CRACK RELIEF LAYER (CRL) is a layer that is placed between the new overlay and the old pavement in order to dissipate pavement movements before they create stress in a new overlay surface.
CRL is an open-graded mix that had around 20 to 35% of air void which act as a cushion layer in order to dissipate cracks development in pavement layer. It has low bitumen content that normally around 3% in order for it to act as a semi-unbound layer in order to prevent horizontal and vertical movement of pavement strata.
PAVEMENT DETERIORATION is a common phenomenon that occurs once it is opened for traffic. Pavement deterioration is the process by which distress develop in the pavement under the combined effects of traffic loading and environmental conditions. It is very common in developing countries.
As it is widely known that pavement cracks is a major problems that can reduce the workability of pavement layers. Common pavement deterioration includes cracking, surface defects, deformation and structural failure when it was found to be experiencing serious damage or deformation behaviour.
CRACKS in conventional pavement initiate at the pavement surface and propagate downward. It also sometimes throughout the entire depth of the pavement.
The main mechanism for cracks is the tensile stresses and strains induced at the top of the pavement structure from the combination of traffic load, temperature, and aging of binder, which may cause shrinkage and differential stiffness between the pavement surface, levelling, and base courses.
A CRL is needed because cracks in a pavement top layer will cause many problems, including water intrusion, pumping soil particles through a crack, and progressive degradation of the road structure near cracks. By adding CRL layer between the bound course and the unbound courses it can prevent the horizontal movement of the layer.
CRL layer is a semi-rigid layer due to its low bitumen content and high resilient modulus. It also had a large amount of air void content that act as a buffer layer in order to reduce the vibration from transmitted to the pavement strata. This characteristic makes CRL able to absorb the stress and supress the development of cracks in pavement layers.