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Govinda S. Pokharel

Kantipur Daily, 2019d, Muhanai Sukayera CrusherSat Saya Pariwarka Dharama Pani aauna Xodyo, Ramesh Kumar Paudel,Chitwan, 05052019

Pokharel G.S., 2018, Nepal-Bharat Relations, EconomicDevelopment and Cooperation, Neeti Anusandhan Pratishthan

Nepal, NeNAP, pp 107–110Sharma C.K, 1983, Water and Energy Resources of the Himalayan

Block,Statistical Information on Nepalese Agriculture 2073/74 (2016/17),

Government of Nepal, 207p.

Bulletin of Nepal Geological Society, 2019, vol. 36

245

Naresh Kazi Tamrakar

Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal.Email: nktam777@yahoo.com

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Overview on causes of flexible pavement distresses

INTRODUCTIONPavements are floors of solid materials laid to make

convenient ground for walking, vehicular movement, sealingor decorating. Pavements of roads generally have two or threeinternal structural layers between the bottommost subgrade andthe topmost surface layers. These two layers are subbase andbase course and presence of capping layer above the subgradewill make an additional internal layer. The capping layer is laidonly when subrade is of poor quality. Above the capping layerare laid respectively from the lower to the upper portion, thesubbase and the base course. These two layers are the loadbearing structural layer. Besides, these layers have functionsof drainage and preparation of platform for the surface layer.Subbase is laid to increase the thickness of pavement structureparticularly where groundwater table is shallow, or to preventsubgrade material from pumping up to the base course and thesurface layer.

Depending on whether the surface layer placed over thebase course is of concrete or asphaltic mix or muddy ground,the pavements are categorized as rigid (concrete layer), flexible(asphaltic layer) and unbound, respectively. Rigid pavementshave their top layers of concrete (non-reinforced or reinforcedcement concrete) whereas flexible pavements have asphaltic(bituminous mix) surface layers and possess flexibility againstaxle loads. Apart from these, a series of composite pavementsmay occur depending on the binding materials used to treat theinternal structural layers of the pavement to achieve load bearingcapacity, drainage, flexibility, durability, etc. Both asphalttreated base or cement concrete treated base can be found incomposite pavements. The functions of asphaltic layers are toavoid excessive flexing of layers and to provide weather resistantsmooth coating or sealing or to make layer waterproof to prevent

ABSTRACTPavements are structural layers of solid materials laid for convenient grounds for walking, vehicle movement, sealing and decoratiingpurposes. Pavements can be flexible (asphaltic bounded), rigid (portland cement bounded) and composite of both rigid and flexiblelayers. Pavements containing basal structural layers of subbase and/or base course and surface layers withot binding cement of asphaltor cement are considered unbound pavements. Four broad categories of flexible pavement distress after Distress Identification Manualfor the Long-Term Pavement Performance Program are (a) surface cracks, (b) surface deformation, (c) deterioration and (d) matproblems. Causes of pavement distress can be single or composite, and are due to poor material characteristics, poor mix designcharacteristics, and poor construction design, apart from traffic loading and environment of heat and moisture, which are to beconsidered in the construction design. Pavement distress causes have been overviewed. Few examples of distress have been presentedin photos by inspecting the Tribhuvan University road and road of the Manang Colony.

Keywords: Pavement distress, deterioration, disintegration, construction material, flexible pavement

drainage into the internal layers of the pavement structures.Therefore each of the structural layers has some specific functionsto keep pavement durable.

Various factors affect durability of pavement structuresand their performance, and cause pavement distresses. Amongthose are subgrade soil characteristic, pavement materialscharacteristic, traffic loading and moisture and temperatureenvironments. Subgrade (formation) over which a pavementstructure is constructed, bears a crucial role in lengthening alife span of the structure. When subgrade is of low quality, apavement gets flexed easily and excessively causes the pavementto distress severely. Pavement materials characteristics have afundamental bearing on pavement structures. Low qualityconstruction materials and construction quality (improper mixingand placing during construction, failure to adequately compactthe structural layers, and inadequate layer thickness) also affectdurability of pavement structures. Traffic loading, whether itis light or heavy axle loads and frequency of loading, has bearingon pavement performance. Moisture environment duringpavement construction and post construction influences pavementperformance. Moisture entering the structure during upwellingof groundwater table may deteriorate pavements with poorlyconstructed shoulder drainage and poorly selected subbase andbase course (Adlinge and Gupta, 2005; Ragnoli et al., 2018).

Two sites: (a) the Tribhuvan University (TU) Road,Kirtipur, and the road of Manang Colony, Kathmandu (Fig. 1)were selected for facilitating description of pavement distresses.

TYPES OF PAVEMENT DISTRESSESPavement distresses occur due to individual or combined

effects of pavement material quality, subgrade, construction

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quality, traffic loading and moisture environment. Four categoriesof asphalt pavement distresses after Distress IdentificationManual for the Long-Term Pavement Performance Program(Miller and Bellinger, 2003) and Pavement distress IdentificationManual for the National Park Service Road Inventory Program(FHWA, 2009) are: (a) Surface cracking. (b) surface deformation,(c) deterioration, and (d) surface or mat problems (Table 1).Severity levels of some of the distresses are provided in thesame manual (FHWA, 2009).

Surface crackingSurface cracking is phenomenon of development of

surface cracks irrespective of their location of development.Longitudinal (Fig. 2) and transverse cracks are respectively the

cross-running along and across the road. They initiate as widespaced cracks but grow into closely spaced and open severecracks with the passage of time. Both longitudinal and transversecracking may intersect one another to yield more or lessrectangular shaped block cracks. Severity levels of bothlongitudinal and transverse cracks are: Low- cracks with < 6mm width, sealed; moderate-crack width between 6 and 19 mm,adjacent low severity cracking; and high-cracks width morethan19 mm with adjacent random moderate to high severitycracking. Major causes of development of all the abovementioned cracks are generally frost heaving, creeping of ground,flowage of subgrade and settlement, improper construction oflanes, etc.

Fatigue cracks or alligator cracks are a series ofinterconnected irregular polygonal cracks of various stages ofdevelopment (Figs. 3 and 4), due to failure of surface layer orbase course owing to repeated loading. Alligator cracks mayalso form due to defects in base when the drainage conditionis poor, and can develop anywhere on the roadway. Fatigue

Fig. 3: Fatigue cracks (alligator cracks) observed on thestretch of the TU road between Tinkune and the Departmentof Management

Table 1: Types of asphalt pavement distress

Fig. 1: Pavements observed: (a) TU road, Kirtipur, and (b)road of the Manang Colony

TU GateTU ServiceCommission Office

TUAdministrative

Office

Tinkune

NepalBank

Dept. ofManagement

ScienceFacultyBlock

CEDA

Manang Colony

(b)

(a)

Fig. 2: Longitudinal crack as observed on the TU road ofstretch between Nepal Bank and the TU AdministrativeOffice

Overview on causes of flexible pavement distresses

247

heavy traffic load and initially a narrow rutting formed growsinto a wide and deep one. The rutting limited to the surfaceasphaltic layer is indicative of improper mixing proportion ofasphalt and aggregates, while one that grows into deeper layerwith deformation of subgrade is indicative of rutting rooted tothe deformation of poor subgrade (Figs. 2 and 5).

Corrugation is a transverse undulation that appears atregular intervals due to the unstable surface layer caused bytraffic (Fig. 6). Corrugation with large wavelength and amplitudeis caused by poor subgrade and frost heaving. Depression andswell are respectively localized surface settlement and upwardbuldge on the pavement. The former is often caused by lateralmovement of structural layers or subgrade, or creeping groundor by solution and piping of ground. Swell is generally causedby expansion of pavement or subgrade due to moisture conditionor frosting.

Shoving is a kind of corrugation, which is sinuous acrossthe pavement surface and is generally perpendicular to the trafficdirection. It often happens where traffic starts and stops at busyintersection of road.

cracks reach severity to give rise to potholes. Severity levelsof fatigue cracks are categorized as low, moderate and high.Too fine hairline cracks with no or only a few interconnectingcracks (< 6 mm) in width) which are not spalled are of lowseverity. Moderate severity cracks are those which form an areaof interconnected cracks that may be slightly spalled. Crackshave width between 6 and 19 mm and cracks in the pattern areno further apart than 150 mm. Severely spalled cracks of morethan 19 mm width with moderate to severe random cracking,are placed under high severity of fatigue cracks.

Other cracks include those that develop over joints inconcrete, called joint reflection cracks, and crescent cracks thatdevelop at the pavement edge adjacent to the poorly constructedshoulder (Fig. 4). These cracks may expand into alligator crackswith the passage of time under the circumstance of lack oflateral support to the pavement edge.

Surface deformationSurface deformation is degradation of structural layers

due to heavy traffic load. Minor causes can be weakening ofsubsurface layers as well as subgrade or formation. Rutting isthe commonest phenomenon that occurs as depression developedin the wheel path of flexible pavement. Rutting occurs due to

Fig. 4: Edge cracks and fatigue cracks (alligator cracks) onthe TU road (arrows indicating distresses): (a) infront ofDepartment of Management Building and (b) between NepalBank and TU Administrative Office

(a)

(b)

Fig. 5: (a) Rutting observed on the TU road near the TUadministrative office and (b) Rutting due to subgradecreeping and settlement as observed on the TU road nearTinkune (arrows indicate distresses)

(a)

(b)

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quality, traffic loading and moisture environment. Four categoriesof asphalt pavement distresses after Distress IdentificationManual for the Long-Term Pavement Performance Program(Miller and Bellinger, 2003) and Pavement distress IdentificationManual for the National Park Service Road Inventory Program(FHWA, 2009) are: (a) Surface cracking. (b) surface deformation,(c) deterioration, and (d) surface or mat problems (Table 1).Severity levels of some of the distresses are provided in thesame manual (FHWA, 2009).

Surface crackingSurface cracking is phenomenon of development of

surface cracks irrespective of their location of development.Longitudinal (Fig. 2) and transverse cracks are respectively the

cross-running along and across the road. They initiate as widespaced cracks but grow into closely spaced and open severecracks with the passage of time. Both longitudinal and transversecracking may intersect one another to yield more or lessrectangular shaped block cracks. Severity levels of bothlongitudinal and transverse cracks are: Low- cracks with < 6mm width, sealed; moderate-crack width between 6 and 19 mm,adjacent low severity cracking; and high-cracks width morethan19 mm with adjacent random moderate to high severitycracking. Major causes of development of all the abovementioned cracks are generally frost heaving, creeping of ground,flowage of subgrade and settlement, improper construction oflanes, etc.

Fatigue cracks or alligator cracks are a series ofinterconnected irregular polygonal cracks of various stages ofdevelopment (Figs. 3 and 4), due to failure of surface layer orbase course owing to repeated loading. Alligator cracks mayalso form due to defects in base when the drainage conditionis poor, and can develop anywhere on the roadway. Fatigue

Fig. 3: Fatigue cracks (alligator cracks) observed on thestretch of the TU road between Tinkune and the Departmentof Management

Table 1: Types of asphalt pavement distress

Fig. 1: Pavements observed: (a) TU road, Kirtipur, and (b)road of the Manang Colony

TU GateTU ServiceCommission Office

TUAdministrative

Office

Tinkune

NepalBank

Dept. ofManagement

ScienceFacultyBlock

CEDA

Manang Colony

(b)

(a)

Fig. 2: Longitudinal crack as observed on the TU road ofstretch between Nepal Bank and the TU AdministrativeOffice

Overview on causes of flexible pavement distresses

247

heavy traffic load and initially a narrow rutting formed growsinto a wide and deep one. The rutting limited to the surfaceasphaltic layer is indicative of improper mixing proportion ofasphalt and aggregates, while one that grows into deeper layerwith deformation of subgrade is indicative of rutting rooted tothe deformation of poor subgrade (Figs. 2 and 5).

Corrugation is a transverse undulation that appears atregular intervals due to the unstable surface layer caused bytraffic (Fig. 6). Corrugation with large wavelength and amplitudeis caused by poor subgrade and frost heaving. Depression andswell are respectively localized surface settlement and upwardbuldge on the pavement. The former is often caused by lateralmovement of structural layers or subgrade, or creeping groundor by solution and piping of ground. Swell is generally causedby expansion of pavement or subgrade due to moisture conditionor frosting.

Shoving is a kind of corrugation, which is sinuous acrossthe pavement surface and is generally perpendicular to the trafficdirection. It often happens where traffic starts and stops at busyintersection of road.

cracks reach severity to give rise to potholes. Severity levelsof fatigue cracks are categorized as low, moderate and high.Too fine hairline cracks with no or only a few interconnectingcracks (< 6 mm) in width) which are not spalled are of lowseverity. Moderate severity cracks are those which form an areaof interconnected cracks that may be slightly spalled. Crackshave width between 6 and 19 mm and cracks in the pattern areno further apart than 150 mm. Severely spalled cracks of morethan 19 mm width with moderate to severe random cracking,are placed under high severity of fatigue cracks.

Other cracks include those that develop over joints inconcrete, called joint reflection cracks, and crescent cracks thatdevelop at the pavement edge adjacent to the poorly constructedshoulder (Fig. 4). These cracks may expand into alligator crackswith the passage of time under the circumstance of lack oflateral support to the pavement edge.

Surface deformationSurface deformation is degradation of structural layers

due to heavy traffic load. Minor causes can be weakening ofsubsurface layers as well as subgrade or formation. Rutting isthe commonest phenomenon that occurs as depression developedin the wheel path of flexible pavement. Rutting occurs due to

Fig. 4: Edge cracks and fatigue cracks (alligator cracks) onthe TU road (arrows indicating distresses): (a) infront ofDepartment of Management Building and (b) between NepalBank and TU Administrative Office

(a)

(b)

Fig. 5: (a) Rutting observed on the TU road near the TUadministrative office and (b) Rutting due to subgradecreeping and settlement as observed on the TU road nearTinkune (arrows indicate distresses)

(a)

(b)

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Naresh Kazi Tamrakar

DeteriorationDeterioration of pavement refers to breakage of portion

of pavement. Severity of development of cracking and ruttingmay lead to deterioration of pavement. Potholes are bowl-shapeddepressions formed gradually from small to large cracks andholes. Generally fatigue cracks with severity and aging giverise to potholes. Some potholes are produced by stripping ofaggregates from the asphalt binder and erosion of aggregates(Fig. 7). Severe development of depression and cracks allowsfor water accumulation, which further induces stripping anddisintegration of aggregates from asphalt, thus leading todevelopment of potholes. Potholes grow in diameter in a shortperiod of time and pose accidental hazard.

Patching is a portion of pavement surface greater than0.1 sq. m that has been removed and replaced after originalconstruction for utility.

Raveling is the process of erosion of aggregates fromthe surface pavement due to poor adhesion between asphalt

binder and aggregates (Fig. 7), or disintegration of poor qualityaggregates. Raveling creates surface roughness and later onasperities of roughness grow larger by repeated axle load.

Stripping is loss of adhesive bond between an asphaltbinder and aggregates (Fig. 8). It commonly happens whenwater is present between aggregates and asphalt during pavementconstruction and during service period due to poor drainagecondition. Stripping typically begins at the bottom of the asphaltlayer and progresses upward as opposed to raveling in whichstripping begins at the surface and progresses downward.

Polishing takes place by wearing of aggregates presentin the surface layer, and exposes aggregates. Extreme polishingmay result in loss of skid resistance of aggregates. Pumping isthe phenomenon of seepage or ejection of water and fines frombeneath the pavement through cracks on to the surface.

Mat problemsMat problems are limited to the surface layer of the

pavement. Some of the remarkable distresses are bleeding,segregation and delamination. Bleeding is a patch of excessiveasphalt cement on the surface of pavement (Fig. 9), as causedeither by excessively high proportion of asphalt binders or byimproper placement of asphalt mix during pavement construction.This happens when workability of aggregate-asphalt mix is low,and is caused by aggregates lacking dense gradation and presence

Fig. 7: A pothole developed on the TU road between theDepartment of Management and CEDA due to stripping

Fig. 6: Corrugation and raveling of portion of the TU roadbetween Centre for Economic Development Administration(CEDA) and the Science Faculty Block

Fig. 8: Stripping and raveling: (a) on the stretch of the TUroad between Service Commission Office and Tinkune, and(b) on the pavement of the Manang Colony

(a)

(b)

Overview on causes of flexible pavement distresses

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of notable amount of flaky and elongate particles. Bleeding iscommon where temperature is high creating asphalt to flow dueto low viscosity.

Segregation is a phenomenon of separation of coarseaggregates from fine aggregates as a result of mishandling ofthe mix during production, hauling, and placing. Segregationresults in heterogeneity in pavement structure and thus densityand packing.

Delamination is a clear separation of pavement surfacefrom the lower layer. Poor bonding between layers is the causeof delamination. Poor bonding is related to constructional defectrather than structural defect.

CAUSES OF PAVEMENT DISTRESSESFactors which affect pavement distresses are pavement

material characteristics, subgrade quality and condition, moistureand temperature environment, and traffic loading. Consideringall these factors, engineers produce designs of pavement structure,material mix, construction technique, etc. Failing to considerthe factors commonly results in poor quality pavement structurethat undergoes distress soon after construction.

Pavement distress due to pavement materialcharacteristics

In a pavement structure, different structural layers havedifferent or specific functions to meet for requirement of durablepavement. Some of desirable properties are aggregate durability,soundness, cleanliness, good angularity, dense grading, etc.,which should be met to achieve good performance. In factdesirable properties of materials that will be used in each of thepavement layers should be met to achieve fully functioneddurable pavement. The coarse aggregates which have to be usedin asphalt mix should have good adhesion with asphalt binderand should have dense grading for well compaction, and goodcoarse aggregate angularity to achieve good binding and highskid resistance. Adhesion properties are due to good bonding

between aggregates and asphalt and for this surface roughnessand aggregate angularity are crucial properties to be considered.To obtain a compact asphaltic layer, dense gradation of coarseaggregates and low indices of flakiness and elongation aredesired. Various tests are required to determine desirableproperties and to select appropriate aggregates and asphalt.When material selection is not give priority, pavement distressbegins soon after its construction.

Various pavement distresses are caused by poor aggregatequality. When aggregates with poor soundness are used thecommon distresses that may likely to occur are stripping andpolishing. Aggregates of poor durability contribute in strippingand polishing of pavements. Aggregates of low cleanliness cancommonly contribute distresses like raveling and stripping, andoccasionally cause delamination, cracking and deformation.Gradation of aggregates in the structural layers of pavement isalso crucial. When the gradation is not given importance,distresses such as pumping, longitudinal and fatigue cracks,edge cracks, rutting, depression and potholes are produced.

Viscosity of asphalt also plays significant role in creatingpavement distresses. When a low viscosity asphalt is used inasphalt-aggregate mix, the distresses which can commonlyoccur are rutting and shoving, and occasionally occur arecorrugation and depression. High viscosity asphalt when usedcan cause cracking and potholes, and occasionally cause ravelingand stripping. Asphalt highly susceptible to temperature variationmay cause deformation and cracking distresses on pavement.

Pavement distress due to poor mix designNot only the material characteristics but also a mix design

of asphalt and aggregate and various additives can cause differentdistresses. When asphalt mix has poor gradation, it can commonlycause rutting, shoving, raveling and segregation distresses. Poormix gradation occasionally brings about cracks, depression andpotholes in the pavement. Similarly, low asphalt content in themix can bring about some of the common distresses aslongitudinal cracks, fatigue cracks, raveling and stripping.Besides, some induced distresses as potholes and edge crackscan also occur. High asphalt content is also detrimental to apavement structure. It invites rutting, corrugation, shoving andbleeding as common distresses and depression as a minordistress. Low air void content in the asphalt mix can causedistresses similar to that caused by high asphalt content. Lowair void content however brings about some common distressesand longitudinal cracks, fatigue cracks, raveling and striping,and occasional distresses as pumping, potholes, patching,transverse and block cracking, shoving and corrugating.Moreover, improper fines content can cause raveling andsegregation apart from other distresses as all the cracks anddeformation, patching, stripping and bleeding.

Pavement distress due to poor construction designPoor construction design includes poor treatment of

ground and subbase and base courses in terms of compaction

Fig. 9: Bleeding observed on the TU road betwen Nepalbank and TU Administrative Office

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Naresh Kazi Tamrakar

DeteriorationDeterioration of pavement refers to breakage of portion

of pavement. Severity of development of cracking and ruttingmay lead to deterioration of pavement. Potholes are bowl-shapeddepressions formed gradually from small to large cracks andholes. Generally fatigue cracks with severity and aging giverise to potholes. Some potholes are produced by stripping ofaggregates from the asphalt binder and erosion of aggregates(Fig. 7). Severe development of depression and cracks allowsfor water accumulation, which further induces stripping anddisintegration of aggregates from asphalt, thus leading todevelopment of potholes. Potholes grow in diameter in a shortperiod of time and pose accidental hazard.

Patching is a portion of pavement surface greater than0.1 sq. m that has been removed and replaced after originalconstruction for utility.

Raveling is the process of erosion of aggregates fromthe surface pavement due to poor adhesion between asphalt

binder and aggregates (Fig. 7), or disintegration of poor qualityaggregates. Raveling creates surface roughness and later onasperities of roughness grow larger by repeated axle load.

Stripping is loss of adhesive bond between an asphaltbinder and aggregates (Fig. 8). It commonly happens whenwater is present between aggregates and asphalt during pavementconstruction and during service period due to poor drainagecondition. Stripping typically begins at the bottom of the asphaltlayer and progresses upward as opposed to raveling in whichstripping begins at the surface and progresses downward.

Polishing takes place by wearing of aggregates presentin the surface layer, and exposes aggregates. Extreme polishingmay result in loss of skid resistance of aggregates. Pumping isthe phenomenon of seepage or ejection of water and fines frombeneath the pavement through cracks on to the surface.

Mat problemsMat problems are limited to the surface layer of the

pavement. Some of the remarkable distresses are bleeding,segregation and delamination. Bleeding is a patch of excessiveasphalt cement on the surface of pavement (Fig. 9), as causedeither by excessively high proportion of asphalt binders or byimproper placement of asphalt mix during pavement construction.This happens when workability of aggregate-asphalt mix is low,and is caused by aggregates lacking dense gradation and presence

Fig. 7: A pothole developed on the TU road between theDepartment of Management and CEDA due to stripping

Fig. 6: Corrugation and raveling of portion of the TU roadbetween Centre for Economic Development Administration(CEDA) and the Science Faculty Block

Fig. 8: Stripping and raveling: (a) on the stretch of the TUroad between Service Commission Office and Tinkune, and(b) on the pavement of the Manang Colony

(a)

(b)

Overview on causes of flexible pavement distresses

249

of notable amount of flaky and elongate particles. Bleeding iscommon where temperature is high creating asphalt to flow dueto low viscosity.

Segregation is a phenomenon of separation of coarseaggregates from fine aggregates as a result of mishandling ofthe mix during production, hauling, and placing. Segregationresults in heterogeneity in pavement structure and thus densityand packing.

Delamination is a clear separation of pavement surfacefrom the lower layer. Poor bonding between layers is the causeof delamination. Poor bonding is related to constructional defectrather than structural defect.

CAUSES OF PAVEMENT DISTRESSESFactors which affect pavement distresses are pavement

material characteristics, subgrade quality and condition, moistureand temperature environment, and traffic loading. Consideringall these factors, engineers produce designs of pavement structure,material mix, construction technique, etc. Failing to considerthe factors commonly results in poor quality pavement structurethat undergoes distress soon after construction.

Pavement distress due to pavement materialcharacteristics

In a pavement structure, different structural layers havedifferent or specific functions to meet for requirement of durablepavement. Some of desirable properties are aggregate durability,soundness, cleanliness, good angularity, dense grading, etc.,which should be met to achieve good performance. In factdesirable properties of materials that will be used in each of thepavement layers should be met to achieve fully functioneddurable pavement. The coarse aggregates which have to be usedin asphalt mix should have good adhesion with asphalt binderand should have dense grading for well compaction, and goodcoarse aggregate angularity to achieve good binding and highskid resistance. Adhesion properties are due to good bonding

between aggregates and asphalt and for this surface roughnessand aggregate angularity are crucial properties to be considered.To obtain a compact asphaltic layer, dense gradation of coarseaggregates and low indices of flakiness and elongation aredesired. Various tests are required to determine desirableproperties and to select appropriate aggregates and asphalt.When material selection is not give priority, pavement distressbegins soon after its construction.

Various pavement distresses are caused by poor aggregatequality. When aggregates with poor soundness are used thecommon distresses that may likely to occur are stripping andpolishing. Aggregates of poor durability contribute in strippingand polishing of pavements. Aggregates of low cleanliness cancommonly contribute distresses like raveling and stripping, andoccasionally cause delamination, cracking and deformation.Gradation of aggregates in the structural layers of pavement isalso crucial. When the gradation is not given importance,distresses such as pumping, longitudinal and fatigue cracks,edge cracks, rutting, depression and potholes are produced.

Viscosity of asphalt also plays significant role in creatingpavement distresses. When a low viscosity asphalt is used inasphalt-aggregate mix, the distresses which can commonlyoccur are rutting and shoving, and occasionally occur arecorrugation and depression. High viscosity asphalt when usedcan cause cracking and potholes, and occasionally cause ravelingand stripping. Asphalt highly susceptible to temperature variationmay cause deformation and cracking distresses on pavement.

Pavement distress due to poor mix designNot only the material characteristics but also a mix design

of asphalt and aggregate and various additives can cause differentdistresses. When asphalt mix has poor gradation, it can commonlycause rutting, shoving, raveling and segregation distresses. Poormix gradation occasionally brings about cracks, depression andpotholes in the pavement. Similarly, low asphalt content in themix can bring about some of the common distresses aslongitudinal cracks, fatigue cracks, raveling and stripping.Besides, some induced distresses as potholes and edge crackscan also occur. High asphalt content is also detrimental to apavement structure. It invites rutting, corrugation, shoving andbleeding as common distresses and depression as a minordistress. Low air void content in the asphalt mix can causedistresses similar to that caused by high asphalt content. Lowair void content however brings about some common distressesand longitudinal cracks, fatigue cracks, raveling and striping,and occasional distresses as pumping, potholes, patching,transverse and block cracking, shoving and corrugating.Moreover, improper fines content can cause raveling andsegregation apart from other distresses as all the cracks anddeformation, patching, stripping and bleeding.

Pavement distress due to poor construction designPoor construction design includes poor treatment of

ground and subbase and base courses in terms of compaction

Fig. 9: Bleeding observed on the TU road betwen Nepalbank and TU Administrative Office

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Naresh Kazi Tamrakar

and gradation, and improper design of thickness of base andsubbase. Subgrade properties and condition are crucial factorsto be considered in the pavement structural design. Wheresubgrade is of poor quality it is generally recommended to usecapping layer followed by thick subbase and base courses.

Poor quality construction that leads to poor compactionof subgrade can arise longitudinal and fatigue cracks, rutting,potholes, depression and pumping. Similar distresses can happenwhen base and subbase courses are poorly compacted duringconstruction. On the other hand, low thickness layers designedfor subbase and base courses can lead to longitudinal and fatiguecracks, rutting, depression, potholes, patching and pumping.

Pavement distresses due to poor construction operationare those that are caused by placement of excessively moisturemix on the surface. Such construction practice may bring aboutstripping. Other distresses that can occur upon excessive moistureare cracking, deformation, delamination, potholes, patching andraveling.

OBSERVATION OF PAVEMENTS OF TU ROAD ANDOF MANANG COLONY

Inspection of flexible pavement of the TribhuvanUniversity (TU) road from the TU Gate to the Science FacultyBlocks that of the Manang Colony, Mhyepi, Kathmandu (Fig.1) was made. From the TU Gate to the Science Faculty Block(Fig. 1a) several kinds of pavement distresses were observed,which have been described in captions of Figs. 2 to 9. Ruttingand potholes dominate the stretch between the TU Gate andTinkune, whereas corrugation, stripping, and potholes dominatethe stretch between CEDA and the Science Faculty Block.Fatigue cracks and stripping and raveling are the dominantdistresses. It was found that the pavement structure of the TUroad was constructed over a subgrade of mud. Poor subbasecourse of less than 15 cm thickness composed of mud andcoarse aggregate, and poor surfacing of less than 4 cm wererecorded from the pit dug for drainage lining (Fig. 10). The TUroad reflects poor construction design, poor selection ofconstruction materials, and poor construction operation.

The pavement of the Manang Colony (Fig. 1b) showssevere stripping, raveling and pothole distresses, which musthave occurred due to poor selection of construction materialsand poor construction of the pavement. No subgrade relatedproblem was identified in the pavement of the colony.

CONCLUSIONS

1. Four broad categories of flexible pavement distressesare cracking, deformation, deterioration and mat problems.

2. Pavement distress can happen due to single or multiplecausative factors.

3. Improper selection of construction materials andpavement structural and constructional design are very much

responsible for pavement distress apart from the traffic loading.

4. Pavement distresses observed in the TU road arecaused by subgrade deformation as well as poor constructiondesign and quality of construction. Pavement distresses observedin the Manang Colony were mainly caused due to poor selectionof construction materials and quality of construction.

5. It is recommended to (a) firstly assess subgradecondition, (b) prepare structural and mix designs consideringsubgrade conditions, traffic and environment (temperature,moisture and drainage), (c) then select appropriate constructionmaterials which meet desirable functions of each of the structurallayers of the pavement structure, and (d) finally control thequality of paving operation.

ACKNOWLEDGEMENTS

Author thanks Sunil Pradhananga for capturing beautifulimages of the TU Road showing pavement distresses.

REFERENCESMiller and Bellinger, 2003, Distress Identification Manual for the

Long-Term Pavement Performance Program. Publication no.FHWA-RD 03-031, June 2003, fourth revised edition, USDOT Fedral Highway Agency, 164p.

FHWA, 2009, Distress Identification Manual for the National ParkService Road Inventory Program, Cycle 4, 2006-2008.USDOT FHA, 25p.

Ragnoli, A., De Blasiis , M.R., and Di Benedetto, A., 2018, PavementDistress Detection Methods: A Review. Infrastructures, 3,58; pp. 1–19. doi:10.3390/infrastructures3040058

Adlinge, S.S. and Gupta, A.K., 2005, Pavement deterioration andits causes. IOSR Journal of Mechanical and Civil Engineering,pp. 9–15.

Fig. 10: A portion of the pavement (TU road) dug formaintaining a drainage line revealing pavement structurallayer and subgrade soil; 1 = Asphaltic layer, 2 = Subbasecourse, 3 = subgrade

0.3 m

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Bulletin of Nepal Geological Society, 2019, vol. 36

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Sunil Shanker Pradhananga and *Naresh Kazi Tamrakar

Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal*Corresponding author: nktam777@yahoo.com

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Los Angeles Abrasion Testing: From the meaning of test to the results of test

INTRODUCTIONThe Los Angeles Abrasion (LAA) is the most common

and widely used method to determine aggregate abrasionresistance. Crushed stone of aggregate, which are obtainedthrough breakdown from different type of rocks, e.g. igneous,metamorphic and sedimentary are subject to LAA test fordetermining resistance to fragmentation of rocks. Crushed stoneof aggregate can be used in various engineering purposes: dam,pavement, concrete, and asphaltic pavement, etc. Trend ofdemand of crushed stone aggregate has increased in worldwidedue to lack of the uncrushed stone of aggregates in differentsources. To evaluate the quality of crushed stone aggregates,one of the commonly tested parameters is Los Angeles Abrasion(Al-Harthi, 2001).

The grade of aggregate can be determined by physicaltest methods. The Los Angeles Abrasion test has been developedto provide quantitative method to determine the quality ofabrasion resistance of aggregates for the specification ofrequirements for their specific uses. The resistance of aggregates’fragmentation due to attrition between rock particles and alsoto impact and crushing by steel spheres (Fernlund, 2005;Kahraman and Fener, 2007; Ugur et al., 2010) is determined inthe LAA test.

Methods for determining the LAA tests of aggregatesparticles have been standardized in various forms in many placesaround the world. The tests to measure the abrasion resistanceof aggregate particles are described in ASTM C131-01 (2003),ASTM C535 -031 (2003), AASHTO T96-02(2006), AS 1141.23(2009) and ASTM C131 /131M (2014).

ABSTRACTLos Angeles Abrasion test is widely a common test for abrasion resistance for multiple engineering applications. The test has beendeveloped since 1980s. To understand the test to the result of test, two types of rocks, i.e. metasandstone and gneiss were tested ongrades A and B of the test samples for Los Angeles Abrasion (LAA) Test. The LAA values of gneiss vary from 62.13 to 63.19%, andthat of metasandstone from 37.30 to 36.65%, showing that relatively consistent results have occurred for different grades A and B ofthe Test Samples. It shows that the material properties play the main role in abrasion and Los Angeles Abrasion loss than the nominalsize selected for different grades of the Test Samples, and in the present study it has been explained by anisotropy in fabric andanisotropy related strength of rock types for LAA loss. It is considered that the aggregates of different petrographic properties haveyielded low or high LAA and hence have bearing on quality of aggregates for engineering purposes. A selection of rock type isimportant to achieve desirable qualities regarding abrasion loss for concrete pavement, asphalt concrete pavement, surface dressing,crushed stone base and subbase courses.

Keywords: Los Angeles Abrasion Testing, Coarse aggregates, Test samples, Anisotropy in fabric

In 1870s France developed the Micro Deval test methodof testing and was the only accepted method to determine thetoughness of aggregates. This method was adopted as a standardtest for use on road materials by ASTM in 1908 and revised in1926. Later on, the LAA test was approximately adopted in1937 (Sweet, 1948). Because the LAA test is related closer withthe performance of aggregates in pavements than the MicroDeval test the LAA test was adopted as a standard test formeasuring the wear of aggregates in 1940 (Sweet 1948).

Woolf and Runner (1935) conducted suitability of LosAngeles testing and the test result for specifying limit for coarseaggregate. West et al. (1970) studied tests for evaluatingdegradation of base course. They concluded that the LAA testappears to be a good indicator of the degradation properties ofcarbonate rocks, but not of basalt rocks. The grain size androundness were related to the LA abrasion wear value.

Larson et. al. (1971) reviewed and investigated andpresented that the LAA test was satisfactory for determiningthe resistance of an aggregate to dry abrasion. At the same timesome state highway departments had developed tests of theirown for determining wear ability of aggregates under wetabrasion conditions. A modification is proposed to the standardLAA test to include 250 revolutions with the aggregate in thedry state plus 250 revolutions after a fixed amount of water hasbeen added.

Wieden et. al (1977) studied to improve the Los Angelestest and concentrated in three aspects, i.e., sample material, testconditions and type of stress. The sample material and testconditions affect test values because of the specific characteristics