How to Lay Geosynthetic Fabric in Highway Construction? [PDF]

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Geosynthetics are extensively used in highway construction as they play the role of a separator, filter, reinforcement, stiffener, drainer, barrier, and the protector of pavements. Geosynthetic materials are planar, polymeric (synthetic or natural) materials used in contact with soil/rock and/or any other geotechnical material.

Geosynthetics are used for the improvement of subgrade and as a reinforcement of pavement base and thus help in increasing the life of the pavement.

In this article, we discuss the material requirement, construction, and installation procedure of geosynthetics in the highway construction.

Material Requirement of Geosynthetics

1. Paving Fabric

1. The paving fabric will be of a nonwoven heat-set material consisting of at least 85 percent by weight polyolefins, polyesters, or polyamides.
2. The paving fabric shall be resistant to chemical attack, rot, and mildew and shall have no tears or defects which will adversely alter its physical properties.
3. The fabric shall be designed explicitly for pavement applications and be heat bonded only on one side to reduce bleed-through of tack coat during installation.
4. The fabric shall meet the physical requirements, as given in Table 1.
5. Heavy-duty paving fabrics should be used in areas experiencing unusually high impact forces or heavy loads such as airport runways and taxiways.

Table 1: Physical Requirements of Paving Fabrics.

Property	Units	Standard Requirements	Test method
Tensile strength	Kg	36.3	ASTM D 4632
Elongation	%	50	ASTM D 4632
Asphalt retention	Kg/10 sq. m.	10	Texas DOT 3099
Melting point	Degree C.	150	ASTM D 276
Surface texture	---	Heat bonded on one side only	Visual inspection

2. Tack Coat

1. The tack coat used to impregnate the fabric and bond the fabric to the pavement shall be a paving grade Bitumen of 80-100 penetration. 
2. A cationic or anionic emulsion may be used, and the use of cutbacks or emulsions which contain solvents shall not be allowed.

Construction and Installation of Geosynthetics

1. Shipment and Storage of Geosynthetics

1. The paving fabric shall be wrapped and kept dry so that it is protected during storage and shipping. 
2. The paving fabric shall not be exposed anytime to ultraviolet light for a time exceeding fourteen days.
3. The paving fabric rolls shall be stored in a manner that protects them from the elements.
4. If stored outdoors, they shall be elevated and protected with a waterproof cover. 
5. The paving fabric shall be labeled as per ASTM D-4873, "Guide for identification, storage, and handling of geotextiles."

2. Weather Limitations

1. The minimum air and pavement temperature shall not be less than 10 degrees Celcius when checked before laying of paving fabric.
2. The temperature of the pavement shall not be less than 15 degrees Celcius for placement bitumen emulsion. 
3. Neither bitumen tack coat nor paving fabric shall be placed when weather conditions, in the opinion of the engineer, are not suitable.

3. Surface Preparation for Laying Geosynthetics

1. The pavement surface shall be cleaned of all dirt, water, and oil to the satisfaction of the engineer. 
2. The cracks of width 3 mm or greater shall be cleaned and filled with suitable bituminous material.
3. The crack filling material shall be cured prior to laying of paving fabric.
4. The potholes and other pavement distress shall be repaired before placing the paving fabric.

4. Application of Tack Coat

1. The tack coat shall be sprayed by means of a calibrated distributor spray bar. 
2. Brush application and hand spraying may be used in locations of fabric overlap. 
3. The tack coat shall be sprayed uniformly to the prepared dry pavement surface at the rate of 1 kg/sq. m.
4. In places such as street intersections, steep grades, or in other zones where vehicle speed changes are common, the normal application rate shall be reduced by about 20 percent.
5. The application rate of the tack coat must be sufficient enough to saturate the paving fabric and to bond with the existing pavement surface.
6. For bitumen, the minimum temperature of the tack coat shall be 140 degrees Celcius. 
7. The width of the tack coat application shall be equal to the paving fabric width plus 150 mm.

5. Placement of Paving Fabric

1. The paving fabric shall be placed on the tack coat using manual or mechanical laydown equipment with a minimum amount of folding or wrinkling.
2. The paving fabric shall be laid before the tack coat cools off and loses its tackiness.
3. The paving fabric shall not be installed in areas where the overlay asphalt tapers to a thickness of less than 40 mm.
4. Excess paving fabric that extends beyond the edge of existing pavement or areas of tack coat application shall be trimmed and removed. 
5. The wrinkles or folds in excess of 25 mm shall be slit and laid flat. 
6. All transverse joints and silt wrinkles or folds shall be shingle-lapped in the direction of the pavement laying.
7. Brooming and pneumatic rolling will be required to increase paving fabric contact with the pavement surface.
8. All areas with paving fabrics placed will be paved the same day. 
9. The damaged fabric shall be removed and replaced with the same type of fabric. 
10. An additional tack coat shall be placed between the overlap to satisfy the saturation requirements of the fabric.
11. Overlaps shall be sufficient to ensure full closure of the joint but not exceed 150 mm.

6. Placement of Overlay

1. The bituminous overlay construction shall be soon followed with fabric placement
2. The paving of overlay shall be carried out on the same day of laying paving fabric.
3. All the excess tack coat which bleeds through the paving fabric shall be removed by broadcasting hot mix or sand on the paving fabric.

FAQs on Geosynthetic in Highway

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1. Geosynthetics in Civil Engineering and Construction Works
2. Geogrids- Types, Functions, Applications and Advantages in Construction