Bituminous materials

What is a bituminous material?

• hydrocarbon based substances used in construction

• used for road pavements - mixed with aggregates

• useful because they have strong adhesion to aggregates, waterproofing properties, flexible, high strength when solid

ideal for highways

• high viscosity at high pavement temperatures so it won’t permanently deform under traffic

• ductile enough at low pavement temperatures so it won’t crack

bitumen vs tar

bitumen

• soluble in petroleum

• made as a by product of petroleum distillation

• can be naturally occurring in lakes

• very sticky and viscous

tar

• resistant to petroleum

• made as a by product of coke from coal

What is an asphalt material?

a material that contains a lot of aggregates and a binder usually bitumen

What are the upper road layers made up of?

• surface - wearing course (less aggregates)

rut resistant (dent resistant), flat, good friction aggregate, crack resistant (water resistant), non structural

• binder - base course (more aggregates)

stiff, structural support, similar to base

• base - road base layers

dissipates high stresses, high stiffness, resistant to cracking, high fatigue life, deformation resistant

What are the two types of bituminous road surfacing materials?

Macadam - high stone content

Asphalt - high binder content

How do roads fail?

• surface deterioration

pot holes, loss of skid resistance, water damage, cracking

• structural failure

rutting, less flat (loss of ride quality), loss of support

fatigue crack will mostly happen in the bituminous layers due to horizontal tensile strain

What is rutting?

• the accumulation of small permanent strains under repeated loading

When does rutting happen?

• under high maintenance loads,

• slow rate of loading,

• raised temp,

• bad support,

• water softened materials,

• high air void contents

How do we maintain our roads?

• can overlay new surfaces

• can repair cracks

• oil is precious resource (won’t fully replace)

What is the function of a pavement?

to protect the subgrade (natural ground) from excessive deformation

• so that it can be used for vehicle loading

How do we assess pavement conditions?

• visual condition surveys - identify defects

• core surveys (samples)

• rut profile assessments

• lab testing

What are the different ways to overlay pavements?

• inlay thickness (where you fill in part of the lane to replace pavement) - will increase stiffness

• overlay thickness (where you add a new layer overall of the lanes - increases thickness