1

Tech Tips

United States Department of Agriculture

Forest Service

National Technology & 

Development Program

For additional information, contact: Transportation Management Program Leader, San Dimas Technology & Development Center, 

444 East Bonita Avenue, San Dimas, CA 91773-3198; Phone 909-599-1267; TDD; 909-599-2357; FAX: 909-592-2309

Lotus Notes: Mailroom WO SDTDC@FSNOTES • Intranet (Web site): http://fsweb.sdtdc.wo.fs.fed.us • Internet e-mail: mailroom_wo_sdtdc@fs.fed.us

Reflective cracking in pavements occurs where 

cracks in older, underlying asphalt or concrete 

layers propagate up through newer overlays. 

Reflective cracking in asphalt-pavement overlays 

is typically caused by traffic loading, age 

hardening, or temperature cycling. When such 

cracking is present, the traditional remedy has 

been to apply thicker asphalt-concrete overlays to 

delay the reappearance of the cracks. In general, 

for each inch of overlay, existing reflective cracks 

are deterred from reaching the surface for 1 to 2 

years.

In the summer of 2001, two segments of the paved 

loop road around the Diamond Lake Recreation 

complex on the Umpqua National Forest were 

treated using a hot-mix asphalt overlay. The first 

road segment accesses a winter-sports area with a 

sledding hill and snowmobile rental shop near the 

lake. The pavement in this road segment suffered 

from severe regularly spaced thermal cracks, 

many that were 1/2- to 1-inch wide (figure 1).

The second segment was a portion of the old 

State highway (figure 2) that originally served 

the area and was over 40 years old. The surface 

was severely cracked due to heat, age, and load 

distress (exhibiting block, longitudinal, thermal, 

and alligator-type cracking).

GlasGrid Fights Pavement Reflective Cracking at Diamond Lake

Gordon L. Hanek, Geotechnical Engineer, Umpqua National Forest

Figure 1—Test section 1, exhibiting large, regularly spaced 

thermal cracks.

Figure 2—Test section 2, exhibiting a variety of pavementcracking distress types.

7700 0877 1306—SDTDC

March 2009

Transportation

Management Coordinated Federal Lands Highway 

Implementation Program 
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Public complaints on the roughness of the surface were common since this segment is one of the main 

access routes into the large resort and boat-launch complex at the lake. The resort and lake are at an 

elevation of about 5,000 feet, and both road segments are plowed throughout the winter. 

As an interim measure—until adequate funding could be obtained for a more comprehensive treatment—a 

2-inch, hot-mix overlay was applied to these two road segments in the summer of 2001. As a study, two 

test sections, one on each overlay segment, were installed using the GlasGrid pavement-reinforcement 

mesh. This product consists of a series of fiberglass strands knitted together into a mesh and coated with a 

black-elastomeric polymer. The fiberglass has a high tensile strength and high modulus of elasticity at low 

elongation (table 1), similar to asphalt-concrete pavement.

Table 1—GlasGrid properties

Property Test Method GlasGrid GlasGrid

8501 8502

Tensile Strength ASTM D 6637

Across width 560 lbs/in. 1,120 lbs/in.

Across length 560 lbs/in. 560 lbs/in.

Elongation at Break ASTM D 6637 < 3% < 3%

When sandwiched between the existing and 

overlay asphalt courses, GlasGrid is designed 

to redistribute crack stresses horizontally and 

dissipate them into the surrounding asphalt mat. 

The high tensile strength and modulus of elasticity 

are relatively unique among geosynthetic fabrics 

used as interlayers in pavements. With these 

characteristics, it was hoped that the GlasGridtreated sections would demonstrate an improved 

resistance to reflective cracking with the relatively 

thin overlay used for this project.

Each of the two test sections totaled 300 feet in 

length and was divided into three 100-foot-long 

subsections (cells). Within each group of three 

cells, cell A was pretreated with a crack sealer, 

cell B was pretreated with a crack sealer and 

GlasGrid, and cell C was a control and not treated. 

All existing cracks within the cells were mapped 

and measured prior to treatment. Permanent 

survey-reference points were established 

so that the reflected cracks could be related 

back to preoverlay conditions. Periodic crack 

surveys were conducted for more than 6 years 

to measure the reflected cracks. The total length 

and pattern of reflected cracking through the new 

overlay were measured and compared with the 

original pavement condition. The percentage of 

reflected cracks was calculated, and plots were 

developed for a comparison between the three cell 

treatments.
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PAVING

The GlasGrid arrived in 5-foot-wide rolls that were 

spooled off a trailer-hitch device as needed to 

cover the test-cell cracks (figure 3).

Figure 3—Placing GlasGrid from the spool, which is attached 

to a trailer hitch.

The 8502 product is twice as strong in one direction 

as the other and is intended for use over individual 

cracks. It was used in test section 1 where the 

individual-crack treatment was applied (figure 4).

Figure 4—GlasGrid Type 8502 was used to treat the individual 

thermal cracks in test section 1. The darker areas are those 

covered by the GlasGrid.

The 8501 product is intended for use where 

cracking is widespread. It was used to cover 100 

percent of the cell in test section 2 (figure 5). 

Figure 5—GlasGrid Type 8501 was applied with 100-percent 

coverage in test section 2. A 2-inch overlap was used at all 

seams.

GlasGrid comes with a pressure-sensitive 

adhesive backing that, according to the 

manufacturer, is sufficient to hold the product in 

place on fresh asphalt surfaces, such as a leveling 

course or between overlay lifts. However, since 

this project was a single 2-inch asphalt lift on older 

asphalt surfaces without any preleveling, a special 

quick-set tack was applied prior to placement of 

the GlasGrid (figure 6).

Figure 6—A quick-set tack was applied to GlasGrid test cells 

to ensure good bondage.
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Following placement, a light-duty vehicle was used 

to roll the GlasGrid and seat it securely to the 

asphalt surface (figure 7).

Figure 7—Seating the GlasGrid by rolling with a light-duty 

vehicle.

Paving occurred the same day as the GlasGrid 

placement, and no problems with grid movement 

under the paver machine or asphalt-concrete 

delivery trucks were observed (figure 8).

Figure 8—GlasGrid remained bonded to the underlying 

surface during paving operations.

RESULTS

Periodic inspections of all test cells were made 

over a 6-year period. Average daily traffic counts 

during this time varied from about 150 to 900, 

depending on the time of year, and consisted 

primarily of recreational and administrative 

vehicles. The site inspections were generally held 

once in the spring and once in the fall of each 

year. During each inspection the locations, lengths, 

orientations, and type of cracks were noted. 

Photos were taken of any developing reflective 

cracks as well as the overall site conditions. Table 

2 is a summary of the reflective cracking observed 

in the two test sections. Initial pretreatment-crack 

types (linear versus area) and lengths are shown 

for comparison. Linear cracks consisted principally 

of thermal and longitudinal cracks or other singlecrack features. Area cracking consisted of block 

and alligator cracking along with areas covered 

by older geosynthetic patching (see figure 2). 

A composite-crack length was calculated that 

sums the linear-crack length and the linear length 

associated with area cracking to provide a more 

representative picture of the extent of reflective 

cracking. This was done since none of the 

reflective cracking progressed to the point of being 

“area” cracks during the 6-year observation period 

(although some linear-reflective cracks did appear 

over locations with underlying “area” cracking). 

Table 2 results are shown in figures 9 to 12.
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Table 2—Reflected Cracking (footage and percentage) 

Test Section No. 1

Initial

 Crack Condition 

Cell Type 6/12/01 4/9/02 7/10/02 10/24/02 4/4/03 6/19/03 9/30/03 3/16/04 4/8/04 11/19/04 6/28/05 9/26/05 5/25/07 11/13/07

A Linear (ft) 162.7 0.0 0.0 0.0 9.9 10.7 11.4 16.0 15.8 16.4 21.1 21.3 34.3 37.2

Area (ft2) 99.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 243.7 0.0% 0.0% 0.0% 4.1% 4.4% 4.7% 6.6% 6.5% 6.7% 8.7% 8.7% 14.1% 15.3%

B Linear (ft) 209.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.9 4.1 3.2 3.9 3.2

Area (ft2) 78.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 287.9 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.3% 1.4% 1.1% 1.4% 1.1%

C Linear (ft) 139.3 0.0 0.0 0.0 13.9 13.9 14.2 21.3 19.3 23.3 37.0 37.5 88.0 88.2

Area (ft2) 94.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 202.3 0.0% 0.0% 0.0% 6.9% 6.9% 7.0% 10.5% 9.5% 11.5% 18.3% 18.5% 43.5% 43.6%

Test Section No. 2

Initial

Crack Condition 

Cell Type 6/12/01 4/9/02 7/10/02 10/24/02 4/4/03 6/19/03 9/30/03 3/16/04 4/8/04 11/19/04 6/28/05 9/26/05 5/25/07 11/13/07

A Linear (ft) 215.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.5 2.7 2.6 2.8

Area (ft2) 1029.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 622.6 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.4% 0.4% 0.4% 0.5%

B Linear (ft) 110.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.9 4.1 1.3 34.0 46.2

Area (ft2) 1111.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 600.2 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.3% 0.7% 0.2% 5.7% 7.7%

C Linear (ft) 101.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.7 25.2 26.5 75.0 87.9

Area (ft2) 1425.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Composite (ft) 644.0 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.4% 3.9% 4.1% 11.7% 13.7%
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Figure 9—Test section no.1.

Figure 10: Test Section No. 2

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

16.0%

4/9/02 7/10/02 10/24/024/4/03 6/19/03 9/30/03 3/16/04 4/8/04

11/19/04 6/28/05 9/26/05 5/25/07 11/13/07

% Reflected Cracking

Cell A - Crack Sealed

Cell B - Glasgrid & Crack Sealed

Cell C - Control (no pretreatment)

Figure 10—Test section no.2.

Figure 9: Test Section No. 1

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%

4/9/02 7/10/02 10/24/024/4/03 6/19/03 9/30/03 3/16/04 4/8/04

11/19/04 6/28/05 9/26/05 5/25/07 11/13/07

% Reflected Cracking

Cell A - Crack Sealed

Cell B - Glasgrid & Crack Sealed

Cell C - Control (no pretreatment)

4/9/02 10/24/02 8/19/03 3/16/04 11/19/04 9/28/05 11/13/07

7/10/02 4/4/03 9/30/03 4/8/04 8/28/05 5/25/07

4/9/02 10/24/02 8/19/03 3/16/04 11/19/04 9/28/05 11/13/07

7/10/02 4/4/03 9/30/03 4/8/04 8/28/05 5/25/07

Reflective Cracking (%) Reflective Cracking (%)
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Figure 11—Test section no.1.

Figure 12—Test section no.2.

Figure 11: Test Section No. 1

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%

12/1/01 12/1/02 12/1/03 11/30/04 11/30/05 11/30/06 11/30/07 11/29/08

% Reflected Cracking

Cell A - Crack Sealed

Cell B - Glasgrid & Crack Sealed

Cell C - Control (no pretreatment)

Figure 12: Test Section No. 2

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

16.0%

12/1/01 12/1/02 12/1/03 11/30/04 11/30/05 11/30/06 11/30/07 11/29/08

% Reflected Cracking

Cell A - Crack Sealed

Cell B - Glasgrid & Crack Sealed

Cell C - Control (no pretreatment)

Reflective Cracking (%) Reflective Cracking (%)
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The GlasGrid-treated cell in test section 1 (where large, regularly spaced, thermal cracks were the primary 

distress) has performed significantly better than either the control cell or the cell with only a crack-sealing 

pretreatment (figures 13 and 14). After 6 years, less than 2 percent of the crack length has reflected 

through in the GlasGrid section versus almost 45 percent in the control section. Originally, crack severity 

in test section 1 was generally medium (mean-crack width greater than 1/4 inch) to high (mean-crack 

width greater than 3/4 inch), whereas all cells after 6 years still have generally low-severity (mean-crack 

width less than 1/4 inch) cracks though a few medium-severity cracks have developed in the cells without 

GlasGrid. Reflective cracks are occurring over original cracks that were of medium and high severity. 

Figure 13—Comparison of reflected crack in GlasGrid-treated cell of test section 1 after 6 years.

Figure 14—Comparison of reflected crack in control cell of test section 1 after 6 years.
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In test section 2, where a variety of crack-distress types including block, alligator, longitudinal, and thermal 

occurred, the GlasGrid-treated cell experienced less reflective cracking than the control cell but more 

than the cell with only crack sealing as a treatment. It appears that the GlasGrid was not as successful 

in retarding the more generally distributed and greater variety of cracking-distress types present in this 

test section. However, given the relatively small amount of overall reflective cracking that has occurred in 

test section 2, it may be premature to draw conclusions until additional future observations can be made. 

As was the case with test section 1, the pretreatment defect-severity in test section 2 was also generally 

medium. After 6 years, the defect severity in all cells of test section 2 is low (figure 15).

Figure 15—Comparison of test-section 2 surface after 6 years.
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COSTS

Current material costs (2008) for the GlasGrid 8501 and 8502 are $0.50 per square foot and $0.64 per 

square foot, respectively. Installation costs are about $0.08 to $0.11 per square foot. Figure 16 shows 

the thickness of asphalt that would be a comparable cost to that of GlasGrid, per square foot, where 

100-percent coverage is assumed for GlasGrid 8501, and 33-percent coverage (i.e., thermal cracks at 15-

foot spacing) for GlasGrid 8502. So, the cost of 100 square feet of GlasGrid 8501 would be similar to 100 

square feet of asphalt 1.7-inch thick, at $60 per ton. 

Given the success of GlasGrid 8502 (in this project) at suppressing the reflective cracking of medium-tohigh severity thermal and longitudinal cracks, the selective treatment of individual cracks appears to offer 

the greatest potential for life-cycle cost savings when using relatively thin overlays. 

Figure 16—The thickness of asphalt that would be comparable to the square-foot cost of GlasGrid, where 100-percent coverage is 

assumed for GlasGrid 8501, and 33-percent coverage for GlasGrid 8502. 

Cost Cmparison of GlasGrid and Asphalt Thickness

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70 80 90 100

Cost of Asphalt ($/ton)

Comparable asphalt thickness

8501

8502
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CONCLUSIONS

Based on monitoring two test sections for 6 years:

• GlasGrid 8502 appears to significantly 

extend the time and reduce the severity of 

reflected cracks through a 2-inch asphaltconcrete overlay placed over medium-to-high 

severity thermal and longitudinal cracking 

when compared to areas without grid 

reinforcement. 

• The conclusion is less clear for GlasGrid 

8501 placed in a test section where other 

types of pavement distress predominate. 

• Selective treatment of individual large 

thermal and longitudinal cracks with GlasGrid 

8502 can be a cost-effective technique 

for minimizing the severity and extending 

the period of time before reflective cracks 

reappear through a 2-inch overlay. 

ACKNOWLEDGMENTS

The author wishes to acknowledge technical 

reviewers, including Peter Bolander, Forest 

Service, Region 6; William Vischer, Forest Service, 

Region 1; and Rene Renteria, Oregon Department 

of Transportation; as well as San Dimas 

Technology and Development Center (SDTDC) 

report editors, and publishers. 

SDTDC’s national publications are available on the 

Internet at: http://www.fs.fed.us/eng/pubs/

Forest Service and U.S. Department of the Interior, 

Bureau of Land Management employees also can 

view videos, CDs, and SDTDC’s individual project 

pages on their internal computer network at: http://

fsweb.sdtdc.wo.fs.fed.us/

For additional information on the GlasGrid project, 

contact Maureen Kestler, project leader, by e-mail: 

mkestler@fs.fed.us.
The information contained in this publication has been developed for the guidance of employees of the Forest Service, U.S. Department of Agriculture, its contractors, and cooperating 

Federal and State agencies. The Forest Service assumes no responsibility for the interpretation or use of this information by other than its own employees. The use of trade, firm, or 

corporation names is for the information and convenience of the reader. Such use does not 

constitute an official evaluation, conclusion, recommendation, endorsement, or approval of any 

product or service to the exclusion of others that may be suitable.

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