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Rubblization Paves Way to Smooth Asphalt Concrete Roads

Wed November 30, 2005 - Northeast Edition
Jonathan J. Cook



A.L. Blades & Sons Inc. and the New York State Department of Transportation (NYSDOT) are cost-effectively transforming western New York’s deteriorated Interstate 86’s concrete sections into the base for a smooth, safe, durable pavement constructed of hot mix asphalt (HMA).

Interstate 86 in the project area was originally constructed in the early 1970s. The 60-ft. (18.3 m) long concrete slabs had broken roughly at the third points, with faulting and open cracks.

Paul McAnany, NYSDOT regional design engineer said, “Significant spalling was not only causing an uncomfortable ride but was becoming a danger to motorists as well. The project’s objective is to restore the pavement to a condition of structural and functional adequacy.”

Seven different alternatives for this project were considered. The alternatives ranged from maintenance to full-depth asphalt or concrete reconstruction. The maintenance alternative was discarded, because it could not meet the objective at a reasonable cost. Because of financial limitations, complete reconstruction was not possible. However, the rehabilitation alternatives could meet the final goals and were cost effective.

The severe deterioration of the existing concrete pavement precluded an overlay, saw and seal approach and ruled out crack, seat and overlay as well. Rubblizing offered the only feasible and affordable pavement rehabilitation solution.

Two construction contracts were developed to build this project: Contract D259577 Pavement Rehab on I-86 in the Towns of Cuba and Friendship, and Contract D259845 Asphalt Concrete Resurfacing and Minor Bridge Rehab in the towns of Friendship, Amity, and Angelica. A.L. Blades & Sons Inc. was awarded both contracts, which totaled approximately $22.7-million and involved more than 308,000 tons (280,000 t) of hot mix asphalt (HMA).

Both contracts included rubblizing followed by a three-course overlay of Superpave asphalt concrete. The Cuba to Friendship contract was completed in June 2005 and the Friendship to Angelica project has an expected completion date of June 2006.

How It’s Done

Rubblization is the process of fracturing deteriorated Portland cement concrete (PCC) to segments of 2 to 6 in. (5 to 15 cm) in diameter. Fracturing the concrete into small pieces reduces the likelihood that joints, cracks, and other defects will “reflect through” the HMA overlay and impair performance, according to the Asphalt Pavement Alliance.

Before the rubblization process began, Blades installed underdrain along the shoulders of the interstate, removed existing HMA patches and replaced the patches with course aggregate base.

Two types of equipment were used for rubblization: multiple head breakers, which employ a number of large hammers, which pound the pavement surface; and resonant breakers, which have vibrating hammers and use a combination of force and vibration to break up the concrete.

Blades selected Resonant Machines Inc, a Tulsa, OK-based firm as the subcontractor to perform the rubblization on the Cuba to Friendship project. Specialties LLC, from Indianapolis, IN, completed the rubblization process on the Friendship to Angelica job, utilizing multiple head breakers.

Production rubblizing for both projects yielded approximately one lane mile, per machine, per day. This rapid method of rehabilitation produces significant cost savings as well as the minimization of delays to the traveling public. The resulting fractured concrete pavement was then rolled, which further broke up the concrete as well as knit the surface particles together and seat them into place.

In areas of uneven or poor subbase and bad joints, as determined by the engineer-in-charge (EIC), the rubblized pavement was excavated and replaced with a coarse aggregate subbase.

The HMA overlay consists of a minimum of 4 in. (10 cm) of 1.5-in. (3.75 cm) Superpave base, 2.5 in. (6 cm) of .75-in. (1.9 cm) Superpave binder, and 1.5 -in. (4 cm) of .4-in. (.95 cm) Superpave top wearing course.

Two percent (solids) SBR Latex was added to the binder and top courses. This polymer modified asphalt (PMA) should increase durability and flexibility resulting in a longer lasting pavement. The improved elasticity and raised softening temperature of the PMA extends the life of the pavement as well as reduces rutting to a fraction of what was previously experienced.

The Asphalt Institute analyzed the DOT’s pavement design using the National Asphalt Paving Association’s PerRoad 2.4 Perpetual Pavement software. Its analysis determined that this pavement rehabilitation met the perpetual pavement criteria.

A perpetual pavement is defined as an asphalt pavement designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction, and needing only periodic surface renewal in response to distresses confined in the top of the pavement, according to the Asphalt Pavement Alliance’s, Perpetual Pavements: A Synthesis.

Challenges

Rubblization on the Cuba to Friendship project was a new pavement rehabilitation practice both to Blades and to the NYSDOT Region 6 engineers. The first issue to arise dealt with the crown and slope of the section after rubblization. The deteriorated PCC pavement had a proper crown and slope before the resonant fracturing process but after rubblization the center crown was destroyed and the surface now had high quarter crowns and an irregular slope.

Bill Hamlin, a DOT representative said, “The rubblization process was extremely operator sensitive. The project had different crews for the east and west bound lanes. The more experienced westbound crew left the grade and slope much less disturbed.”

The Friendship to Angelica project did not experience the crown and slope issues that arose after the resonant rubblization. Project Superintendent Tom Richardson said, “Multiple head breakers seemed to better match the existing soil sub-grade conditions and as a result left the proper crown and slope of the Interstate intact.”

The next challenge involved the actual design of the asphalt concrete Superpave overlay. Specifications called for a 4-in. (10 cm) lift of 1.5-in. (3.75 cm) Superpave base, however, actual depths of asphalt concrete varied anywhere from 4 to 9.5 in. (10 to 24 cm) on the outside of banked curves.

Therefore, the base course had a less than ideal ride because of the single lift of such varying depths. This issue arose as a result of the non-uniform subbase that the rubblization technique produced. A potential remedy, for future projects, to the less than uniform base is to modify the pavement design to include two lifts of 1-in. (2.5 cm) Superpave binder, in place of the single 1.5-in. (3.75 cm) lift.

Conclusion

The I-86 pavement rehabilitation projects drastically improved the quality and rideability of the Southern Tier Expressway (I-86) and met or in most cases exceeded initial project goals.

Rubblization is a viable and cost-effective rehabilitation option that delivers economic savings over reconstruction, while minimizing delays to the traveling public.

The NYSDOT Region 6 Design Group was responsible for the design of these projects. The group provided highway engineering, geotechnical engineering and environmental expertise and overall project management. The Region 6 materials unit, the Materials Bureau and Geotechnical Engineering Bureau of DOT’s Technical Services Division provided technical support for the project.

A.L. Blades & Sons applauded the NYSDOT and looks forward to future partnering projects to make New York roads among the smoothest, safest, and most durable asphalt concrete pavements in the country.

(Jonathan Cook is project manager of A. L. Blades Inc. Hot Mix Asphalt Promotion Steering Committee.)

(This article appears courtesy of “Material Matters” magazine.)