In this post, we are going to detail discuss the practical and theoretical concepts of repair and maintenance of Earth Roads, Gravel Roads, W.B.M. Roads, Bituminous Roads.
Repair and maintenance of Earth Roads
In general, it may be stated that the surface of earth roads be easily disrupted and more often than other types of roads hence, the earth roads will require frequent maintenance. Following are the usual damages noticed on earth roads:
- formation of dust in dry weather;
- formation of cross ruts along the surface after the rainy season due to surface water; and
- formation of longitudinal ruts along wheel path of slow moving vehicles.
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For the purpose of convenience, the maintenance of earth roads can be grouped in the following two categories:
(1) Normal maintenance
(2) Preventive maintenance.
(1) Normal maintenance:
The items to be attended in normal day to day maintenance are as follows:
- Damaged road surface
- Road surface proper
- Side drains
- Stumps and rocks.
(i) Damaged road surface:
The ruts, potholes, etc. formed on the road surface should be repaired as early as possible. The delay in repairs would cause obstruction and inconvenience to the traffic and it may also lead to heavy repairs subsequently. A regular pattern is cut along the damaged portion up to the depth of the pothole and it is filled up with the same type of soil and compacted thoroughly. If a large portion of the road surface is damaged, the entire pavement is resurfaced with the help of suitable mechanical equipment.
(ii) Road surface proper:
During normal maintenance work, the camber and side slope should be checked and if found defective, they should be suitably rectified.
(iii) Side drains:
The side drains of earth roads are not lined and hence, it is very important to clean them frequently during the process or normal maintenance.
(Iv) Stumps and rocks:
It sometimes so happens that during the earth work compaction, harder materials like boulders, bricks, timber pieces or stones get mixed up with earth and form part of the pavement. If such materials are noticed during normal maintenance, they should be immediately removed.
(2) Preventive maintenance:
The purpose of preventive maintenance of earth road is to take such measures beforehand so that the cost of subsequent maintenance is reduced to a great extent. Following are the two ways in which preventive measures can be taken:
(i) Control of moisture content
(ii) Restricting traffic after rains.
(i) Control of moisture content:
The increase or decrease of moisture control seriously affects the stability of earth road surface. Depending upon the climatic conditions, suitable measures should be taken to maintain the desired degree of moisture in the pavement. It will also help in controlling the dust nuisance.
(ii) Restricting traffic after rains:
It is evident that the surface of earth roads will become soft during rains and if heavy vehicles are allowed to move on such surface, considerable damage would occur to the surface. Hence, at places where it is possible to restrict the flow of heavy traffic for a few hours after rains, the earth roads would be maintained in a better way. The road barriers may be used at either end of the road for this purpose.
Repair & Maintenance of Gravel Roads
The maintenance of gravel road surface consists in keeping it smooth, free from ruts, etc. by repairing the holes and ruts as they are formed and replacing the lost materials. It can thus be classified in the following two ways:
(1) Normal repairs
(2) Periodical renewal.
(1) Normal repairs:
The normal repairs of the gravel road consist of the following two items:
- Repairs to pot holes and ruts
- Upkeep of surface.
(i) Repairs to pot holes and ruts:
The pot holes and ruts should be repaired as soon as they are formed. If this precaution is not taken, the subgrade structure of the road gets damaged due to the seepage of water and it may lead to large scale repairs and inconvenience to traffic.
(ii) Upkeep of surface:
The surface camber must be correctly maintained and it should be seen that no stagnant pools of water are formed on the carriageway in the rainy season.
(2) Periodical renewal:
If a fairly long stretch of road length, say 1 km or more, is badly damaged, it should be renewed. If a suitable diversion is available, the entire width of road may be taken up for renewal. Otherwise the work may be carried out in two half widths, one half being left for the traffic.
The surface is scarified or cut up to a depth of 80 mm or up to the depth of ruts, whichever is large. The material thus removed is screened and reused along with fresh material and it is compacted by rolling with light road roller.
Sometimes calcium chloride, sodium chloride or bituminous material at the rate varying from 30 kg to 90 kg per m² of road surface may be used for achieving the purpose of dust prevention and stabilization.
Repair and Maintenance of W.B.M. Roads
The W.B.M. road surface deteriorates mainly because of the following reasons:
(1) Fast moving vehicles: The fast moving vehicles will loosen the interlock between finer particles and the road metal is broken. The finer particles are then carried away by the wind.
(2) Grinding of stones: Due to abrasive action of steel tyres of bullock carts, the grinding of stones takes place and it results in bad shape of the road surface.
(3) Hoofs of the animals: The pounding effect of the hoofs of the animals cause the dislocation of stones and soft pieces are formed. These finer particles are then carried away by the wind.
The maintenance of W.B.M. roads can be grouped in the following two categories:
(1) Normal repairs
(2) Surface renewal.
(1) Normal repairs: The items to be attended in normal repairs are as follows:
- Cleaning of surface
- Repairs to pot holes and ruts
- (iii) Replacement of blindage.
- (i) Cleaning of surface:
The finer particles lying on the wearing course of road should be swept aside regularly and stacked separately on the berms in the form of small stacks. The sweeping process is done by the maintenance road gang. Similarly the mud formed on the surface should also be removed because it makes the pavement slippery during rains and may cause serious accidents.
- (ii) Repairs to pot holes and ruts:
The patch repair is continuous work and it is generally carried out by the maintenance gang. The damaged portion due to pot holes, ruts or depressions is marked in a rectangular shape and it is dug out upto the affected depth. The entire area is then cleaned and filled with water for 3 to 4 hours before packing. The excavated material is cleaned, screened and reused in such a way that stones of large size are placed at bottom, those of medium size in the middle and those of fine size at the top.
The metal is then compacted with hand rammer by using plenty of water and the compacted surface is kept about 10 mm above the general pavement surface to allow for settlement under subsequent traffic. The repairs to berms and shoulders are also carried out by replacing the displaced earth and compacting the same with usual precautions.
- (iii) Replacement of blindage:
The loss of blindage or covering material should be met with from time to time. Blinding of the surface shall be resorted periodically as soon as the blinding material applied earlier has been eroded away due to a traffic or weather action and the surface has started showing signs of ravelling. Blinding operations shall consist of application of blinding material in thin layers and grouping. For this purpose, the road side screenings collected during sweeping along with fresh blindage are mixed, relaid, watered and rolled.
(2) Surface renewal:
W.B.M. wearing course shall be renewed when the surface is worn out, is corrugated and badly ravelled or has a profusion of potholes and depression which cannot be treated economically with patching or blinding operations.
For renewal, the existing surface shall be scarified to a depth of 50 mm to 75 mm and the resulting material removed to berms for screening to salvage and usable course aggregates. The exposed pavement shall be scarified again at high spots so as to ensure proper grade and camber.
The salvaged coarse aggregates mixed with sufficient quantity of fresh aggregates shall then be used to construct a new W.B.M. coarse.
Repair and Maintenance of Bituminous Roads
The maintenance of bituminous roads naturally varies over an extremely wide range of processes because there are large varieties of bituminous materials and numerous forms of constructions. The surface treatments and carpets are themselves maintenance operations.
However, the selection of repair techniques involves a comparison of techniques ranging from patching to overlays or resurfacing. For successful functioning, the bituminous roads require proper and timely maintenance. The maintenance works of bituminous surfaces can be grouped as follows in five categories:
(1) Patch repairs
(2) Preventing skidding of vehicles
(3) Reducing reflection cracking
(4) Stripping and ravelling
(5) Waves and corrugations.
(1) Patch repairs:
The localized depressions cause pot holes and the patch repairs involve the following operations:
(i) Marking the patches: The affected or damaged surface areas of the road are marked in rectangular shape.
(ii) Cutting and digging: The portion is then excavated till the sound materials are encountered. The holes so formed, are cleaned and applied with primers.
(iii) Filling the holes: In the case of premix pavement, the excavated portion is filled with premix bituminous concrete of the type used in the original construction. If the original 348 bituminous pavement is of penetration type, the excavated portion is filled with stones and then the hot bitumen is poured to fill up the voids.
(iv) Ramming: The filled material is hand compacted by using iron rammers or tamping bars. The compaction may also be accomplished by using portable, hand-operated vibratory compaction plates. The finished level of the patches should be kept slightly above the original level to allow for subsequent compaction under the traffic.
(V) Sand covering: A layer of sand is sprinkled over the finished surface and the repaired surface is opened to traffic after a period of about one day.
Preventing skidding of vehicles:
It has been noticed that poor skid resistance offered by the pavement surface contributes to the large number of accidents on the highways. The presence of materials like clay, dry sand, oll, grease and water on the pavement surface causes skidding. These materials loosen the grip between tyres of vehicles and pavement surface.
The skidding is of the following three types:
(i) Impending skidding: It is encountered when the braking is gradual and the wheel of vehicle continues to revolve
(ii) Sideway skidding: It occurs on curves where sufficient super-elevation is not provided or when the coefficient of friction is inadequate.
(iii) Straight skidding: It occurs in the direction of travel when the sudden brakes are applied.
The skid resistance of highways is substantially increased, if they are properly cleaned and maintained in dry on. If the pavement has become slippery due to the bleeding of surface materials, it is customary to spread blotting materials such as aggregate chips of maximum size of about 10 mm or coarse sand during summer.
It is then followed by necessary rolling for developing permanent bond between the existing surface and the new materials after heating the surface, if necessary.
(3) Reducing reflection cracking:
The methods which are found helpful in reducing reflection cracking of asphalt mixes placed over concrete pavements are as follows:
- pretreatment of the old concrete such as mud jacking. sub-sealing or cracking the old pavement by a heavy rolling or with an hydraulic or pneumatic hammer,
- use of additives such as rubber and other modifications in the composition of the asphalt mix
- use of bond breakers between the concrete and asphalt layers
- wire mesh reinforcement in the asphaltic concrete overlay, etc.
It should however, be noted that there is no known effective method of completely eliminating reflection cracking.
Stripping and ravelling:
The term stripping is used to indicate the separation of the asphalt from aggregate particles in the presence of moisture. It leads to the loss of the matrix of the mix, first by removal of the asphalt binder and subsequently by the loss of the loosened aggregate. The cause of stripping may be attributed either to loss of adhesion or to chemical reactivity.
The term raveling is used to indicate the progressive separation of aggregate particles in the pavement. Usually, the fine aggregate comes off first and leaves small pockmarks on the surface. As the erosion continues, the larger particles are broken free and the pavement surface has a rough appearance.
The cause of ravelling may be attributed either to abrasion by traffic or improper gradation of aggregate or hardening of the asphalt or insufficient asphalt.
The stripping and ravelling lead to the loss of the pavement surface. When the problem becomes acute and serious, it becomes necessary to provide a protective layer in the form of an additional surface coat on the existing surface.
(5) Waves and corrugations:
When waves and corrugations are found on the pavement surface, it is absolutely necessary to investigate the basic reason and to suggest the preventive measure accordingly. This is due to the fact that a leveling coarse applied on the deformed surface without any such deep investigation usually develops waves and corrugations again in a short time.
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