Requirements of Bituminous mixes
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 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.
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:
- Bitumen content to ensure proper binding and water proofing.
- Voids to accommodate compaction due to traffic.
- Flexibility to meet traffic loads, especially in cold season.
- Sufficient workability for construction.
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