How Terracon extends pavement life cycle at Love’s Travel Stops with polymer-modified asphalts and fiber-reinforcement
Of all the infrastructure that gets used constantly, pavements are one of the most overlooked, and perhaps the most neglected. Heavy traffic, heavy loads, water and weather extremes lead to rutting and cracking, shortening pavement’s potential lifetime.
Founded in 1964, Love’s Travel Stops & Country Stores has more than 480 locations in 41 states. With more than 2,000 acres of pavement to maintain, Love’s pays close attention to constructing and maintaining its pavements with the help of Terracon Consulting, Salt Lake City, UT.
In both maintenance and construction Love’s considers a variety of pavement alternatives, and two projects were monitored: their decision to implement polymer-modified asphalts and fiber-reinforcement when constructing truck stops in Kentucky and Louisiana.
Love’s Travel Stop in Sadieville, KY, was constructed in 2015 with fiber reinforcement added to both base and surface course layers in all areas of the site subjected to heavy truck traffic. Subsequent on-going monitoring of pavement conditions in 2018 revealed the only cracks identified are at some paving cold joints, and rutting and surface deformation is extremely minimal throughout the site.
The improvement afforded by the fiber reinforcement was evident when comparing an adjacent county road, constructed concurrently, but without fiber. Rutting and deterioration were observed in the non-fiber reinforced asphalt whereas no observable distress was noted in the reinforced materials.
In Greenwood, LA, a Love’s Travel Stop facility was expanded in 2016, and the expansion included resurfacing existing pavements. Asphalt concrete both with and without fiber was placed at the entrance to a new parking lot addition to provide direct comparison between the two materials.
During the summer of 2018 the facility was inspected. No deformation was noted in the fiber-reinforced asphalt areas, however early signs of rutting were noted in the non-fiber areas. Additionally, the overlay, placed without fiber, in the original pavement areas indicated signs of heavy rutting and shoving distress near the truck fueling areas after just two years of use.
Proper planning, design, and especially construction all play a key role in ensuring pavements have a long life and at the lowest cost. Here’s a process Love’s, through guidance by Terracon, follows in care of the pavement.
Design from the Ground Up
A correct pavement design is the first step to creating a long-lasting pavement asset. It’s here that spending a little extra time considering the lifecycle of the project to be an important investment.
To find the right design solution, consider:
o What vehicles will operate on your pavement?
o How many and how often?
o How heavy are the vehicles and where will they drive?
Some owners have difficulty arriving at the answers, but this information must be quantified for any pavement design.
o What soil conditions will be present at time of construction? Your geotechnical engineering partner can prepare a study with adequate scope and field investigation to provide the basis for your pavement design to define:
§ Native soils in poor condition?
§ Select engineered fill?
§ Are the soils undocumented fill?
§ Swampy mud or beach sand?
- Materials
o What asphalt mixes are available and what mixes has your pavement designer considered for the asphalt mix in preparing pavement section designs?
Traffic loading and weather conditions are key factors in selecting the right asphalt mix for each unique site and usage.
Quality Materials Are Cost Effective
Materials are often the major cost item for a pavement project, and economies taken here can affect the total investment for new construction or major repairs. As high as site development costs might seem, cutting corners at this stage of a project often results in increased maintenance and management of paved assets.
Quality materials typically carry a higher price tag, though fortunately the proper use of quality materials typically reduces your lifecycle costs. For example, using an asphalt mix intended for low traffic such as an automobile parking lot, in a heavy truck traffic area, such as a driveway or main entrance, can result in premature failure, frequent maintenance, and a need for early repairs. Similar outcomes may be experienced if cheaper recycled asphalt concrete is selected instead of Department of Transportation-approved aggregate base, unless the engineer accounted for recycled materials during design.
Selecting the right asphalt concrete mix is important to development of long-lasting pavements. Pavement materials and mix designs have advanced significantly over the years, leading to several choices for asphalt concrete. High-traffic situations call for more robust asphalt concrete; Superpave mixes with larger ½-inch or ¾-inch aggregate are well-suited to withstand heavy and frequent wheel loads. Likewise, performance graded (PG) polymer-modified asphalt binders have proven to provide better rut resistance in heavy load and high temperature environments.
Aramid “Kevlar” fiber reinforcement is also an effective technique for strengthening asphalt concrete subjected to frequent, heavy or concentrated traffic. Fiber is easily added during the batching process and fiber suppliers commonly work closely with the plant operators to verify proper mixing. Fiber does not affect the placement or compaction of hot-mix, which makes it an ideal admixture. Most importantly, fiber provides key tensile strength that is missing from unreinforced asphalt. Tensile strength is the property that helps to reduce and control cracking and rutting, which in turn reduces long-term maintenance costs.
Another example where quality materials provide benefit is the use of geogrid and geosynthetic products. Sites with poor subgrade conditions are often great candidates for the use of geogrids or reinforced geosynthetics. Geogrids are like “rebar for soil” and when used with select engineered fill can effectively stabilize and bridge soft, muddy and “pumping” soil conditions. Likewise, reinforced geosynthetics provide both strength and separation/filtration in one product, which speeds installation at sites with fine-grained subgrade soils.
When incorporated into the design process, geogrids and geosynthetics are effective in reducing the overall pavement section thickness. By strengthening the soil mass in which they are installed, grids and geosynthetics commonly reduce the required aggregate base layer by several inches, and often the asphalt concrete layers by up to an inch.
If there’s a large pavement area, the material cost savings from reduced layer thickness can be substantial – frequently several times the cost of the grids/geosynthetics. Additionally, the reinforcement provides long-term stability and resilience to the subgrade that just doesn’t exist without these materials. This results in pavements that require less maintenance and provides a better base below to support pavement preservation such as milling, overlaying or resurfacing.
Construction Quality is Essential
Construction is the final piece to helping pavements last longer and one of the most important as even the best materials won’t last as intended if not properly constructed. Achieving minimum specified compaction is the primary goal and, like soils, asphalt must be tested to determine in-place density. Contractors should conduct quality control (Q/C) testing to manage the placement and compaction work. Owners should conduct quality assurance (Q/A) testing to verify the Q/C results and for final acceptance.
Planning is the key to a successful paving operation. Pre-paving meetings with the general contractor, paving contractor, supplier, owner and testing firm are excellent opportunities to discuss the challenges of each project. Key topics include: schedule, approved materials, logistics, weather conditions and contingencies. It’s also important to clarify who has authority to stop or suspend paving operations, if necessary.
Pavement performance is like a journey: we set out on a trip at the beginning of construction, but we don’t know how it ends until the pavement has been subject to traffic and weather for five, 10, or 15 years. Consequently, the results of the effort and expense put into a quality pavement aren’t realized until sometime later; monitoring of the pavement over time is important to quantify the benefits. You will get the most from your pavement investment when you plan well and engage the right partners for your project needs.
