PD&R

open gradation of aggregate

lacks the mid-sized aggregates

Dense graded. Gap graded

Open graded

• Open-graded and gap-graded aggregate

skeleton, nominal aggregate sizes of 12.5 mm or

less, and higher than normal asphalt binder

contents and are placed in thicknesses of less

than 1 in.

OGFC consists of an aggregate with relatively uniform grading

and little or no fine aggregate and mineral filler

OGFC is composed of open

porous gradation

an internal

structure of

interconnected

voids

Minimum 18% air voids

Where to use?

– High traffic to aid in cleaning mixture and justify

added cost.

– Areas with high frequency of wet weather

accidents.

– Balance against possible increase winter

accidents.

– Should not be used on short segments or bridge

decks.

To provide high skid resistance and superior

surface drainage OGFC is used. So the ride

quality and safety is the main concern to

use OGFC.

Their macro texture facilitates drainage of

water from the tire/pavement interface,

Reduce the potential for hydroplaning:

by providing drainage channels for water to

flow beneath the pavement surface

The sheet of surface water that causes

hydroplaning is drained through the mix to

the edge of the pavement.

Graded Aggregate Base

Subgrade

Dense Graded Asphalt

OGFC SurfaceWate

r

OGFC reduces the amount of splash and

spray.

SKID RESISTANCE - Which pavement

would you rather drive on in a storm?

Quiet, it's smooth, silent

it feels like you're driving on sponge rubber

• Experiencing glare while driving is irritating

and dangerous for all drivers.

• visual acuity and peripheral vision are

reduced as people get older.

• Rain and night-time driving are the biggest

contributors to accidents.

"Low textured" surfaces reflect more light

and act like mirrors.

The color of the road surface affects daytime

visibility. The lighter the surface color, the

greater the potential for glare.

•Mitigation of Flushing and Bleeding: Its open void

structure increases the pavement friction and allows

absorption of free surface asphalt to overcome

bleeding pavements.

Provide and maintain good high speed, frictional qualities

• durability and flexibility.

• increases resistance to moisture damage.

• increases resistance to bleeding.

• reduces aging of the mix.

• increased resistance to rutting.

• noise level decreases.

• the tolerance to higher stress and strains.

• maintain viscoelastic properties for a much

longer period

Asphalt rubber OGFC

Winter Maintenance

• Freeze early and last to thaw

• Difficult to remove snow and ice

• icy areas where tire chains, or snowplows

are commonly used, OGFC has exhibited

raveling distress.

• May need special deicing chemicals

• Require more treatments.

• Possible issue on bridge decks

• Problems with transitions to normal

surface

The fines from mud and sand can fill the

voids and reduce the drainage capacity of

the OGFC.

The OGFC must be kept clean to prevent

clogging.

Measurements to improve its properties:

• Production temperatures are increased

to dry aggregate components and thus

improve AC adhesion.

• Coarser gradations and thicker layers

are used to improve permeability.

• Setting minimum percentages for air

voids at 18%.

How to improve the performance

of OGFC mixes

• Polymer additives:

– reduces premature oxidation.

• Hydrated lime:

– stripping agent

• Rubberized asphalt:

– improving durability

• Mineral fibers:

– increase the ability of asphalt to coat

the aggregate

• Raveling due to softened binder from oil

and fuel drippings.

• Raveling due to oxidation and hardening

of the binder.

• Raveling due to lack of compaction or low

asphalt content.

• Delamination due to improper tack coat

application

OGFC overlays may exhibit the following

distress modes:

• Shear failures in high stress areas.

• Cracking due to fatigue.

• Cracking due to reflection from below