Pavement Materials In Highway Construction

Highway components and materials used in highway construction. Highway constructions are typically built above ground level and include the following elements.

1. Fill or embankment
2. Subgrade
3. Flexible and rigid layers of pavement construction

If the highway’s vertical alignment necessitates lowering the formation level below the general. The highway could be built-in cutting at some points, and the highway structure would be different including the following elements.

1. Preparation of cutting
2. Subgrade
3. Flexible and rigid layers of pavement construction

Highway Embankment and Cutting Materials

Organic waste materials such as garbage and other biodegradable materials should not be used in embankments because of undesirable characteristics such as high compressibility, settlement, and high variations instability and volume with water content. Local materials make up the road stretches in cutting; these are often diverse types of soils present along the alignment; nevertheless, rocky and other forms of strata are occasionally encountered along the cut stretches.

Layers of Flexible Pavement Materials

1. In the drainage layer, select granular soils or crushed aggregates with suitable permeability.
2. Granular base course with stone aggregates and fine aggregates
3. Bitumen binder, coarse aggregates, and fine aggregates in the binder and surface course

Rigid Pavement Layer Materials

1. In the drainage layer, select granular soils or crushed aggregates with suitable permeability.
2. For dry lean concrete in the sub base course, coarse aggregates, fine aggregates, and Portland cement are used.
3. Coarse and fine aggregates, as well as Portland cement, are used to make a high-quality concrete pavement slab that acts as both a foundation and a surface course.

Subgrade Soil

The subgrade soil is an essential component of the road pavement structure, receiving traffic loads directly from the pavement layers. In the construction of a pavement structure, the subgrade soil and its qualities are critical. The major purpose of the subgrade is to provide appropriate support for the pavement, and it must be stable under poor weather and loading conditions to do so.

Poor subgrade conditions are sometimes blamed for the production of waves, corrugations, rutting, and pushing in black top pavements, as well as the phenomena of pumping, blowing, and subsequent cracking in cement concrete pavements.

Desirable Features

• Stability
• Incompressibility
• Permanency of strength
• Minimum changes in volume and stability under severe weather and ground water conditions
• Good drainage
• Ease of compaction are all desired features of soil as a highway material.

The soil should be stable or resistant to permanent deformation under load, as well as weathering resistance, in order to maintain the desired subgrade support. A minimum variance in volume will ensure a minimum variation in the subgrade’s differential strength values. To avoid excessive moisture retention and subsequent frost action, good drainage is important. Under certain types and amounts of compaction, ease of compaction provides increased dry density and strength.

Index Properties of Soil

The soil properties on which their identification and classification are based are known as index properties.

• Grain size distribution: It is found by mechanical analysis. That is Coarse grained soil by sieve analysis and fine soil by sedimentation analysis or Hydrometer method. The grain size analysis is carried out to determine the percentage of individual grain size present in a soil sample.
• Liquid limit: It is defined as the minimum water content at which the soil will start flowing under the application of very small shearing force. It can be determined in the laboratory using a mechanical device like Casagrande apparatus or cone penetration method.
• Plastic limit: It is the minimum moisture content at which the soil remains in a plastic state or undergoes plastic or non recoverable deformation under applied load.
• Plasticity index: It is the numerical difference between the liquid limit and plastic limit. It indicates the range of moisture content over which the soil is in plastic condition.
• Shrinkage limit: It is the maximum moisture content at which the further reduction in water content does not cause reduction in volume. It is the lowest water content that can occur in clayey soil sample which is completely saturated.