Liquid Anti-Strip – A liquid additive (adhesion promoter) made with proprietary ingredients and mixed with the asphalt binder. The proportioning system for batch and continuous mix plants differs greatly. Continuous mixing facilities utilize a mass flow, Coriolis effect meter to introduce the liquid anti-strip into the asphalt binder. Batch plants use a weigh pot to measure the amount of liquid anti-strip needed for each batch of asphalt concrete. Pre-heating liquid anti-strip to near 150° F prior to its use, reduces the viscosity of the anti-strip and make it easier to move through a pump.
PBA Grade Asphalt - The term “PBA” signifies “Performance Based Asphalt”. There are at least seven different PBA grades of asphalt binder, ranging from PBA-1 to PBA-7. PBA binders were developed for specialized circumstances, such as extremely
cold and polymers currently
extremely hot environments.
Most often paving asphalt is modified with
to meet the minimum requirements for PBA binders. These asphalt types being used in the majority of asphalt pavements produced for Caltrans.
Modified Asphalt - AR grades of paving asphalt are heated to 400˚F ± then blended with extender oil, high natural rubber and finely graded crumb rubber, then the rubberized asphalt binder is allowed to react in a mixing tank for a minimum of 45 minutes before being mixed with crushed aggregates. Caltrans is currently looking at other types of modified asphalt for use in the future.
Terminal Blended Rubberized terminal and blends AR-Grade
Asphalt Binder – This process occurs at the refinery
ingredients are combined at high temperature near 400°F and
a high shear mixer blends
the rubber and asphalt together. The asphalt binder and the crumb rubber react then loaded into a tanker truck and shipped to the asphalt plant. blended rubberized asphalt binder is then stored in the contractor’s tanks at
are allowed to The terminal the AC plant.
Recommended Bitumen Ratio Range
This is applicable to asphalt concrete
laboratory recommends an optimum
made for bitumen
content or range, lets say inspector may order from
instance is from 5.8 to 6.1 percent. to 6.2 percent asphalt binder without
The Engineer/plant having to adjust the
asphalt binder bid price and/or requesting a new mix design. difference between the two ranges indicated by ± 0.1 percent.
Asphalt Concrete Types - Type “A” and Type “B’ asphalt concrete are differentiated by a couple of characteristics, such as, aggregate crush counts and stabilities. The maximum nominal aggregate size for asphalt concrete is designated by dimension, such as 19 mm, 12.5 mm or 9.5 mm. “Dense Graded” is referring to a well-graded aggregate and “Gap Graded” is referring to an aggregate that has openings in the grading to allow for additional asphalt binder. “Maximum Medium” AC is a well-graded aggregate throughout the range of sieves, whereas “Maximum Coarse” AC is just that, a coarser grading, meaning fewer percent passing all sieves. “Open Graded” asphalt concrete has very few, if any, fine aggregates passing the 2.36 mm sieve.