What is the Requirements of Good Bituminous mixes

Requirements of Bituminous mixes

Bituminous mixes

Stability

Stability is defined as the resistance of the paving mix to deformation under traffic load.

Examples of failure under stability

Shoving : A transverse rigid deformation which occurs at areas subject to severe acceleration.
Grooving :Longitudinal ridging due to channelization of traffic. Stability depends on the inter-particle friction, primarily of the aggregates and the cohesion offered by the bitumen. Sufficient binder must be available to coat all the particles at the same time should offer enough liquid friction. However, the stability decreases when the binder content is high and when the particles are kept apart.

Durability

Durability is defined as the resistance of the mix against weathering and abrasive actions. Weathering causes hardening due to loss of volatiles in the bitumen. Abrasion is due to wheel loads which causes tensile strains.

Typical examples of failure under Durability

Pot-holes : Deterioration of pavements locally.

Stripping : Lost of binder from the aggregates and aggregates are exposed. Disintegration is minimized by high binder content since they cause the mix to be air and waterproof and the bitumen film is more resistant to hardening.

Flexibility

Flexibility is a measure of the level of bending strength needed to counteract traffic load and prevent cracking of surface. Higher bitumen content will give better flexibility and less fracture.

Typical examples of failure under Durability

Fracture : Fracture is the cracks formed on the surface (hairline-cracks, alligator cracks),

Shrinkage cracks : Shrinkage cracks are due to volume change in the binder due to aging. main reasons are shrinkage and brittleness of the binder.

Brittleness : Brittleness is due to repeated bending of the surface due to traffic loads.

Skid Resistance: It is the resistance of the finished pavement against skidding which depends on the surface texture and bitumen content. It is an important factor in high speed traffic. Normally, an open graded coarse surface texture is desirable.Workability

Workability is the ease with which the mix can be laid and compacted, and formed to the required condition and shape. This depends on the gradation of aggregates, their shape and texture, bitumen content and its type. Angular, flaky and elongated aggregates workability. On the other hand, rounded aggregates improve workability.

The desirable properties of a bituminous mix can be summarized as follows: