Asphalt CONCRETE

Question 1

What is asphalt concrete?

Answer 1

Asphalt cement + mineral agg (+ possible admx)

Question 2

Why is the agg. heated when mixing with asphalt cement?

Answer 2

for good bond between asphalt cement agg. if water in agg., bubbles will be created in asphalt cement?

Question 3

What classifies the asphalt concrete?

Answer 3

type of binder
Agg. classification
Production materials

Question 4

Type of binder for asphalt concrete?

Answer 4

Asphalt cement

Question 5

Type of agg. gradation for asphalt concrete?

Answer 5

Dense graded (well compacted): combination of small particles agg. with large and medium agg.
Open graded: large and medium agg. only (still voids)

Question 6

Type of production materials for asphalt concrete?

Answer 6

Hot-mixed hot laid mixtures: elevated T
Cold-mixed , cold-laid mixtures: above ambient T (usually for maintenance)

Question 7

Stiffness of asphalt concrete (Scon) depends on___?

Answer 7

Scon=f(Sac,Cv)
Sac= stiffness of asphalt cement
Cv= volume of compacted agg.

Question 8

what is Stability for asphalt concrete ?

Answer 8

indicates the resistance of asphalt concrete to permanent deformation under trafic loading.

Question 9

What is flexibility for asphalt concrete?

Answer 9

allow asphalt concrete to adjust, without fracturing, to minor long-term settlements of the base/sub-grade layers under pavement.
Enhanced by:
- open grade agg. mix
- high asphalt content

Question 10

What is the compromisse for more flexibility for asphalt concrete?

Answer 10

it lower stability

Question 11

What does tensile strength depend on for asphalt concrete?

Answer 11

-It depend on the tensile strength of the binder and agg. (tensile strength of binder decreases as the T increases and loading rate decreases(i.e. viscous material))
-amt of binder in mix
- voids content of the mix
Under rapid loading and/or low T, max tensile strength of asphalt concrete is 4 MPa to 10 MPa

Question 12

When does permanent def. for asphalt concrete occur?

Answer 12

Occurs under high shear or normal load and could be in diff form, such as rutting (when high load induce permanent deformation — big lines on roads)

Question 13

What is rutting and what causes it?

Answer 13

channelized depressions in the wheel-path of heavy trucks resulting from densifications and lateral mvt.
Causes:
- high asphalt cement content (flexible)
- high filler content
- rounded agg. (no friction between agg.)
- high temp
-high loads

Question 14

what result in a permeable asphalt concrete?

Answer 14

high asphalt cement, dense agg., and good compaction

Question 15

how do you improve durability of asphalt concrete?

Answer 15

agg are fullly covered with asphalt cement with little air voids as possible
(no entry water–>no stripping (breaking adehsive bond between agg. and ac)& no freezing)
(no entry air and light–> no age hardening)

Question 16

How to reduce stripping of agg. for the asphalt conctrete?

Answer 16

less void content
no hydrophilic agg
washing dust on agg.
Pre-coating with bitumen
Use higher T in mixing phase

Question 17

How can asphalt concrete react to temperature?

Answer 17

thermal expansion and contraction of asphalt concrete is largely affected by the asphalt cement.
Mixtures that have high stiffness at low temperature are most prone to thermal cracking

Question 18

what are the chemical response of asphalt concrete?

Answer 18

petroleum solvents dissolve asphalt cement (grosse tache sur le asphalt concrete)
Asphalt cement are resistant to most acids, alkalis and salts

Question 19

What are the additives and fillers for asphalt concrete?

Answer 19

Anti-stripping agent (enhance agg.-asphalt interface bonding)
Anti-oxidants(added to asphalt cement to retard the age hardening processs)
Fillers(added to the agg. to achieve a max. density and min. void content)