THIN HOTMIX ASPHALT OVERLAY Thin HotMix Asphalt Overlay

THIN HOTMIX ASPHALT OVERLAY

Thin Hot-Mix Asphalt Overlay ØDense-graded ØOpen-graded friction course ØGap-graded

DENSE-GRADED

OPEN-GRADED

GAP-GRADED

Binder Selection ØDense: § Conventional ØGap- and open-graded: § Modify binders to increase viscosity § Drain down test

Asphalt Concrete (Hot-Mix Asphalt) Ø Asphalt binder + aggregates (dense gradation) Ø Asphalt binder is about 4 - 6% by weight of mix, but it needs to be carefully designed Ø AC is produced in batch or drum plants 8

THIN HOTMIX ASPHALT OVERLAY

Thin Hot-Mix Asphalt Overlay ØDense-graded ØOpen-graded friction course ØGap-graded

DENSE-GRADED

OPEN-GRADED

GAP-GRADED

Binder Selection ØDense: § Conventional ØGap- and open-graded: § Modify binders to increase viscosity § Drain down test

Aggregate Selection ØConventional quality requirements ØGood surface texture required for stability

Asphalt Concrete (Hot-Mix Asphalt) Ø Asphalt binder + aggregates (dense gradation) Ø Asphalt binder is about 4 - 6% by weight of mix, but it needs to be carefully designed Ø AC is produced in batch or drum plants 17

Mix Design ØDense & Gap-graded § Superpave or Marshall ØOpen-graded § Based on surface capacity of aggregate

Batch Plant Secondary Collector Batch Tower Primary Collector Storage Silos Asphalt Storage Tanks rye r D RAP Bin Cold Feed Bins 19

Drum-Mix Plant Secondary Collectors Slat Conveyor Storage Silos Asphalt Storage Tanks r/M e ry r e x i D RAP Bin Cold Feed Bins 20

Thin Overlay Uses ØExtends pavement life ØImproves ride quality ØCorrects surface defects ØRestores skid resistance

Conditions for Success ØNew or old pavement surface ØStructurally sound ØMill or leveling course if rough ØRepair cracks and distresses

Open-Graded Advantages ØImproves skid resistance ØReduces/eliminates spray ØReduces noise ØImproves visibility

Gap-Graded Advantages ØResists rutting ØGood low-temperature performance ØSlow aging ØResistant to abrasion from studded tires

Construction ØConventional HMA process ØCools quickly ØGap-graded mixes are “harsh” § Higher temperature § Compaction

Weather Conditions Since the mixture cools fast, better compaction can be achieved in warm weather ( 50 o. F)

Cooling Time

Fast Compaction

Construction Precautions ØWarm weather ØMill or repair if needed ØApply tack coat ØAppropriate top aggregate size (12 – 19 mm) ØGood quality control

Tack Coat

Loading in the Paver

Placement & Compaction

Traffic Control Open road to traffic when mix is cool

Variations on Gap-Graded Thin HMA Overlay ØStone matrix asphalt (SMA) ØHot rolled mix (sand asphalt) ØUltrathin bonded wearing course (NOVACHIP) ØAsphalt rubber

Definition of SMA ØRelatively thin (10 – 40 mm) gapgraded hot mixture ØHigh proportions of coarse aggregate, binder, and mineral filler ØLow amount of middle-size aggregates ØStabilizing additives

SMA Materials ØCoarse aggregate ØCrushed / natural sand ØAsphalt cement ØAdditives

Introducing Fibers

SMA Construction

Ultrathin Bonded Wearing Course (NOVACHIP) Ø 3/8 – 3/4 in. thick Ø Gap-graded mix Ø 5. 1 -5. 5% conventional AC Ø Polymer modified tack coat

Spraying Tack Coat

Ultrathin Bonded Wearing Course Texture

Asphalt Rubber ØAbout 1” overly on existing pavement is common in Arizona (AR-ACFC) ØBinder Ø 80 % Asphalt Ø 20 % Ground tire rubber ØGap or open graded aggregate, although dense graded has also been used ØReacted and Activated Rubber (RAR)

Asphalt Rubber

Improve Highway Safety • Increase driver visibility, reduce standing water, and improve skid resistance

Reduce Highway Noise