An unbonded concrete overlay project was constructed n Route D (Holmes Road) spanning the border of Cass and Jackson Counties south of Kansas City, MO.
Unbonded concrete overlay. Existing Pavement Condition: The existing concrete pavement is experiencing severe durability cracking (D-cracking), defined by the significant deterioration of the concrete near the pavement joints.
Preparation of Surface Before Placement of Interlayer:
Before placement of the overlay, patching and repair of the damaged concrete near the joints was undertaken unless an existing patch appeared intact and flush with the existing pavement surface. Where applied, the repair technique used on this project included removal of all existing patch and loose material from these areas. This was followed by placement of a flowable (cementitious-based) fill.
Method and Equipment for Placement:
The geotextile material was delivered to the project on 300-ft (91-m) rolls, 15 ft (4.5 m) wide. A telescopic forklift was used to transport the rolls from the yard to the roadway and to assist with application. Two rolls of geotextile were used to span the width of the pavement. As a result, both longitudinal and transverse lapping of the geotextile were necessary. Immediately before construction, the geotextile material was wetted using a tanker truck, shown in figure 10. The surface was reportedly saturated, and it was later concluded that less water would ensure more ideal moisture content.
Method for Securing:
A Hilti gas-powered system was used to drive the fasteners (collated pins) into 2.25-in (57 mm) metal discs, through the geotextile, and into the underlying concrete pavement.
On this project, nonwoven geotextile interlayer was specified as an alternative to the conventional 1-in (25.4-mm) hot-mix asphalt (HMA) interlayer. The intent was to separate the 22-year-old, 8-in (203-mm) existing concrete pavement surface from the proposed 5-in (127-mm) unbonded concrete overlay. While the interlayer does separate two cementitious-bound layers, this application differs from the typical German practice of separating a cementitious base from a new concrete pavement. In the few instances in Germany in which a nonwoven geotextile was used to separate two concrete layers, the existing concrete pavement was rubblized first.
In theory, as an overlay interlayer, the nonwoven geotextile must prevent reflection of the distress of the existing concrete pavement while providing a stable and drainable platform for the overlay. Following these principles, two nonwoven geotextiles were used for various parts of the project, including Geotex 1201 and Geotex 1601, manufactured by Propex. It was recognized that these geotextiles did not fully comply with the German specifications, but because they were immediately available and complied with some of the more critical aspects of the German specification, they were considered viable for use on this project.
Some concern was raised initially with the lighter geotextile (Geotex 1201) about what appeared to be areas of the geotextile that were thinner than the German specification. The material not only appeared thin, but also had areas that appeared to be partially melted. Further investigation confirmed that the Geotex geotextile is normally exposed to heat (calendared or infrared (IR)) to partially fuse one side of the material. What was observed was likely material from the end of a production run, where excess heat was inadvertently applied.
Subsequent discussions of this phenomenon with experts in Germany did not yield significant concern, but did underscore the German practice of discouraging the use of geotextiles with thermal treatment. While firsthand observations were not made of the subsequent use of the Geotex 1601 material, it is believed that the denser material would be more likely to partially mitigate potential drawbacks of the thermal treatment. Furthermore, subsequent testing of the 1601 material has confirmed compliance with all but the thermal treatment requirements in the proposed interim specifications.
No problems were reported with the geotextile during the paving process. In general, the project proceeded as it would have using a conventional interlayer. After construction, cores were extracted from the pavement structure. The geotextile was found to have bonded to the fresh concrete. Bonding did not occur between the geotextile and the underlying concrete pavement, which is ideal considering the necessity for separation from this layer.
Overall, the Route D project appears to be a success. It has been reported that the long-term performance of this section will be monitored.
Westbound Interstate 40 in Oklahoma.
Method and Equipment for Placement:
On this project, the geotextile selected was imported from Germany. The product, HaTe nonwoven B 500, is manufactured and distributed by the U.S. subsidiary of Huesker Synthetic GmbH.
The rolls of geotextile were delivered directly to the project and placed atop the new CTB. Immediately before the paving, a modified backhoe loader was used to lift the rolls and assist in the installation. A crew of three to five people installed the geotextile.
The 5-m-wide (5.4-yd-wide) geotextile rolls were placed two across, resulting in a need for both longitudinal and transverse laps.
The majority of the geotextile appeared to be in good to excellent condition. Two haul roads flanked the project, limiting the need for vehicle maneuvering atop the installed geotextile, however, an isolated instance of shoving was observed, likely because of a short-radius turning maneuver. The severity of the shoving does not appear to be significant enough to warrant replacing the geotextile, but it underscores the need to avoid the potential for its occurrence.
Paving on the geotextile appeared to proceed with no variance from normal construction procedures. Haul trucks traveled on the geotextile, backed up to the paver, and deposited the fresh concrete onto the geotextile in advance of the spreader. The edge of the geotextile was not damaged by the paver and appeared behind the paving train intact.
Method for Securing:
The geotextile was fastened to the underlying CTB using a Hilti powder-actuated system with X-DNI fasteners (consisting of integrated pins and washers). The washers used on this project are smaller than those recommended in German practice. Additional care may be necessary to ensure that the geotextile does not tear free of these fasteners during subsequent concrete placement.
In this case, the project was similar to the typical German application with the interlayer used to separate a new cement-treated base (CTB) from a new concrete pavement.
The project in Oklahoma appeared to be a success. The contractor believed it saved money and time without compromising performance.