Asphalt roads are continually exposed to different types of stresses leading to asphalt deterioration over time. Heavy traffic, temperature, humidity, and dislocation of bed soils occurring for a variety of reasons may cause stresses to roads. Asphalt pavements may undergo various types of deterioration, which will ultimately lead to asphalt wear and tear at times that depend on the quality of asphalt and infrastructure. Cracks, puddles, subsidence, and other types of deteriorations may appear at the asphalt pavements.
In general, not all deteriorations occur on all pavements and the type of deterioration depends on environmental factors and the volume and type of traffic. For instance, low-temperature cracks are not seen in asphalt pavements in warmer climates. In highways and freeways with a huge volume of traffic, grooves and skid marks are prevalent, while such deteriorations usually do not occur in the parking pavements.
There may also visible one or more types of deteriorations at varying severities. Asphalt deteriorations vary from surface defects to failures that can lead to rupture of the beneath layers. Most pavement deteriorations can be repaired and restored if detected early, which prevents a remarkable shortening of the pavement life. Early identification of defects and their timely repair prevent wider deteriorations and asphalt wear and tear. Early detection of deteriorations helps to easy identification of underlying factors and techniques needed for asphalt restoration.
In all maintenance procedures, the best way is to discover the underlying cause of deterioration. This will help to adopt the right technique of repair and elimination of deterioration. Therefore, identifying deterioration is the first step to any pavement maintenance program. A formal and pressing program for the cyclic pavement inspection to identify deteriorations is key to the success of any road maintenance program. Pavement and road inspection and repair programs are known as the pavement management system or plan. This program or system is applicable to all types of pavements, from parking lots and low traffic roads to highways and high-traffic roadways. A comprehensive pavement management program covers data collection and evaluation of asphalt pavement characteristics.
Evaluation of pavement properties includes the study of road roughness, surface damage, sliding resistance, and pavement properties. Initially, visual inspection is practiced to grade the road status for deteriorations.
Deteriorations can be graded by severity as low, medium, and high, or using a numerical scale grading from one to 10. The visual inspection gives a picture of the pavement and can be employed to make the right maintenance and repair decisions. The Pavement Surface Evaluation and Rating (PASER) system is a simple pavement inspection and management plan that is available to road maintenance engineers and specialists.
A typical PASER plan includes the following main components:
• A list of all local roads, streets, and parking lots
• Cyclic assessment of the situation of all pavements
• Prioritization of projects according to pavement conditions, and the choice of appropriate operations to repair (if necessary)
The key element of PASER plans is to identify different types of pavement deteriorations and determine underlying factors. Recognizing factors causing the deterioration in the pavement makes it feasible to employ appropriate repair operations and strategies.
Asphalt pavement deteriorations can be classified into four main groups:
• Surface defects (granulation of asphalt layers and pebbles bouncing off the wheel wells, oxidation, polishing, and pavement bleeding)
• Surface deformation (grooves, ripples, subsidence, and swelling)
• Cracking (transverse, longitudinal, reflective, mosaic, and crocodile cracking [alligatored asphalt])
• Granulation and pebble bouncing
Granulation or abrasion is the gradual detachment of stone materials from the pavement surface, which can be caused by bitumen removal and oxidation. Asphalt aggregate particle displacement by traffic loads or stresses caused by water freezing leads to tensile stresses and strains in asphalt that may exceed the adhesion resistance of bitumen. Peebles bouncing or low or medium-intensity granulation will separate only a small portion of fine-grained rock material, but in high-intensity granulation, coarse rock materials are additionally removed from the surface.
Granulation is the product of moisture or bitumen membrane separation from and around the aggregates, bitumen oxidation, poor or low density of asphalt layers during the operation, or a low volume of bitumen in the asphalt mixture. Peebles bouncing and granulation usually occur more often in cold or humid climates. Granulation within the road surface due to heavy traffic loads will usually be more severe in cold weather and under higher bitumen strengths. Granulation can further happen due to the wear of wheels or the spread of sand and salt to prevent freezing, which is more obvious in intersections and parking lots. Oil, diesel, and gasoline spills are additional common causes of intermittent granulation in parking lots. Granulation is classified by severity as follows:
Low severity: Fine-grained stone materials or bitumen start to separate from the surface. Under this situation, the upper parts of the coarse aggregate are exposed to the air and are gradually removed from the pavement surface.
Moderate severity: Further erosion leads at least one-third of the diameter of coarse-grained aggregates to protrude from the pavement surface. The texture of the road surface is rather hard.
High severity: A substantial portion of fine-grained rock materials are separated from the road surface and coarse-grained rock materials start to be excavated. The road surface is extremely eroded.
Puddles leading to asphalt deterioration are divided into two main environmental and structural groups.
Environmentally-occurred stresses are due to oxidation, moisture, and aging, while structural stresses are mainly due to heavy traffics. Pavement deterioration usually occurs due to heavy traffic and weathering. Defects and surface deteriorations include pebble bouncing, bitumen bleeding, bitumen oxidation, and polishing. This type of deterioration occurs on both low-traffic and high-traffic roads.