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SAMI: The choice for resilient pavement

SAMI’s newest production and terminal facility in Kwinana, Western Australia.

SAMI Bitumen is cementing its place as an innovator in road resiliency and sustainability according to Dr. Hamidreza Sahebzamani – Technical Services Manager.

Infrastructure Australia’s defines resilience as communities that “have the ability to resist, absorb, accommodate, recover, transform and thrive in a timely, effective manner in response to the effects of shocks and stresses to enable positive economic, social, environmental and governance outcomes.”

There are two terms in this definition to understand: shocks and stresses. 

Shocks are sudden disasters like storms, floods, earthquakes, and fires that cause immediate damage. 

Stresses are long-term issues, like ageing infrastructure or rising sea levels, that gradually weaken systems over time. These shocks and stresses are happening more frequently and severely due to climate change. 

According to Advisory Paper One by Infrastructure Australia in June 2022, the cost of natural disasters in Australia is expected to more than double by 2050. It will increase from around $18 billion per year to over $39 billion annually. These numbers show how much money natural disasters could cost in the future and highlight the need for measures to increase resilience.

Laying high-performance asphalt mix produced with SAMIfalt I-Brid binder in Victoria.
Laying high-performance asphalt mix produced with SAMIfalt I-Brid binder in Victoria.

Resilient pavements

Roads and airports are some of the most important pieces of infrastructure, especially during times of disaster. They play a vital role in connecting people and places, enabling essential assistance and support.

Resilient roads include various features across different aspects, including geometric design, elevation, location, and subgrade properties. Another crucial aspect is the road pavement which carries the traffic load.

The concept of resilient pavement has gotten significant attention and discussion among industry professionals, owner agencies, and academics. 

The majority of Australia’s heavy-duty pavements are constructed using asphalt, known for its strength, flexibility, durability, and rapid repair capabilities to withstand varying conditions and recover swiftly from unexpected events. Although the resilient features of asphalt pavements are inherent, they are often not viewed through the lens of resilience by typical pavement engineers and designers. 

Examples of these resilient features include quick constructability for responding to disaster damage, component materials with climate adaptability, asset strengthening through stage construction, utilisation of sustainable technologies to increase haul distances and insitu recycling of reusable pavement materials, mixtures designed to store and infiltrate stormwater, mitigating flooding risks and the use of EME2 structural asphalt to future-proof pavements.

Traditional pavement design relies on historical climate data to anticipate local temperature ranges and precipitation patterns. However, shifting climate trends, evolving rain events and the escalation of extreme weather occurrences challenge the validity of this approach. 

It becomes evident that various pavement distresses are closely tied to climatic parameters when analysing the influence of temperature, precipitation, and sea-level rise on pavement performance and service life.

Beyond pavement potholes, varied environmental conditions lead to an array of distresses including cracking, rutting, shoving, and corrugation – each governed by temperature variations. Similarly, subsurface moisture variations affect rutting, cracking, and load-bearing capacity, while precipitation fluctuations impact the pumping of fine materials which weakens the base. 

Drought can also lead to shrinkage and significant deflections (ground subsidence) in certain types of soils. This phenomenon is currently quite prevalent in some countries, where the water table is receding, resulting in frequent reports of substantial sinkholes appearing. 

On the contrary, long periods of drought can lead to reduced pavement maintenance requirements due to less damage from moisture.

Significant future trends influencing pavement performance encompass temperature-related factors like elevated temperatures, increased extreme temperature events, heightened frequency and duration of extremes, and reduced freezing days. 

Additionally, precipitation-induced impacts entail shifts in average annual precipitation – resulting in wetter winters and drier summers in some regions and vice versa in others – alongside intensified precipitation intensity. 

Furthermore, rising sea levels and associated phenomena like flooding, groundwater elevation, and saltwater intrusion contribute to the complexity.

Elevated average temperatures yield consequences such as enhanced rutting and shoving potential, necessitating rut-resistant asphalt mixtures through adjustments in bitumen grade, polymerisation, and aggregate structure. Likewise, addressing bitumen aging requires the adoption of age-resistant binders and increase utilisation of surface preservation techniques. Concurrent drought situations amplify the risk of subgrade shrinkage and exacerbate asphalt rutting and shoving during heat waves, underlining the need to revise historical binder grade selection criteria.

The effects of precipitation on pavement components are multifaceted.

Enhanced surface friction necessitates attention to texture, skid resistance, cross slope, and porous surface mixtures to mitigate water spray. Whereas expanded surface drainage requirements warrant increased capacity for ditches, culverts, and elevated pavement sections.

Here optimal subdrainage design, installation, and maintenance are imperative. Elevated precipitation jeopardises embankment stability, structural capacity reduction of unbound bases and subgrades during inundation highlights the need for in-depth understanding and mitigation strategies.

Moisture susceptibility mitigation measures for unbound base and subgrade materials are necessary and enhanced pavement drainage at the surface and subsurface levels requires implementation of various strategies.

SAMI offers a variety of products and solutions that play a significant role in enhancing the resilience of road pavements.


 

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Thickness reduction using ETB and FTB instead of conventional granular base course.
Thickness reduction using ETB and FTB instead of conventional granular base course.

High quality hybridisation

Hybrid modification of bitumen is a concept that involves incorporating two or more additives and polymers with different properties into the bitumen. 

This is done to harness the beneficial properties of each component. SAMIfalt I-Brid is a high-performance hybrid-modified binder that exemplifies resilience in flexible pavement construction. It combines the advantages of both elastomeric and plastomeric modified binders.

The performance grading of this binder is PG88-28. This designation indicates its ability to withstand extreme temperatures, making it resilient to unexpected climatic shocks and stresses. SAMIfalt I-Brid can effectively endure thermal fluctuations that occur between day and night, as well as summer and winter conditions. 

In addition, it exhibits a higher modulus than normal elastomer-modified binders, particularly at elevated temperatures. This characteristic alleviates concerns about potential structural capacity issues in hot climatic conditions in the future.

The moisture sensitivity of this modified binder is lower compared to conventional elastomeric and plastomeric modified binders. This property renders it suitable for application in very wet conditions. SAMIfalt I-Brid also boasts superior rutting resistance and fatigue performance when compared to conventional plastomer and elastomer-modified binders. Furthermore, it exhibits fuel-resistant properties.

Emulsion-treated base courses

Stabilising granular base courses is one of the solutions to enhance the resiliency of pavements. This process reduces the susceptibility of pavements to the effects of fluctuations in the water table. Additionally, it improves the impermeability of the pavement structure. Special emulsions, formulated by SAMI, are utilised for treating the base courses. 

The stiffness modulus of this mixture is higher compared to other forms of treated bases, resulting in a reduced final pavement thickness. This reduction contributes to lowering greenhouse gas emissions, energy consumption, and the use of raw materials. 

A recent study, which was presented at the second AustStab conference in August 2023, highlights that the utilisation of Emulsion-treated base (ETB) and foam-treated base (FTB) can lead to a substantial reduction in pavement thickness. 

Specifically, in the case of very high-traffic roads, employing ETB has the potential to decrease pavement thickness by 43 per cent, while FTB can achieve a reduction of 36 per cent. 

Moreover, adopting these treatments has a positive environmental impact, as greenhouse gas (GHG) emissions are projected to decrease by 44.1 per cent for ETB and 31.0 per cent for FTB when compared to conventional designs that rely on granular base course. 

GHG emission reduction using ETB and FTB instead of conventional granular base course.
GHG emission reduction using ETB and FTB instead of conventional granular base course.

Multigrade binders

Enhancing temperature susceptibility is a critical attribute for resilient pavement, as roadways must now endure more pronounced climatic shocks and stresses than ever before.

SAMIfalt Multigrade Plus is an unmodified multigrade bitumen that boasts a significant advancement in temperature susceptibility when compared to standard bitumen. This solution is accurately engineered to improve crack and rut-resistance, ensuring enhanced durability over time. 

One of its standout advantages lies in its ability to exhibit heightened stiffness at operational temperatures and lower stiffness at low temperatures, coupled with remarkable resistance to stripping. These qualities have made SAMIfalt Multigrade Plus the preferred binder for the intricate project of Sydney Airport taxiway rehabilitation projects.

The improved cohesive properties inherent in SAMIfalt Multigrade Plus have also rendered it exceptionally effective for runway rehabilitation endeavours, exemplified by its successful deployment at the HMAS Albatross military base in Nowra, New South Wales. 

Moreover, SAMIfalt Multigrade Plus has earned a reputation as the binder of choice for Brisbane City Council, which prioritises its utilisation for maintaining its expansive road network due to its cost and versatility.

Spray sealing solutions

Ensuring a proper seal on the base courses is essential to render the granular layers impermeable from surface water. This aspect becomes particularly critical in situations where the risk of damage arises due to water penetration into the granular layers. 

SAMI offers a range of products to address this, such as the SAMIfloat, a polymer-modified cationic high-float emulsion with a substantial residual binder content.

This emulsion is applied to create various types of seals, such as primerseal, graded seal, Otta seal, and spray seals. The gel-like structured thick binder covers the entire aggregate surface, even in dusty conditions, eliminating the need for pre-coating the aggregates. The high residual content of the emulsion minimises the runoff while maintaining sufficient flexibility to prevent brittleness in cold conditions.

In addition to SAMIfloat, the SAMIflex E range offers polymer-modified bitumen emulsion. This emulsion contains SBS-modified binders as its base bitumen. Utilising these binders in spray sealing applications brings several advantages. 

This approach reduces the negative environmental impact, as there is no longer a need for kerosene. Furthermore, it eliminates risks and hazards for users.

Tack and bond coats

Making resilient pavement requires utilising the full capacity of the pavement layers, which rely on ensuring their unified integration. This integration is essential for treating the pavement layers as a unified, monolithic structure. 

To achieve this, it is vital to have a reliable high-performance tack or bond coat. This type of bond coat ensures the secure attachment of all pavement layers, even under prolonged stress conditions.

SAMIbond 007 is a high-performance polymer-modified, trackless tack coat specifically designed to serve as a binding layer, effectively uniting all pavement layers. Notably, the bonding shear strength offered surpasses that of conventional tack coats. 

Furthermore, its trackless properties play a pivotal role in maintaining the proper placement of bitumen particles throughout the construction stage, which means preventing the pickup of bitumen because of sticking to the truck and paver tyres.

With specialised products, SAMI offers solutions for making and preserving resilient pavements and plays a pivotal role in protecting the infrastructure against deterioration and enhancing sustainability. 

By offering versatile solutions that not only improve pavement performance but also contribute to reduced environmental dependency, SAMI helps shape the future of resilient transportation systems. 

References:

• A Pathway to Infrastructure Resilience – Advisory Paper 1, Infrastructure Australia, August 2021

• Resilience Principles, Infrastructure Australia, June 2022

• Resilient asphalt pavements, NAPA, October 2022

• Boosting pavement resilience, Public roads, FHWA-HRT-19-001, Autumn 2018

This article was originally published in the September edition of our magazine. To read the magazine, click here.

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