Block Cracking in Flexible & Rigid Pavement : Causes & Effects

Block cracking is another type of cracking seen on highway pavements that form a box-like crack on the surface.

This type of cracking is associated with the unusual expansion and contraction of concrete in the rigid pavement and due to improper mixing or ageing of asphalt or poor quality asphalt in flexible pavement.

Block cracking is mainly caused by shrinkage of the asphalt or concrete and daily temperature cycling, and it is not load-associated.

Figure: Block Crack

  i. Block Cracking in Flexible Pavement  

Causes 

1. Use of improper mix

2. Fine aggregates mixed with low penetration asphalt

3. Poor asphalt binder

4. Ageing of asphalt

5. Temperature cycling

Repair 

Quicker this cracking is detected; it becomes easier to repair.

The sealing method of repair can be used for cracks less than ½ inch or lesser.

In case of severe cracks, the deteriorated pavement must be removed and replaced by an overlay.

  ii. Block Cracking in Rigid Pavement  

Causes 

1. Use of improper mix

2. Lack of expansion joints in the pavement

3. Temperature cycling

Repair 

If the crack is lesser than 1/2 inch; cracks can be filled with fillers ( mostly flexible fillers).

If cracking is higher than 1/2 inch; then the affected section of the road is removed and replaced by an overlay. Sometimes, joining of the sections with metal plates also can be done if traffic is low.

To eliminate the problem of block cracking; it is better to provide expansion joints at regular intervals.