How properties of pavement materials contribute to overall performance of flexible pavement.
Aggregate physical properties have the most direct effect on how an aggregate performs either as pavement material?
Gradation and size. Instability may result from excessively small maximum sizes. Otherwise, poor workability or segregation may result from excessively large maximum sizes. Thus, we can know that the gradation properties affect density, strength, workability, stability, durability, permeability and economy of pavement structure.
Toughness and abrasion/wear resistance. Aggregate should be hard and it can resistance of wear and polishing due to traffic. If not, degradation occurring during production can affect the overall gradation and, thus, widen the gap between properties of the laboratory designed mix and field produced mix.
Durability and soundness/resistance to weathering. The aggregate must be resistant to breakdown or disintegration when subjected to the weathering like wetting, drying, freezing or thawing. It is essential to use durable and sound aggregates to maintain the integrity of the asphalt concrete mix during service. Raveling, stripping and, in extreme cases, rutting of asphalt concrete pavement can result from the use of aggregate which is not resistant to weathering.
Particle shape and surface texture. Since aggregates are relied upon to provide stiffness and strength by interlocking with one another, angular-shaped particles with a rough surface texture are best. The angular particles provide poor workability and the rough surface particles provide more area to which the cement paste can bond thus it is suitable for the HMA.
Specific gravity. Aggregate absorption depends on aggregate types. Aggregate that is used in HMA production will have an absorption just 0-5%. More than 5%, it is uneconomical because extra asphalt binder is required to account for the high aggregate absorption. If absorption is incorrectly accounted for, means lower than the actual value, the resulting HMA could be overly dry and have low durability or over-asphalted and susceptible to distortion and rutting have happened for the value is higher than the actual.
Cleanliness and deleterious materials. The deleterious substance like clay, dirt, and dust are not desirable because they generally affect performance by quickly degrading, which causes a loss of structural support and/or prevents binder-aggregate bonding.
Chemical Stability. Aggregate chemical stability can determine how well an asphalt cement binder will adhere to an aggregate surface. Poor adherence, commonly referred to as stripping, can cause premature structural failure.
Bitumen is a one of the material that used in asphalt concrete. Bitumen comes from petroleum distillation residue that can combine with aggregate. The function of bitumen is a binds the surface, acts as a cushion and seal the surface. The properties of bitumen that contribute to the performance of flexible pavement are the durability of the weather, consistency, resistance against water and ductility.
Firstly, bitumen is the durability of the weather. Durability is to ensure a long life the pavement. Bitumen is thin layers that used in a surface of the pavement and it will directly respond to the weather and causes it to lose its elasticity and become fragile. This is because, when physical and chemical changes or weathering process happen it will affect the bitumen and can cause cracking to the pavement. Because of that, bitumen used as a pavement material should remain in an elastic state so that its role as a binder is effective. So, the bitumen material must be selected properly to resist the weathering action.
Secondly, characteristic of bitumen is a consistency. The consistency of bitumen is dependent on temperature changes. This is because, when the temperature of the surrounding is higher than the temperature that bitumen can receive it will affect the pavement and can cause bleeding and rutting. Besides that, it also will affect the consistency of bitumen. There are few tests that can be conducted to determine the consistency of bitumen which is penetration test and softening point test.
Next, the characteristic of bitumen is resistance against water. The failure of the road structure wills occurs with the presence of water. Therefore, the durability and viscosity of bituminous give an important function to remain adhered to the surface material. Besides that, it can prevent water to infiltrate through surface then run to subgrade layer.
Lastly, the property of bitumen is ductility. Ductility is important in the pavement to coat the bitumen around aggregates to improve the physical interlocking of the aggregates. This is because when the binder materials do not have enough ductility it will cause cracking to the pavement because of the traffic load. Ductility of a bituminous material is measured by the distance which it will elongate before breaking when the material is pulled apart at a specified speed and specified temperature.
• Fillers and Additive
The fillers should be inert materials. The functions of fillers are to fill up the voids between the aggregates and provides interlocking effects thus the pavement becomes more stable and durable. Examples of filler like fly ash, stone dust, brick dust, carboxyl latex, rubber, nanomaterial, etc. In fact, the fillers with Marshall properties better than the conventional fillers (cement and stone dust) to provide the maximum stability.
Additive controls the performance of types of asphalt like hot, warm or cool like using Sasobit. At temperatures below the melting point, it as a long chain aliphatic hydrocarbon forms a crystalline network structure in the binder that is reported to provide added stability. Increase the content, improve on the performance of modified bitumen against permanent deformation at high temperature; reduce the strength of asphalt mixture against fatigue cracking at warm temperature; and reduce the mixing and compaction temperature range of asphalt mixture at the lower temperature.