The roads having their wearing surface consisting of cement concrete state (plain or reinforced) are called cement concrete roads or simply concrete road. These roads fall under rigid pavement category. These are high cost roads. These are all weather roads. These roads being having excellent riding surface, pleasing appearance and long life are much preferred. It has a high initial cost. These are more popular in advanced countries. These roads are superior to any other roads.

Advantages

Long life

More durable

Better riding surface

Impervious surface

Dustless and sanitary surface

Do not develop any corrugation

Can be laid on any sub-grade

Can be easily reinforced

Non slippery

Offer less tractive resistance

Low maintenance

Good visibility during night


Disadvantages

High initial cost

Requires skill supervision for construction

Noisy under iron-wheeled traffic

Liable to crack and warp due to temperature vibration

Causes glare due to reflected sun-light

Requires long time for curing

Less resilient than bituminous or WBM roads.

Difficult to locate sewers or water mains.


Structural components of concrete pavements

Sub-grade

Sub-base

Concrete slab


Materials required for concrete road slab and their requirements

Cement
Ordinary Portland cement is mostly used for concrete road side construction. Rapid hardening cement may also be used in emergency.

Coarse aggregate
Crushed stone, crushed gravel (shringle) other suitable stone is used as coarse aggregate for concrete road slab construction. It must be clean, strong, durable and free from any other materials.

Fine aggregate
Natural sand is commonly used as fine aggregate. When natural sand is not available, crushed stone sand may be used. It should be sharp and clean.

Water
It is required for mixing and curing concrete. It should be free from harmful substance. The water fit for drinking purpose is to be used.

Reinforcement
It consists of mild steel bars or steel wire fabrics. It is provided when the subgrade is poor and the road is subjected to heavy traffic. The purpose of providing reinforcement is to prevent widening of cracks developed in the concrete road slab.


Method of laying cement concrete road slab

Alternate lay method

Continuous construction method

Construction of cement concrete roads: stages

Preparation of sub-grade

Provision of sub-base

Placing of forms

Batching of materials and mixing

Transporting and placing of concrete

Compaction

Floating

Belting

Grooming

Edging

Curing

Filling of joints

Opening to traffic


Joints in concrete roads

Longitudinal joints

Transverse joints


Objects of providing longitudinal joints

To control development of longitudinal cracks

To facilitate construction of road slab in convenient widths with hand tampers.

To help to maintain the two slabs together at the same level.

The function of transverse joints is to allow for expansion, contraction and warping of road slab and thus to prevent development of cracks in the transverse direction.