Pavement Preservation Journal - Winter 2014 - (Page 35)

Detail of texture of diamond-ground PCC pavement IMAge CReDIT: IggA Digging PCC 'Buried Treasure' Beneath Asphalt Overlays By Kristin Dispenza R oad agencies and contractors alike are "digging" the buried treasure that lies concealed under asphalt overlays. The Buried Treasure approach to concrete pavement preservation (CPP) got its name because it reclaims assets that have been previously hidden below grade. It's a pavement preservation strategy that uncovers and renews aged portland cement concrete (PCC) pavement which has been overlaid with asphalt due to non-structural issues such as poor ride quality and excess tire/pavement noise. The method has been gaining popularity due in part to paving materials' price escalation, as well as the need to minimize unnecessary traffic disruptions for today's motorists. Because it's imperative to determine an underlying pavement's viability before a project can be planned and executed, the advancement of Buried Treasure CPP has been predicated on the availability of modern non-destructive testing tools. Ground penetrating radar, for example, can be useful in determining whether existing concrete pavements under an asphalt overlay are experiencing void problems. Alternatively, if concrete core samples are taken as part of the project scope, the core hole can be used as a pathway for a dynamic cone penetrometer to be used to measure the stiffness of the subbase material. Another option for determining the strength of underlying pavement is to compare falling weight deflectometer values from before and after placement of the asphalt overlay, if those data have been collected. For example, New Jersey S.R. 21 - an urban freeway in Newark, N.J. - was 5.9 miles long and consisted partly of elevated roadway using curbs and gutters for storm water drainage, and partly of rural interstate design with paved shoulders and open ditch drainage. By the early 1990s, this stretch of Highway 21 was experiencing a large number of wet weather accidents and had less than desirable skid numbers. To address the problem, a micro surfacing treatment was applied in 1993. Delamination of this treatment led to a second micro surfacing treatment in 2001, which also suffered from delamination, partially due to the condition of the underlying pavement. By 2008, major repairs were deemed necessary. In addition to using precast panels for full depth repair on some areas and performing partial depth patching on other areas, the New Jersey DOT decided to try an innovative CPP approach: removing the asphalt overlay and diamond grinding the underlying concrete pavement. Due to the potential for slab cracking, slab stabilization was included in the contract. The underlying soils were primarily unstabilized silts and sands and were therefore susceptible to washouts under the transverse concrete joints. Polyurethane grout was chosen for the slab stabilization work that was done at each joint along the 9.8 miles of roadway, totaling 400 joints in the northbound lane and 300 in the southbound lane. The shallow placement of the steel reinforcing mesh in the original pavement had been a concern for project engineers from the outset of the job. In order to minimize contact with the steel mesh, the asphalt milling and removal operations had to be performed within tight tolerances in order to leave as much of the protective concrete cover as possible. The diamond grinding contractor, Interstate Improvement, Inc. of Fairbault, Minn., requested that the asphalt milling contractor leave a thin layer of asphalt on the concrete surface. This remaining asphalt would be removed later by the diamond grinding equipment minimizing section removal and possible contact with the steel mesh. Ride quality data collected at the completion of the project exhibited a big improvement over the pre-grind ride profile. In December 2007, the pavement had an average IRI of 160.94 inches per mile. After diamond grinding was completed on the underlying pavement, the final IRI was an average of 112.00 inches per mile - an improvement of 30 percent. The bid price for the removal of the micro surfacing overlay was $784,245 for 266,750 sq. yd. at a unit price of $2.94. The bid price for the diamond grinding was $1.9 million for 266,720 sq. yd. at a unit price of $7.63. With the ever increasing cost escalation of paving materials, the value of the asphalt millings should be considered in the overall cost of a Buried Treasure CPP project. Using the bid tabs on the S.R. 21 project, it was determined that a one inch micro surfacing overlay generated approximately 0.05 tons of RAP per sq. yd. The value of the RAP can be taken into account at the time of bids. The concrete pavement on New Jersey S.R. 21 is yet another example that an urban freeway with curb and gutter drainage can be rehabilitated with concrete pavement preservation techniques at a competitive cost in an environmentally friendly manner. Edited from information submitted by the International Grooving & Grinding Association. Winter 2014 pavement preservation journal 35

Table of Contents for the Digital Edition of Pavement Preservation Journal - Winter 2014

President's Message
NCAT, MnROAD Partnership - New Era in Preservation Study
R26 Workshop: Breakout for High Volume Highway Preservation
Penetrating Emulsion, Double Chip Seal Saves Unpaved Road
Open Graded Warm Mix Boosts County Dirt Roads
You’ll Benefit from PPRS Paris 2015
CIR, Thin Seal Work Wins Norjohn Ontario Green Award
Digging PCC ‘Buried Treasure’ Beneath Asphalt Overlays
Polymer-Based Materials for Unpaved Road Maintenance
Index of Advertisers

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