Flexible Pavement Construction

Flashcards covering the construction of flexible pavements for highway and traffic engineering.

What is pavement?

The structure which separates the tires of vehicles from the underlying foundation material, grants friction, and transfers traffic load.

From what materials are Flexible Pavements constructed?

Bituminous or unbound material.

What are the four layers of flexible pavement structure?

Sub-grade soil, sub-base, road base, and surface layer.

What are the functions of flexible pavement?

To provide a level, comfortable and safe surface; to receive and distribute load; and to protect lower layers from water.

What are some characteristics of flexible pavement?

Using material made of bitumen, simple maintenance work, does not require expansion joints, and waterproof.

What is subgrade?

Natural soil or filled soil, ready to receive the pavement material.

What functions does the sub-base perform?

Supports the road base, prepares drainage, provides cover, bears pressure from heavy vehicles, and prevents the sub-grade from traffic flow.

What is the function of the road base?

Absorbs force from the surface and spreads it to the thickest layer, preventing undue deformation of the sub-grade.

What are the functions of the surface layer?

Provides a smooth and dense riding surface, takes up wear and tear, provides a watertight surface, and can withstand pressure from tires.

What are five methods for the construction of a road base course in flexible pavement?

Macadam Crusher-Run Road Base, Dry Bound Macadam Road Base, Wet-Mix Macadam Road Base, Bituminous Bound Macadam Road Base, and Cement-Treated Road Base.

What are the advantages of Macadam Crusher-Run Roadbase?

Low construction costs, easy to cut and trim, fast compaction, less human energy usage.

What are the disadvantages of Macadam Crusher-Run Roadbase?

Isolation of aggregates, fine aggregate sinking to the bottom causing a loose surface.

What are the advantages of Drybound Macadam Road Base?

Avoid aggregate isolation during the trip, low cost.

What are the disadvantages of Drybound Macadam Road Base?

Fine aggregates will wet and cannot fill the void in rainy conditions.

What are the Advantages of Wet-Mix Macadam Roadbase?

Not applicable to isolation, tractable and easily compacted.

What are the Disadvantages of Wet-Mix Macadam Roadbase?

The compacted layer should have time to dry.

What are the advantages of Bituminous Bound Macadam Roadbase?

Good load distribution, reducing base course thickness, stability, elasticity, plasticity properties, protection to the subbase and subgrade, can be used for traffic during construction.

What are the disadvantages of Bituminous Bound Macadam Roadbase?

High cost.

What are the advantages of Cement-Treated Roadbase?

Good load distribution, stable, and moderate cost.

What are the disadvantages of Cement-Treated Roadbase?

Need curing time.

What is involved in the preparation of the sub-grade layer?

Done after placing drainage, piping, and electric cables; involves compacting, leveling, and cambering the sub-grade surface.

Describe the construction of the Sub-base.

Prepared materials are placed and constructed into two layers if thickness exceeds 150mm; compacted carefully, starting from the side of the road.

What are the sub-base material specifications?

Liquid limit not more than 25%, Plasticity Index not more than 6%, Aggregate Crushing Value not more than 35%, CBR value of 30 or more when compacted to 95% of the MDD.

Describe the construction of the Roadbase

Sub-grade surface and sub-base must be formed perfectly and compacted; road base commonly constructed with crusher run in two layers not exceeding 150mm each.

What tests are used to evaluate the strength properties of the soil?

C.B.R test, Plate bearing test, Triaxial compression test, LI, LL and PL, ACV, FI, Soundness, and Grading.

What is the curing time for Prime Coat liquids, post application?

Cured for 24 hours to achieve maximum penetration.

What is a Prime Coat?

Liquid bitumen, sprayed onto a clean unbound road base.

What is a Tack Coat?

Bitumen emulsion, sprayed onto a bituminous layer.

How is the road surface constructed?

Constructed with bitumen materials like concrete asphalt or macadam bitumen; requires a prepared base course and a prime coat.

What are the pavement works involved in Surfacing?

Binder course laid on a broomed, clean, and prime coated road-base, followed by a tack coat and then the wearing course.

What is premix laying?

The process of surfacing after spraying the prime coat, typically using a paving machine with temperature approximately 150 degrees Celsius.

What materials are used in Premix?

Asphaltic concrete and bituminous macadam.

What materials are used in Non-premix?

Cold mix asphalt, dry sand mix, and wet sand mix.

What are the functions of the binder course?

Distributes load to the road base and provides a flat surface for the wearing course.

What are the functions of the wearing course?

Provides a smooth and dense riding surface, receives traffic forces, and acts as a drainage system.

What are characteristics of Wearing Course material?

ACW20, BMW14
Provides smooth and dense ridding surface, Takes up wear and tear due traffic, Provides water tight surfaceagainst filtration of surface water, Provides hard surface which can withstand the pressure exerted by tyres of vehicles

What atre characteristics of Binder Course Material?

ACB28, BMB20
Second layer before the wearing course, Spread the force from the surface

What are the Premix Compaction Steps?

Breakdown, Intermediate, and Final.

What machinery is used in PAVING TRAIN?

Tip-truck, asphalt paver, tandem roller, and pneumatic roller.

What materials are used for Shoulders?

Is constructed as a normal bituminous layer, using approved material for gravel surfacing, or suitable earthwork material.

What are the shoulder Types?

Furnishing, compacting, and shaping earth, gravel, or paved shoulder.

What is the purpose of road shoulder design?

Safety, Structure, and Recreation.