Roads and highways are the most important mode of transportation systems for development of a nation. In order to fulfil this purpose, the pavement must be able to provide a safe and comfortable riding surface for the road users. However, pavement deterioration is a major obstacle that can prevent pavement from serving its main purposes. The most common type of pavement deterioration is reflective cracking which occurs when a crack in an overlay layer reflect the pattern of cracks and joints of the old pavement underneath it. 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. Previous implementation of CRL in airport and runways shows that CRL performance is promising for it to be used in roads and highways in order to overcome pavement distress. Further research is needed in order to ensure CRL implementation in pavements industry.
This article reviews the behaviour and function of the crack relief layer (CRL) in a pavement. The significance and effectiveness of implementing CRL into pavement layers to prevent reflective cracking are also included. Over the years, crack in pavement has been a major problem that causes obstacle to transportation system which has cost multi-millions of dollars. This is especially true in airport runway business industry where the traffic flow of aircrafts cannot be easily diverted or disturbed as it involve many parties and would jeopardize public safety. The characteristic of the CRL will be thoroughly investigated to achieve it desirable functional capability to act as the crack relieving agent. CRL is a layer made out of hot mixed asphalt that to the strata of the pavement with thickness of 100 to 150mm on top of base layer and under surface course. The significant of this hot mixed asphalt layer is in its capability to reduce reflective cracks development by separating bound and unbound layer and acting as buffer zone between those layers. Thus the layer designed to be semi-unbound layer to efficiently in creating the buffer zone for the crack transfer from the bottom to the top of the pavement. The layer also acts as the reducer by allowing cracks to develop on the layer thus the crack generate on top of the pavement surface would decrease in the process.
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