CONCRETE PAVEMENT RECYCLING By JOHN W. McCREE Bureau of Local Roads and Streets, IDOT

Highway authorities who are responsible for maintaining concrete pavements eventually face the decision whether to remove and replace a pavement or stage a patching and resurfacing project. Depending on the condition of the pavement, usually the best alternative is complete removal and replacement. However, the high cost of removing the old pavement and constructing a new one may be prohibitive and other options may be necessitated. Although patching and resurfacing do extend the service life of a concrete street for a few years, repeat applications are required at relatively frequent intervals. A different solution to concrete pavement rehabilitation has been used recently by two communities, the Village of LaGrange and the City of Rock Island.

In 1985, the Village of LaGrange was faced with an extensive sewer replacement beneath a concrete street which was scheduled for resurfacing. Faced with the cost of saw cutting a trench for the sewer repairs and replacing the concrete pavement, the Village elected to try a new approach. The old concrete pavement was totally fractured into small, rubble-sized pieces and the fractured material was left in place as a flexible base course for the new resurfacing. After the pavement was fractured, sewer repairs and soft sub-grade replacement were accomplished without sawing the pavement. When all sewer work and soft sub-grade replacement had been completed, the street was resurfaced.

To fracture the old concrete pavement, a pavement breaking machine that utilizes low amplitude, high frequency vibrations was specified for this project. Vibrations are transmitted to the pavement through a direct contact shoe which is fastened to one end of a forged steel resonating beam. Since the shoe is in constant contact with the pavement, there is no sudden impact noise or high amplitude vibrations that are commonly associated with a drop-hammer type of pavement breaker. The resonant frequency pavement breaker is also equipped with a water spray system for dust suppression. The size of the pavement fragments is related to the speed with which the breaker travels and the amount of sub-grade support under the pavement. A slower travel speed results in smaller fragments. Voids or soft soil under the pavement produce larger fragments that may require a second pass of the breaker or fracture by other methods. After the old pavement is fractured, it is rolled with a heavy roller to seat and consolidate the fragments. A layer of fine aggregate (screenings or sand) should then be spread on the pavement and consolidated with a vibratory roller. A final leveling course of coarse aggregate (CA-6 or CA-10) approximately 2" thick is then spread on the surface and compacted. The bituminous binder and surface courses are then placed by conventional methods.

The evaluation process to determine whether the fragmentation process is a viable alternative must address several different factors. The final elevation of the completed roadway will be approximately 6 inches higher than the existing elevation. The topography of the surrounding terrain must be able to accommodate this change. If the existing roadway has curb and gutter, it will be necessary to replace all of it to meet the new elevation. The resonant frequency pavement breaker does not function as efficiently on an asphalt surface as it does directly on concrete pavement. If the concrete has been patched or resurfaced with asphalt, it is recommended that all of the asphalt be removed prior to fracturing the pavement. When a project of this nature is completed, the agency will have a flexible base pavement in place of a rigid pavement. Projected traffic conditions for the roadway should be such that a flexible pavement is suitable.

The Village of LaGrange was impressed enough by their first project to use this process each year since 1985. The City of Rock Island employed the fragmentation process on a portion of one resurfacing project in 1987 and is considering the process for future work. •

August 1988 / Illinois Municipal Review / Page 7