Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85919
Powerful blenders create asphalt or polymer modified asphalt emulsions. Hot liquid asphalt, water and an emulsifying agent are brought together in a colloid mill, where spinning blades break or shear the liquid asphalt into suspended microdroplets, making emulsions as fast as 28,000 gallons per hour for asphalt emulsions, or 15,000 gallons per hour for polymer modified asphalt emulsions Image credit: Dalworth Machine Products, Inc. The emulsifier – commonly a surfactant or surface-active agent – maintains the microscopic asphalt droplets in a stable suspension within the water, keeping them from recombining. Emulsifiers also control "break" time following placement on a road, in which the water evaporates, leaving the asphalt behind Image credit: Akzo Nobel storage-stable asphalt emulsion product Image credit: MeadWestvaco droplets from recombining, thus providing a Emulsifiers will have an oil-soluble and a water-soluble part, and can have a cationic (positive) or anionic (negative) electrical charge that keeps the asphalt An asphalt emulsion is a homogeneous mixture of two insoluble substances, oil and water. In it particles of liquid asphalt (in the dispersed phase) are surrounded by molecules of water (the continuous phase). Asphalt emulsions have greatly reduced viscosity, are safe to use at lower temperatures, and allow expensive liquid asphalt to be spread more thinly, saving money Rejuvenators are engineered cationic emulsions containing liquid asphalt components of maltenes and saturates (light fractions). They soften aged, stiff, oxidized asphalt pavements, fluxing or fusing with the existing asphalt binder, changing the properties of the asphaltic concrete, quelling aggregate loss and extending surface life Image credit: Tricor Refining, LLC granite, trap rock or basalt generally are negatively charged and react best with a cationic (positive) emulsion (see image); positively charged sedimentary rocks of carbonate mineralogy like limestone or dolomite react best with an anionic (negative) emulsion To ensure adhesion to rock chips, match emulsifier type to the right aggregate. Igneous chips of silicate mineralogy like Image credit: MeadWestvaco Polymer modified emulsions provide enhanced performance at a higher price. They will provide low temperature flexibility in pavement, stiffness at high temperatures, and extend surface treatment life. Like asphalt modifiers they include SBS (styrene butadiene styrene), SB (styrene butadiene), EVA (ethylene vinyl acetate), and many others, in which the polymer penetrates the oil droplet, see image; and SBR (styrene butadiene rubber) and ground tire rubber (rubberized asphalt), in which the polymer exists outside the droplet Image credit: BASF Corp. Better Roads June 2012 19