CHAPTER ONE: INTRODUCTION
- Background of study
Road failure is defined as a discontinuity in road network resulting in cracks, potholes, bulges, and depressions. Road failure can also be defined as a condition that occurs when an asphalt surface no longer holds its original shape as a result of material stress. According to Agbedion (2007), these potholes, bulges, depressions, may hinder smooth ride. Hence, this hindrance or punctuations in smooth ride is generally referred to as road failure.
From the beginning of civilization, road pavement has functioned to prevent the ground from being deformed by traffic passing over it. Besides, one of the greatest achievement of the ancient Roman engineers was the ability to devise a system of layers that greatly stabilized the road surface to reduce the pressure of wheels across the entire surface thereby making it resistant to rutting and pothole formation.
Road failure in Nigeria is a major problem which has caused setbacks to the economy, loss of lives and properties worth millions of naira annually (Obi, 2010). Vehicles spend longer hours before getting to their destinations due to poor road hence, the socio-economic activities of the people are greatly affected (Igomu, 2011).
Keywords: Asphalt, pavement, material stress, rutting, pothole, road failure.
- Types of Road Failure
There are various types of road failures, each with its own unique classifications and repair approaches.
- Fatigue (Alligator) cracking:Fatigue cracking is characteristics as a series of interconnected cracks creating small, irregular shaped pieces of pavement. The cracking pattern is similar to the pattern found on alligator skin, and therefore the source of its name, Alligator cracking is found at intersections where vehicles are stopped for a continuous amount of time due to loading. As the wheel loading continues, more cracks are formed as a result from stress and tension on the road surface. Alligator cracking is usually caused by water intrusion and weakened base layer.
- Rutting: This is a channeled depressions in an asphalt surface that forms over time from exceeded weight limits and improper base construction. Overtime, heavy vehicles will begin to compact the road way creating tire ruts. If rutting occurs in an asphalt surface, the base must be repaired or restructured to account for heavier vehicle traffic.
- Raveling: Raveling occurs when the asphalt bitumen causing the bond with the aggregate rock begins to break apart. It occurs in older pavement that has already oxidized due to water and sunlight intrusion.
- Longitudinal Cracking: This occurs predominantly parallel to the pavement Centre line. It can occur anywhere in the lane. Longitudinal cracks occur in the wheel paths when the joint between two passes are weak, the pavement don either path of the road shrinks away.
- Potholes: Potholes are small, bowl-shaped depressions in the pavement surface that penetrates the asphalt layer down to the sub-base. Potholes are caused by prolonged water infiltration from existing cracks in the surface. This is due to the untreated alligator cracks and otherasphalt stress cracks. When these happen, water will begin to erode the surface thereby causing sharp edges and vertical sides to spread on the road, and hence cause damage to the vehicles.