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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.

are

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

asphalt

binders

and

15

percent

crumb

rubber.

The

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

non-QC/QA

projects.

The

Materials

  • This is applicable to asphalt concrete

laboratory recommends an optimum

made for bitumen

content or range, lets say inspector may order from

for 5.7

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.

You

will

notice

there

is

a

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.

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