Glass Fibre Geogrid (GFG) - Fibreglass Asphalt Reinforcement Grid for Roads, Highways & Airfields

GFG installation is a pre-overlay operation. Four things determine whether it performs: surface preparation, tack coat rate, tension during placement, and keeping traffic off the grid before the overlay is laid. Both plain and self-adhesive grades require a hot bitumen tack coat. On self-adhesive grades the pressure-sensitive backing holds the grid in position while that bond develops, it does not replace it.

Store rolls between -30 and 80 degrees C at a maximum relative humidity of 85%, on a dry flat surface, preferably under cover. Self-adhesive rolls must be stored standing vertically upright, not laid flat. Rolls kept outdoors must be covered with proper waterproof covering.

Prepare the existing pavement surface. It must be clean, dry and free of dust, dirt, loose material, standing water and contamination. Do not place grid on a surface that is wet or contaminated with oil, soil or excessive dust.

Check surface temperature before starting. The road surface must be between 5 and 60 degrees C. On a paved surface less than 24 hours old, between 5 and 46 degrees C.

Seal all cracks wider than 6 mm with an approved sealant or the appropriate levelling course mix. Repair potholes, failed and cracked sections as instructed by the engineer. The surface must be level enough for the grid to make solid contact with the base course.

Apply a hot bitumen tack coat at a residual rate of 0.25 to 0.35 kg/m2 for plain grades, or 0.40 to 0.60 kg/m2 for self-adhesive grades. The rate varies with existing surface condition and ambient temperature. The tack coat must extend 75 mm beyond the grid on all sides. Tack coat and grid must be applied by trained personnel.

Confirm roll orientation against the design drawings before unrolling. Self-adhesive grades are laid adhesive face down. GFG 100/200 is asymmetric, with its higher strength in the cross direction, so its orientation must follow the design engineer's direction of principal stress.

Fasten the leading edge firmly to the road, then unroll in the direction of paving. Maintain tension from the end of the roll continuously until the remaining grid is fastened down. Placement may be mechanical, using a purpose-built laydown frame, hydraulically controlled device or modified tractor, or manual on smaller and awkward sections.

Brush the laid grid down vigorously with a stiff broom, or roll it with a rubber-coated drum roller or pneumatic tyre roller, to achieve full bond. Apply vegetable oil to pneumatic tyre roller tyres to stop the grid lifting during rolling.

Overlap transverse joints by 75 to 150 mm in the direction of the paver, and longitudinal joints by 25 to 50 mm. Tack thoroughly at all joints and overlaps. Use shortened lengths through curves. Where nails are specified, size them to the sub-surface thickness and use washers larger than the grid aperture.

Stop the grid 100 to 150 mm short of the pavement edge to prevent capillary water ingress.

Remove all wrinkles and wrap-ins before paving. Sufficient tension during placement is how they are avoided. To remove one, cut through the middle of the wrinkle and fasten the repair area down firmly to eliminate lifting or movement.

On self-adhesive grades, verify the bond before paving. Insert the hook of a calibrated spring balance into the centre of a representative installed section and pull vertically upward until four to five apertures lift on all sides, recording the force. A reading of 9 kg or more means it is safe to pave. Below 9 kg, stop and establish the cause, usually water or debris contamination, before continuing.

Keep traffic off the exposed grid. Where unavoidable, keep it below 10 km/h with no sudden stopping or starting, and keep static front-wheel turning to an absolute minimum. Any section damaged by construction traffic must be removed and patched before paving. To protect the grid from displacement by loaded asphalt trucks, apply a light cover of 8 to 12 mm stone chips or a thin asphalt mix layer.

Pave only once the tack coat is fully cured and the grid is firmly and uniformly bonded. Place hot mix asphalt directly over the grid, feeding mix under the paver with a shovel to prevent displacement. The polymer-modified coating, stable to at least 232 degrees C, remains intact through standard paving temperatures. Do not use plant with damaged, worn or broken tyres. Compact the overlay to the contract specification. Personnel handling glass fibre grid must wear protective clothing, gloves and safety glasses.