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      Pavement Design CoursePavement Project     Name: Muhannad HaddadinID: 1410256Subject: FlexiblePavement Distresses Table of ContentsLiterature review 3introduction 3Objective 3Types of distresses 14Cost Estimation………………………15Recommendation 19References 20         IntroductionDistress is something that isimportant to consider in any pavement design as each expected failure should beseparately developed and to be taken care of for every distress that couldoccur, mainly distresses happen due to deficiencies in more than an aspect thatcould happen during construction, could be in materials used in constructionand also could be in the maintenance phase after the construction has beendone. An engineer should have a good knowledge about all types of distressesthat could happen in any pavement design in order to deny it from happening orat least to know how to handle it if it occurs in his/her project. Objective We must know all types of distressesthat could occur in any pavement design process, their causes (reasons ofhappening), how to prevent them from happening, and how to deal with them ifany of them happens during construction period or afterwards which is themaintenance period. LiteratureReview1The first literature review willvisually inspect & evaluate the failures of flexible pavements formaintenance planning. It is quite important to identify and examine the causes thatled to the pavement to fail to select an option for treatment. From previous experiences, and whatis obtained through literature reviews, systematic guidelines for evaluation ofdamaged pavement are there to provide information that are useful for maintenancework.

The study consisted of two tasks: 1)     Visualinspection of the existing pavement failures.2)      Investigating the actual causes of thesefailures. As of this study, Obeid Khatim roadin Khartoum was the selected road for investigation. A field work was done onthe existing pavement condition of this road. It was found that most of thedamaged pavement sections suffered from severe cracking & rutting failures.These failures might have been caused by fatigue failure on pavement structuredue to the movement of heavily loaded truck-trailers. The damage could also beattributed to the inadequate design, poor water drainage and improper pavementmaterials used.

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The experimental work programconsists of two tasks; field work and laboratory testing. Three trail pitholesof two meter depth were excavated in the road, a pithole in each section.Disturbed soil samples were collected from 1 to 2m depth to represent thesubgrade soil. The tests performed include sieve analysis, Atterberg limits, andcompaction and California Bearing Ratio (CBR) tests. The tests results aregiven in Table 4. From Table 4 it is cleared that thesubgrade soils in sections C and B compared to A have high values of liquidlimit and plasticity index and low CBR values.

These soils of sections B and Ccan be classified as expansive clay. While the subgrade soil in section A haslow liquid limit and plasticity index and relatively high CBR and classified asnonexpansive soil. Thus the subgrade soils in sections B and C is considered asweak subgrade. The Dynamic Cone Penetration (DCP) tests were carried out on thepavement structure at three locations. The penetration depth measured up to 75cm below the base course level. The data from DCP tests were proceeded todetermine the penetration resistance (mm/blow), which is simply the distancethat the cone penetrates with each drop of the hammer.

The field CBR value wasdetermined using Transportation Research Laboratory (TRL) correlation as follows:Log (CBR) =2.48 – 1.057 Log (DCP) The DCP test is used to evaluate thestrength of granular pavement materials; base and subbase. The results of DCPtests are given in Table 5. For the road, the average CBR values of the base,subbase and embankment materials are 67%, 37% and 18% respectively.

The resultsillustrated that the base materials is not comply with the specifications (i.e.CBR ? 80%). While the subbase and embankment materials comply with thespecifications.This study has been undertaken toinvestigate the pavement failures and propose a method for inspection andevaluation of failed pavement.

The results and the conclusions drawn asfollows: 1)      The method developed in this research has beenbased on previous experiences. The focus is on establishing a systematic, andyet simple and easy to understand guidelines that is flexible enough for use ina variety of situations. 2)     Thepavement failure investigation method developed in this research can serve as auseful guide for the inspection and evaluation of pavement failures. Themethod, combined with the experience of the highway engineer and adequatematerials investigation, will help to ensure that the cause of a pavementfailure can be reliably determined. 3)     Themethod developed for inspection and evaluation was trialed in pavement failuresof Obeid Khatim road, to evaluate the effectiveness of the method for real use.It was found that the method was good as a general guide, particularly forjunior highway engineers. However, the experience of the engineer is also animportant factor in correctly diagnosing the pavement failures cause anddetermining the best maintenance option.2Thispaper summarizes the development of a method for predicting pavementperformance in terms of present serviceability index and four primary distresstypes (area and severity) and application of the method to the design offlexible pavements.

The method is based upon an s-shaped performance curve.These parameters have been found for 164 pavement test sections throughout theState of Texas. The pavement test sections were categorized in three maintypes: asphaltic concrete pavements on unbound base course, asphaltic concretepavements on bituminous base course, and asphaltic concrete overlays. The pavementstructure including the elastic modulus of each layer, the environment, and thetraffic data for these pavements were used to develop regression models for thecurve fit parameters.

A sensitivity analysis was made of these models todetermine the effects of climate in four highway districts in Texas and theresults proved to be satisfactory performance curves. The regression modelsalong with the proposed performance equations and the stochastic form of theseequations have been incorporated into the Texas Flexible Pavement Systems (FPS)design computer program. The modified version of FPS provides a listiny of theoptimal pavement designs selected on the basis of least total cost includingmaterial and user costs, overlay costs, and salvage values. This version of FPSlists all of the costs, the performance periods, the thickness of overlays thatwere placed, and the ultimate pavement failure mode for ·each period.

Typicalresults of these analyses are given.The form of the performance equationas developed from the AASHO Road Test is as follows: Where:G = damage function ranging from 0to 1N = the applied load (theaccumulated 18-kip equivalent single axle loads or total elapsed time)  = a curve fit parameter which represents theapplied load when g reaches a value of 1 = a curve fitparameter which defines the degree of curvature or the rate at which damageincreases.The primary concern in the use ofEquation arises from the following imposed boundary conditions:1)     Thefunctional (structural) performance curve must have a maximum (minimum) value,at the traffic level or time equal to zero, and must be strictly decreasing(increasing) as the traffic level or time increases. 2)     Theperformance curve cannot predict negative values of serviceability index norcan it predict a distressed area greater than 100 percent of the total area forlarge values of traffic level or time. 3)     Theperformance curve should asymptotically approach the limiting values, as it isphysically unrealistic to predict complete pavement failure, i.e. PSI=0 ordistressed area=100 percent, at a specific traffic level or point in time.Studies are continuing to developnew rules for selecting a desirable level of reliability but in the meantime,even this result is encouraging for it indicates that the new FPS program,revised as described in this paper, is more realistic than the former version,more sensitive to the factors which cause pavement deterioration, and thus moreuseful in the design of flexible pavements.

 3Existing data is required when maintenanceof a pavement is needed; and also detail data of the current distresses isrequired. Therefore, pavement has to be visually inspected prior to eachmaintenance program to determine the type, severity and extent of eachdistress. This process has a high cost and takes a lot of time. The main objectiveof this paper is to develop distress prediction model for flexible pavements.

The model parameters that are in this paper cover the common types of pavementdistresses appear on Riyadh’s main and secondary streets. Pavement distressdensity is used as the dependent variable for the developed model. Pavement distress behavior isexpected to be affected by several parameters. Considering types of collecteddata, distress behavior can be expressed as a function of: ? 1)     Distresstype, (the common distresses in main and secondary streets); ?2)      Distress Severity, (three levels: low, medium,high) ?3)      Percentage of distress density ? 4)     UrbanDistress Index (UDI) ? 5)     Time,in years ? 6)     Highwayclass (two classes: main and secondary) ? 7)     TrafficLevel, (either low or high)Thehypothesis is that distress severity, traffic level and time are directlyproportional to the distress density. The pavement condition (UDI) is expectedto decrees with increase in distress density. Based on the literature reviewand engineering judgment, the following assumptions can give a general ideaabout the expected shape and behavior of the distress density prediction model:?1)       In general, distress densitystarts its propagation process very slowly, but this propagation acceleratesmore at a later stage. This can be represented in distress density model by thepower, exponential function, or polynomial function.

? 2)      Distress density propagation, on a new or recently overlaidpavement section having poor UDI, will deteriorate faster than pavement sectionhaving excellent UDI. ? 3)      Distress density behavior on pavement sections that are subjectedto high traffic will be damaged more than pavement sections that have lowtraffic. ? 4)      Distress severity levels have an effect on behavior and propagationof distress density. For example, high severity level will propagate fasterthan low severity level.Toimprove the fit and the ability to predicate the distress density, non-lineartransformation function was tried.

The transformed function used has thefollowing form:  Inthis paper, model for predicting individual distress density on flexiblepavement was developed. The developed model was based on data collected fromthe Pavement Maintenance Management System of Riyadh city. The modelsconstructed for the most common types of distress on main and secondary streets.The model works in predicting the distress density over a period of time associatedwith each level of severity, the condition of the pavement, and both trafficlevel and highway class.

A total of 61 and 28 cases were developed for main andsecondary streets, respectively. All the cases developed by the model werefound to be statistically significant in the prediction of the distressdensity. Reserved data points where to validate the model used. The validationprocess indicated that the model could adequately predict the distress densitywith reasonable accuracy. Therefore, the developed model can be used to updatedistress data prior to each maintenance program.

This will minimize the needfor comprehensive visual inspection which proven to be costly and very timeconsuming.           4Pavement condition survey normallyincludes surface distresses, such as cracking, rutting, and other surfacedefects. Broadly, pavement roughness is also included as a condition surveyitem in some literature.

This paper reviews past research efforts in this areaconducted at several institutions, including the automated survey system ofpavement surface cracking at the University of Arkansas. The paper alsoproposes a new direction of technology development through the use of stereovisiontechnology for the comprehensive survey of pavement condition in its broaddefinition. The goal is to develop a working system that is able to establishthree-dimensional (3D) surface model of pavements for the entire pavementlane-width at 1 to 2-millimeter resolution so that comprehensive conditioninformation can be extracted from the 3D model.

  With rapid advances in digitalcamera and computing power of microcomputers, we believe that the time is rightto integrate such a system with commonly available devices and developefficient and accurate algorithms in software sub-systems to achieve thefollowing goals: 1)       High-resolution. The 3Dsurface model will provide 1 to 2-millimeter resolution in all three coordinateaxis directions, X, Y, and Z. 2)      Comprehensive survey. The information obtained from the 3D surfacemodel includes cracking, roughness, rutting, potholes, and other surfacedefects associated with both flexible and rigid pavements. 3)      Real-time at highway speed for both image acquisition and processing.Based on the new real-time technology developed at the University of Arkansasfor pavement cracking with 2D images, the realization of this goal will provideall condition results while images are being acquired at real-time.As apart of a larger research effort to develop a digital highway data vehiclestarted in the mid 1990s, the researchers at the University of Arkansas focusedon the development of a real-time automated system for distress survey. Afterexamining the feasibilities of using neural net and fuzzy sets, traditionalimaging algorithms and customized approaches have been developed to achieve thegoal of real-time processing at highway speed.

Figure 2 shows the digitalhighway vehicle at the university. Its basic features are: 1)      The vehicle is based on a full-digital design. 2)      The vehicle includes two sub-systems for pavement surface imagecollection and automated distress analyzer to identify and classify pavementcracks at real-time.3)       The vehicle collectsright-of-way video or still frame images and save them in digital format inreal-time. 4)      The vehicle acquires the location through the use of a GPS deviceand a distance measuring instrument (DMI).

5)      Real-time relational database engine, inter-computer communicationtechniques, and multi-computer and multi-CPU based parallel computing.  A four-camera system to cover 5,000 kilometers of lane-mile at fulllane-width would require two computers and one-terabyte storage. It is expectedthat 500 GB single drives will be available in less than two years. At the costof a high-end laser profiler vehicle, the new system, including four cameras,two high-end microcomputers, and all necessary peripherals and circuits, willbe able to collect the vast majority of pavement condition and serviceabilitydata, produce comprehensive survey results, including roughness, cracking,rutting, and other surface deficiencies, at the spatial resolution of 1 to2-millimeter.    Types ofdistressesBleeding: bleeding is one of many types of distresses that take place on thepavement surface that will cause it to appear shiny and will have some blackspot areas.

Causes: bleeding will occur when the asphalt binder fills the voids of theaggregates that takes place during summer time that will make it expand onto thepavement surface; the problem occurs when summer time is over and winter timearrives as this effect is not reversible and thus will accumulate on thesurface of the pavement over a period of time. High amounts of asphalt binderin the pavement while having low air void content causes it to happen. Leads to: bleeding leads to a reduction in the friction characteristics ofthe pavement surface leading to lowering the skid resistance that increases thecrash rate of vehicles. Repair/maintenance: maintenance depends on the severity of bleeding as if it wasminor, coarse sand is enough when applied to the pavement surface that willabsorb the excess asphalt binder, but if the pavement was severely bleeding,the surface of the pavement may need to be replaced with a new surface layerwith a better binder mixture for bleeding to not occur again anytime soon.   Cost Estimation Work Description Material Used Cost 1m2 (JD) Damaged  Pavement Removal Loader 0.5 Removal of loose material (cleanining) Labor s+ Compressor 0.4 Addition of MC MC Material + Labor 0.

32 Addition of Asphalt binder (HMA) + Compaction Labor + Material + Machines 4 TOTAL   5.22 Note: Prices are estimated for athickness of 5cm.The price depends based on the arearequired to repair (the larger the area the less the cost per 1m2)    Patching: A patch has a clear visible area on the pavement surface that isdue to a replacement of surface that had a distress. Causes: patches are meant to be a short term solution as a temporaryreplacement for an area that had been damaged due to distresses. Leads to: patches that are well placed will minimize the quantity of waterthat will enter the first layer; on the other hand a badly placed patch willcause water to enter the surface layer that will lead into differentialsettlement and weakness in the surface strength that will cause cracks. Repair/maintenance: well, a patch is by itself a repair method but it will lookdefected even if it was well placed, but it must be to prevent water fromentering into the pavement. Potholes/Debonding: potholes are voids found on the pavement surface that has a shapeof a bowl. Debonding happens when there is a separation between the surfacelayer and its underlying asphalt layer.

Causes: potholes start to show in small areas due to inadequate bondingbetween layers, segregation of binder and aggregates during placement, but willexpand with time with every repetition of vehicle load on it. Leads to: potholes causes’ water to enter the pavement that will causesubgrade failure and could even lead to vehicle damage if a person passes overa pothole at a high speed. Repair/maintenance: usually a patch is applied to eliminate the differential elevationof the pothole, but it is preferable (best treatment) to make a rectangular cutaround the pothole and to remove the rectangular layer then for the cut to befilled with new asphalt and to be compacted well in order to prevent waterintrusion. LongitudinalCracking: it is usuallyobserved at the center of the road and its direction is known to be parallel tothe direction of flow of vehicles. Causes: longitudinal cracking cause is related to poor joint construction,besides other reasons that could be fatigue, especially when the cracks areseen near the edge of the road.Leads to: the cracks will allow water to enter through the pavement thatwill lead to a decrease in the pavement strength through damaging theunderlying support material. This distress is the beginning form of the otherdistresses.

Repair/maintenance: as this distress leads into other distresses, the longitudinalcracking should be avoided in the first place, but if happened, early cracksealing must be applied as soon as observed to minimize the spread ofdeterioration.  Recommendation:Most of the failures due todistresses in flexible pavement happen from materials used in construction thatare the binder mixture, aggregates and water ratio. It is recommended for eachmixture to be tested in a lab In order to meet the requirements and specificationsof the mixture and the ratio intended to be used in our pavement construction.                    References:1 Magdi M.E.

Zumrawi – Universityof Khartoum, Department of Civil Engineering, Khartoum, Sudan – Survey andEvaluation of flexible Pavement Failures.2 M. Riggins, R. L. Lytton, and A.

Garcia-Diaz Texas Transportation Institute Texas A&M University SystemCollege Station, Texas – Washington, D.C., January 1985 – Developing stochasticflexible pavement distress and serviceability equations.3 Flexible pavement distressprediction model for the city of Riadh, Saudi Arabia, A. Al-Mansour – (ReceivedDecember 2003 and accepted May 2004) – Emirates Journal for EngineeringResearch, Vol. 9, No.1, 20044 Wang, Gong, submitted to 2002 Pavement Evaluation Conference,21-25, 2002, Roanoke, Virginia – Automated Pavement Distress Survey: A Reviewand A New Direction


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