Pavement Review

8/3/2019 Pavement Review

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Pavement Design Exam Review 2011

1. What is meant by empirical method?An empirical approach is one which is based on the results of experiments or experience. Generally, it requires anumber of observations to be made in order to ascertain the relationships between input variables and outcomes. It isnot necessary to firmly establish the scientific basis for the relationships between variables and outcomes as long asthe limitations with such an approach are recognized

2. Talk about the AASHTO ROAD TEST? Determine relationship between traffic and performance Determine effect of loads on bridges Perform special studies (base types, paved shoulders, tire pressures) Develop instrumentation, test procedures, data, charts, graphs, and formulas for future highway design

Started Nov. 1958, Ended Nov. 1960 Loops 3-6: 6 vehicles/lane 10 vehicles/lane (Jan 60) Operation 18 hours, 40 minutes per day 6 days/week 1,114,000 Applications Avg. ESAL - 6.2 million Max ESAL - 10 million (Flex)

3. The equations developed by the AASHTO road test have limitations, mention them?

The equations were developed based on the specific pavement materials and roadbed soil present at the AASHORoad Test.The equations were developed based on the environment at the AASHO Road Test only.The equations are based on an accelerated two-year testing period rather than a longer, more typical 20+ yearpavement life. Therefore, environmental factors were difficult if not impossible to extrapolate out to a longer

period.The loads used to develop the equations were operating vehicles with identical axle loads and configurations, asopposed to mixed traffic.


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4. What are the input/outputs of the road test?

The predicted loading . The predicted loading is simply the predicted number of 80 kN (18,000 lb.) ESALsthat the pavement will experience over its design lifetime . Reliability . The reliability of the pavement design-performance process is the probability that a pavement

section designed using the process will perform satisfactorily over the traffic and environmental conditions forthe design period.

Pavement structure . The pavement structure is characterized by the Structural Number (SN). The StructuralNumber is an abstract number expressing the structural strength of a pavement required for given combinationsof soil support (M R), total traffic expressed in ESALs, terminal serviceability and environment.

Serviceable life . The difference in present serviceability index (PSI) between construction and end-of-life isthe serviceability life. The equation compares this to default values of 4.2 for the immediately-after-construction value and 1.5 for end-of-life (terminal serviceability). Typical values used now are:

Post-construction: 4.0 - 5.0 depending upon construction quality, smoothness, etc.End-of-life (called "terminal serviceability"): 1.5 - 3.0 depending upon road use (e.g., interstate

highway, urban arterial, residential) Subgrade support . Sub grade support is characterized by the sub grades resilient modulus (MR). Intuitively,

the amount of structural support offered by the sub grade should be a large factor in determining the requiredpavement structure.

Outputs:

.

The Structural Number determines the total number of ESALs that a particular pavement can support. This isevident in the flexible pavement design equation presented in this section.. The Structural Number also determines what the 80 ken (18,000 lb.) ESAL is for a given load.

5. what is the mechanistic model?Mechanistic models are used to mathematically model pavement physics. There are a number of different types of models available today (e.g., dynamic, viscoelastic models) but this section will present two, the layered elastic modeland the finite elements model (FEM), as examples of the types of models typically used. Both of these models caneasily be run on personal computers and only require data that can be realistically obtained.

6. What are the advantages of the mechanistic method?

It can be used for both existing pavement rehabilitation and new pavement constructionIt accommodates changing load typesIt can better characterize materials allowing for:

Better utilization of available materialsAccommodation of new materialsAn improved definition of existing layer properties

It uses material properties that relate better to actual pavement performanceIt provides more reliable performance predictionsIt better defines the role of construction
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7. What is the traffic distribution factor?

DL is lane distribution factor, expressed as a ratio, that accounts for the distribution of loads when two or morelanes are available in one direction. For instance, on most interstate routes, the outside lane carries a majority of the heavy truck traffic.

8. What is the reliability concept?

"The reliability of the pavement design-performance process is the probability that a pavement section designedusing the process will perform satisfactorily over the traffic and environmental conditions for the designperiod." (AASHTO, 1993)

. The reliability factor is comprised of two variables:

Z R = standard normal deviate . The standard normal table value corresponding to a desired probability of exceedance level. For example, a designer may specify that there should only be a 5 % chance that the designdoes not last a specified number of years (e.g., 20 years).

So = combined standard error of the traffic prediction and performance prediction . This variable defines howwidely the two basic design inputs, traffic and performance, can vary. For instance, traffic may be estimated at2,000,000 ESALs over 20 years. However, actual traffic may turn out to be 2,500,000 ESALs over 20 yearsdue to unanticipated population growth.
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9. briefly explain(surface course ,base course ,subbase course)

Surface Course

The surface course is the layer in contact with traffic loads and normally contains the highest quality materials.It provides characteristics such as friction, smoothness, noise control, rut and shoving resistance and drainage.In addition, it serves to prevent the entrance of excessive quantities of surface water into the underlying base,subbase and sub grade (NAPA, 2001). This top structural layer of material is sometimes subdivided into twolayers (NAPA, 2001):

. Wearing Course . This is the layer in direct contact with traffic loads. It is meant to take the brunt of traffic wearand can be removed and replaced as it becomes worn. A properly designed (and funded) preservation programshould be able to identify pavement surface distress while it is still confined to the wearing course. This way,the wearing course can be rehabilitated before distress propagates into the underlying intermediate/bindercourse.

. Intermediate/Binder Course . This layer provides the bulk of the HMA structure. It's chief purpose is todistribute load.

Base Course

The base course is immediately beneath the surface course. It provides additional load distribution and

contributes to drainage and frost resistance. Base courses are usually constructed out of:

. Aggregate . Base courses are most typically constructed from durable aggregates (see Figure 2.5) that will notbe damaged by moisture or frost action. Aggregates can be either stabilized or unstabilized.

. HMA . In certain situations where high base stiffness is desired, base courses can be constructed using a varietyof HMA mixes. In relation to surface course HMA mixes, base course mixes usually contain larger maximumaggregate sizes, are more open graded and are subject to more lenient specifications.

Subbase Course

The subbase course is between the base course and the sub grade. It functions primarily as structural support

but it can also:

. Minimize the intrusion of fines from the sub grade into the pavement structure.

. Improve drainage.

. Minimize frost action damage .

. Provide a working platform for construction.

The subbase generally consists of lower quality materials than the base course but better than the sub gradesoils. A subbase course is not always needed or used. For example, a pavement constructed over a highquality, stiff sub grade may not need the additional features offered by a subbase course so it may be omittedfrom design.
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10.briefly explain the Sub grade Resilient Modulus (M R)?

The resilient modulus is the material property used to characterize the support characteristics of the

oadbed soil in flexible pavement design. In general terms, it is a measure of the soils deformation in

esponse to repeated (cyclic) applications of loads much smaller than a failure load.

The AASHTO design procedure requires the input of an effective roadbed soil resilient modulus. This

ffective resilient modulus is a means of representing the combined effect of all the seasonal modulus

values by a type of weighted average.

11.what are the basic design procedures?

Basic Procedure:

Deter mine the traffic (ESAL)

Calculate the effective subgrade modulus (MReff)

Select the performance level (PSI)

Solve for the required SN needed to protect the subgrade

13. what is pavement performance defiend by?

Roughness (often called "smoothness") Surface distress Skid resistance Structural evaluation

14.briefly talk about roughtness?

avement roughness is generally defined as an expression of irregularities in the pavement surface that adversely affect the

ide quality of a vehicle (and thus the user). Roughness is an important pavement characteristic because it affects not onlyide quality but also vehicle delay costs, fuel consumption and maintenance costs. The World Bank found road roughness toe a primary factor in the analyses and trade-offs involving road quality vs. user cost (UMTRI, 1998). Roughness is alsoeferred to as "smoothness" although both terms refer to the same pavement qualities.
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Measurement

Today, roughness is typically quantified using some form of either present serviceability rating (PSR),international roughness index (IRI) or other index with IRI being most prevalent.

Present Serviceability Rating (PSR)

The AASHO Road Test (Highway Research Board, 1962) developed a definition of pavement serviceability,the present serviceability rating (PSR), that is based on individual observation. PSR is defined as "The

judgment of an observer as to the current ability of a pavement to serve the traffic it is meant to serve"(Highway Research Board, 1962). To generate the original AASHO Road Test PSR scores, observers rodearound the test tracks and rated their ride using the quantitative scale shown in Figure 9.1. This subjective scaleranges from 5 (excellent) to 0 (essentially impassable). Since PSR is based on passenger interpretations of ridequality, it generally reflects road roughness because roughness largely determines ride quality.

International Roughness Index (IRI)

The international roughness index (IRI) was developed by the World Bank in the 1980s (UMTRI, 1998). IRI isused to define a characteristic of the longitudinal profile of a traveled wheeltrack and constitutes a standardizedroughness measurement. The commonly recommended units are meters per kilometer (m/km) or millimetersper meter (mm/m). The IRI is based on the average rectified slope (ARS), which is a filtered ratio of a standardvehicle's accumulated suspension motion (in mm, inches, etc.) divided by the distance traveled by the vehicleduring the measurement (km, mi, etc.). IRI is then equal to ARS multiplied by 1,000. The open-ended IRIscale is shown in Figure 9.2.
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15. talk about the roughness measurement techniques?

Dipstick Profiler

The dipstick profiler can be used to collect a relatively small quantity of pavement profile measurements.The Dipstick Profiler (see Figures 9.3 and 9.4) consists of an inclinometer enclosed in a case supported bytwo legs separated by 305 mm (12 in.). Two digital displays are provided, one at each end of theinstrument. Each display reads the elevation of the leg at its end relative to the elevation of the otherleg. The operator then "walks" the dipstick down a premarked pavement section by alternately pivotingthe instrument about each leg. Readings are recorded sequentially as the operator traverses the section.The device records 10 to 15 readings per minute. Software analysis provides a profile accurate to 0.127mm ( 0.005 in.). A strip can be surveyed by a single operator in about one-half the time of a traditionalsurvey crew. The dipstick is commonly used to measure a profile for calibration of more complexinstruments.

Profilographs

Profilographs have been available for many years and exist in a variety of different forms, configurations,and brands. Due to their design they are not practical for network condition surveys. Their most commonuse today is for rigid pavement construction inspection, quality control , and acceptance . The majordifferences among the various profilographs involve the configuration of the wheels and the operation andmeasurement procedures of the various devices.

Profilographs have a sensing wheel, mounted to provide for free vertical movement at the center of theframe (see Figure 9.5). The deviation against a reference plane, established from the profilograph frame,is recorded (automatically on some models) on graph paper from the motion of the sensing wheel (seeFigure 9.6). Profilographs can detect very slight surface deviations or undulations up to about 6 m (20 ft)in length.

16.what are the Profiling Devices ?

Profiling devices are used to provide accurate, scaled, and complete reproductions of the pavement profilewithin a certain range. They are available in several forms, and can be used for calibration of RTRRMs.The equipment can become fairly expensive and complex. Three generic types of profiling systems are inuse today:

Straight edge . The simplest profiling system is a straight edge. Modifications to the straight edge, suchas mounting it on a wheel, result in a profilograph.Low speed systems . Low speed systems such as the CHLOE profilometer are moving reference planes.The CHLOE is a long trailer that is towed at low speeds of 3 to 8 kph (2 to 5 mph). The slow speed isnecessary to prevent any dynamic response measurement during the readings. A few agencies still usethe CHLOE to calibrate their RTRRMs.Inertial reference systems . Most sophisticated road profiling equipment uses the inertial referencesystem. The profiling device measures and computes longitudinal profile through the creation of aninertial reference by using accelerometers placed on the body of the measuring vehicle to measure thevehicle body motion. The relative displacement between the accelerometer and the pavement profile ismeasured with either a "contact" or a "non-contact" sensor system.
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17.briefly explain the Surface Distress?

Surface distress is "Any indication of poor or unfavorable pavement performance or signs of impendingfailure; any unsatisfactory performance of a pavement short of failure" (Highway Research Board, 1970).Surface distress modes can be broadly classified into the following three groups:

. Fracture . This could be in the form of cracking (in flexible and rigid pavements) or spalling resulting fromsuch things as excessive loading, fatigue, thermal changes, moisture damage, slippage or contraction.

. Distortion . This is in the form of deformation (e.g., rutting , corrugation and shoving ) , which can resultfrom such things as excessive loading , creep, densification, consolidation, swelling, or frost action .

. Disintegration . This is in the form of stripping . raveling or spalling , which can result from such things asloss of bonding, chemical reactivity, traffic abrasion, aggregate degradation, poorconsolidation / compaction or binder aging.

Measurement

Measures of distress can be either subjective or objective. A simple example of a subjective measurementmay be a rating of high, medium, or low based on a brief visual inspection. Objective measurements,which are generally more expensive to obtain, use di fferent types of automated distress detectionequipment.

Measurement Techniques

Measurement techniques are mostly visual. Older techniques, used teams of individuals who drove acrossevery mile of pavement to be measured. Speeds were usually quite slow (on the order of 16 km/hr (10 mph))and measurement was done visually.

Modern methods advantages

Safety . Data are collected at highway speed, eliminating the need for driving at slow speeds or on the shoulder. Accurate and complete distress data . Each distress along with its extent, severity and location is identified and stored in adatabase. The system is also less prone to rating errors.

More effective quality control . A centralized evaluation location and less subjective data make quality control muchbetter.

More efficient data collection . Surface distress, rut and roughness data are all collected at the same time using the samedata collecting vehicle.Video and digital images are available for other users . They are available to bridge and maintenance personnel and canbe made available on the Internet in the future.
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18.briefly describe the skid resistance?

Skid resistance is the force developed when a tire that is prevented from rotating slides along thepavement surface (Highway Research Board, 1972). Skid resistance is an important pavement evaluationparameter because:

Inadequate skid resistance will lead to higher incidences of skid related accidents.Most agencies have an obligation to provide users with a roadway that is "reasonably" safe.

Skid resistance measurements can be used to evaluate various types of materials and constructionpractices.

Measurement

Skid resistance is generally quantified using some form of friction measurement such as a friction factor orskid number.

Friction factor (like a coefficient of friction): f = F/L

Skid number: SN = 100(f)

where: F = frictional resistance to motion in plane of interface

L = load perpendicular to interface

In general, the friction resistance of most dry pavements is relatively high; wet pavements are theproblem. The number of accidents on wet pavements are twice as high as dry pavements (but otherfactors such as visibility are involved in addition to skid resistance). Table 9.3 shows some typical SkidNumbers (the higher the SN, the better).

Typical Skid Numbers (from Jayawickrama et al., 1996)

Skid Number Comments

< 30 Take measures to correct

30 Acceptable for low volume roads

31 - 34 Monitor pavement frequently

35 Acceptable for heavily traveled roads


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Skid testing in the U.S. may occur in a number of ways, this section covers some of the more commonmethods including:

The locked wheel tester The spin up testerSurface texture measurement

Locked Wheel Tester

The most commonly used method in the U.S. for skid resistance testing uses some form of a lock wheeltester (see Figure 9.13). Basically, this method uses a locked wheel skidding along the tested surface tomeasure friction resistance. A typical lock-wheel skid measurement system must have the following:

A test vehicle with one or more test wheels incorporated into it or as part of a towed trailer.A standard tire for use on the test wheel. The standardized skid-test tire, a tubeless, bias-ply G78x15 tirewith seven circumferential grooves, is defined by AASHTO M 261 or ASTM E 501. A newer tire, one withno grooves, appears to be gaining acceptance as well. By defining the standard test tire, the tire type anddesign are eliminated as variables in the measurement of pavement skid resistance.

A means to transport water (usually 750 to 1900 liters (200 to 500 gal lons)) and the necessary apparatusto deliver it in front of the test wheel at test speedA transducer associated with the test wheel that senses the force developed between the skidding testwheel and the pavementElectronic signal conditioning equipment to receive the transducer output signal and modify it as requiredSuitable analog and/or digital readout equipment to record either the magnitude of the developed force orthe calculated value of the resulting Skid Number (SN)

19.how does the Lock wheeled skid tester work?

To take a measurement, the vehicle (or trailer) is brought to the desired testing speed (typically 64 km/hr(40 mph)) and water is sprayed ahead of the test tire to create a wetted pavement surface. The test tirebraking system is then actuated to lock the test tire. Instrumentation measures the friction force actingbetween the test tire and the pavement and reports the result as a Skid Number (SN).
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20.talk about Pavement surface deflection?

Pavement surface deflection measurements are the primary means of evaluating a flexible pavementstructure and rigid pavement load transfer. Although other measurements can be made that reflect (tosome degree) a pavement's structural condition, surface deflection is an important pavement evaluationmethod because the magnitude and shape of pavement deflection is a function of traffic (type andvolume), pavement structural section, temperature affecting the pavement structure and moistureaffecting the pavement structure. Deflection measurements can be used in backcalculation methods todetermine pavement structural layer stiffness and the subgrade resilient modulus . Thus, manycharacteristics of a flexible pavement can be determined by measuring its deflection in response to load.Furthermore, pavement deflection measurements are non-destructive.

Measurement

Surface deflection is measured as a pavement surface's vertical deflected distance as a result of anapplied (either static or dynamic) load. The more advanced measurement devices record this verticaldeflection in multiple locations, which provides a more complete characterization of pavement deflection.The area of pavement deflection under and near the load application is collectively known as the"deflection basin".


There are three broad categories of nondestructive deflection testing equipment:

Static deflections Steady state deflections Impact load deflections (FWD)

Static Deflection Equipment

Static deflection equipment measure pavement deflection in response to a static load.

Benkelman Beam

The Benkelman Beam (see Figure 9.16), developed at the Western Association of State HighwayOrganizations (WASHO) Road Test in 1952, is a simple device that operates on the lever arm principle.The Benkelman Beam is used with a loaded truck - typically 80 kN (18,000 lb) on a single axle with dualtires inflated to 480 to 550 kPa (70 to 80 psi). Measurement is made by placing the tip of the beambetween the dual tires and measuring the pavement surface rebound as the truck is moved away. TheBenkelman Beam is low cost but is also slow, labor intensive and does not provide a deflection basin.
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Steady State Deflection Equipment

Steady state deflection equipment measure the dynamic deflection of a pavement produced by anoscillating load. These devices consist of a dynamic force generator (that produces the oscillating load), amotion measuring instrument (to measure the oscillating load), a calibration unit and several deflectionmeasuring devices (transducers, accelerometers, seismometers, etc.). The main advantage that steadystate deflection equipment offer over static deflection equipment is that they can measure a deflectionbasin. The most common steady state deflection equipment are the Dynaflect and the Road Rater.

21.what does pavement condition rating system base on?

Based on measurements of roughness , surface distress , skid resistance and deflection , pavements can beassigned a score that reflects their overall condition. This score, sometimes called a pavement condition rating,quantifies a pavement's overall performance and can be used to help manage pavement networks . By carefully

choosing the rating scale (called the condition index), pavement condition scores can be used to (Deighton,1998):

Trigger treatment . For instance, once a pavement's condition rating reaches a certain level, it can be scheduled formaintenance or rehabilitation.

Determine the extent and cost of repair . A pavement condition score is a numerical representation of a pavement's overallcondition and can thus be used to estimate the extent of repair work and the likely cost.

Determine a network condition index . By combining pavement condition scores for an entire road network, a single scorecan be obtained that gives a general idea of the network condition as a whole.

Allow equal comparison of different pavements . Since a pavement condition score accounts for all types of pavementperformance measures it can be used to compare two or more pavements with different problems on an equal footing.

22.What is pavement condition index?

A pavement condition index is simply the scale, or series of numbers, used to describe a pavement condition.Typical pavement condition indices may be based on a scale of 0 to 5 or perhaps 0 to 100. The properpavement condition index depends upon the objectives of whatever system is used to manage a particularpavement network (called a Pavement Management System or PMS ).

23. talk about the Present Serviceability Index (PSI)?

The present serviceability index (PSI) is based on the original AASHO Road Test PSR . Basically, the PSR wasa ride quality rating that required a panel of observers to actually ride in an automobile over the pavement inquestion. Since this type of rating is not practical for large-scale pavement networks, a transition to a non-panelbased system was needed.

About one-half of the panel of raters found a PSR of 3.0 acceptable and a PSR of 2.5 unacceptable. Suchinformation was useful in selecting a "terminal" (or failure) serviceability (PSI) design input for empiricalstructural design equations . It is interesting to note that the original AASHO Road Test rater opinions arebased on car ride dynamics; it is unclear whether such levels are acceptable for trucks.
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23.what is structural distress?

Structural distress Distress that is caused by the loss of the structural capacity of the pavement structure.

Types describtion couses repiairFatigue(Alligator)Cracking

Series of interconnectedcracks caused by fatiguefailure of the HMAsurface (or stabilizedbase) under repeatedtraffic loading

Decrease in pavement load supportingcharacteristics

o Loss of base, subbase orsubgrade support (e.g., poordrainage or spring thawresulting in a less stiff base).

o Stripping on the bottom of theHMA layer (the strippedportion contributes little topavement strength so theeffective HMA thicknessdecreases)

Increase in loading (e.g., more orheavier loads than anticipated in design)

Inadequate structural design Poor construction (e.g., inadequate

compaction)

Small, localized fatigue crackingindicative of a loss of subgrade

support . Remove the crackedpavement area then dig out andreplace the area of poor subgradeand improve the drainage of thatarea if necessary. Patch over therepaired subgrade.

Large fatigue cracked areasindicative of general structural

failure . Place an HMA overlay overthe entire pavement surface. Thisoverlay must be strong enoughstructurally to carry the anticipatedloading because the underlyingfatigue cracked pavement mostlikely contributes little or nostrength

Bleeding A film of asphaltbinder on the

pavement surface. Itusually creates a shiny,glass-like reflectingsurface (as in the thirdphoto) that canbecome quite sticky.

Excessive asphalt binder in the HMA(either due to mix design or

manufacturing ) Excessive application of asphaltbinder during BST application (as inthe above figures)

Low HMA air void content (e.g., notenough room for the asphalt toexpand into during hot weather)

Minor bleeding can oftenbe corrected by applying

coarse sand to blot up theexcess asphalt binder. Major bleeding can be

corrected by cutting off excess asphalt with a motorgrader or removing it witha heater planer. If theresulting surface isexcessively rough,resurfacing may benecessary (APAI, no dategiven).
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Types describtion couses repiair

Block cracking

Interconnected cracks that dividethe pavement up into rectangularpieces. Blocks range in size fromapproximately 0.1 m 2 (1 ft 2) to 9 m 2 (100 ft 2). Larger blocks aregenerally classified as longitudinal and transverse cracking. Block cracking normally occurs over alarge portion of pavement area butsometimes will occur only in non-traffic areas.

HMA shrinkage and dailytemperature cycling.Typically caused by aninability of asphalt binder toexpand and contract withtemperature cycles becauseof:

Asphalt binder aging Poor choice of

asphalt binder in themix design

Low severity cracks (< 1/2inch wide) . Crack seal toprevent (1) entry of moisture into thesubgrade through thecracks and (2) furtherraveling of the crackedges. HMA can provideyears of satisfactoryservice after developingsmall cracks if they arekept sealed (Roberts et.al., 1996).

High severity cracks (> 1/2inch wide and cracks with

raveled edges) . Removeand replace the crackedpavement layer with anoverlay .

Patching An area of pavement that has been

replaced with new material torepair the existing pavement. Apatch is considered a defect nomatter how well it performs

Previous localized

pavementdeterioration that hasbeen removed andpatched

Utility cuts

Patches are themselves a repair

action. The only way they can beremoved from a pavement's surfaceis by either a structural or non-structural overlay.
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Types describtion couses repiairPotholes Small, bowl-shaped

depressions in the pavementsurface that penetrate all theway through the HMA layerdown to the base course.They generally have sharpedges and vertical sides nearthe top of the hole. Potholesare most likely to occur onroads with thin HMAsurfaces (25 to 50 mm (1 to2 inches)) and seldom occuron roads with 100 mm (4inch) or deeper HMAsurfaces

Generally, potholes are the end result of alligatorcracking . As alligator cracking becomes severe,the interconnected cracks create small chunks of pavement, which can be dislodged as vehiclesdrive over them. The remaining hole after thepavement chunk is dislodged is called a pothole.

In accordance withpatching techniques .

Ravelling The progressivedisintegration of an HMAlayer from the surfacedownward as a result of thedislodgement of aggregateparticles

Loss of bond between aggregateparticles and the asphalt binder as aresult of:

o A dust coating on the aggregateparticles that forces the asphaltbinder to bond with the dustrather than the aggregate

o Aggregate Segregation . If fineparticles are missing from theaggregate matrix, then the

asphalt binder is only able tobind the remaining coarseparticles at their relatively fewcontact points.

o Inadequate compaction duringconstruction . High density isrequired to develop sufficientcohesion within the HMA. Thethird figure above shows a roadsuffering from raveling due toinadequate compaction caused

by cold weather paving . Mechanical dislodging by certain typesof traffic (studded tires , snowplowblades or tracked vehicles). The firstand fourth figures above show ravelingmost likely caused by snow plows.

A raveled pavementshould be investigatedto determine the rootcause of failure.Repair strategiesgenerally fall into oneof two categories:

Small,localized areas

of raveling .Remove theraveledpavement andpatch .

Large raveled areasindicative of general HMA

failure .Remove the

damagedpavement andoverlay .
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Rutting:

Description: Surface depression in the wheelpath. Pavement uplift (shearing) may occur along the sides of therut. Ruts are particularly evident after a rain when they are filled with water. There are two basic types of rutting: mix rutting and subgrade rutting. Mix rutting occurs when the subgrade does not rut yet the pavementsurface exhibits wheelpath depressions as a result of compaction/mix design problems. Subgrade rutting occurswhen the subgrade exhibits wheelpath depressions due to loading. In this case, the pavement settles into thesubgrade ruts causing surface depressions in the wheel path.

Causes: Permanent deformation in any of a pavement's layers or subgrade usually caused by consolidation orlateral movement of the materials due to traffic loading. Specific causes of rutting can be:

Insufficient compaction of HMA layers during construction. If it is not compacted enough initially,HMA pavement may continue to densify under traffic loads.

Subgrade rutting (e.g., as a result of inadequate pavement structure) Improper mix design or manufacture (e.g., excessively high asphalt content, excessive mineral filler,

insufficient amount of angular aggregate particles)

Repair : A heavily rutted pavement should be investigated to determine the root cause of failure (e.g.insufficient compaction, subgrade rutting, poor mix design or studded tire wear). Slight ruts (< 1/3 inch deep)can generally be left untreated. Pavement with deeper ruts should be leveled and overlaid .
http://training.ce.washington.edu/wapa_web/modules/07_construction/07_surface_preparation.htm#levelinghttp://training.ce.washington.edu/wapa_web/modules/07_construction/07_surface_preparation.htm#levelinghttp://training.ce.washington.edu/wapa_web/modules/07_construction/07_surface_preparation.htm#levelinghttp://training.ce.washington.edu/wapa_web/modules/09_maint_rehab/09_rehabilitation.htm#structural_overlayshttp://training.ce.washington.edu/wapa_web/modules/09_maint_rehab/09_rehabilitation.htm#structural_overlayshttp://training.ce.washington.edu/wapa_web/modules/09_maint_rehab/09_rehabilitation.htm#structural_overlayshttp://training.ce.washington.edu/wapa_web/modules/09_maint_rehab/09_rehabilitation.htm#structural_overlayshttp://training.ce.washington.edu/wapa_web/modules/07_construction/07_surface_preparation.htm#leveling

Pavement Review

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