OBJECTS OF BITUMINOUS PAVING MIX DESIGN

According to Asphalt institute design manual, the over all objective for the design of the bituminous paving mixes, to determine an economical blend and grading of aggregates and a corresponding bitumen content which would yield a mix having the following characteristics.

• Mix should exhibit sufficient stability to satisfy the service requirements of the pavement and the traffic conditions, without undue displacements.

• It should have sufficient bitumen content to ensure a durable pavement by coating the aggregates and bonding them together and also by water-proofing the mix.

• Bitumen mix should have sufficient voids in the total compacted mix as to provide a reservoir space for a slight amount of additional compaction due to traffic to avoid flushing, bleeding and loss of stability.

• It should have sufficient flexibility even in the coldest season to prevent cracking due to repeated application of traffic loads.

• The mix should have sufficient workability while placing and compacting the mix. 

• The mix should be the most economical one that would produce a stable, durable and skid resistant pavement.

REQUIREMENTS OF BITUMINOUS MIXES

A good bituminous paving mix should exhibit stability, durability, flexibility, skid resistance, and workability properties, besides economy. 

1. Stability is defined as resistance of the paving mix to deformation under load and thus it is a stress which causes a specified strain depending upon anticipated field condition. Stability is a function of friction cohesion.
2. Durability is defined as the resistance of the mix against weathering and abrasive actions.
3. Flexibility is a property of the mix that measures the level the bending strength.
4. Skid resistance is defined as the resistance of the finished pavement against skidding and is function surface texture and bitumen content.
5. Workability is the ease with which the mix can be laid and compacted. It is function gradation of aggregates, their shape and texture, bitumen content and its type.