Use of Nonwoven Geotextiles as Interlayers in Concrete Pavement Systems (Dahee)
This wiki subject demonstrates the potential use of nonwoven geotextile materials as interlayers in concrete pavement systems (NGICP), in particular unbonded overlays, in United States. This subject consists of Germany’s experience, availability and cost of nonwoven geotextiles in the United States, specifications, recent field tests, recommended construction practices, and issues requiring additional research.

1. Basic structure of NGICP

Figure.1 depicts basic NGICP structure. As can be seen in Figure.1, a nonwoven geotextile is laid down on the existing pavement and then new concrete pavement is paved on the nonwoven geotextile.
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Figure.1 Nonwoven geotextile structure

2. The need of nonwoven geotextile interlayer

In the United States, hot-mix asphalt (HMA) is the material traditionally used to separate cementitious pavement layers. In the case of unbonded concrete overlays on existing concrete pavements, a 1-in. thick HMA interlayer is typically required. Although HMA interlayers provide adequate cushioning and layer separation, HMA can have some drawbacks. For example, using HMA as an interlayer requires setting up two separate paving operations, one for concrete and one for asphalt, which can be expensive and time consuming. Some HMA mixes do not provide adequate drainage and can be subject to stripping under heavy truck traffic. The 1-in. typical HMA interlayer depth for unbonded overlays on concrete pavements can be problematic in tight vertical clearance situations, particularly in urban areas. Because of these shortcomings of HMA interlayers, contractors and roadway agencies could benefit from an alternative to HMA.
In May 2006, a team of public and private sector representatives participated in a scanning study of long-life concrete pavements sponsored by the Federal Highway Administration (FHWA), the American Association of State Highway and Transportation Officials (AASHTO), and the National Cooperative Highway Research Program (NCHRP). During this scan, the team learned about the German use of nonwoven geotextile as an interlayer between lean concrete bases and concrete pavement surfaces.
For 25 years, German engineers have been using nonwoven geotextile materials as interlayer material between new cement-treated bases and jointed concrete surface layers (figure. 1). These pavement systems are of excellent quality and have long lives, despite carrying significant traffic loads. German engineers also use nonwoven geotextiles as interlayer material on occasion when they construct unbonded concrete overlays. Before they place the geotextile interlayer, however, the existing pavement is either rubblized or cracked-and-seated, which is not common U.S. practice. German engineers have steadily improved the following characteristics and functions of nonwoven geotextiles for use as interlayer materials:

1. Separation. Prevents joints or cracks from reflecting to the surface layer (Figure. 2). Needs to prevent bonding and accommodate the normal movements of the two cementitious layers.

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Figure.2 Reflective cracking

2. Drainage. Allows infiltrated water between layers to drain to the pavement edge (Figure. 3). Must be terminated next to adjacent drainage layer or daylighted. Needs a degree of permeability that allows minimum flow in three dimensions.



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Figure.3 Drainage ability of NGICP
3. Bedding. Provides a degree of cushion that reduces bearing stresses while providing adequate support stiffness (Figure. 4).

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Figure.4 Role of NGI as a cushion

As a result of what they learned in Germany, scanning tour participants recommended that field tests be conducted in the United States to examine the effectiveness of nonwoven geotextile material as an interlayer between cementitious pavement layers.

3. Availability and cost

Several U.S. manufacturers produce nonwoven geotextile materials that are used for a variety of purposes. However, until very recently, none of the U.S.-produced materials was marketed specifically for use as an interlayer in cementitious pavement systems, and most U.S.-produced materials do not conform to German specifications for such use. Recently, agencies and contractors have expressed an increased interest in using nonwoven geotextiles as interlayers in pavement systems in the U.S. As a result, some U.S. manufacturers now produce materials that meet specifications. Costs of U.S.-produced materials can vary, but estimators should assume $1.50 to $2.50 per square yard for the material and installation. German-made nonwoven geotextiles are available through many U.S. suppliers. They can also be imported directly from Germany at a slightly lower source cost than U.S.-produced material, but organizations should expect additional freight costs of $0.05 to $0.10 per square yard. Importing directly from Germany will likely increase project lead time by six to eight weeks.
Moreover, some experts insisted that in comparison of NGICP system to other methods such as asphalt concrete overlay since this is not required to prepare a specific treatment for the existing pavement (Figure. 5), NGICP system cannot only save construction duration, but also construction cost.
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Figure.5 Specific surface treatments for asphalt concrete overlay


4. Specifications and testing of nonwoven geotextile

Nonwoven geotextile interlayers were first standardized in Germany in 2001, and the specifications have evolved over time to reflect continuing improvements by German engineers. Table 1 shows proposed interim U.S. specifications for nonwoven geotextiles used as interlayers in cementitious pavement systems, based on German concrete pavement guide documents. Until the proposed U.S. specifications are finalized and test standards (e.g., ASTM) are verified for use with nonwoven geotextile materials, use of the German specifications and test standards (e.g., ISO, EN, DIN) is recommended.

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Table 1. Summary of proposed specifi cations for nonwoven geotextiles (derived from German guide documents)


5. Installation practices

The two U.S. field tests conducted in 2008 provide encouragement that nonwoven geotextile fabric may be an efficient and cost-effective alternative to HMA as an interlayer in cementitious pavement systems in this country. In general, the following construction practices have resulted in successful installations:

• Place the material as shortly before paving as possible (ideally no longer than 2 to 3 days) to reduce the potential for it to be damaged.
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Figure.6 Geotextile installation on an existing pavement


• Before placing the nonwoven geotextile material, if required, repair the existing pavement to correct any significant cracking or faulting, and sweep the pavement surface clean.
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Figure.7 Examples of required repairing


• Roll the material onto the base or other surface, keeping the nonwoven geotextile tight with no wrinkles or folds.
• Roll out sections of the material in a sequence that will facilitate good overlapping, prevent folding or tearing by construction traffic, and minimize the potential that the material will be disturbed by the paver.
• Overlap sections of the nonwoven geotextile material a minimum of 6 in. and a maximum of 10 in., and ensure that no more than three layers overlap at any point.
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Figure.8 Overlap of geotextile


• Secure the material with pins (nails) punched through 2.0–2.75 in. galvanized discs placed 6 ft apart or less, depending on conditions.
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Figure.9 Fastening geotextile to an existing pavement


• Lightly dampen the nonwoven geotextile prior to concrete placement to prevent its drawing water from the mix.
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Figure.10 Pre-wetting geotextile before placing concrete


• If concrete is being delivered in front of the paver, place no more than 650 ft of nonwoven geotextile material ahead of the paver at any time.
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Figure.11 Overlay placement


• Avoid driving on the nonwoven geotextile material unless necessary, and never make sharp turns on the material with vehicles. Avoid having the nonwoven geotextile exposed to heavy turning traffic until paving is completed.
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Figure.13 An example of localized shoving of geotextile


6. Field Tests in the United States

Two notable field tests using nonwoven geotextile interlayers have been conducted recently in Missouri and Oklahoma.

6.1 Missouri

The first field test was conducted on Route D south of Kansas City, Missouri, in 2008. Nonwoven geotextile material was used as an alternative to a 1-in. HMA interlayer in an unbonded concrete overlay. Before placing the nonwoven geotextile interlayer, the existing concrete pavement was thoroughly cleaned, and deteriorated areas were patched with flowable mortar to create a uniform surface (figure 13). The nonwoven geotextile was placed dry (figure 14) and fastened to the underlying concrete pavement with pins (nails) air-driven through 2.25-in.galvanized discs spaced 2 to 6 ft apart (figure 15).
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Figure.13 Repair and replacement of damaged concrete


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Figure.14 application of geotextile from rolls along the road


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Figure.15 fasteners (collated pins) and discs used



Two U.S.-manufactured nonwoven geotextiles, Propex Geotex 1201 and 1601, were used. Neither was fully compliant with German specifications. As a rule of thumb, a nonwoven geotextile interlayer between an existing concrete pavement and a concrete overlay should bond to the overlay but not to the existing pavement. If the nonwoven geotextile is too thin, it has the potential to become saturated by mortar from the overlay and bond to the underlying pavement surface. Initially, Geotex 1201 was placed. After the thinness of the Geotex 1201 was observed, the contractor switched to the thicker Geotex 1601 for the remainder of the project. A core sample of the Missouri overlay field test revealed that the nonwoven geotextile material had bonded with the overlay but not with the existing concrete pavement, as desired. Therefore, the installation was considered a success. The ongoing performance of the interlayer material and the overlay pavement system will continue to be evaluated.

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Figure.16 Pre-wetting geotextile before placing concrete


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Figure.17 Overlay placement along the road


6.2 Oklahoma

In 2008 a second field test was conducted on a new construction project on I-40 in Oklahoma. This project was typical of a standard German application in which nonwoven geotextile material is used as an interlayer between a new cement-treated base and a new concrete pavement. A German material, HaTe nonwoven B 500, was imported to ensure compliance with German specifications. The galvanized discs used to secure the nonwoven geotextile to the cement-treated base were approximately 1 in. in diameter (smaller than German specifications). Paving was conducted as in any normal project. Haul trucks were driven on the geotextile material as they were backed up to deposit fresh concrete in advance of the spreader. Th e nonwoven geotextile material was not damaged by the haul trucks or the paving machine, as long as the vehicles did not turn on the geotextile. The material appeared intact behind the paving train. A core sample revealed that the nonwoven geotextile material had bonded slightly to the new pavement and not at all to the cement-treated base, making this installation a success.

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Figure.18 Delivery and installation of geotextile rolls on the road


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Figure.19 Geotextile installation


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Figure.20 Installed fastener and disc


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Figure.21 Lapping seams of geotextile


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Figure.22 Paving new concrete pavement on geotextile


7. Conclusion and recommendations

It appears from both the literature and firsthand field observations that the use of a nonwoven geotextile interlayer between cementitious layers is not only viable, but also potentially a superior alternative to more conventional interlayer materials.

Benefits of the nonwoven geotextile interlayer include the following:
◗◗ Lower cost for material and installation

◗◗ Equivalent performance, at least for separation of cementitious bases and new concrete pavements

◗◗ Ease of installation, requiring a minimum of training and equipment

◗◗Rapid installation, with firsthand observations revealing installation rates exceeding that of paving

[References]


1. “Moving Advancements into Practice" MAP Brief 7-1: Describing promising technologies that can be used now to enhance concrete paving practices, ROAD MAP TRACK 7 High-Speed Concrete Pavement Rehabilitation and Construction(2009).
2. Nonwoven Geotextile Interlayers for Separating Cementitious Pavement Layers:German Practice and U.S. Field Trials Prepared by the International Scanning Study Team: Robert Otto Rasmussen and Sabrina I. Garberfor Federal Highway Administration U.S. Department of Transportation, May 2009.
3. Sabrina Garber and Robert Otto Rasmussen, "Nonwoven Geotextile Interlayers in Concrete Pavements", Transportation Research Record: Journal of the Transportation Research Board, No. 2152, Transportation Research Board of the National Academies, Washington,D.C., 2010, pp. 11–15.
4. Keivan Neshvadian Bakhsh, "Evaluation of Bond Strength between Overlay and Substrate in Concrete Repairs", Master degree thesis, Infrastructure Engineering
Division of Concrete Structures School of Architecture and the Built Environment Royal Institute of Technology (KTH).