Hot Mix Asphalt 101Zoeb Zavery, PE

NYSDOT Materials Bureau518 485 5277

zzavery@dot.state.ny.us

Objectives

Describe mix types

Define ingredients

Discuss mix design procedures

Discuss mix production

Discuss mix placement

Defining Mix Types

Dense gradedWell gradedMixes used in NY

Open gradedPorous mixesCoarse stones only

Gap gradedStone Mastic Asphalt (SMA) mixesMostly coarse stones, little fines, and high mineral fillerCellulose fiber may be added to reduce drain down

Primary Ingredients

PG Binder

Aggregates

Aggregate Quality

Particle shapeRoundedAngular

ToughnessResistance to abrasion and impact

PG Binder

Superpave grading systemStandard grades in NY are:

PG 64-22, 70-22Polymer modified grades are:

PG 58-34P, PG 64-28P, PG 64-22P, PG 76-22P 0° C

64° C

-22° C

What do these numbers mean?

Mix Design Procedures

Superpave DesignAll 402 items

DOT standard items

Marshall DesignAll 403 items

Used by municipalities

Job Mix Formula

In the laboratoryAggregate (coarse, fine, mineral filler) and PG binder is combined in proportionsExample: 57% 1A’s, 41% Sand, 2% Filler, and 6.0% AC

Must meet the design volumetricsAir voids, VMA, VFA

Batch or Drum Plant?

Both make quality mix

Choice based on business decision

Batch Plant

Batch Tower

StorageSilos

Cold Feed Bins

Dryer

AsphaltStorageTanks

SecondaryCollector

PrimaryCollector

Drum Mix Plant

Storage Silos

RAP Bin

Slat Conveyor

Dryer/Mixer

Cold Feed Bins

AsphaltStorageTanks

SecondaryCollectors

Job Mix Formula

At the plantJMF aggregate proportions and PG binder are usedQC tests performed for complianceAdjustments are made to meet the volumetric targets

Transporting HMA

3 or 5 drops at plantReduce segregation

Trucks must be covered with tarp

Reduce heat lossMust use release soap-based release agents

Not fuel oil

This could happen…

Placing HMAGeneral good paving practice must be followed

Paver must travel at constant speedTrucks should not bump the paver

Will affect smoothness

Avoid this mess

Placing HMA

Check mix tempsHelps in achieving the required density

Compaction

It very critical that HMA layer is properly compactedOtherwise,

RuttingMoistureRavelingOxidize

Density Measurements

CoresDensity gauges

NuclearNon-nuclear

If all Goes Well…

You will have a long lasting HMA pavementLess maintenanceLess disruption to traveling publicNow that’s a winning combination for the tax payers

If not….

Job Mix Formula

Questions?????