Hot Mix Asphalt Production Chris Lange PMP, Pr.Tech.(Eng) Director (Technical) Much Asphalt (Pty) Ltd Road Pavement Forum: 10 th April 2006

Hot Mix Asphalt Production Plant types and basic components Plant calibration Dust extraction Filler handling and control Aggregate heating Procurement / handling of raw materials Finished product storage Delivery

Drum Mix Plant - Conventional HMA made continuously and sent to storage silos Drying and mixing drum Bitumen Tanks Scalping screen to remove oversize aggregate Cold Feed Bins Belt scale Primary dust collector Filter Baghouse Hot Storage Bins Exhaust Fan

TWIN DRUM PLANT : COUNTER-FLOW

Old Drum Mix Mix Plant:

Twin Drum Plant RAP Feed Aggregate feed Drying & heating Drum Coating & mixing drum Finished product storage Plant filler storage and feed Filter Baghouse

Parallel-Flow Drum- mixer Zones Combustion Heating Drying Air BIT. Hot Mix Asphalt Mixing

Counter-Flow Drum- mixer Zones Aggregate Air Bitumen Hot Mix Asphalt CombustionHeatingDryingMixing

Counter-Flow Batch Plant Dryer Zones Hot Aggregate CombustionHeatingDrying Aggregate Air

Batch Plant Elements Cold feed bins Dryer Drum Bitumen storage tanks Hot Storage silos Primary collector Filter Baghouse Batch/Mixing tower RAP Feed

Hot aggregate travels up bucket elevator Pugmill Aggregate weigh hopper Bitumen weigh pot Hot mix asphalt dispensed into truck / hot-bin Aggregate from dryer Aggregate to screens Screens size aggregate

Bitumen Weigh- hopper Aggregate and bitumen weigh hoppers

Aggregate Hot Bins

Warren Brothers Patent Application Drawing: Original Batch Plant

Belt Scale Calibration Cold feed system Belt scale Reference scale

Cold Feed Bins and RAP Bin

“Graphing the Feeders”

Tachometer Mounted on Tail Pulley of Cold Feed Bin Belt

“No Flow” Paddle at Feeder Discharge

Induced Air Burner

Fuel Reticulation and Heating System In-line heater HFO Sampling pt HFO Tank

Temperature Profile of Counter-Flow Dryer 150º C 100º C 20º C Gases Aggregates Combustion Heating Drying 150º C 300º F 760º C 120º C 400º C 800º C 0º C Aggregate

Drum Flights / Lifters

Primary and Secondary Emission Control Drying Drum Primary Dust Collector Secondary Dust Collector Exhaust Fan Filtered Air Fines collected and returned

Primary Collector: Cyclone

Multi-Tube Collector Outlet tube Spin vanes Inlet tube Valve Collector element Gas inlet

Discharge Housing Functions as a Knockout Box Gas flow Air Optional knock down plate Bitumen Fines mix with hot mix asphalt

Cutaway Section of a Typical Baghouse

Pulse Jet Baghouse Dust screw Exhaust fan Manifold

Automatic Damper Controls

Cyclone, Screw Collector, and Hot Elevator Batch tower Hot Elevator Cyclone feeding fines directly back

Filler Weigh-Pod After Surge Silo

Emission Control Summary Remove particulate matter –Primary –Secondary Return fines to the mix –Affects void content –Affects mix stiffness –Difficult to control

Batch plant filtration

Aggregate storage

Aggregate Storage

BITUMEN TANKS – ELECTRICALLY HEATED/ 24 HR TEMPERATURE MONITOR AND CONTROL Bitumen Storage

Old Style Operating Cabin

Plant automation: Modern control cabin:

Plant automation

Roodepoort Op Screen Plant Automation – Operating System Graphics

Batch Plant Schematic

Batch Plant Op Screen

Laboratory from the past

Modern Asphalt Laboratory

Quality Control Trends Monitored Binder Content Voids in Mix Filler Content

Slat Conveyor Feeding Storage Silos

Hot Storage – Skip and Winch System Plant Mixing Tower Skip Bucket Winch

Storage Silo: 165 t Capacity

Correct Loading Sequence

The good old days The End