Asphalt mixes are designed to withstand everything from high traffic loads to extremes in temperature changes. This includes moisture resistance, which plays an important role in safeguarding roadway surfaces from wear. Liquids of any kind can directly impact an asphalt mix’s ability to resist raveling, rutting, or giving way to potholes. Rainwater, runoff, and even fuel oils can worsen surface durability as these fluids seep into paved asphalt roads.
Mix designers are tasked with addressing the demand for pavements that can manage stormwater and fuel oil exposure from regular use while also accounting for moisture introduced during mix production and capillary action from under the subgrade. Over time, exposure to liquids can cause stripping, or the separation of binder and aggregate in a mix, causing the foundational layers of the asphalt roadway to degrade. In addition, water trapped in the different layers of a roadway can cause pore pressure and lead to cracking. All of this can impact ride quality in addition to structural integrity, often necessitating frequent and costly repairs.
Anti-strip agents were developed to address this problem. Anti-strip agents are chemical additives that improve the bonds between aggregates and binder in a mix. Also known as adhesion promoters, they have traditionally been formulated with hydrated lime or amine liquids. Additives containing amines are also hazardous to handle. An amine-free anti-strip agent like SriCote® can provide the same benefits of improved aggregate and binder adhesion while remaining safe to handle.
Anti-strip agents for asphalt work by making it more difficult for moisture to come between aggregates and binder in a mix. This occurs through a chemical modification to the binder that helps the bitumen adhere to the aggregate particles in a mix. They are typically incorporated during the production process at a mix plant. Tests such as Wet Strength, Hamburg Wet Wheel Rutting, Aggregate Stripping, and Tensile Strength Retention (TSR) enable engineers to measure performance specifications for a mix dosed with an anti-stripping agent. Using an anti-strip agent for bitumen mixes should not impact the binder grade itself.
Improving this bond, or the adhesion, has a direct effect on the asphalt mix’s durability. Preventing stripping helps prevent costly and disruptive damage that can occur as the surface layer becomes distorted. This is especially important in environments where asphalt surfaces are exposed to consistent sources of water and fuels including airport runways and seaports.
Anti-strip additives remain an important component in developing long-term durable roadways. While moisture remains a key contributor to stripping in asphalt, the chemical composition of the mix and the aggregate quality also impact likelihood of stripping. When working with variable aggregate sources, anti-strip agents can create adhesion where the binder itself could fail to do so.
Since 2006, Sripath has supported the asphalt industry with innovative additives engineered to solve specific challenges. SriCote was designed to enhance the bond between aggregate and binders from around the world including polymer modified bitumen (PMB) mixes. Stable at processing and paving temperatures, smokeless and odorless, and liquid at ambient temperatures, SriCote is easy to use and safe to work with.
To learn more about SriCote for reduced moisture damage and improved fuel resistance, email info@sripath.com.
