Pavement Priming

Prime coat is the layer which is laid before paving of asphalt concrete.  Prime coat material is the mixture of bituminous material and kerosene at a ratio of 65% and 35% respectively.

PURPOSE OF PRIME COAT

        i.            Prime coat is used to remove the dust,

      ii.            To maintain moisture content of the soil on the layers of the road,

    iii.            It act as a binder for asphalt in bituminous road construction,

     iv.            To provide adhesion between the base coarse and succeeding asphalt coarse.

PLANTS AND TOOLS USED IN PRIMING

        i.            Mechanical broom

  It is a tractor mounted with a road sweeper for the purpose of removing a heavy dust on                    the road and other unwanted materials.

      ii.            Compressor machine

  This is the machine which operates by using pressure, and is used for removing a light dust after the finishing of the mechanical broom.

    iii.            Warning tapes

This are red and white colored which are used for the purpose of alerting a road users on work that is going on the road and to stop them temporarily from using the road until the exercise of priming is over.

     iv.         Bituminous distributor

Is a truck which is responsible for spreading a prime coat on the road. There various kind of bituminous distributor, for instance a bituminous distributer commonly used is having a mass of 27 tons and can carry 9000 liters of prime.

       v.          Truck

For carrying sand for the purpose of botting.

MATERIALS USED IN PRIMING.

        I.           Prime coat

Is the mixture of bituminous material and kerosene at a ratio of 65% and 35% respectively.

      II.          Sand

The is spread one hour after the spread of prime coat so as to ensure the vehicle to not destroy the prime coat.

CALCULATION ON THE QUANTITY OF PRIME TO BE USED.

Factors affecting the quantity of prime to be used,

a.      Length of the road

b.      Carriage width

c.       Specification of the quantity of prime per square meter, the specification of prime range from 0.5 liters to 1.0 liter per square meter.

For the purpose of understanding

Assume;

v  Length of the road = 50m

v  Carriageway width = 7.5m

v  Specification of prime coat = 0.9 liter/m²

Now,  

     Area of the road  A = 50 * 7.5 m²

       Area of the road  A = 375m²

Then,

Quantity of prime = area of the road * specification of prime

Quantity of prime = 375m² * 0.9 liter/m²

Quantity of prime = 337.7 liters

Therefore , the quantity of prime to be use for a road of 50m length and 7.5m width with a prime specification of 0.9 liter/m² is 337.5 liters.

PROCEDURES OF PRIMING

        i.            Closing the road,

The road is closed and the motorized traffic are strictly forbidden to use the road temporarily. Warning tapes are placed on the entrance and exit of the road.

      ii.            Road preparation before priming

The road is cleaned by the mechanical broom and compressor machine so as to remove heavy and light dust and make the road ready for priming.

    iii.           

Priming of the road

Priming is done by the bituminous distributor which start at the edge of the road, centre and finishing at the other edge of the road. During priming, the temperature of prime should range from 90°C to 110°C

     iv.             Botting

This  involve spreading of sand after priming. Botting is done atleast  one hour after priming so as to allow the prime material to fully diffuse on the ground and ensure vehicles do not destroy the layer o prime coat.

       v.            Open to traffic

The road is opened to traffic soon after botting and is left for 4 to 7 days before paving of asphalt.