Pavement Types & Material, Highway Engineering.pptx

Pavement types & material
Highway Engineering, B. Tech, M. Tech Civil, prepared by Kuldeep Sharma

1. PAVEMENT ANALYSIS & DESIGN PAVEMENT TYPES & MATERIALS

2. What is a Pavement? Pavement   is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied loads to the sub-grade. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the sub-grade.

3. Requirements of a Pavement An ideal pavement should meet the following requirements: Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil, Structurally strong to withstand all types of stresses imposed upon it Adequate coefficient of friction to prevent skidding of vehicles Smooth surface to provide comfort to road users even at high speed Produce least noise from moving vehicles Long design life with low maintenance cost.

4. Types of Pavements: 1. Flexible Pavements 2. Rigid Pavements The pavements can be classified based on the structural performance into two, flexible pavements and rigid pavements.

5. 1. Flexible Pavements The flexible pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous road). These components are placed on a subgrade to support the traffic load and distribute it to the roadbed soil.  Flexible pavement may be constructed in a number of layers and the top layer has to be of best quality to sustain maximum compressive stress, in addition to wear and tear.

6. Typical layers of Flexible Pavement Typical layers of a conventional flexible pavement includes: Seal Coat, Surface Course, Tack Coat, Binder Course, Prime Coat, Base Course, Sub-Base Course, Compacted Sub-Grade, and Natural Sub-Grade.

7. Sub-grade The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from the layers above. It is essential that at no time soil sub-grade is overstressed. It should be compacted to the desirable density, near the optimum moisture content.

8. Sub-base Course The sub-base course is the layer of material beneath the base course Provides structural support Improves drainage Reduce the intrusion of fines from the sub-grade in the pavement structure. A sub-base course is not always needed or used.

9. Base Course The base course is the layer of material immediately beneath the binder course. Provides additional load distribution Contributes to the sub-surface drainage. It may be composed of crushed stone, crushed slag, and other untreated or stabilized material.

10. Prime Coat Application of low viscous cutback bitumen to an absorbent surface like granular bases on which binder layer is placed. Provides bonding between two layers. Unlike tack coat, prime coat penetrates into the layer below, plugs the voids, and forms a water tight surface.

11. Binder Course Provides the bulk of the asphalt concrete structure. Distributes load to the base course . Consists of aggregates having less asphalt and doesn't require quality as high as the surface course, Replacing a part of the surface course by the binder course results in more economical design.

12. Tack Coat Very light application of asphalt usually asphalt emulsion diluted with water . Provides proper bonding between two layer of binder course Must be thin, uniformly cover the entire surface, and sets very fast.

13. Surface Course Surface course is the layer directly in contact with traffic loads and generally contains superior quality materials. They are usually constructed with dense graded asphalt concrete (AC). The functions and requirements of this layer are: It provides characteristics such as friction, smoothness, drainage, etc . It prevents the entrance of excessive quantities of surface water into the underlying base, sub-base and sub-grade, It must be tough to resist the distortion under traffic and provide a smooth and skid- resistant riding surface, It must be water proof to protect the entire base and sub-grade from the weakening effect of water.

14. Seal Coat Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.

15. 2. Rigid Pavements Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below. Compared to flexible pavement, rigid pavements are placed either directly on the prepared sub-grade or on a single layer of granular or stabilized material. Since there is only one layer of material between the concrete and the sub-grade, this layer can be called as base or sub-base course.

16. Load distribution in Rigid Pavement In rigid pavement, load is distributed by the slab action , and the pavement behaves like an elastic plate resting on a viscous medium. Rigid pavements are constructed by Portland cement concrete (PCC).

17. The Difference: Flexible Pavements It consists of a series of layers with the highest quality material at or near the surface of the pavement. Its stability depends upon the aggregate interlocks, particle friction, and cohesion . Pavement design is greatly influenced by the subgrade strength . Temperature variations due to change in atmospheric conditions do not produce stresses in flexible pavements.  Flexible pavements have self-healing properties due to heavier wheel loads that are recoverable to some extent. Rigid Pavements  It consists of one layer Portland cement concrete slab of relatively high flexural strength. Its structural strength is provided by the pavement slab itself by its beam action. Flexural strength of concrete is a major factor for design. Temperature changes induce heavy stresses in the rigid pavement. Any excessive deformation occurring due to heavier wheel loads are not recoverable.

18. AIRPORT PAVEMENT In essence, a highway pavement and an airport pavement are similar to each other. Both receive loads from rubber tyred vehicles travelling at high speeds. Both are built up of material such as cement concrete, stone aggregates and bitumen bound layers. Both rests on natural soil subgrade .

19. Types of Airport Pavements: 1. Flexible Pavements 2. Rigid Pavements The pavements can be classified based on the structural performance into two, flexible pavements and rigid pavements.

20. Airport & Highway Loading

21. Airport Pavement Design For ensuring smooth flow at very high speed, runway surfaces need to be build to a very high degree of finish, free from bumps . Airport pavements are generally thicker than highway pavements & require better surfacing materials because the loading & tire pressure of aircraft are much greater than those of highway vehicles.

22. PAVEMENT MATERIAL Pavement materials can be versatile to cater a variety of road types and categories. Commonly used pavement materials range from natural soils, aggregates, binders and assorted products used as admixtures for improved road quality.

23. Purpose of Characterization of Materials To classify/grade To obtain necessary inputs for design of new pavement To ensure proper quality during construction To obtain inputs regarding the condition of materials in an existing pavement.

24. Pavements Materials Recycled materials Etc. Soil Aggregate Bitumen Cement

25. Pavement Materials: Aggregates Major components of road construction Aggregates have to bear stresses occurring due to the wheel loads on the pavement On the surface course aggregates also have to resist wear due to abrasive action of traffic.

26. Uses of Aggregates Pavement construction in Cement concrete, Bituminous concrete and other Bituminous constructions . Granular base course underlying the superior pavement layers.

27. Types of Aggregates Natural Aggregates Obtained from rock Artificial Aggregates Slag (metallurgical process)

28. Origin of Aggregates Gravel aggregates are small rounded stones of different sizes which are generally obtained as such from some river beds . Aggregates are obtained from weathering or crushing of rocks . The properties of the coarse aggregates depend on the properties of parent rock. The properties of the rock depends on the constituent materials and the nature of bond between them.

29. Natural Aggregates 1. Igneous Rock Formed by cooling of magma Predominantly crystalline Very good for bituminous courses and cement concrete pavements 2. Sedimentary Rock Sedimentary rocks are deposited in layers, they have stratified or laminated structure. Formed either from the deposition of – insoluble granular material resulting from the disintegration of pre-existing rocks, or – inorganic remains of marine and animals deposited in great quantities on the sea floor. 3. Metamorphic Rock These are sedimentary or igneous rocks that have been subjected to great heat or great pressure or both, which has resulted in the formation of minerals and in textures different from those of the original rock. Good for base courses, bituminous courses and cement concrete pavements

30. Igneous Rock Granite Basalt (Trap) Hard and durable Resistant to abrasion Low absorption of water Fine grained to coarse grained. Very good for bituminous courses and cement concrete pavements.

31. Sedimentary Rocks Limestone Sandstone Reasonably hard and durable Liable to a smooth polish Fine grained High absorption of water Soft to medium hard gravels are good for sub-base and base courses

32. Metamorphic Rocks Quartzite Reasonably hard and durable Resistant to abrasion Low absorption of water Fine grained to medium grained texture Good for base courses, bituminous courses and cement concrete pavements.

33. Requirements of Aggregates They must be crushed aggregates. They shall be clean, hard, durable and cubica l in shape. They must be free from the dust, organic matter and other deleterious matter. They must not be flaky or elongated. They must not consist of harmful materials since they reduce the strength of pavements. They should resist wear due to abrasive action of traffic on the surface course.

34. Desirable Properties of Aggregates Strength: Sufficiently strong to withstand the stresses due to traffic wheel. (Crushing Strength Test) Hardness: The aggregates used in the surface course are subjected to constant rubbing or abrasion due to moving traffic. They should be hard enough to resist the wear due to abrasive action of traffic. (Los Angeles abrasion test, Deval abrasion test, Polished stone test)

35. Desirable Properties of Aggregates Toughness: Jumping of the steel tyred wheels from one stone to another at different levels causes severe impact on the stones. The magnitude of impact would increase with the roughness of the road surface, the speed of the vehicle and other vehicular characteristics. Aggregates - ability to sustain impact loading (Impact test).

36. Desirable Properties of Aggregates Durability : The stone used in the pavement construction should be durable and should resist disintegration due to the action of weather. The property of the stones to withstand the adverse action of weather may be called soundness. (Soundness Test).

37. Desirable Properties of Aggregates Shape of Aggregates: Based on the shape of the aggregate particle, stones may be classified as rounded, angular, flaky and elongated. It is evident that the flaky and elongated particles will have less strength and durability. Highly angular, flaky and elongated aggregates have more voids in comparison with rounded aggregates. Desirable shape: Angular or rounded Shape (Flakiness index, elongation index, angularity number)

38. Desirable Properties of Aggregates Adhesion with Bitumen: The aggregates used in bituminous pavements should have less affinity with water when compared with bituminous material; otherwise the bituminous coating on the aggregates will be stripped off in presence of water. (Stripping test).

39. Pavement Materials: Bitumen Is a visco -elastic material. Does not have a distinct melting point. Gradually softens when heated More solid at low temperatures and more liquid at high temperatures Is black or dark brown in colour Has adhesive properties Has water proofing properties Forms good bond with variety of aggregates

40. Pavement Materials: Binder Tar: A viscous liquid obtained from distillation of coal or wood. Rarely used in road construction. Coke Oven Tar: Produced at temperatures above 1200 C during manufacturing of coke High aromatic content Pitch content - 50 %

41. Pavement Materials: Emulsions When bitumen globules are mixed with water, binders will generally settle out. An emulsifier must be added to give a stable solution . When used, the water evaporates and the bitumen remains on the surface . The current types of cold rolled materials are based on emulsions.

42. Binder Properties Adhesion: Bituminous materials adhere to clean dry surfaces. Viscosity: All bituminous materials are viscous, i.e. when subject to a long term load they deform continuously. Softening point: This is the temperature at which the binder softens to a predetermined point.

43. Performance Parameters of Binders Mix and form a good bond with aggregate (at high temperature) Do not melt on the road at highest atmospheric temperature Do not crack at extreme low atmospheric temperature Able to withstand repeated cycles of loading and unloading Able to withstand repeated cycles of temperature change Be free from impurities.

44. Tests on Bitumen Penetration test Softening point test Ductility test Viscosity test Specific gravity test Flash and Fire point test Solubility test Thin film oven test

45. THANK YOU