INNOVATION SPOTLIGHT: Wetfix G 400, innovation in asphalt antistrips

Contributed by: Christine Gorsuch, Senior Researcher, Nouryon

Asphalt pavements consist of two main components: asphalt binder and aggregate. The asphalt binder is the glue holding together the aggregate skeleton, forming the structure. A strong bond between the aggregate and asphalt binder is essential to durable asphalt pavement. This bonding, or adhesion, depends on the chemistry of the asphalt binder and the aggregate. Common asphalt pavement failures such as raveling, flushing, and potholes are the result of moisture damage due to poor adhesion, which results in stripping. The use of liquid antistripping chemicals, or antistrips, is one effective way of improving the bond between the asphalt binder and aggregate. When used properly in a well-designed and constructed road, antistrip in the binder can add years of service life by reducing early failures due to moisture damage and improving coating and compaction.

Antistrips based on amine chemistry have been used successfully for decades; they are especially good at improving the asphalt bond with acidic, siliceous aggregates, like quartzite, which are prone to stripping. With modified asphalt binders containing polyphosphoric acid (PPA), amine-based antistrip chemistry can be less effective; this limitation led to the development of Wetfix G 400.

Wetfix G 400 has a unique, non-amine chemistry that makes it a versatile antistripping additive and compaction aid. It improves the asphalt bond with both siliceous and calcareous (limestone) aggregates and in dry or damp conditions. A low odor liquid surfactant made from renewable resources, it is effective in PPA modified and standard binders without effecting the binder viscosity.

During development, Wetfix G 400 was validated using a combination of loose mix tests and compacted mix tests conducted in-house and by external labs. Here are examples of data that demonstrate some innovative features of Wetfix G 400.

Figure 1: Loose mix boiling stripping test results

Loose mix tests are used by many states to screen the ability of mixtures to withstand moisture damage. The pictures in Figure 1 show two mixes after boiling 10 minutes in water, with a PPA modified PG64-22 binder and siliceous aggregate. The sample with 0.5% Wetfix G 400 in the binder retained almost all its asphalt coating, while the control without antistrip retained less than half. This demonstrates improved adhesion between binder and aggregate with 0.5% Wetfix G 400 in the binder.

Figure 2: Improved compaction with Wetfix G 400

This figure shows Marshall compaction results for a 9.5 mm coarse-graded asphalt mixture with a PG 76-22 SBS polymer modified binder from the Rutgers Asphalt/Pavement Laboratory. The mix containing 0.5% Wetfix G 400 had lower air voids compared to the control mix without additive at each compaction temperature. This demonstrates that with Wetfix G 400 in the binder, the mixture was more workable and easier to compact than the control.

In February 2020, Wetfix G 400 was added to the Virginia DOT’s approved product list for Antistripping Additives, having passed the boil test requirements of Virginia Test Method—13. This method uses a moisture-sensitive quartzite aggregate, as well as demonstrating compatibility with binder rheology requirements (AASHTO M332).

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