Grading

Question 1

Is Hot Mix Asphalt (HMA) is what grade?

Answer 1

Dense- graded mix

Question 2

What are the features of a dense-grade? And what can it be classified as?

Answer 2

Impermeable to water- suitable for all pavement layers and traffic conditions

Dense grades are well graded asphalt materials-
Can be classified as fine graded or course graded.

Question 3

SMA is what grade?
Features?

Answer 3

Gap graded

1)Maximises rutting resistance and durability.
2)Lower tire noise!- due to coarser surface texture
3)Less severe reflective cracking

It is able to reduce rutting as gap graded materials have stone on stone contact. so as stone/ aggregate does not deform as much as asphalt binder under load then it reduces rutting.

Question 4

is SMA or HMA more expensive?

Answer 4

SMA is generally more expensive than a typical dense-graded HMA because it requires more durable aggregates, higher asphalt content, modified asphalt binder and fibers. In the right situations it is cost-effective because of its increased rut resistance and improved durability.

Question 5

Features of open- graded mix? And what is it made of?

And when is it used?

Answer 5

1) Water permeable
- made of crushed stone (gravel) only and small amount of sand.

2) Used for surface course only- to reduce tire splash/ spray in wet weather so for smoother surfaces than dense graded HMA.
Has higher aid voids which reduces tire-road noise.