Types of Failures in Rigid Pavements
The different types of distresses responsible for failures in rigid pavements are:- Joint Spalling
- Faulting
- Polished Aggregate
- Shrinkage Cracking
- Pumping
- Punch out
- Linear Cracking
- Durability Cracking
- Corner Break
Joint Spalling in Rigid Pavements
Excessive compressive stress causes deterioration in the joints, called as the spalling. This may be related to joint infiltration or the growth of pavement, that are caused by the reactive aggregates. Poor quality concrete or construction technique will also result in joint spalling. Small edges to large spalls in the back of the slab and down to the joints can be observed. Main causes of joint spalling in rigid pavements are:- Joints subjected to excessive stress due to high traffic or by infiltration of any incompressible materials
- The joint that are constructed with weak concrete
- Joint that is accumulated with water that results in rapid freezing and thawing
Fig.1: Joint Spalling in Rigid Pavement Slabs
The joint spalls can be avoided by using good construction techniques, or by sealing the joints.Faulting in Rigid Pavements
The difference in elevation between the joints is called as faulting. The main causes of failures in rigid pavements due to faulting are:- Settlement of the pavement that is caused due to soft foundation
- The pumping or the erosion of material under the pavement, resulting in voids under the pavement slab causing settlement
- The temperature changes and moisture changes that cause curling of the slab edges.
Fig.2: Faulting with difference in elevations found between the joints
Polished Aggregate in Rigid Pavements
The repeated traffic application leads to this distress. These are the failures in rigid pavements caused when the aggregates above the cement paste in the case of PCC is very small or the aggregates are not rough or when they are angular in shape, that it cannot provide sufficient skid resistance for the vehicles. The polishing degree should be specified before the construction is carried out. This study is included in the condition survey, where it is mentioned as a defect.
Fig.3: Polished Aggregates
Shrinkage Cracking in Rigid Pavements
These are hairline cracks that are less than 2m in length. They do not cross the entire slab. The setting and curing process of the concrete slab results in such cracks. These are caused due to higher evaporation of water due to higher temperature cracks. Improper curing can also create shrinkage cracks in rigid pavements.
Fig.4: Shrinkage Cracking in Pavements
Pumping Effects
The expulsion of water from the under a layer of the pavement is called as pumping. This distress is caused due to the active vehicle loads coming over the pavement in a repetitive manner. This will result in the fine materials present in the sub base to move along with water and get expelled out with the water. Larger voids are created under the pavement due to repeated expulsion. The stains on the pavement or on the shoulder surface are the method through which this type of failure of rigid pavement is evidenced. Pumping can be avoided by the prevention of water accumulation at the pavement sub-base interface. This can be achieved by reducing the deflection to a minimum value and by the provision of a strong well-constructed sub-base. The constructed sub-base must have a sufficient drainage facility so that the subgrade below is not saturated. Modern pavement construction makes use of underground drainage system that is the best solution for pumping distress.
Fig.5: Pumping Effect
Corner Breaks in Rigid Pavements
These are the failures in rigid pavements that is caused due to pumping in excessive rate. When the pumping completely remove the underlying support that no more support exists below to taken the vehicle load, the corner cracks are created. The repair method is either full slab replacement or the repair for the full depth must be carried out.
Fig.6: Corner Break Failures in Rigid Pavement
Punch-out in Rigid Pavements
A localized area of concrete slab that is broken into pieces will be named as punch out distress. This distress can take any shape or form. These are mainly defined by joints and cracks. The joints and cracks will mainly keep 1.5m width. The main reason behind punch outs is heavy repeated loads, the slab thickness inadequacy, the foundation support loss or the construction deficiency like honeycombing.
Fig.7. Punch-out Failures in Rigid Pavements
Linear Cracking in Rigid Pavements
These types of failures in rigid pavements divides the slab into two or three pieces. The reason behind such failures is traffic loads at repeated levels, the curling due to thermal gradient and moisture loading repeatedly.
Fig.8: Linear Cracking
Durability Cracking in Rigid Pavements
The freezing and thawing action will create regular expansion and contraction which will result in the gradual breakdown of the concrete. This type of distress is patterns of cracks on the concrete surface as layers that are parallel and closer to the joints. Joints and cracks are the areas where the concrete seem to be more saturated. Here a dark deposit is found and called the 'D' cracks. This failure of rigid pavement will finally result in the complete disintegration of the whole slab.
Fig.9. Durability Cracking or 'D' Cracks Failure in Rigid Pavements
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