Asphalt

Question 1

what were the first asphalts?

Answer 1

Macadam and later tarmac using tar to bind aggregates
later bitumen replaced tar.
This was proceded by bitumen and has later been coined asphalt

Question 2

where does bitumen come from?

Answer 2

Crude oil

Question 3

Why is crude oil appropirate for roads?

Answer 3

Because its viscoelastic

Question 4

what is viscoelastic? Why is it appropriate?

Answer 4

it is a material that becomes less viscous as it is heated up. makes it perfect for reuse, repair and quick application

Question 5

problems with asplat being viscoelastic?

Answer 5

creep over time
deforms with cyclical loaing (fatigue)

Question 6

What are plolymer modified bitumens?

Answer 6

bitumens with enhanced mechanical properties.

Question 7

whats another type of road?

Answer 7

rigid pavements, concrete slabs

Question 8

how do we test bitumen?

Answer 8

with a penetration test
measures the penetration of a needle at 1n for 5 seconds into bitumen at 25C (container 55mm dia and 53mm deep)

Question 9

what pen values are preffered for different climates?

Answer 9

warm climates require a lower pen value
cold climates require a higher pen value

Question 10

what is the softening point test?

Answer 10

the softening point test is creating small discs of bitumen
with a steel ball placed on them
they are lowered into water wich raises in temperature by 5c per minute.
they are timed to se how long it takes for the ball to reach the bottom

Question 11

what three tests are appropriate for aggregate used in roads?

Answer 11

Polished stone value - skid resistance
Los Angeles Coefficient - resistance to wear
Flakiness index - inherently weak and susceptible to breaking down

Question 12

what is hot rolled asphalt?

Answer 12

its gap graded/ gaps
not alot of smaller content
40-50% aggregate
lots of bitumen
expensive

Question 13

types of asphalt?

Answer 13

Hot rolled asphalt
asphalt concrete
stone mastic asphalt
pourous asphalt

Question 14

how many kn does a standard axle give?

Answer 14

80Kn
7.5kn for a car

Question 15

what is the makeup of a road?

Answer 15

subgrade - formation
capping layer - formation
sub-base
base course
binder course - surfacing
surface - surfacing

Question 16

character of base binder and surface course?

Answer 16

surface course, 25 - 50 thick, waterproof, agg size 14mm max, HRA
Binder course - 50mm, waterproof, evens the base course, agg 20mm max, HRA
basecourse- 100-200mm, main structural layer, agg 32mm max, typically AC

Question 17

what is geogrid?

Answer 17

layer to assist load spread and prevent cracking

Question 18

characteristics of the unbound layers?

Answer 18

sub-base - 200mm thick, forms structural layer, unbound agg
capping layer - required if subgrade (ground) is unsuitable, can invole a geogrid
subgrade - will be checked for its load bearing ability with the califonia bearing ration test

Question 19

what are the factors for failure of asphalt?

Answer 19

Magnitude of cyclical loading
Water (ability of the upper layers to shed)
integrity of subgrade (ground)

Question 20

examples of failure?

Answer 20

potholes caused by water, freeze and thaw cycles
slippage of layers
excess bitumen bleeding
cracking from weak subgrade and errosion

Question 21

what is surface dressing?

Answer 21

cheap and easy routien surface maintenence
spray with bitumen
scatter with single sized small aggregate
let road users work it in

Question 22

reuse of asphalt materials?

Answer 22

remixing trains can
heat the pavement
scratch it up
re mix it with more virgin mix
relay the pavement