The 7 frequently asked questions when it comes SMA asphalt mixtures

1 What does the designation S.M.A. ..?

The SMA designation corresponds to the initials of the words in English: Stone Matrix Asphalt, which means that it is an asphalt mixture consisting of particles of stone arranged in a matrix asphalt.

2 What are the mixtures called: Open-Graded and Gap-Graded?

There are two variants of a mixture S.M.A. type. In the first case, the mention of a mixture Open-Graded means that it is an SMA, an open texture. When you mention a Gap-Graded mixture, it is also an SMA mixture., But with a semi-open texture.

3 When an asphalt mix type S.M.A. is used as a binder in a pavement that have structural difference when compared with a traditional type of asphalt?

(The so-called traditional asphalt, correspond to the type Denso)

The structure of an SMA type asphalt form a "skeleton stone", in which the forces generated by traffic are transmitted from stone to stone, allowing a thinner folder, you have a greater capacity to withstand stresses without deformation, and this in turn allows each particle of stone have an increased thickness of the overlying asphalt. It results in longer service life for asphalt comparative cases subject to the same efforts.

4 What cellulosic fiber is used in a SMA type asphalt?

Hot asphalt tends to slip. To avoid this and keep it in the right place for the work that has to develop within an SMA type asphalt is used cellulose fiber. Even if it requires a very small amount of fiber to achieve its function (of the order of 0.45%) is an important aspect for the proper use of the mixture.

5 What cellulosic fiber is normally required, per cubic meter of mix?

Example:

If a mixture S.M.A. Loose Unit had a weight of 1680 kg/m3, and the design requires indicate that 0.45% of cellulose fibers:

1.680 x 0.0045 = 7.56 kg. of fiber per m3 of mixture produced

The amount of fiber used is based on the weight of the SMA mixture

6 Is it expensive to use SMA asphalt mixture as a folder on a pavement?

The initial cost of a mixed type S.M.A. is larger than a conventional asphalt mix per cubic meter. However, from the structural point of view, a SMA requires only 55% of the material would be required with the conventional mixture to form a square meter of the folder. This means that an SMA, for each inch of thickness supports the same effort for which a conventional asphalt needs 1.82 cm. in thickness.

Example:

Structurally S.M.A. folder of 3.5 cm. thick, equivalent to a conventional asphalt folder of 6.4 cm. in thickness. This means that with 3.5 cm. SMA thickness has the same ability to withstand the stresses of traffic, that conventional mixing a folder of 6.4 cm. thick compact.

Conclusion:

Comparing the costs between the two types of folders (mixed conventional and SMA), we have:

If you compared the two mixtures are of good quality in design, development and hard and stony and asphalt materials used appropriate and proven quality, initial cost per square meter covered with pavement, is almost the same between the two types of folders , considering that the conventional should have a thickness greater than the SMA folder, with equal effort. However, if factors are considered life compared with a similar conservation work, from one folder SMA can expect a long life superior to that of a conventional folder.

So if you consider the cost / benefit result from a lower cost, SMA folder per year of service.

Warning:

The thickness of a mixture of SMA, it is recommended that not more than 4 cm. compact in order to maintain an efficient transmission system efforts "stony skeleton." The thickness of the mixture compact SMA, will depend on the maximum size of aggregate that is used in the project design sieve.

A mixed type 7 S.M.A. can be used as folder or another must always be placed on asphalt?

A mixture type S.M.A. used as a binder and can be placed on a good layer of base material is stabilized or not the latter.

It can also be placed as a folder of contact with a surface traffic asphalt pavement is deteriorated, but not its structure. Or in reconstructed pavements, in which take advantage of existing material to form a stabilized layer, on which place the folder type SMA

In either case above, shall be under the folder of SMA, a properly calculated pavement structure for the operating conditions that will be submitted.

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