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CRACKS, CRACKS SEALING AND FILLING IN FLEXIBLE ROAD PAVEMENTS

It is essential that Highway Engineers responsible for Road Maintenance, understand the full nature of Cracks in Flexible pavements, what causes them and what are the remedies.

Cracks in Road pavement is a results of stresses that occur over and above the shear strength of the pavement material.

 

Types of Cracks in Hot Mixed Asphalt pavement could be listed out as follows;

  1. Fatigue Cracks
  2. Longitudinal Cracks
  3. Transverse Cracks
  4. Block Cracks
  5. Reflective Cracks
  6. Edge Cracks
  7. Slippage Cracks

 

Fatigue Cracks These Cracks form a pattern similar to Alligator’s skin. They occur due to repetitive traffic loads or High deflection due to weak bases or sub bases usually associated with water logging in sub grade. Neither crack sealing nor crack filling can treat this type of failure show ever it can retard deterioration until pavement restoration is planned and carried out.
Longitudinal Cracks These Cracks run longitudinally to the pavement, usually caused by thermal stress or traffic. They frequently occurs adjacent to travel lanes or between travel lanes and shoulders. These could been effectively treated with cracks sealing.
Transverse Cracks They occurs perpendicular to center line of the pavement, usually caused due to thermally induced shrinkage at low temperatures. These could be effectively treated with cracks sealing.
Block Cracking These types of cracks forms regular blocks. They forms as a result of age hardening coupled with temperature rise and fall. These could be effectively treated with crack sealant.
Reflective Cracks Reflection cracks are caused by cracks, or other discontinuities, in an underlying pavement surface that propagate up through an overlay due to movement at the crack.  They exhibit any of the crack patterns mentioned and must be treated according to the original distress mechanism.
Edge Cracks These are fairly continuous cracks, inter selected the pavement egde, they usually locate within .6m of pavement edge.Edge cracks are usually caused due to overloading at edge of the pavement shear failure or erosion of shoulder. These cracks cannot be treated with crack sealants
Slippage Cracks These are crescent shape and are caused when top layer of the asphalt shears often due to high deflection and poor bond, they cannot effectively treated with crack sealant.

 

Cracks sealing or Cracks Filling

Crack sealing and filling prevent the intrusion of water and incompressible materials into cracks. Also infiltration of water into the pavement structure. When crack width is smaller crack sealing is done where as crack filling when cracks are larger than 5mm. Crack sealing is considered longer term treatment than crack filling. Timely intervention can prevent propagation of cracks due to infiltration of water through cracks. The thumb rules to decide whether to seal or filling in cracks are decided as follows.

  • Surface Cracking
  • Cracks in the pavement Structure-Local sealing or filling-in and patching in case of severe cracking

Carrying out crack sealing

  • Sweep the area (a): This is carried out by hand. The road surface must be clean and dry following this operation.
  • Mark out the area to be sealed (b): The surfacing that is to be covered is outlined in
  • The binder is distributed over the surface using a spray lance or watering can at the following specified rates
  • The aggregate: Coarse sand up to 5mmis scattered by shovel from the truck or trailer. The whole surface must be covered

 

Treatment of Single Cracks

  1. Clean the cracks thoroughly
  2. Apply crack sealant with spray lance or watering can
  3. Level off with a squeegee if excessive binder is poured
  4. Cover with aggregate

Timely treatments of cracks saves the pavement deterioration preventing pavement renewals prematurely saving large sums of  money which could be used elsewhere for road improvement.

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