Wrestling With Resilience
This content originally published in the Winter 2024 print edition of NAPA Quarterly. Subscribe here.
THE ROAD FORWARD SABBATICAL PROGRAM LOOKS AT AGILE ADAPTATION IN PAVEMENT CONSTRUCTION.
JO E. SIAS, Professor, University of New Hampshire
2024 The Road Forward Sabbatical Participant
NAPA’s The Road Forward Sabbatical Program for university faculty provides the opportunity for professors to actively participate in NAPA’s The Road Forward and engage with industry, joining an exclusive community of scholars that forge lasting relationships within our industry.
Applications for the 2027 sabbatical year will open later this year.
The concept of resilience has rapidly gained attention in the transportation infrastructure realm over the last few years.
The Infrastructure Investment & Jobs Act (IIJA) defines resilience as:
“the ability to anticipate, prepare for, and/or adapt to changing conditions and/or withstand, respond to, and/or recover rapidly from disruptions, including the ability: (A) to resist hazards or withstand impacts from weather events and natural disasters, or reduce the magnitude or duration of impacts of a disruptive weather event or natural disaster on a project; and (B) to have the absorptive capacity, adaptive capacity, and recoverability to decrease project vulnerability to weather events or other natural disasters.”
Resilience is not just about strengthening or hardening the transportation asset or system but also about the ability to recover quickly and adapt to changing conditions. While this definition within IIJA is primarily related to transportation assets and operations, the significance of resilience within the asphalt industry extends beyond the impacts of climate on pavement performance and roadway operations and includes considerations of plant operations, production, and construction.
Before we discuss resilience, we need to have a solid understanding of the potential impacts that weather conditions and events have on asphalt pavements and construction operations.
Resilient asphalt pavements can significantly contribute to the stability and safety of transportation systems during and after extreme events while ensuring economic and environmental sustainability.
Temperature: Asphalt is a temperature sensitive material and thus any changes to expected temperature conditions, both gradual changes and extremes, can have the potential to substantially change the performance of the material. This includes potential increases in rutting under high temperatures and cracking under low temperatures. Increased aging under high temperatures can also lead to earlier and more extensive cracking. Ambient temperatures also impact construction operations in terms of construction windows, energy required to heat materials at the plant, and conditions in the field during construction.
Precipitation/Flooding/Sea Level Rise (SLR): Precipitation in any form has a direct effect on plant and construction operations, slowing or stopping operations and increasing the energy and time required to dry aggregates. In terms of the pavement itself, increased exposure to moisture will exacerbate any stripping issues in the mix and will cause an increase in the moisture content of unbound pavement layers, decreasing the load-carrying capacity and making the pavement more prone to accelerated damage from traffic loading. Fast moving floodwaters can cause undermining and partial or complete washouts. In coastal areas, SLR induces groundwater table rise that increases subsurface moisture content in the subgrade and granular layers, decreasing the structural capacity. Coastal roadways can experience increased frequency and duration of surface flooding from higher tides that increase the moisture content of unbound layers and increased potential for erosion of embankments and the pavement itself from wave action and storm surge.
Drought: Less water is typically good for pavement, but there are soils that are susceptible to substantial volume changes when water content is decreased, and the resulting land subsidence can affect pavement performance and cause pavement cracking. There are also instances of substantial pavement subsidence in drought prone areas due to pumping of water combined with reduced recharge and areas of the world where water for compaction of unbound layers is scarce.
Cascading effects: Road closures during extreme events force traffic to travel on alternate routes, and in some cases, the pavements used for detour routes are not designed to handle the additional loading and will therefore degrade more quickly. This situation also occurs during post-event cleanup when substantial debris needs to be hauled by trucks to the disposal location and new materials must be brought into a community for rebuilding.
ROAD TO RECOVERY
Jas. W. Glover, Ltd., a Hawaii-based asphalt mix producer and laydown contractor started asphalt paving work in September 2019 to reopen Highway 132 after the 2018 Kilauea volcanic eruption. Read more about the “Road to Recovery” for Kopoho Road from Glover’s Jayanth Kumar Rayapeddi Kumar, who wrote about the project for Hawaii Asphalt Pavement Industry (HAPI) in 2023.
Once the vulnerability of a pavement or plant to any one or combination of these stressors is identified, there are many strategies that can be applied to increase resilience. These include: strategic selection of materials, pavement design, and rapid constructability for quick return to service after an event, or modifications to plant or construction operations.
This article delves into the various aspects of resilience in the asphalt industry with specific examples of resilience in action across the country.
Once the vulnerability of a pavement or plant is identified, there are many strategies that can be applied to increase resilience.
DESIGN
Let’s start with design – of both the asphalt mixture and the pavement.
Material selection is a critical component in the design of resilient asphalt mixtures and pavements. The right choice of materials can significantly enhance a pavement’s ability to withstand and adapt to changes in environmental and traffic loading over time and recover from disruptive events. We already do this in many cases but may not think about it from a resilience perspective.
Selecting an appropriate Performance Graded (PG) asphalt binder that can resist temperature extremes is crucial for resilience. PG binders are designed to perform in specific temperature ranges, ensuring that the pavement remains flexible enough in intermediate and cold temperatures to resist cracking and stiff enough in hot temperatures to resist rutting.
PG binders are also selected at a desired level of reliability to balance the risk of premature distress with the criticality of the pavement. In regions with high temperature fluctuations or extreme temperatures, additives or modifiers can be used to provide enhanced properties and therefore desired performance over a wider range of conditions.
Polymer-modified binders (PMBs) can offer improved resistance to both rutting and fatigue. PMBs maintain their stiffness at high temperatures and have a more elastic response which provides increased resistance to rutting. The improved flexibility of PMBs resists initiation of fatigue and low temperature cracking while increased toughness slows propagation of cracks. Rubber may be added to the binder to increase elasticity, flexibility, and stiffness to improve durability and longevity.
While the selection of aggregates is typically more limited to locally available materials, it still can have an impact on the resilience of the resulting mixture. Aggregate mineralogy is important with respect to moisture susceptibility and the addition of anti-stripping agents can be used to reduce the potential for moisture damage and increase resistance to stripping. The addition of rubber has also been shown to improve adhesion to aggregates and therefore reduce stripping potential in moisture susceptible materials. The shape and texture of aggregates are important for maintaining appropriate skid resistance over time and under wet weather conditions.
And finally, the aggregate gradation controls the structure and permeability of the mixture. Porous asphalt pavements and open graded friction courses facilitate rapid drainage of surface water, reducing standing water and the potential for hydroplaning in areas that are prone to flooding or heavy rainfall. SMA mixtures provide the capacity to handle heavy traffic volumes and loads, particularly under higher temperature conditions.
ENSURING RESILIENCE BEYOND INFRASTRUCTURE
Season 6, Episode 8 of NAPA’s official podcast, Pave It Black, explores resilience with AJAX Paving of Florida’s Andy Decraene.
When Hurricane Ian hit Florida in 2022, AJAX was called on to rebuild the Sanibel Causeway within weeks after the disaster. Richard and Brett explore what resilience is with Andy and learn that it goes far beyond just infrastructure and begins with building resilient companies who take care of their people.
Stream wherever you get your podcasts to learn the importance of having a disaster recovery plan in place and practicing it annually, filling silos with aggregate for weight as part of securing everything, and considering how energy and fuel options may change post-disaster.
MIX DESIGN
Resilience is inherently considered in the mix design process by optimizing the mix components to balance the resistance to rutting and cracking. Balanced mix design procedures and associated performance related tests can explicitly consider the mixture’s capacity to withstand temperature and traffic.
Warm-mix asphalt (WMA) technologies can be used to improve the workability of the asphalt mix, allowing for better compaction and, consequently, a more durable and resilient pavement structure. Some WMA technologies also provide anti-strip benefits.
Pavement design includes the determination of the number, type, and thickness of the various layers in the pavement structure. Rubber modified materials can also be used as stress absorbing layers to mitigate reflective cracking. Aggregate materials for base and sub-base layers can be selected to allow for rapid drainage and recovery of the load-carrying capacity of the pavement structure.
Aggregate materials with stiffness properties that are less susceptible to changes in saturation level and therefore do not lose as much structural capacity under higher moisture conditions can also be selected. This allows for the fast resumption of traffic on the roadway, particularly for recovery efforts following extreme events. In addition to the pavement itself, strategies that minimize the impact of extreme events on the pavement such as nature-based solutions can be considered in combination with pavement selection.
Flexible production processes that can be adjusted for material shortages or equipment failures are important for resilience in the production of asphalt mixtures.
Perpetual pavements are designed to last longer than 50 years without requiring major structural rehabilitation or reconstruction, while only needing periodic surface renewal. The bottom layer is designed to be fatigue resistant to prevent bottom-up cracking, the intermediate layer provides rut resistance and additional structural capacity, and the top layer resists abrasion and top-down cracking. This durable design provides perpetual pavements with the absorptive capacity to handle changing conditions with respect to traffic and environmental loads.
The design ensures that distresses such as cracking or rutting are confined to the top layer, which can be easily and cost-effectively milled and replaced with materials selected for changing or anticipated climate conditions. The underlying pavement layers remain intact and structurally strong, avoiding costly and time-consuming reconstruction and contributing to the overall resilience of the pavement.
The strong and relatively thick structure also means that the pavement’s load-carrying capacity is less susceptible to changes in the moisture content of the subgrade materials and therefore is more resilient to flooding events.
PRE-PRODUCTION / PRODUCTION
Now, what about resilience at the asphalt plant? This includes the production of the asphalt mix and the operation of the plant itself.
Flexible production processes that can be adjusted for material shortages or equipment failures are important for resilience in the production of asphalt mixtures. Appropriate inventory management and multiple sources for raw materials or advance stockpiling can be particularly important during and after extreme events when transportation and access to material sources may be limited. Robust QC systems that allow for quick adjustments to alternative sources can help with the ability to maintain or quickly return to production.
Resilience in plant operations is really about maintenance, training, and planning. First, it is critical to prioritize regular maintenance and plant component upgrades including process automation, remote monitoring, and predictive maintenance systems for reliable and consistent plant operations. If your company owns multiple plants, standardization of components and processes will help with resilience of overall operations during and after an event. Just having a complete and updated inventory of parts and personnel can be extremely helpful. Redundant systems for critical components are important as well as the potential for flexible fuel sources to allow for continued production.
Training and planning are needed for possible events – conducting risk assessments and training drills for each facility under different scenarios as well as developing appropriate action and disaster recovery plans. This includes coordinated communication protocols with backup methods (e.g., satellite phones) if normal lines are compromised. Updated training and cross-training of employees for multiple roles will increase resilience when individuals are unable to get to work during or after an event.
Adequate insurance and emergency cash funds available can be important as well as plans to help provide family support and recovery for employees so they can return to work as soon as possible. Cultivating cooperative relationships with competitors so the industry works as a team to respond also enhances overall resilience and can decrease the time to return to normal operations.
Finally, advance work to harden or adapt assets to minimize or prevent damage from occurring during events (e.g., flood protection measures) and pre-event mitigation measures such as securing components and filling silos with aggregate for weight will increase the resilience of the plant operations and allow for quicker return to production post-event.
CONSTRUCTION
The physical construction of the pavement comes next and has its own resilience attributes. Some things such as maintaining equipment in optimal condition and having backups available and providing ongoing training/cross-training of crews are similar to those discussed in the preceding Pre-Production/Production section. Flexible project scheduling to account for unforeseen events and strategies for paving in less-than-ideal conditions or adaptive construction techniques for changing conditions can help increase resilience.
Many technologies are available to leverage in this space and some of these are a normal part of construction operations now but may not be recognized for their contribution to resilience. Also, advanced planning prior to an event to strategically deploy equipment, allocate resources, and run through logistics will increase response time and overall resilience.
Post-event, asphalt concrete has a distinct advantage of rapid constructability to return damaged roadways to service. This can also include the recycling of debris into pavement layers which helps with overall sustainability as well as resilience. Finally, coordination and communication with agencies and other contractors as well as keeping the public aware is critical.
CONCLUSION
In summary, the resilience of asphalt pavements is a multifaceted concept that extends beyond durability to include adaptability and recovery from disruptions. With the looming challenges of climate change and the necessity for sustainable infrastructure, asphalt pavements provide opportunities to enhance the resilience of pavement networks.
Through strategic material selection, pavement design, strategic plant and construction operations, and rapid constructability, resilient asphalt pavements can significantly contribute to the stability and safety of transportation systems during and after extreme events while ensuring economic and environmental sustainability.
As we continue to innovate and adapt, resilient asphalt pavements will undoubtedly play a critical role in the infrastructure of tomorrow.
MEMBER-TO-MEMBER DISASTER ASSISTANCE PILOT PROJECT
The asphalt pavement industry deeply cares about the communities we serve – and each other. At all times, but especially during times of need, NAPA Members stand ready to lend a hand, equipment, or supplies to help one another.
To support NAPA Members in communities recovering from disasters, we launched a pilot project in the wake of Hurricanes Helene and Milton to help impacted members connect with members who wanted to help.
This program leveraged the NAPA website – specifically, AsphaltPavement.org/Help – as a central place for affected members to request aid (parts, equipment, diapers, water – whatever is needed), and for other members to view those requests and reach out directly to offer assistance if they can.
The program will be activated when appropriate (when disaster strikes) and is available to NAPA Members only.