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Concrete Road:

However in recent years, in USA, Canada and Europe and in Indian fly ash has been successfully used to

replace a part of cement to make dry lean concrete (DLC) and pavement quality concrete (PQC) to obtaincertain advantages better durability of concrete in pavement. This has helped in reducing the overall cost

of concrete pavement and therefore acceptable to clients and used also.

Figure **** gives the composition of a Concrete Road

CONCRETE SLAB (PQC)

SUB-BASE (DLC)

SUB-GRADE (GSB)

Dry Lean Concrete: Dry lean concrete is a semi-rigid material which provides a stable foundation for theconcrete slab. It also has better load dispersion quality as compared to unbound granular layers and is

resistance to softening action of water serving as an effective working platform for week foundations. asmall thickness of DLC is required compared to unbound layers used in flexible pavements (bituminous /

asphalt roads) for catering similar loading and environmental conditions. This is just because of DLCssuperior performance. Furthermore is preparing such Dry Lean Concrete (DLC) the requirement ofcement is also nominal due to which it becomes economical. The concept and use of dry lean concrete

along with specification has recently been made available to engineers by MOST, it is most importance toimplement quality control measure at all stages of works at site.

Characteristic of DLC:

The functions of the various layers in a concrete road are:

Layer Functions

Concrete Slab (PQC) To provide a hard, durable, dustproof riding surface To bear the traffic loads

Sub-base (DLC) To provide a uniform and firm support to the pavement To prevent mud-pumping To act as a capillary cut off

Drainage Layer (GSB) To drain away the water that may enter through the joints in the concreteslab and cracks in the sub-base

Construction of concrete Road:

Construction is usually done by one of the three methods:

(a) Manual method, providing steel or wooden forms, pouring concrete and compacting by meansof needle and vibrating screeds, and giving the texture by brushing.

(b) Fixed form paver, which has spreader, vibrator, texturing unit and membrane curing compound

sprayer, the whole unit moving on fixed forms formed by steel channels.

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(c) Slip form paver, which is the latest technique, requiring no fixed forms, the alignment, gradeand thickness controlled by electronic sensors. The equipment also inserts dowel bars,

imparts texture, cuts the joints and applies the curing compound.

In all the methods, concrete is mixed in a weigh batcher and mixer. The aggregates of various sizes areadded as per a job mix formula. The joints are sealed with a sealant. Modern practice is to seal with cold

poured sealants like polysulphide or silicone. Curing is done by initial application of curing compoundfollowed by watering over wet hessian for 14 days. Traffic is allowed only after concrete has attained the

desired strength, which may be after 21-28 days.