FUNCTIONS AND CAPABILITIES OF ASPHALT MIXED
Asphalt Concrete Mixture Characteristics
The characteristics of the mixture that must be owned by hot mix asphalt concrete mixtures, in addition to being watertight, are:
- Stability
- Durability
- Flexibility
- Skid resistance
- Fatigue resistance
- Ease of implementation (workability)
1. Stability
The stability of the pavement layer is the ability of the pavement layer to accept traffic loads without permanent changes in shape such as waves, grooves or bleeding. The need for stability is equal to the amount of traffic and vehicle loads that will use the road. Roads with high traffic volumes and mostly heavy vehicles demand greater stability compared to roads with only passenger vehicle traffic volume.
However, the stability that is too high causes the pavement layer to become stiff and quickly cracks, besides that, because the volume between the aggregates is less, the required asphalt content is also low. This results in a thin asphalt film and causes the asphalt bond to be easily separated so that the durability is low Stability occurs from the result of shearing between grains, inter-particle locking and good bonding power of the asphalt layer. Thus high stability can be obtained by trying to use:
- Dense graded aggregates
- Aggregate with a rough surface.
- Cube shaped aggregate
- Asphalt with low penetration
- Asphalt in sufficient quantity for bonding between grains.
a. What is VMA (voids in mineral aggregate)?
VMA is a cavity between grains. If the VMA is small, it will produce high stability, but requires a low asphalt content to bind the aggregate. The small VMA results in limited bitumen covering the aggregate and producing a thin asphalt film. The thin asphalt film is easy to peel off which causes the coating to be impervious to water, oxidation is easy to occur, and the pavement layer is damaged.
b. What is VIM (voids in mix) called?
VIM is the air cavity in the mixture. The use of a lot of asphalt causes the asphalt to no longer be able to cover the aggregate well (because the VMA is small), and also results in a small VIM (small air voids in the mixture). The traffic load which adds to the compaction of the pavement layer causes the asphalt layer to melt out which is called bleeding.
2. Durability (durability / durability)
Durability is required on the surface layer (surface dressing) so that the coating is able to withstand wear and tear due to the influence of weather, water and temperature changes or wear due to vehicle friction. Factors that affect the durability of asphalt concrete layers are:
- Asphalt film or asphalt blanket, a thick asphalt film can produce a high-durability asphalt-concrete layer, but the possibility of bleeding is high.
- small VIM so that the waterproof layer and air do not enter into the mixture which causes oxidation and the asphalt becomes brittle/brittle.
- Big VMA, so that the asphalt film can be made thick. If the VMA and VIM are small and the asphalt content is high, there is a high probability of bleeding. To achieve this large VMA, gap graded aggregates are used.
3. Flexibility
Flexibility in the pavement layer is the ability of the layer to be able to follow the deformation that occurs due to repeated traffic loads without cracking and volume changes. High flexibility can be obtained by:
- The use of gap graded aggregates in order to obtain a large VMA.
- Use of soft asphalt (high penetration asphalt)
- The use of asphalt is quite a lot so that a small VIM is obtained.
4. Skid resistance
Shear resistance is the resistance provided by the pavement so that the vehicle does not slip either when it is raining or wet or when it is dry. The roughness is expressed by the coefficient of friction between the road surface and vehicle tires. Tahanan geser tinggi, jika :
- The use of the right asphalt content so that bleeding does not occur.
- Use of aggregates with a rough surface.
- Use of cube-shaped aggregates.
- Sufficient use of coarse aggregate.
5. Resistance to fatigue (fatique resistance)
Fatigue resistance is the resistance of the asphalt concrete layer to receive repeated loads without fatigue in the form of grooves and cracks. Factors that affect resistance to fatigue are:
- High VIM and low asphalt content will result in faster fatigue.
- High VMA and high asphalt content can cause the pavement layer to be flexible.
6. Ease of implementation (workability)
What is meant by ease of implementation is the ease with which a mixture can be spread and compacted so as to obtain results that meet the expected density. Factors that affect the ease of implementation are:
- Aggregate grading. Good graded aggregates are easier to work with than other graded aggregates.
- Mix temperature, which also affects the hardness of the thermoplastic binder.
- Filler content high, making implementation more difficult.
