Fiberglass Mesh Reduces Reflective Cracking on California Highway

Dec. 28, 2000
State Highway 89 originated as an old logging road and consisted of approximately 0.57 ft of asphaltic concrete (AC) over a granular base of volcanic origin. It receives a high volume of logging trucks due to the timber harvesting in the area. The sections of the highway in northern California--through the Sierra Nevada Mountains--are located in an area of high tensile stress where the primary thermal fatigue factor is cold temperatures.

Don Wion, maintenance superintendent in Alturas, Calif., recommended a section on Highway 89 to be scheduled for a maintenance overlay.

State Highway 89 originated as an old logging road and consisted of approximately 0.57 ft of asphaltic concrete (AC) over a granular base of volcanic origin. It receives a high volume of logging trucks due to the timber harvesting in the area. The sections of the highway in northern California--through the Sierra Nevada Mountains--are located in an area of high tensile stress where the primary thermal fatigue factor is cold temperatures.

Don Wion, maintenance superintendent in Alturas, Calif., recommended a section on Highway 89 to be scheduled for a maintenance overlay. Thermal expansion and contraction has caused high tensile stress and distress consisting of pavement bleeding, rutting and alligator and transverse cracks. Previous maintenance treatments consisted of digouts and grader blankets to repair broken pavement base failures.

From Caltrans' past experience, pavement reinforcing fabrics (PRF) have been minimally effective in areas of high tensile stress caused by thermal- and moisture-related expansion and contraction. It was decided to evaluate Glasgrid to determine its effectiveness in retarding reflective cracking.

Glasgrid is a high-strength, high-modulus fiberglass mesh capable of turning crack stresses horizontally and dissipating these stresses within the new overlay, its maker says.

The site's average annual daily traffic for 1992 was 1,600 with 32% trucks and an equivalent single axle load count of 107,000. The proposed maintenance strategy for this area consisted of a 1 1/2-in. AC overlay.

Paving begins

On the day of construction the road was swept clean with a leaf blower to ensure that the surface was not contaminated. Cracks wider than 1/4-in. were filled with an asphalt mix prior to the placement of the fiberglass mesh. The mesh was installed from the back of a 1-ton dual tired Caltrans maintenance truck and then rolled by the same truck. The mesh was unrolled without any problems and adhered well to the pavement without wrinkles. It was placed in the northbound lane full width for a 330-ft long section.

The asphalt was delivered to the site in belly-dump trailer trucks and dumped directly onto the Glasgrid in a windrow at a temperature of approximately 190 deg. The tires of the asphalt trucks did not stick to the mesh or cause separation from the pavement or wrinkle. A Blaw-Knox PR200B pneumatic tired paver with a pick-up machine was used to pave over the grid. No sagging problems occurred between the paver and the grid. A control section was set up in the southbound lane opposite the mesh section. The control also was one lane wide and 330 ft long.

The test site was visited in 1994 and 1995. In 1994, one partial transverse crack was observed on the outer edge of the pavement over a culvert at the north end of the mesh section, but no other pavement distress was present. There were no changes in 1995 from the 1994 evaluation.

During the 1994 evaluation of the control section, three partial transverse cracks and approximately 15 ft of longitudinal cracks were observed. In 1995, alligator cracking with associated pumping appeared in the control section.

It appears that the mesh has reinforced the AC overlay and retarded reflective cracking in an area of high tensile stress. Due to the heavy traffic on this highway, consideration is being given to an extensive rehabilitation within the next three years. Glasgrid will be considered as an option in the overlay strategy.

More information on products and/or services mentioned is available by writing in the appropriate number on the reader service card found in this issue.

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