construction of flexible pavement in brief

Construction of Flexible PavementBY:SHILPA KUMTHE FP15054KIRAN D R FP15056ARUN RAVINDRANATH FP15058AJINKYA THAKRE FP15059

NATIONAL INSTITUTE OF CONSTRUCTION MANAGEMENT AND RESEARCH, PUNE.

INTRODUCTION PAVEMENT:-

“Pavement is load bearing and load distributary component of road”

PURPOSE OF PAVEMENT:-1. LOAD SUPPORT2. SMOOTHNESS3. DRAINAGE4. ALL WEATHER OPERATION5. DIRECTION AND GUIDANCE

TYPE OF PAVEMENT Type of pavemen

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Flexible pavemen

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Rigid pavemen

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1 .FLEXIBLE PAVEMENT:Those pavements which reflect the deformation of subgrade and the subsequent layers to the surface.

2. RIGID PAVEMENT: The pavement are associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil. Rigid pavement is laid in slabs with steel reinforcement.

FLEXIBLE PAVEMENT THE ADVANTAGES OF FLEXIBLE PAVEMENTS INCLUDE - Adaptability to stage construction Availability of low-cost types that can be easily built Ability to be easily opened and patched Easy to repair frost heave and settlement THE DISADVANTAGES INCLUDE - Higher maintenance costs Shorter life span under heavy use Damage by oils and certain chemicals Weak edges that may require curbs or edge devices

THICKNESS DESIGN Several Procedures are used. Based on volume and weight of traffic Load supporting capacity of soil is important. Heavy vehicle wheel load has greater impact. Traffic analysis in necessary. Designs are chosen based on 1) Designed traffic in terms of cumulative numbers of std. axels. 2) CBR value of subgrade.

Total thickness of pavement consists of :- Bituminous Surface (Wearing Course).  Base Course.  Subbase.  Subgrade.

WEARING COURSE

Three types of bituminous layers-

1. Bituminous Macadam.2. Penetration Macadam.3. Built up spray Grout.

BITUMINOUS MACADAM

It consist of crushed aggregate and bituminous binder heated and mixed in a hot mix plant at specified temperature, transported to the construction site, laid with a mechanical pawer and compacted by roller.

Material used : Bitumen binder of grade VG -30,20 and Max size of aggregate 50mm.

BITUMINOUS PENETRASION MACADAM.The coarse aggregate of specified size are first spread and compacted well in dry state. Compacted thickness 50-75 mm. After compacting of dry aggregates, hot bituminous binder of specified grade is spread in large quantity on the top of this layer. Filling up a part of void and binding by key aggregate.

BUILT UP SPRAY GROUTIt consist of a two layer composite construction of compacted crushed stone aggregate with bituminous binder applied after each layer and key aggregate placed on the top surface of the second layer.

BASE COURSE The base course is immediately beneath the surface course. It

provides additional load distribution and contributes to drainage and frost resistance. Base courses are usually constructed out of

AGGREGATES: Base courses are most typically constructed from durable aggregates that will not be damaged by moisture and frost action. Aggregates can be either stabilized or un-stabilized.

SUB-BASE COURSE

Intermediate layer between subgrade and granular base course

Essentially a drainage layer Distributes the stresses imposed by traffic

FUNCTION OF SUB-BASE COURSE OF FLEXIBLE PAVEMENTIt functions primarily as structural support but it can also help:

Minimize the intrusion of fines from the sub-grade into the pavement structure.

Improve drainage. Minimize frost action damage. Provide a working platform for construction. The subbase generally consists of lower quality materials than the

base course but better than the sub-grade soils.

MATERIALS FOR SUB BASE LOCALLY AVAILABLE MATERIALS

Natural sand Gravel or moorum Kankar Crushed stone Laterite

INDUSTRIAL WASTE AND OTHER MATERIALS Steel slag Pond ash or Pond ash – Bottom ash mix Crushed concrete Brick bats

SUBGRADE

It forms the foundation of the pavement system Subgrade soils are subjected to lower stresses than the surface,

base, and subbase courses. Since load stresses decrease with depth, the controlling

subgrade stress usually lies at the top of the subgrade. The combined thickness of subbase, base, and wearing surface

must be great enough to reduce the stresses occurring in the subgrade to values that will not cause excessive distortion or displacement of the subgrade soil layer.

FACTORS TO BE CONSIDERED

General characteristics of the subgrade soils. Depth to bedrock. Depth to the water table. Compaction that can be attained in the subgrade. CBR values of uncompacted and compacted subgrades. Presence of weak or soft layers or organics in the subsoil. Susceptibility to detrimental frost action or excessive swell.

METHODS FOR SUBGRADE PREPARATION COMPACTION

In fill areas, subgrade below the top 150 mm (6 inches) is often considered adequate if it is compacted to 90 percent relative density.

In order to achieve these densities the subgrade must be at or near its optimum moisture content (the moisture content at which maximum density can be achieved).

Usually compaction of in situ or fill subgrade will result in adequate structural support.

STABILIZATION

The binding characteristics of these materials generally increase subgrade load-bearing capacity.

Typically, lime is used with highly plastic soils (plasticity index greater than 10), cement is used with less plastic soils (plasticity index less than 10) and emulsified asphalt can be used with sandy soils.

For flexible pavements, a primecoat is not effective on silty clay or clay soils because the material cannot be absorbed into such a fine soil (TRB, 2000).

OVER-EXCAVATION

The general principle is to replace poor load-bearing in situ subgrade with better load-bearing fill.

Typically, 0.3 – 0.6 m (1 – 2 ft.) of poor soil may be excavated and replaced with better load-bearing fill such as gravel borrow.

CONSTRUCTION STEPS1. Preparation of Base2. Provision of lateral confinement of aggregates3. Preparation of Mix4. for small quantity concrete mixer may be used5. find OMC after replacing retained on 22.4 mm with material

4.75 to 22.4 mm6. Spreading of Mix

Spreading of mix to be done uniformly / evenly Should not be dumped in heaps

Finishing by Paver /exceptional cases grader Due importance for segregation

7. Compaction 8to 10 tonne static compactor up to 100 mm 8-10 vibratory roller up to 200 mm Speed of compactor not to exceed 5 km/hour Displacement occurring due to roller operations are to be

rectified Use small compactors near kerb/places not assessable to roller Rolling not be done when subgrade is soft/yielding/causes wave

like motion

8. Any defections on the surface to be rectified

9. Setting and Drying

10. Opening to traffic after sealing

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