Warm mix asphalt (WMA) production remains an alterative to traditional hot mix asphalt (HMA) approaches as manufacturers explore options for reducing costs and emissions. For example, mixes developed using warm mix asphalt technologies represent 39.6% of all asphalt mix production in the United States. In the European Union, WMA market share has increased to an average of 18.3%, with some countries reporting closer to 30%. 

Despite rising interest and application of warm mix asphalt technologies, concerns regarding durability and long-term surface integrity may be holding some departments of transportation and producers back from using WMA more widely. However, the lower production and compaction temperatures associated with warm mix asphalt applications do not necessarily result in poor performance in comparison to HMAs when properly formulated.  

 

The Importance of Compaction in Asphalt Paving 

Central to the questions surrounding warm mix asphalt is compaction, which plays a critical role in material density and extended roadway lifespan projections. Asphalt compaction is the process of compressing an asphalt mix on a roadway surface until it achieves a targeted density. Properly compacted asphalt is more likely to resist deterioration due to use and exposure to weather conditions over time. In one study by the New Jersey Department of Transportation, adjusting in-place density and air voids by a 1 percent decrease with more accurate compaction can improve a roadway’s service life by 10%.  

Typically, HMA is compacted in line with a set of ideal conditions to minimize the need for future repair and maintenance. The asphalt mix is applied to the roadway and precise pressure is applied to avoid crushing or over-compacting the material. Moisture damage and increased oxidation are also exasperated due to high air voids or poor compaction. 

In the case of HMA, the material must also be compacted at high temperatures. As the asphalt mix cools in place, it becomes more susceptible to cracking, rutting, and other deformities, requiring hotter temperatures to ensure the mix remains workable throughout the application process.  

 

Challenges with Warm Mix Asphalt and Compaction 

The key differentiator for warm mix asphalt is that it can be produced and compacted at temperatures significantly lower, between 30-120 °F less, than its HMA counterpart. However, some concerns remain that lower temperatures could lead to issues with compaction with WMA. After all, HMA that cools too quickly can lead to prematurely failing roadway surfaces.  

While temperature should be monitored and maintained throughout any asphalt surface application, WMA offers a unique opportunity to meet density or void volume specifications without sacrificing long-term performance. In fact, warm mix asphalt has been shown to improve workability and enable enhanced compaction compared to HMA when formulated with a warm mix additive.  

 

The Role of Warm Mix Additives in Achieving Compaction Specifications 

Key to WMA performance is the incorporation of a warm mix additive. These materials are incorporated into an asphalt mix to allow for lower production and compaction temperatures. Engineers understand these additives to work by lowering binder viscosity, which allows for lower temperatures that can also reduce binder aging during the heating process.   

Warm mix additives also improve mix wettability by lubricating aggregates and making a mix more workable. A byproduct of this is a lower friction coefficient that can enable more effective packing at lower temperatures than HMA.  

 

Warm Mix Asphalt Compaction Research Findings 

Research has demonstrated that WMA additives can increase cracking resistance, resilient modulus, and moisture resistance. Additionally, studies have shown that WMA additives do not impact binder properties such as PG Grade or Pen. 

PHALANX®, a superior warm mix additive, has undergone a number of studies and field trials to determine its compaction efficacy. A trial conducted by the Royal Melbourne Institute of Technology (RMIT) in Melbourne, Australia, found that a PHALANX-dosed polymer modified bitumen (PMB) mix exhibited better compactability when compared to the same PMB dosed with other WMA additives. Just 0.25% of PHALANX was required to reduce the percent air voids at a compaction temperature of 115°C with an improvement of 33% compared to fatty amine derivative liquid and synthetic wax pellet WMA additives. 

 

About PHALANX Warm Mix Additive 

PHALANX is designed to improve compactability of hot asphalt mixes and polymer modified bitumen (PMB) mixes. It helps both production temperatures and compaction temperatures required when laying down a roadway. PHALANX may also help lower carbon emission, reduce energy consumption, and deliver overall cost savings.  

For more information about PHALANX and warm mix asphalt, contact info@sripath.com. 

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