What is hot asphalt?
 

What is hot asphalt?

Sunday، 07 November 2021 | Article Rating

Hot-mix asphalt is a combination of hot tar and graded fine aggregates and filler which is produced and mixed in asphalt factory in a pre-defined specific situation and heat and is carried, distributed, profiled and crushed on surfaces of base and sub-base or layers of concrete.   

Ratio of combination of these materials together depends on application and type of usage and regulations of their design.

Also thickness of the layer which is supposed to be executed is also efficient in this combination.

Long durability and strength for loads and promptitude make up some features of hot-mi asphalt in traffics. More than 90 to 95 percent of asphalt combination includes stone materials.

Marshall test based on ASTM D1599 standard is used to create asphalt design.

Using asphalt has no limitation in different ways.

Hot-mix asphalt is utilized in making surface of ways, airports and roofs of buildings.

The word ‘asphalt’ is used as tar in French, but in our country it means asphalt concrete which is borrowed from an ancient Greek word.

It can be also used for making moisture insulation and protecting roof of buildings. Although asphalt has a longer durability for roofs, it weighs more in comparison with Bitumenous water proofing, tar and sack.

The tar used in asphalt concrete and hot-mix asphalt must be pure tar which is produced from sedimentation of crude oil in distillation tower and must not foam up to heat of 175 degrees.


Tars used in Iran are the ones with penetration degree and grade viscosity or PG.

Climatic conditions of execution location are the most important factors in choosing type of tar. For example, tar with more viscosity (with less penetration) is suggested for ways with heavier traffic and tar with less viscosity (with more penetration) is suggested for light traffic and cold weather.

Different layers of asphalt for pavement from top to bottom are as what follows:

A.  Surface asphalt (Topka)

This layer is in direct contact with loads of vehicles passing and is affected by environmental and climatic factors.

This layer must tolerate all loads and also endure climatic effects such as heat, frost and heat degree changes. Moreover, it should be consistent and without any wave, crack and overloaded tar.

Stone materials are smaller and percentage of tar is more in this layer and the empty space is more among aggregates and thickness of this layer is measured based on design of pavement.  

Maximum diameter of stone materials changes in this layer from 9.5 to 19.

In order to increase durability of this layer and improve its resistance, a kind of asphalt named coarse grain mastic (SMA) with fully broken stone materials with gap gradation accompanied by more filler can be used.

Cold-mix asphalt

This layer is placed between surface and sub-base layers or asphalt treated base (if existing).

Its gradation is coarser than Topka asphalt and its tar is less. Maximum size of stone materials in this layer is 19 to 37.5 millimeters.

Based on calculations, provision of pavement design for binder layer can be executed in two layers and its thickness is determined by designing road pavement. 

C: Asphalt treated base (black base)

Refer to All-asphalt pavement

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