Tag Archives: pavement

Comparison of Wintertime Asphalt and Concrete Pavement Surface Temperatures in Utah

Because winter maintenance is so costly, UDOT personnel asked researchers at Brigham Young University (BYU) to determine whether asphalt or concrete pavements require more winter maintenance. Differing thermal properties suggest that, for the same environmental conditions, asphalt and concrete pavements will have different temperature profiles. Climatological data from 22 environmental sensor stations (ESSs) near asphalt roads and nine ESSs near concrete roads were used to determine which pavement type has higher surface temperatures in winter.

Twelve continuous months of climatological data were acquired from the road weather information system operated by UDOT, and erroneous data were removed from the data set. In order to focus on the cold-weather pavement surface temperatures, a winter season was defined as the period from November through April, and the data were divided into time periods that were based on sunrise and sunset times to match the solar cycle.

To predict pavement surface temperature, a multiple linear regression was performed with input parameters of pavement type, time period, and air temperature. As shown in Table 1, the statistical analysis predicting pavement surface temperatures showed that, for near-freezing conditions, asphalt is better in the afternoon, and concrete is better for other times of the day. However, neither pavement type is better, on average, across the locations studied in this research. That is, asphalt and concrete are equally likely to collect snow or ice on their surfaces, and both pavements are expected to require equal amounts of winter maintenance, on average.

To supplement these analyses, which provided useful information about average pavement temperatures across the statewide pavement network, additional analyses of asphalt and concrete pavement surface temperatures were performed for a particular location in a mountainous region of northern Utah more typical of canyon areas. Asphalt and concrete pavement surface temperatures were directly compared at a location on U.S. Route 40 near Heber where asphalt and concrete meet end to end at the base of a mountain pass. As shown in Figure 1, an ESS was installed to facilitate monitoring of asphalt and concrete pavement surface temperatures, as well as selected climatic variables, at the site.

Data collected during the three winter seasons from 2009 to 2012 were analyzed in this research, and the same months and time periods used in the previous study were applied in this analysis as well. To compare the surface temperatures of the concrete and asphalt pavements during freezing conditions, multivariate regression analyses were performed. Equations were generated for three response variables, including the asphalt surface temperature, concrete surface temperature, and difference in temperatures between the asphalt and concrete surfaces.

The statistical models developed in the analyses show that the surface temperature of both asphalt and concrete pavement increases with increasing air temperature and decreases with increasing relative humidity and wind speed, and that the difference in pavement temperatures decreases with decreasing air temperature. For the studied site, the data indicate that concrete pavement will experience freezing before asphalt pavement for all time periods except late afternoon, when the pavement types are predicted to freeze at the same air temperature (see Table 2). Therefore, for material properties and environmental conditions similar to those evaluated at this U.S. 40 site, asphalt would require less winter maintenance, on average, than concrete.

Due to the interactions among albedo, specific heat, and thermal conductivity, the actual thermal behavior of a given pavement will depend on the material properties and environmental conditions specific to the site. As shown in this research, concrete pavement can be warmer than asphalt, which is typical of the statewide pavement network, on average, during late morning, evening, night, and early morning. However, the research also clearly shows that, in mountainous regions of northern Utah more typical of canyon areas, engineers may expect asphalt pavement to be warmer than concrete, or equal in temperature to it, during all time periods at sites that receive direct sun exposure, such as the one on U.S. Route 40 that was studied in this research. At such sites, selection of asphalt pavement may facilitate reduced winter maintenance costs; however, though statistically significant, relatively small differences in temperature between asphalt and concrete pavement surfaces may not warrant differences in actual winter maintenance practices. Other factors beyond pavement type, such as rutting and surface texture, may more strongly affect winter maintenance and should also be considered.

The results of the statewide comparison of wintertime temperatures of asphalt and concrete pavements, as well as the specific results for the U.S. 40 site near Heber, are detailed in two separate research reports available on the Research Division website.

This guest post was written by W. Spencer Guthrie, Ph.D., M.ASCE, Brigham Young University, and David Stevens, P.E., Research Program Manager, and was originally published in the Research Newsletter.

A behind-the-scenes look at the materials lab

Clint Tyler Materials Technician

Clint Tyler, a materials technician, looks on as an asphalt sample cools before conducting further tests. This machine runs a metal wheel over the sample 20,000 times to measure its durability.

Before UDOT employees reroute traffic, before they begin paving the road and even before they put out orange cones, they are hard at work. This work requires communication between traffic signal engineers, project managers and others – but none of it would happen without the approval from the materials engineers. The behind-the-scenes work done by engineers in the materials lab ensures the durability of the road before construction begins, making the lab testing a vital part of the preconstruction process.

Steve Park, Region Three Materials Engineer, explained that the purpose of the materials lab is to test road materials for strength and durability. “We get long-lasting roads by demanding high-quality materials, and it’s our job to test those materials before they’re in the road,” Park said. “We save taxpayer money that way, because we won’t have to tear it up later.”

Asphalt Sample

An asphalt sample cools following some tests. The asphalt tests conducted in the materials lab help materials technicians determine the mixture’s durability.

The materials lab has a few different functions. One function is to mix and test the materials that a contractor wants to use for a project. In this process, the materials engineers and technicians use the lab to mix the materials according to the contract specifications. After they have been mixed, the materials engineers analyze the results, and the mixtures are evaluated according to strict safety and durability standards.

After the materials engineers complete their analysis, UDOT materials technicians then test the mixes. One test assesses the durability of an asphalt mix by placing a sample in a machine that simulates a car driving on it. The machine runs a metal wheel over it 20,000 times, and it meets durability standards if the wheel creates a rut less than 10 mm deep. Another test cures concrete samples for 28 days in at least 95 percent humidity before crushing them to measure their durability.

Clint Tyler, a materials technician, said that the importance of these tests cannot be understated. “We do these tests because it’s easier to make changes now, before it’s in the road,” Tyler said. “Our roads last longer that way.”

Road Core Samples

A stack of road core samples waits to be examined. Every so often, materials technicians will take core samples of a road to determine whether or not it needs maintenance work.

A second function of the materials lab is to test the health of the roads. Every so often, materials technicians will take a core sample of a road to determine whether or not it needs maintenance work. These projects, such as resurfacing, minimize future construction by prolonging the life of the road.

“In the end, analyzing the materials and doing these tests is just as important as the construction itself,” Park said.

While materials technicians’ work will always be behind the scenes, the results they gather will continue to directly affect Utah drivers. Their hard work ensures that UDOT’s roads will provide safe and smooth travels for years to come.

2013 Strategic Direction — Part 1

This is the first part of a 4 part series about the 2013 Strategic Direction. Please also check out Part 2: Optimize Mobility, Part 3: Zero Fatalities, and Part 4: Strengthen the Economy.

After a record breaking construction year, with more than 200 projects completed, worth just over $3 billion, what is in store for UDOT in 2013? The newly completed 2013 Strategic Direction and Performance Measures highlights accomplishments by the department in 2012 and introduces goals for 2013 and the coming years.

Key to the Strategic Direction document are the UDOT Strategic Goals. These goals ensure that we focus our efforts and capital on the most important activities. This year we have revised our goals, which include:

  • Preserve Infrastructure
  • Optimize Mobility
  • Zero Fatalities
  • Strengthen the Economy

Details on each goal will be provided in a four part series, beginning with:

Preserve Infrastructure

Preserving Utah’s multi-billion dollar investment is the single largest expenditure year to year within UDOT. Keeping the state’s bridges and pavement in good condition is the most effective way to extend the life of the transportation system. This is accomplished by applying well-timed preservation treatments to roads, and addressing critical needs first. By applying a combination of routine maintenance, preservation and minor and major rehabilitation projects, UDOT is able to utilize limited funding to maximize the pavement condition.

In 2012:

  • More than 100 preservation and rehabilitation projects were completed,
  • Approximately 350 miles, or six percent of the system, received a specific preservation or rehabilitation treatment,
  • Six critical bridges were replaced,
  • Eighty-four new bridges were built by capacity-driven project,
  • Two pedestrian bridges were built,
  • Bridge preservation and rehabilitation activities were performed on more than 170 bridges.

Please also check out Part 2: Optimize Mobility.

HIGH FIBER

Added fiber may help make asphalt pavement more durable.

 

UDOT hopes a new product will extend the life of asphalt pavement. This photo shows an area where flexible and conventional microsurfacing is being tested side by side.

 

UDOT roads are built to last. “UDOT typically designs our asphalt pavements for a 20 year design life, meaning they have the structural thickness to support 20 years worth of traffic,” says Gary Kuhl, UDOT’s Statewide Pavement Management Engineer.  Once built, preservation keeps the road surface in good shape so pavement can reach or extend beyond that 20 year life.

UDOT is testing a new preservation treatment called flexible microsurfacing. Conventional microsurfacing is a thin asphalt “wearing course” that contains aggregate, emulsion and binder (usually cement) that is mixed on-site and applied to the road.

The new product has an additional ingredient – a strong, flexible type of fiber – that is intended to help the asphalt reduce cracking and resist damage from traffic and snow plows. Flexible microsurfacing uses a regular microsurfacing machine and a blower to add fibers to the conventional mix.

Fiber adds durability to conventional microsurfacing.

The two products were placed side by side on a busy arterial road in Davis County. After a two year evaluation, the flexible microsurfacing “shows little to no damage from snowplow activities and no raveling,” states a report on the test. Raveling happens when binder fails and rocks and asphalt chunks break loose. The conventional microsurfacing side shows reflective cracking (cracks from the bottom up) that stops where the flexible microsurfacing starts.

Scott Nussbaum, Materials Engineer for UDOT Region One, thinks “the initial performance is positive.” But its use is “still experimental” continues Nussbaum. UDOT will need to continue to study this product and develop specifications for its use.

UDOT engineers believe that the additive increases the toughness and durability over conventional microsurfacing to help reduce or delay cracking and resist raveling and snowplow damage. Kuhl is optimistic about the new product. “For a small extra cost we expect to get a stronger surface that will have less cracking.  UDOT continues to test new ideas and will be monitoring how this one performs.”

For more information:

  • Read a report on the test
  • Read about how good roads cost less in UDOT’s Strategic Direction Performance Review and Measures
  • More from Gary Kuhl: “UDOT found out a long time ago that ‘Good Roads Cost Less,’ so our approach has been to try and keep our pavements in good condition by strategically utilizing lower cost preservation treatments on a regular basis.  Combined with a mix of rehabilitative overlays this has had the effect of extending the pavement life indefinitely. For the most part our reconstruction work is primarily due for widening and capacity needs, and rarely due to pavement failure needs.”

DESIGNED TO LAST

I-15 CORE pavement layers stack up to a durable, weather resistant, low maintenance, 40-year life.

Traffic has switched to new concrete pavement between Lindon and American Fork, marking I-15 CORE as twenty-five percent complete. The new smooth ride is a predictor of good things to come.

 

PAVEMENT PANORMA: Click on this image to view a larger version. Thanks goes to John Butterfield, UDOT Materials/Pavement Engineer, for this great photo.

More than just a pretty surface

“Any pavement design is a multi-layered system,” says John Butterfield, UDOT Materials and Pavement Engineer on the I-15 CORE project. I-15 CORE pavement consists of four layers from the bottom up: granular borrow, drainable granular borrow, asphalt base and Portland Cement concrete.

The amount of material in each layer is adjusted according to different factors, like drainage requirements, availability of materials or project budget. Traffic volume is the most important factor engineers consider when designing pavement.

Where the rubber hits

“The main thing that drives pavement design is traffic,” says Butterfield.  “It all has to add up to the structural value that is predicted from traffic volume expected on that road.”

The forty-year pavement design on the I-15 CORE project is a value-added feature that the contractor, Provo River Constructors, included in their winning proposal.  UDOT asked for 30-year pavement, “they gave us forty,” says Butterfield.

Why concrete?

Going the extra mile: A worker makes smooth concrete even smoother for a bump-free ride.

UDOT prefers concrete on high-volume roads. “Under heavy interstate traffic, concrete is the best investment,” Butterfield explains, because it’s smooth, rigid and less maintenance is required compared to asphalt. “We just know it works and it will last if it’s done right.”

Concrete is also weather resistant. In engineer-speak, concrete has “an air void system to allow for the pressures generated when internal water freezes.”

Translated, that means potholes are exceptionally rare!

VIDEO: This  KSL story below shows concrete installation, and the video after the story shows the layers that make up the pavement.

 

Video Courtesy of KSL.com