additional preservation treatments were placed on the NCAT test track.  Funding for the study was provided by Alabama, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, and Tennessee Departments of Transportation, as well as by FP² via Auburn University and the Lee County Commission.

The PG Study was extended into the sixth cycle and in the summer of 2015 treatment sections were placed on Alabama’s US 280 (high volume traffic). Following a decision to partner with NCAT, MnROAD placed pavement preservation treatments on its US 169 and CSAH-8 test sites. With these installations, studies can cover both low and high volume roadways in both Alabama’s hot, wet, no freeze environment and Minnesota’s cold, wet, freeze environment as the chart below describes.

Following the first cycle of testing, the goal of the PG study was further defined as developing independent life-extending benefit curves for a range of pavement preservation treatments under varying traffic levels and climates.

Surface treatments evaluated include crack sealing, fog seal, chip seal, scrub seal, micro surfacing and a variety of combination treatments. In addition, sections of Cold In-Place Recycling and Cold Central Plant Recycling with 1” overlay as well as a variety of segments with a thin overlay were included.

Vargas then spoke on performance measurements to date in the NCAT PG Study, describing that after consideration, it was determined that MAP-21 criteria, including cracking, rutting, and roughness (IRI) provided a good overall measure of performance.  When reviewing performance on the low-volume roadway (Lee Road 159), Vargas noted that cracking seems to be the most influential, while rutting appeared to be good to fair in all sections, but all measurements exceed the  guidelines established by FHWA thus far.

NCAT Test Track Conference attendees toured the accelerated loading test track, Lee Road 159 and the US-280 study locations.  Here, attendees get a first-hand look at the conditions of the Lee Road 159 pavement preservation test sections.

For both the low-volume and high-volume roadways, when compared with the control sections, all treatments are outperforming control sections. 

Preliminary observations from both low- and high-volume roadways had the following notable, but maybe not surprising, findings:

• Treatment performance is highly dependent on pretreatment condition
• More deterioration at time of treatment leads to a shorter life extension
• Which therefore illustrates that timely intervention with pavement preservation treatments is highly important
• Crack sealing in combination with surface treatments (single layer chip seal and single layer microsurfacing were both tested) provides significant additional benefit
•  More robust treatments (double and triple-layer chip seals, double-layer micro surfacing, thin overlays, cape seals) have shown improved cracking performance
• Cold recycling shows promising results

Vargas noted, however, that continued data collection and analysis is required as some trends are still not clear.  She also noted that these tests only measured performance, while other factors such as cost-effectiveness still need to be considered.

NCAT senior researcher Michael Heitzman explains the friction value evaluation measures used to determine the safety benefits of high friction micro surfacing in cells W7A & W7B in the west curve of the NCAT test track.

Minnesota DOT Research Operations Engineer Jerry Geib also provide an overview of the results to date at the US 169 and CSAH-8 pavement preservation sections.  With only one year of data, IRI is the most significant measurement.  Most treatments are showing initial improvement and continued improved IRI measurements.  As data continues to be gathered, measurement in other performance areas will provide more information on the life extending benefits of these in a colder environment.

The evaluation measures of the treatments placed in the Preservation Group Study will continue so that the true life extending benefits may be measured over time. Once completed, the finding from this study will greatly assist the study sponsors in managing the pavements within the networks.