Distresses in Pavement and probable repair remedies

Distresses in Pavements and probable repair remedies

Summary of Distresses

Type of Distress	Symptoms	Probable Cause	Possible treatment
Surface Defects
1. Fatty Surface	Collection of binder on surface	Excessive binder in premix , spray or tack coat, loss of cover aggregates, excessively heavy axle loads	Sand blinding: Open graded premix , liquid seal coat, burning of excess binder, removal of affected area.
2. Smooth Surface	Slippery	Polishing of aggregates under traffic or excessive binder	Resurfacing with surface dressing or premix carpet
3. Streaking	Presence of alternate lean and heavy lines of bitumen	Non-uniform application of bitumen or at low temperature	Application of new surface
4. Hungry Surface	Loss of aggregates or presence of fine cracks	Use of less bitumen or use of absorptive aggregates	Slurry seal or fog seal
5. Bleeding of Asphalt	Slippery	Excess of Asphalt while mixing	Sand blinding
Cracks
1. Hair line crack	Short and fine cracks at close intervals on the surface	Insufficient bitumen, excessive filler or improper compaction	The treatment on depend on whether pavement structurally sound or unsound. Where the pavement is structurally sound the cracks should be filled with a low viscosity binder or a slurry seal or fog seal depending on the widths of the cracks. Unsound cracked pavement will need strengthening or rehabilitation treatments.
2. Alligator cracks	Interconnected cracks forming a series of small blocks	Week pavement , unstable conditions of subgrade or lower layers, excessive overloads, or brittleness of binder
3. Longitudinal	Cracks on straight line along the road	Poor drainage, shoulder settlement, weak joint between adjoining spreads of pavement layers or different frost heaves.
4. Edge Crack	Crack near and parallel to pavement edge	Lack of support from shoulder, poor drainage, frost heave or inadequate pavement width.
5. Shrinkage Cracks	Cracks in transverse direction or interconnected cracks forming a series of large blocks	Shrinkage of bitumen layers with age
6. Reflection cracks	Symptomatic cracks over joints and cracks in the pavement	Due to joints and the cracks in the pavement layer underneath
Deformation
1.Slippage	Formation of crescent shaped cracks pointing in the direction of thrust of wheel	Unusual thrust of wheels in a direction, lack or failure of bond between surface and lower pavement courses	Removal of surface layers in the affected area and replacement with fresh material
2.Rutting	Longitudinal depression in the wheel tracks	Heavy channelized traffic, inadequate compaction of pavement layers, Poor stability of pavement materials or Heavy bullock cart traffic	Filling the depressions with premix material
3.Corrugations	Formation of regular undulations	Lack of stability in the mix, Oscillations set up by the vehicle springs, Faulty laying of surface course	Scarifications and relaying of surfacing's or cutting of high spots and filling of low spots
4.Shoving	Localized bulging of pavement surface along the crescent shaped cracks	Unstable mix , lack of bond between layers of heavy start-stop type movements and those involving negotiation of curves and gradients.	Removing the material upto firm base and relaying a stable mix
5.Shallow depressions	Localized shallow depressions	Presence of inadequately compacted pockets	Filling with premix materials
6.Settlements and upheaval	Large deformations of pavement	Poor compaction of fills, Poor drainage, inadequate pavement strength or frost heave	Where the fill is weak the defected fill should be excavated and redone. Where inadequate pavement strength is the cause, the pavement should be strengthened.
Disintegration
1. Stripping	Separation of bitumen from aggregates in the presence of moisture	Use of Hydrophilic aggregate, Inadequate mix composition in continuous contact with water, Poor bond between binder and aggregate, Poor compaction etc.	Spreading and compacting heated sand over affected area in the case of Surface dressing, Replacement with fresh bituminous mix with added anti-stripping agents in other cases
2. Loss of Aggregates	Rough surface with loss of aggregates in some portions	Ageing and Hardening of binder stripping poor bond between binder and Aggregate, Insufficient binder, Brittleness of binder etc.	Application of Liquid seal, Fog seal or Slurry seal depending on the extent of damage
3. Raveling	Failure of binder to hold the aggregate shown up by pock marks or coded areas on the surface	Poor compaction, Poor bond between binder and aggregate, Insufficient binder, Brittleness of binder etc.	Application of cutback covered with course sand , slurry seal or premix renewal coat.
4. Pot-Hole	Appearance of bowl shaped holes, Usually occurs after rain	Ingress of water into the pavement, Lack of bond between surfacing and WBM base, insufficient bitumen content etc.	Filling potholes with Premix material or Penetration patching
5. Edge Breaking	Irregular breaking of pavement edges	Water infiltration, Poor lateral support from shoulders, inadequate strength of pavement edges etc.	Cutting the affected area into regular sections and rebuilding with simultaneous attention paid to the proper construction of shoulders.

Types

1) Structural failure

        Collapse of Pavement components of such magnitude as to make pavement incapable of sustaining the loads imposed upon its surface.

    Factors Responsible for development of structural distress

    a) Preparation of Foundation

        i) Strength

            Although the bearing capacity of a pavement can be increased by the use of macadam and an asphalt base course , if the foundation has insufficient strength to resist the traffic stresses transmitted through through the surfacing , the whole structure will fail, weak areas in existing paving  may be detected by their typically crazed pattern.

            Other weaknesses in newly constructed flexible pavement may not be easily recognized because they may be due to lack of uniformity in grading, clay pockets and insufficient compaction, the practical method of testing under the conditions is to drive over the foundation of roller , equal in weight specified for surfacing and take note of deflections occurring under load however , a few passes of roller are not equivalent to repetitive loading of traffic. This test cannot be used to identify inadequate design.

            Weaknesses in foundation in whatever form they occur are serious and must be remedied by replacing with sound material or by ensuring that sufficient thickness of pavement is provided in relation to the bearing capacity of Sub Soil.

        ii) Shape

            The composition of mixtures and the thicknesses to which they are laid are inter-related (i.e. as the depth becomes greater , the size of the largest stone increases). To maintain this relationship during laying, the existing foundations has to be within certain limits of regularity, transversely and longitudinally, which may require filling depressions or removal of high spots.

            To raise low areas to correct level it is desirable that material is of same temperature group as the course superimposed. The nominal size of material used to fill in low places will depend on depth to be regulated. It may sometimes be necessary to use two grades in size and 1st large enough to make up for deeper parts of levels.

            The places that are too high to be treated according to extent to which they occur scarifying or breaking out with compressor are suitable methods for localized peaks.

        iii) Permeability

            When the foundation is porous and proposed surface is open in texture there is an easily accessible avenue for water percolation and thus weaken the whole structure by attacking the subgrade. To avoid such phenomenon Proper surface dressing is important.

        iv) Compaction

            i) The mixtures will not behave satisfactorily under traffic unless they are correctly compacted. Compaction through the pressure applied by steel wheeled and rubber tyred rollers reduces the voids. Under the compacting surface the bitumen acts as a lubricant between the aggregate particles and so assists in packing them together. Thus the controlling factor is primarily the viscosity of the binder at the rolling temperature, although by comparison with the considerations of viscosity in mixing processes, this may be a more complex mechanism particularly when a material contains a high filler content. This is because one of the effects of adding filler to a mixture is to stiffen the binder and so alter its viscosity behavior. The ease or difficulty with which a mixture may be compacted is also related to the characteristics of the aggregates consequent upon its particular shape and texture.

            ii) The attainment of a given standard of density shall be prescribed for mixes through vigorous lab testing.  Asphalt concrete can seriously fall short of the specified criteria unless compacted to produce a finished paving within the stated limits of density and void contents.

            iii) Any attempts to specify the number of rollers as a straight forward relationship to tonnage or area laid in a given time is misleading. The ruling factor lies in temperature at which material is rolled and this takes on a different perspective according to the material being compacted. For example, in mixtures containing penetration grade binders, particularly of the harder variety as in rolled asphalt there will be noticeable effects as the temperature falls, whereas loss of host is of negligible importance in a cold asphalt made with a fluxed binder The relationship between rolling temperatures and binder's consistency shall be determined from trial patches.

            iv) The rate at which heat is lost in materials, that cool as they are laid depends on variables such as the course thickness, wind conditions and the air temperature. The result of raising laying rate is to increase the area exposed to the effect of atmosphere. Consequently, there is a relationship between the laying rate. the number of rollers and correct compaction. Sufficient capacity in terms of machines must therefore, be provided to ensure that the first compacting effort is given to the material while it is within the specified limits of temperatures.

            v) The procedure by which rollers are used depends on the type of machines although there are certain common rules, conductive to good workmanship. Apart from circumstances such as rolling transverse joints, the roller should move longitudinally in a series of forward and reverse passes with each pass slightly over lapping the other so that the area is progressively covered. By varying the length of each pass the chances of leaving a marked difference in the surface are reduced because the reversed points will not be in the same place. Smooth acting clutch operation is essential to avoid surging when reversing. If the roller is allowed to stand on material that is not completely compacted, the wheels will indent the surface and it may be difficult to remove the imprint. This default will be avoided it movement is as continuous as possible and if it is necessary to stop rolling by diving the machine on to work that has reached a state of compaction that will not be marked by a standing load.

            vi) Where compaction is specified qualitatively, a rolling procedure can be established by field trials followed by tests on samples cut from the finished work. Apart from considerations mentioned previously in connection with temperature and the first pass of the roller, compaction should be continued until the surface shows no further reaction and is uniform in texture.

            vii) The three wheeled roller is driven so that its rear rollers pass over the work first if these rollers are too narrow[less than 45cm in width for a road roller] or the weight distribution is uneven, the risk of indentation which will be difficult to remove, is high. On this type of roller co overlapping of the passes is important and on high temperature materials, the longitudinal runs should not be extended beyond a point where the machine leaves the wheel marks which cannot be removed as the temperature of the mixture falls.

    b) Shear

            Shear failures exist when cohesion and internal friction are lacking in the pavement base structure. Upheaval accompanied with wheel path depression is its basic characteristics.

            It may be caused due to poor shear strength of pavement mixes.

Upheaval outside the tyre tracks and subsequent cracking of the bituminous surface is peculiar. The shear failure normally exists in the subgrades and a small amount of movement outside the pavement and in the shoulder may result. The type of distress in such a case is illustrative of the need for proper shoulder design to reduce edge failures of flexible pavements.

        Edge Breaking :- 

                Pavement edges getting broken due to lack of shoulder support or heavy tracking at pavement edges.

        i) Longitudinal cracks

            Single or multiple cracks in longitudinal direction.

            Movement of a flexible pavement can also take place essentially in horizontal direction because of lack of internal friction the base or subgrade or their differential settlement of very plastic subgrade. The pavements built over fine sands can reflect longitudinal cracks which in future gets open up and permits infiltration.

    c) Consolidation

            Surface distortion can be caused by consolidation of one or more paving layers. Rutting can be  observed on pavements which are under designed in so far thickness is concerned. The Consolidation takes place in Subgrade and to lesser extent in base course itself.

            It is observed that ruts are somewhat wider than the tyres, which indicates that consolidation took place in the surface or base. Trenching of the roadway section indicated that the primary consolidation took place in Subgrade.

    d) Cracking

            Causes of Cracking

                1) Structural Failure

                    a) Rutting:- Depression in wheel path without upheaval in adjacent area.It may caused due to Consolidation of beneath layers.

                2) Rolling too hot

                3) Excessive use of water on roller wheels

                4) Reflection from underlying layers

                5) Fatigue damage

            i) Cracking Without Pattern

            ii) Cracking of Unstable Mix

            iii) Reflection cracking

                    Reflection of cracks from semi-rigid or rigid base, but generally regular in occurrence. It is caused due to reflection of cracks from underlying layer.

            iv) Alligator cracking

                    Class I :- Cracks in more than one direction joined with each other to form map pattern. Crack edges are not raised or spalled or there is no rocking under the load.

Cracks edges Not raised , Type 1

                                It may caused due to Fatigue of surface with excessive resilience from base and subgrade.

                    Class II :- Cracks in more than one direction joined with each other to form map pattern. Crack edges are raised or spalled and pieces rock under the wheel loads.

Cracks edges raised , also filled with water , Type 2

                                It may caused due to Pavement in serious distress, excessive movement of underlying layers or pavement is structurally in adequate or by shrinkage of some soils in very cold weather or by swelling and heaving in soils with such index properties (Example is Black Cotton soil, shrinkage and swelling indices are around 300%).

        It seems logical to apply crack filler or slurry , it is recommended that a careful observation be made for atleast one complete cycle of season before taking corrective action.

    e) Adverse Ground water conditions

            Pavement distress can result from adverse ground water conditions which in turn result in subgrade weakening, Instances of pavement which has proved satisfactory over a major portion of its service, but localized failures are apparent at the road inter sections where ground water seep in to the pavement structure causing deterioration of the wearing surface are moving. The remedy for the condition requires removal of water near its source, Minor resurfacing will not aid the situation for any length of time since the adverse condition is always present and the pavement distress will soon reappear.

Pot-Holes :-

    1) Isolated Pot-Holes

         Potholes at isolated locations not associated with other failure modes, caused due to 

        a) Local distress

        b) Local Soft spot

        c) Local locking up of water

Water runs through ravelled area and stored in Local pothole

    2) Pot-Holes associated with cracking

         Potholes associated with alligator cracks , cracked pieces getting removed under traffic, caused due to 

        a) Pavement in severe distress

        b) At its last phase of life

        c) Structurally inadequate

        d) Lack of Binder

        e) Excessive openings in the mix permitting moisture to gather

        f) Traffic Causing breaking down of bond

        g) Poor Drainage

        Pot-Holes are most dangerous of failures and should have immediate attention. The pot hole is allowed to progress, wheel develop in to a dangerous wheel catcher and a difficult repair job. 

    f) Heating and Drying

            From the working temperature given for the different materials it will be seen that for bitumen macadam and cold asphalt it is necessary to control the temperature of the aggregate in relation to the consistency of the binders used, Further more the aggregate temperatures are in some instances below that at which water can be removed by heating. By comparison, rolled asphalt does not make these demands.

            The circumstances under which the aggregates are stored before drying will have some influence on this part of the process, Material stock field and exposed to rain will clearly represent the worst conditions. Aggregates routed through a crusher direct to screens, storage hopper and then a mixer will below in moisture, Slag cooled by the ladle method may even retain sufficient heat for low temperature mixes Gravel sand taken from a wet or passed through a washing plant will naturally be difficult to heat and dry. As such aggregates form the greater part of a mixture, poor temperature. control can radically affect the quality of finished paving.

    

2) Functional failure

        It may not be accompanied by structural failure but is such that the pavement will not carry out its intended function without causing high stresses in roads and Vehicles which passes over , due to its roughness.

    Functional failures

        a) Surface Defects

            i) Segregation

            This may be result of poor mixing and rolling technique but can also be caused during laying particularly through excessive hand work with rakes and Forks. The effect is not only unsightly but in addition areas of differing density and permeability are produced.

            Some mixtures are more prone to segregation than others both in transit and laying. Cold asphalt with correct binder content will display hardly any such behavior whereas rolled asphalt base course with gap graded stone content of 70% can be highly susceptible.

            The distributing screw on a paver assists in remixing segregated material but it is doubtful if this will mix the Mixture to the same degree of uniformity as it left the mixer, parts of mix segregated in transit should be shoveled in to the centre of the hopper and allowed to flow with largest volume of material possible.

            ii) Dragging

            Dragging appears as an openness in texture occurring laterally across the strip. Material laid too thinly for the maximum size stone will lack sufficient thickness required for compaction and surface will drag.

            If the dragging is continuous on a mechanical paver and is not due either to thickness or temperature, the forward speed is probably too fast for the material being laid, closely spaced drag marks can often be remedied by higher tamping frequency.

            iii) Weathering

                        Manifestation :- Surface appearing dry and bitumen seems oxidized

                        Cause/Mechanism :- Too old surfacing or use of less bitumen

            iv) Bleeding

                        Manifestation :- Surface appearing rich in bitumen , free bitumen on surface particularly in wheel paths.

                        Cause/Mechanism :- Too much bitumen in mix, Use of soft grade (Low Viscosity) Bitumen.

        b) Accumulation of binders

            Accumulation of binder resulting from layers of surface dressing or the nature of existing foundation material can flush through the new paving and have a softening effect leading to the deformation. The excess binder can be removed by heating and planing after which the traffic should be allowed for the use the surface for short time before the new paving is applied.

        c) Joints Failures

            Joint filling compounds which have extended above their original level or have been badly filled will certainly aggravate the problem of reflective cracking. In severe cases the compounds should be removed from the joints and the gap filled with finely graded material compatible with the proposed over layer.

        d) Adhesion failure

            

            If a mixture is laid on a wet surface or on contaminated with foreign matter or Excessively smooth there is danger that under the action of traffic, the surface will not bond but slip or in extreme cases be removed. Where such conditions exists a key has to be provided between the foundation and the over layer.

        e) Failure due to Temperature issues

            In case of Low viscosity bitumen of 'base course' care shall be taken while laying hot Surface course which can mobilize base course due to its high temperature. 

            The difference in cooling of Aggregates and Bitumen causes stripping of Bitumen.

            When matching existing strip the joint should be overlapped slightly. This should be done with care and with just sufficient material to knit the joint neatly. If the overlapped joint is too much the matched joint will be scarved. This will be more noticeable on macadam mixtures where the fine aggregates particles will be forced into the voids of the adjacent lane and leave a permanent difference in texture at the joint.

            A common fault in hand laid work is tendency for the surfacing to become divided into series of sections, each of which is bounded by area in which man is working if the skill of operative varies this will obviously be reflected in a standard of finished work.

        f) Roughness

            When surface shows signs of roughness it is probably that it has been incorrectly rolled.

            This may be related to temperature effects particularly on materials sensitive to cooling. On a mechanical Paver uneven wear or improper adjustment along the tamper can produce variations in texture some of which may be rough.

            By allowing the severed plate to corrode with the old material the surface can be finished unevenly which will cause rough appearance.

        g) Ravelling

            Aggregates both course and fine getting out of the pavement and getting collected in the areas other than wheel paths.

Causes

        1) Stripping abrasion by traffic

        2) Degradation of aggregates

        3) Insufficient bitumen

        4) Bitumen oxidation

Causes of Pavement Distresses

1) Overloaded vehicles

2) High repetitions of Loads

3) High Tyre pressure

4) Climatic & Environmental Conditions

        a) Heavy Volume change in soil due to wetting and drying

        b) Break up resulting from Freezing and Thawing

5) Improper drainage

        The greatest single enemy of any pavement structure is a saturated sub-grade. This condition must be prevented as far as possible, so that maximum stability of pavement structure is maintained.

6) Disintegration of Paving materials

        Base materials can breakdown generating fines resulting in unstable mix as well as Loosing " Intergranular locking".

        once The pothole formation process gets starts, the quinscent load action produces excessive stress on underlying materials.

Stress produced 

$${\sigma_1}=\sigma\sqrt{{2h}\over e}$$

Where,

$${\sigma_1}={\text{Stress due to Quinscent Load after falling from height 'h'}}$$

$${\text{In some cases in terms of velocity 'h' can be expressed as;  h}}={{V^2}\over {2g}}$$

$${\sigma}={\text{Quinscent Load stress}}$$

$$e={\text{Deformation due to Quinscent Load}}$$

7) Construction Practices

        Rutting of Subgrade during construction which permits accumulation of water and subsequent softening of the subgrade after the construction may cause permanent distress.

        Use of Dirty aggregates and inadequate inspection during construction may cause deterioration hence design procedures therefor must be accompanied by stringent inspection and field control in order to provide adequate strength to pavement structure.

8) Lack of maintenance

        Sealing of cracks and Joints at proper intervals will insure a water tight wearing surface as a provision against surface infiltration of water, the case why Open Graded Carpets must be sealed by Seal Coats.