Cracks in the asphalt
Mosaic crack (lizard skin) in asphaltine, the cracks are also called lizard cracks or snake skin due to their resemblance to the skin on the back of a lizard's body. This type of failure appears with the cracking of all or part of the surface of the asphalt surface in the form of relatively small polygonal pieces, and the extent of the failure is usually increased by repeated loading.
The cause of mosaic cracks is excessive deformation of the pavement layers due to loading, or excessive fatigue of the top layer due to the loads applied to it. Pavements that are built on soils with low resistance and high deformability usually crack in this way.
Also, if the base and sub-base layers do not have the necessary resistance due to insufficient compaction, it may cause mosaic cracks to appear. In cases where mosaic cracks cover all or a large part of the pavement, the cause is usually excessive fatigue of the asphalt surface under the effect of heavy vehicles.
To repair mosaic cracks, if the damage is localized and occurs on a relatively small surface, the damaged part of the pavement must be repaired using a deep patch. If damage is observed in a large area and length of the top surface, the cause of the damage is the insufficient bearing capacity of the pavement, and to strengthen it, an asphalt coating layer with sufficient thickness should be used.
Lizard skin cracks have the following severities:
Lizard skin crack with low intensity (L) in asphalt, parallel and fine longitudinal cracks, which are still limited to a small number of transverse connection patterns. There is no asphalt peeling in lizard skin cracking.
Lizard skin cracking with medium intensity (M) in asphalt, the formation of a network of lizard skin is clear, but the creation of pits and the loosening of asphalt parts have rarely happened.
Cracking of lizard skin with high intensity (H) in the asphalt, creating holes, loosening and corrosion of the surface can be observed periodically on the surface of the lizard skin, and also after rains, there is a possibility of mud and mud spreading in the cracks. is a lot
Shear (side) cracks in asphalt Shear or side cracks are called cracks that are parallel to the longitudinal axis of the road and at a short distance from the edge of the pavement. Possible shear cracks
In addition to the longitudinal cracks, there are also transverse cracks.
Transverse cracks usually cut one or more longitudinal cracks and lead to the edge of the pavement.
The cause of shear cracks is the lack of stability and shear strength of the soil or pavement side materials.
Other examples of this damage can be seen in cases where the road is built on embankments with high and unstable slopes. Shear cracks also occur in cases where shoulders are not properly designed and constructed, or the pavement is basically devoid of shoulders.
In order to repair damage caused by shear cracks, before proceeding with the repair of the cracked surface, efforts should be made to fix the cause of damage, i.e. consolidation of soil and unstable materials from the sides of the pavement. If the cause of failure is insufficient compaction of the soil on the sides of the pavement, its specific weight should be brought to the required level by compacting the soil.
In cases where shear cracks have occurred due to the lack of shoulders, it is necessary to build shoulders by using appropriate materials to strengthen the sides of the pavement.
After fixing the cause of the damage, then by removing the unstable parts of the pavement and filling it with hot asphalt concrete, the surface of the damaged and possibly settled parts of the pavement should be brought back to the original level before the damage. This operation is usually possible by patching.
Shrinkage cracks in asphalt
Cracks that occur due to the volume change and shrinking of the asphalt layer due to the drop in ambient temperature are called contraction cracks. Shrinkage cracks are usually transverse and sometimes appear in the form of a series of interconnected cracks that form large pieces.
In the latter case, the apparent difference between these cracks and mosaic cracks is that the contraction cracks divide the top surface into larger parts and the corners of these parts are also sharper.
The cause of shrinkage cracks is the use of bitumen, which is hard for the climate of the region. To repair this type of damage, the cracks must first be filled with bitumen or bitumen containing fine sand and gravel (depending on the width of the cracks) and then, if necessary, covered with a thin layer of pavement.
Cracks between two lines in the asphalt
These types of cracks are actually the longitudinal seams between the road lines that have been opened due to the incorrect implementation of the asphalt procedure. The entry of water in these cracks will aggravate the damage and make them more open.
The cause of cracks between two lines is the non-simultaneous implementation of the asphalt procedure of adjacent lines.
Because after spreading and pounding the asphalt of the first line and then the line next to it, a seam will appear between these two lines, which will cause damage in the future.
This type of damage can also occur between the side line and the asphalt shoulder of the road. The cause of its occurrence, like what was said about the crack between the two lanes, is the simultaneous implementation of asphalt on the side lane and the shoulder of the road.
To avoid this failure, it should be tried as much as possible to spread and pound the entire width of the road simultaneously by using a sufficient number of asphalt spreading machines.
To repair the cracks between the two lines, these cracks should be filled with bitumen or bitumen containing fine sand and pebbles to prevent water from entering the crack and thus into the pavement.
Reflective cracks in asphalt
Reflective cracks are called cracks that appeared on the surface of the asphalt coating in places where there were cracks on the surface of the old pavement. These cracks are actually the reflection of the cracks of the bottom layer in the asphalt coating layer.
Reflective cracks often appear on the surface of asphalt pavements that are built on concrete pavements or cement-reinforced materials. These cracks also appear on the surface of the asphalt pavement that is built on the asphalt pavement with wide cracks and not repaired.
The reason for the occurrence of reflective cracks is the horizontal and vertical movements of the layer located under the asphalt coating. These movements occur due to changes in humidity and temperature of materials in pavement materials, as well as due to the passage of heavy vehicles.
To repair reflective cracks, these cracks must be filled using bitumen or bitumen containing fine sand and pebbles.
Crescent (sliding) cracks in asphalt Crescent cracks usually appear in the path of vehicle wheels due to the introduction of strong horizontal forces (braking) on the surface of the asphalt surface.
The reason for the formation of these cracks is the lack of sufficient adhesion between the asphalt top layer and the layer below it.
The presence of substances such as dust, petroleum oils or water, which may be present on the road surface due to inaccuracy before the implementation of the asphalt procedure, can lead to the formation of these cracks.
Failure to use surface coating between the lining layer and the asphalt top layer can also cause it to occur Hallelian cracks are formed.
The most appropriate way to repair this type of damage is to dig out the damaged part and use hot asphalt concrete to patch the surface.
Deformation of the top surface in asphalt
Sitting the carved place in the asphalt
This failure is referred to the settlement that is created in the place where the pavement is carved for the passage of water and gas pipes or telephone cables and the like. The cause of this failure is the lack of sufficient density of the materials used to fill the excavated place again.
To prevent this failure, the carved areas should be filled with suitable materials immediately after the operation is completed and compacted well, and then its paving should be done using hot asphalt concrete.
It should be noted that the thickness of the asphalt surface of the restored place should not be thicker in any way
The top of the adjacent parts should be less. To repair the damaged area, the damaged part should be filled with hot asphalt concrete and compacted well.
The thickness of the asphalt concrete layer used should be such that after compaction its surface is slightly higher than the surface of the rest of the pavement. Compliance with this point makes the final level of the part
It has been restored after it was subjected to the traffic of cars, and the level of the rest of the pavement will be paved.
But it should be noted that this level difference should not be such that it does not disappear and remains in the form of a bulge (fish pollen), because then this bulge itself will cause the surface of the pavement to be uneven.
Waves in the asphalt
This failure occurs in the form of a wave in the direction of the movement of vehicles on the surface of the asphalt surface. Asphalt pavements, whose top layer materials are not properly designed and selected, as a result, do not have sufficient shear strength, are damaged in this way.
Waves occur in places where strong shear forces are applied to the pavement. Strong shear forces are usually applied near intersections where vehicles stop or start from a standstill, or at speed change locations, by vehicle wheels to the pavement.
It is entered.
The cause of the wave is usually one or a combination of the following factors:
- A) excessive consumption of bitumen in asphalt mixture.
- b) Using bitumen that is too soft for the climate of the area to be used.
- c) Excessive consumption of fine-grained materials in asphalt mixture.
- d) The presence of a large amount of rounded corner materials in the asphalt mixture.
- e) Not aerating the asphalt mixtures that are made from soluble bitumen.
To repair this type of damage, in cases where the extent of the damage is small and the intensity of the waves is high, it is necessary to remove and remove the damaged part of the top completely. In this case, the excavated area should be filled with warm asphalt concrete.
In cases where the extent of the damage is relatively large and the intensity of the waves is low, a thin layer of asphalt coating should be used to fix the damage.
Wheel tracks (grooving) in the asphalt
The pit of the wheel track is called a transverse wave that occurs on the surface of the asphalt surface. The pit points of these waves are located in the tracks of the wheels of heavy vehicles. The cause of wheel track pitting is the consolidation of pavement layers or road bed soil.
The amount of wheel track pitting depends on the severity of the damage, and the more heavy vehicles there are, the more severe the damage will be. The amount of pitting of the wheel track can be observed by placing a long metal or wooden bar across the road and measure it.
This failure may also occur as a result of lateral movement of asphalt materials in the direction perpendicular to the movement of vehicles. In order to avoid this type of failure, the issues and problems of road pavements in Iran should be investigated, the technical specifications of pavement materials should be selected in such a way that they have sufficient endurance and stability.
The stone materials used in asphalt mixtures should be broken and the use of stone materials with rounded corners should be avoided. It is also necessary to avoid using excessive amounts of bitumen and fine-grained materials that reduce the strength of the mixture.
To repair the potholes of the wheel tracks, the potholed areas should be filled with warm asphalt concrete, and if necessary, covered with a thin layer of asphalt pavement.
local seating in asphalt
Local settlement is said to be a failure in which a relatively limited part of the pavement is lower than the other parts of the pavement due to settlement. This failure may occur with or without the appearance of cracks.
The local settlement is felt by the occupants of the vehicles that pass over it, and its location by the water that immediately after the rain usually investigates the issues and problems of road paving in Iran.
In other cases, local subsidence can be recognized by the difference in color between the subsided area and other parts of the pavement due to the effect of water.
The cause of local settlement is the settlement of bed soil or pavement materials that are unevenly compacted.
To repair this type of damage, the sitting area must be filled and compacted using hot asphalt concrete.
Swelling in asphalt
Swelling is the rise of a part of the surface of the asphalt pavement due to the increase in the volume of the pavement bed soil or its materials. The increase in soil volume usually occurs for two reasons:
- A) Swelling due to frost.
- b) Swelling due to humidity.
To repair this type of damage, the surface of the pavement must be patched after digging and removing the material of the swollen part and replacing the swelling soil with suitable material.
Crushing and chipping in the asphalt
Holes in asphalt
This damage is called the pits that are caused by the crushing and tearing of part of the surface and foundation of the pavement. Holes usually appear in late winter and early spring.
The reason for this is the high level of soil moisture at this time of the year and as a result the soil resistance is low.
The pavement is provided by the base and sub-base layers and the soil is more severe.
Other factors that are effective in the formation of holes are:
- A) Insufficient amount of bitumen used in the asphalt mixture.
- b) Using too much or too little amount of fine-grained materials in the asphalt mixture.
- c) Absence of proper drainage system.
The basic method of repairing this type of damage is that after cleaning the hole from foreign materials, water, and loose grains of materials, the inner surfaces and the bottom of the hole must be sprayed with bitumen and then these holes are filled with hot asphalt concrete and be condensed
Separation of grains in asphalt
This damage usually starts from the sides of the pavement and progresses towards the inner parts of the asphalt surface, it has different causes, which are:
- A) Implementation of asphalt procedure in cold or wet weather.
- b) Insufficient density of asphalt materials.
- c) Using contaminated or less durable stone materials in the asphalt layer.
- d) lack of bitumen consumption in asphalt mixture.
- e) Overheating the asphalt bitumen during its cooking.
To repair this type of damage, the surface of the damaged part of the pavement must be tarred, and in cases where the extent of the damage is large, a thin layer of asphalt pavement must be covered.
The slippery surface of the pavement in asphalt
Bitumen leakage in asphalt
Bitumen extrusion refers to the rising and removal of a part of the used bitumen on the asphalt surface, which is caused by the traffic of cars. The bitumen that comes out of the asphalt material in this way is spread by the wheels of the vehicle as a thin layer on the road surface and causes it to be polished.
The main cause of bitumen swelling, which always occurs in hot weather and under the influence of heavy vehicles, is the presence of an excessive amount of bitumen in the asphalt mixture.
Bitumen extrusion also occurs in mixtures that have less voids than required.
Bitumen spilling is usually associated with other failures, such as waves and dents in the wheel track, which have similar causes.
To repair this type of damage, if the size of the damaged part is small, sand or fine sand is sprinkled on the surface of the road and pounded. Covering the road with a thin and low bitumen layer is another suitable solution to repair this type of damage.
Polishing of grains in asphalt
The grains of stone materials used in the preparation of asphalt mixtures, if they do not have sufficient hardness, their surface may be polished under the effect of abrasives. This may cause accidents especially during rain due to the lack of sufficient friction between the road surface and vehicle wheels.
The cause of this type of failure is the use of rounded stone materials or less durable broken materials such as some limestone in the asphalt mixture. The way to restore the surface of the road whose top layer grains have been smoothed and polished is to use a thin layer of asphalt coating prepared from broken stone materials.
Salt used in snow removal
A traditional way of winter maintenance of roads in Iran has been common ever since it became common, no test or control has been studied regarding its effect on the bitumen used in paving and the adhesion of grains, even its effect on paving stone materials. has not taken
The amount of damages and its economic and social effects reveal the necessity of this study and investigation. The life of the asphalt pavement is specified in the standards and regulations as fifteen years. If it is determined that the type of bitumen or the type of salt and their mutual effects are the cause of the failures, a fundamental change will be necessary to get out of the reliance and emphasize the traditional and harmful way of winter roads.
This development will lead to a drastic reduction in costs and a big step towards solving some of the problems caused by everyday life, even specialized devices with a large number of experts and similar equipment and experiences.
As mentioned, in our belief, either the type of bitumen used in road paving, or the type of salt used in de-icing, or their behavior in action and reaction with each other leads to the destruction of asphalt during a cold season.
In addition to this method of rebuilding the destroyed surface, in different sections of roads and roads, especially in urban areas, it has reduced the durability and effectiveness of the restoration measures in a way that many municipalities have experienced that if the road is repaired only by removing and renewing the asphalt surface. repaired, it will not have significant durability.
Roads and highways are almost everywhere and many marshes, streams and lakes are located next to these roads. These bodies of water are the habitats of many animals and plants, and as a result, any substance we throw on the road affects the lives of the creatures living in the bodies of water. One of these substances is salt.
When winter and snow and storms arrive, rock salt helps keep our roads safe and reduce road accidents. But this salt can have serious negative effects on aquatic ecosystems.
Salt in high concentrations is fatal for some aquatic organisms. Salt can change the way the water layers mix, leading to the formation of salt pockets on the lake bed and creating areas that are considered biologically dead.
As winter approaches, many municipalities turn to sprinkling salt to de-ice roads. These salts are similar to table salt and are composed of sodium and chloride, but they are coarser.
Salt dissolves quickly on the road, leaving chloride that enters surrounding waters through runoff and runoff. Almost all of these chloride ions eventually find their way to downstream waterways. Chloride is toxic to aquatic organisms in high concentrations.
A study conducted in North America shows that salt concentrations in many US lakes will exceed the limits necessary for plants, animals and aquatic microorganisms by 2050.
Canada is also facing a similar problem. Nearly five million tons of salt are sprinkled on the country's roads every year. Many municipalities in Northern Ontario use more than 100,000 tons of salt each year for this purpose.
Meanwhile, some researchers are looking for alternative solutions for salt that are safe and environmentally friendly. Sugar beet effluent – left over from sugar beet processing, brine from the cheese production process, pickle juice and potato extract are some of the unconventional antifreezes that have been tested.
Carbohydrates or sugar present in beet waste reduce the melting point of ice from minus 20 to minus 10 degrees Celsius and are more effective at low temperatures than
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