Geosynthetic Reinforcement: A Sustainable and Economic Solution for Texas State Highway 21, Part 2

All photos courtesy of HUESKER Inc.

See Part 1 here.

SH21 Rehabilitation in Bastrop County, Texas (Summer 2022):

With such proven confidence in the geosynthetic-reinforced asphalt overlay design, TxDOT considered rehabilitation of another stretch of SH21 roadway in Bastrop County. Specifically, the rehabilitation of SH21 roadway in Bastrop County comprised of portions of the roadway to the east and the west of the intersection with U.S. Highway 290 (US290). The total length of SH21 roadway rehabilitation was approximately 16 km (10 mile) and the distresses in this roadway stretch comprised longitudinal, fatigue cracks and ruts along the traffic wheel path. Specifically, the distresses were caused due to significant swell-shrink behavior due to volumetric changes in the highly plastic and expansive subgrade soil and repeated loads from heavy truck traffic. The distresses and their causes in the SH21 roadway stretch in Bastrop County were similar to those previously witnessed in Lee County. Consequently, the stretch of SH21 roadway in Bastrop County was rehabilitated by adopting the same geosynthetic-reinforced asphalt overlay design as that adopted in Lee County. The design comprised adopting a polymeric geocomposite interlayer with a reduced asphalt overlay thickness of 75 mm (3-inch) instead of an asphalt overlay thickness of 125 mm (5-inch). The polymeric geocomposite interlayer product used in this project was HaTelit C40/17, manufactured in the United States by HUESKER Inc. HaTelit C40/17 is composed of a high tenacity polyester grid and a lightweight nonwoven fabric, impregnated with a bituminous coating of 65% residual asphalt. 

The rehabilitation program comprised applying a binder tack coat and installing a polymeric geocomposite interlayer as shown in Fig. 9. A performance grade (PG) 76-22 binder was applied at an application rate of 0.50 l/m² (0.11 gal/yd²) through multiple nozzles of a tack distributor truck, so as to obtain a full-width tack coverage without any streaks. Subsequently, the polymeric geocomposite interlayer was installed on the applied tack coat using the paving interlayer installation tractor without any folds or wrinkles. It can be observed from Fig. 9 that the tack coat application and polymeric geocomposite interlayer installation is proficient as well as consistent with the SH21 rehabilitation project in Lee County.

Subsequently, the asphalt trucks dumped the hot mix asphalt on top of the interlayer and the material transfer vehicle picked the dumped asphalt mix and transferred to the paver, as shown in Fig. 10. The material transfer vehicle in this project had to pick the dumped asphalt mix since the asphalt trucks did not feed the asphalt mix directly to material transfer vehicle as the SH21 rehabilitation in Lee County. While the remaining stages of overlay construction remained similar to that of the rehabilitation program in Lee County, comprising the installation of polymeric geocomposite interlayer and constructing an asphalt overlay with a compacted thickness of 75 mm (3-inch). Finally, the rehabilitation of SH21 roadway in Bastrop County was completed in Summer 2022.

Current Condition of SH21 Roadway in Bastrop County, Texas:

The rehabilitation of SH21 in Bastrop County was completed in Summer 2022. The ride quality and the roadway condition has been excellent without any form of distress or any annual maintenance requirement since completion of rehabilitation. This stretch of SH21 roadway in Bastrop County also adopted the asphalt overlay design comprising geosynthetic-reinforced asphalt overlay with reduced thickness similar to the stretch of SH21 roadway in Lee County. Additionally, the adopted asphalt overlay design has been efficiently capable of handling the increased truck traffic without any failures or concerns. Fig. 11 shows the condition of the SH21 roadway stretch in Bastrop County, which was captured in May 2025 (i.e., about 3 years since the completion of rehabilitation). As shown in the figure, the roadway condition is excellent without any distresses such as longitudinal cracks, fatigue cracks, and ruts that were previously witnessed along the roadway prior to the rehabilitation program in Summer 2022. Additionally, the geosynthetic-reinforced asphalt overlay design adopted by TxDOT has also improved the ride quality and road user serviceability by reducing the rut depth and improving the skid resistance. Also, Fig. 11 highlights that the rehabilitation program comprising geosynthetic-reinforced asphalt overlay with reduced thickness adopted by TxDOT has been successful in mitigating reflective cracks and other distress. Additionally, the adopted overlay design has improved the structural capacity of the SH21 roadway and also reduced the carbon footprint, construction and annual maintenance costs significantly. 

Sustainability Analysis:  

The global warming potential of any product can be assessed by performing a carbon audit at various stages of the product life cycle. A holistic Life Cycle Assessment (LCA) shall include the emissions associated with the product from producing the raw materials required to the end of its useful life when the product is recycled or discarded. Fig. 12 summarizes different stages of a pavement LCA, per conventional Environmental Product Declaration (EPD). As shown in the figure, the product stage comprises material extraction, transportation, and production in the manufacturing plant. Subsequently, the construction stage comprises of transportation of the produced material to the construction site and finally, construction activity. The emissions associated with the product and construction stages could be directly measured. While the use stage and the end-of-life stages comprise multiple sub-stages and the emissions from these stages cannot be directly measured. Additionally, in the case of roadways, it is often difficult to determine the outcome at the end of the project design life, hence, assessing the end-of-life emissions is challenging. For the construction material production, the environmental product declaration (EPD) values published by individual manufacturers of various construction materials provide the best estimate of their carbon emissions and global warming potential. While the emissions related to the transportation of construction materials from production plants to the project site have been estimated based on the unit emission values reported by the US Environmental Protection Agency (EPA). Furthermore, the emissions due to construction activities were estimated based on the unit emission factors reported by Chappat and Bilal (2003).

The sustainable benefits of adopting an asphalt overlay design involving polymer geocomposite interlayer and a reduced asphalt overlay thickness against that of a conventional overlay design involving a thicker asphalt overlay along the SH21 roadway could be determined by conducting carbon audits for both the overlay design methodologies. Specifically, emissions from the production, transportation, and construction of the materials required for the overlay construction were estimated for both overlay designs. After analyzing the emissions from various stages of production, transportation, and construction for both the design alternatives, it was determined that the material production stage contributes to the maximum emissions compared to those associated with transportation and construction stages. Specifically, material production resulted in emissions of about 60.74 tons of CO₂/lane-km (97.75 tons of CO₂/lane-mile) and 40.71 tons of CO₂/lane-km (65.51 tons of CO₂/lane-mile) respectively, for conventional and geosynthetic-reinforced asphalt overlay designs. While transportation and construction resulted in a combined 5.75 tons of CO₂/lane-km (9.25 tons of CO₂/lane-mile) for conventional and 4.21 tons of CO₂/lane-km (6.77 tons of CO₂/lane-mile) for geosynthetic-reinforced asphalt overlay designs. In summary, total emissions from conventional and geosynthetic-reinforced asphalt overlay designs were estimated to be about 66.49 tons of CO₂/lane-km (107 tons of CO₂/lane-mile) and 44.91 tons of CO₂/lane-km (72.27 tons of CO₂/lane-mile), respectively. Thus, resulting in emission reductions of about 32.4% for geosynthetic-reinforced asphalt overlay design in comparison with conventional design. With asphalt overlay constructions being the most commonly adopted method for state DOTs and other transportation agencies across the world to extend the pavement service life, the use of geosynthetic reinforcement not only mitigate reflective cracking but also increase the roadway structural capacity. Such increased roadway structural capacity would result in increased pavement service life and reduced asphalt thickness, leading to significant reductions (approximately 32.4% in this case) in carbon footprint of the roadway as well as the construction costs. Detailed analysis and carbon footprint quantification is presented in Zornberg et al. (2024).

Cost-Benefit Analysis:

The cost benefits of adopting an asphalt overlay design involving polymer geocomposite interlayer and a reduced asphalt overlay thickness against that of a conventional overlay design involving a thicker asphalt overlay along the SH21 roadway could be determined by conducting cost audits for both the overlay design methodologies. Specifically, cost of production, transportation, and construction of the materials required for the overlay construction were estimated for both overlay designs. The cost analysis revealed that the cost of construction for both the design alternatives was almost the same, however the major difference between them was in terms of the material production cost. Specifically, the cost of material production and transportation were approximately $145,000/lane-km ($233,354/lane-mile) and $98,000/lane-km ($157,715/lane-mile) of conventional and geosynthetic-reinforced asphalt overlay designs. Thus, resulting in approximately 33% reduction in the cost for the geosynthetic-reinforced asphalt overlay in comparison with the conventional asphalt overlay design. Overall, it can be inferred that the geosynthetic-reinforced asphalt overlay with reduced thickness has proven to be a sustainable and cost-effective solution to mitigate reflective cracks and other distress along with an increased roadway structural capacity.

References:

1. Kumar, V. V., Roodi, G. H., Subramanian, S., Zornberg, J. G. (2023). Installation of geosynthetic interlayers during overlay construction: Case study of Texas State Highway 21. Transportation Geotechnics, 43, 101127.
2. Zornberg, J. G. (2017). Functions and applications of geosynthetics in roadways. Procedia Engineering, 189, 298-306.
3. Correia, N. S., Zornberg, J. G. (2016). Mechanical response of flexible pavements enhanced with geogrid-reinforced asphalt overlays. Geosynthetics International, 23(3):183-93.
4. Correia, N. S., Zornberg, J. G. (2018). Strain distribution along geogrid-reinforced asphalt overlays under traffic loading. Geotextiles and Geomembranes, 46:111-20.
5. Kumar, V. V., Saride, S., Zornberg, J. G. (2021). Mechanical response of full-scale geosynthetic-reinforced asphalt overlays subjected to repeated loads. Transportation Geotechnics, 30:100617. https://doi.org/10.1016/j.trgeo.2021.100617.
6. Kumar, V. V., Roodi, G. H., Subramanian, S., Zornberg, J. G. (2022). Influence of asphalt thickness on performance of geosynthetic-reinforced asphalt: Full-scale field study. Geotextiles and Geomembranes, 50(5):1052-9.
7. Kumar, V. V., Roodi, G. H., Zornberg, J. G. (2025). Influence of paving interlayer material on performance of full-scale asphalt overlays. Proc. Geotechnical Frontiers 2025, GSP 364, 454-463.
8. Chappat, M., Bilal, J. (2003). The Environmental Road of the Future: Life Cycle Analysis, Energy Consumption and Greenhouse Gas Emissions. Colas Group.
9. Zornberg, J. G., Subramanian, S., Roodi, G. H., Yalcin, Y., Kumar, V. V. (2024). Sustainability benefits of adopting geosynthetics in roadway design. International Journal of Geosynthetics and Ground Engineering, 10:47. https://doi.org/10.1007/s40891-024-00551-5