Pavements

Concrete

• Concrete– Rigid pavement

• Used where strength is an issue• Runways, interstates and major roads

– Continuous reinforcing• Must have a good base and joints and cracks must

be sealed• Long life – 50 years• Major rehab is a major problem

Concrete

• Forming and pouring– Old way – set forms and have equipment ride

the forms • Paving train – mix, place, finish, cure all in one

train of equip• Standard forms 10 ft long 8 – 12 inches deep

– New Way• Slip form, Use 0 slump concrete • Machine pulls form with it slab comes out finished• F 8-1, 8-2

Concrete

• Roller Compacted Concrete– Dam construction, landfills– 0 slump concrete is placed on a site and

compacted w/vibratory roller– Higher strength, low air entrainment

Asphalt

• Bituminous– Bituminous distributor

• F8-4• Used on all types of bituminous construction• Application rate depends on spray bar length,

travel speed, pump output• Control by bitumeter• S = (9xP)/(WxR)• S= road speed, P = pump output, W= spraybar

width, R= application rate

Asphalt

• Surface treatments– Prime coat – goes on unpaved surface

• Provides waterproofing and wear surface• 0.25 – 0.5 gal/sq. yd.- cures in 24 – 48 hours

– Tack coat – goes on a paved surface to act as bonding agent

• 0.1 gal/sy – quick cure

– Dust pallitive – keeps dust down for 30 days– Fog seal – slow setting, 1-3 parts water– Emulsion slurry sealer – driveway sealer– Sand seal – fine aggregates and asphalt

Asphalt

• Single pass treatments– Spray bitumin– Cover with aggregate 1 stone deep

• 25 – 30 # of aggregrate/sy• 0.25- 0.3 gal/sy binder• Sweep surface• Apply prime coat, cure• Apply binder• Apply aggregate• Roll surface• Sweep to remove loose stone

Asphalt

• Multi pass treatments– Spray bitumin– Multiple single pass treatments

• 25 – 30 # of aggregrate/sy• 0.25- 0.3 gal/sy binder• Each layer’s aggregate is ½ size of previous layer

Asphalt

• Asphalt Paving– Hot mix – high type pavements– Cold mix – patching– Penetration macadam – old way of paving

• Place and compact 4” of coarse aggregate• Cover with asphalt binder and a smaller aggregate

(key aggregate) and rolled• Cover with asphalt binder and a smaller aggregate

(key aggregate) and rolled

Asphalt

• Road Mix– Mixed on roadway– Grader, rotary mixer, travel plants– Hard to get a consistent result

Asphalt

• Hot Mix (HMA) –highest form of asphalt pavement– Can be used as soon as compacted and cooled to

ambient temp– Flexible, frost resistant

• Cold mix – like hot mix – Advantages – can haul long distances, stockpile,– Disadvantages – slow curing, low initial stability,

difficult to compact in cold weather

Asphalt

• Hot mix paving operations– Delivery of asphalt mix,spreading and compaction– Spreader couples with the delivery truck and pushes it

along as asphalt is unloaded– Spreader spreads and compacts– Spreader consists of pusher unit and screed unit– Spreaders control depth and width of pavement using

laser, stringline, shoe to control screed elevation

Asphalt

• Towed pavers – smaller jobs – usually driveways– Max width 10 ft– Large paver

• To lay a 3” deep, 12 ft wide, strip at 50 ft/min need 600 tons/hr of asphalt

Asphalt

• Compacting immediately after spreading– Breakdown rolling – provides initial

compaction - static steel rollers with drive wheel forward

– Intermediate rolling – pneumatic rollers – better surface sealing

– Finish rolling – tandem steel rollers – final compaction

Asphalt

• Superpave– Developed due to asphalt concrete failures

• Uses lower asphalt content ,crushed stone and optimizes for local conditions- NYS thruway uses 7 different mixes

Repair and Rehab

• Highways – Resurface, restoration, rehabilitation and

reconstruction – 4Rs– Resurfacing surface treatments, overlays,– Restoration and Rehab – return highway to

acceptable condition• Planning or milling top layer , fixing lower level,

repave

– Reconstruction – complete redo of roadway

Repair and Rehab

• Recycling pavement– Concrete is broken up and sent to a recycling

plant which removes steel and crushes concrete into aggregate

– Asphalt is milled and recycled in an asphalt plant F- 8-10&8-11

– HMWK Ch 7 # 2,3,9 Ch 8 # 5,7,9