What are the reason for Cracks on the road

Thankshttps://www.rhino-uk.com/

There are numerous factors influencing the performance of a pavement, the following five are considered the most influential (Transportation research board, England; April 1985)

 1)Traffic

 Traffic is the most important factor affecting pavement performance. The performance of pavements is mostly affected by the loading scale, arrangement and the number of load repetitions. The damage caused per pass to a pavement by an axle is defined relative to the damage per pass of a standard axle load, which is defined as a 80 kN single axle load (E80). Thus a pavement is designed to withstand a certain number of standard axle load repetitions that will result in a certain terminal condition of deterioration.(Kamal M.A. et al., 2009)

2) Moisture

Moisture significantly reduces the supporting ability of gravel materials, especially the sub grade. Moisture enters the pavement structure through capillary action. The resulting action is the wet surface of particles, excessive movement of particles and dislodgment which ultimately results in pavement failures. (Terrel 1990)

3)Sub grade

The sub grade is the lower layer of soil that supports the wheel loads. If the sub grade is not strong enough the pavement will show flexibility and finally the pavement will fail. Pavement will fail to perform ideally if the variation in particles behavior is not catered for in the design.

4)Construction quality

Pavement performance is affected by poor quality construction, inaccurate pavement thicknesses, and adverse moisture conditions. These conditions stress the need for skilled staff and the importance of good inspection and quality control procedures during construction.

Causes of cracking in road surfaces: Cracks in the highway emanate from either:

 1.The surface, where traffic induced fatigue, thermal movement and warping stress will initiate cracking
2.The sub-base, where seasonal expansion and contraction of the pavement causes reflective cracking

The sort of cracks that can be treated are:

      • reflective cracks
      • surface generated cracks
      • shrinkage cracks
      • longitudinal lane joints
      • concrete spalling
      • asphalt/concrete interface joints
      • mid bay cracking
Cracks generated from the surface are caused by fatigue from traffic, especially HGVs. These types of cracks when excavated, will often not show further cracking in the layers below the surface course.
Cracks generated from movement in the sub-base are called reflective cracks and will show through in the wearing course because movement in the underlying layers is being mirrored in the top surface. Traditional asphalt road surfaces, whilst being called ‘flexible’ roads when compared to concrete ones, are not able to contain concentrations of such high movement.

Why is this movement taking place? This all depends on the structure of the road. Traditionally roads are built in layers and these layers are designed to bear the load of traffic in varying degrees. Many roads have concrete in those lower layers. As temperatures change, road surfaces (like other materials) expand and contract. Concrete is designed in slabs and designed to focus this movement at the joint between slabs. Lean mix and continually reinforced concrete also focuses movement in concentrated points. Asphalt reacts differently to temperature changes, expanding and contracting evenly over the entire surface area.

This incompatibility of the concrete and asphalt to react similarly, leads to asphalt overlays cracking when laid on top of concrete sub-bases.
Couple this with variations in which the different layers of the road surface heat up from the sun, the lower layers expand at a slower rate to the surface ones, and it is no wonder that a road surface cracks as it does.
What is important to consider is that in most cases, a substantial crack in the road surface is likely to be in a position where movement is the cause. Repair methods should consider materials with the flexibility to accommodate that movement when it occurs again in the future.