A large amount of research has been conducted to investigate the influence of incorporating geosynthetics in highway pavements in laboratory-scale and full-scale experiments, and performance improvement has been well documented. In most cases, geosynthetics have been found to improve rutting resistance or reduce vertical pressure on the subgrade. Airfield pavements are typically thicker than highway pavements and are subjected to higher wheel loads and tire pressures. Thus, the benefit of geosynthetics within airfield pavements may not be as pronounced as that observed in relatively thin highway pavements. Prior to the writing of this dissertation, few documented studies focused on the performance of geosynthetic inclusion in airfield pavements and existing Department of Defense (DOD) guidance for geosynthetic inclusion had not been updated for several decades. The primary objectives of this dissertation were to update the DOD geosynthetic design methodology, to interpret results of laboratory-scale and full-scale experiments conducted specifically to evaluate geosynthetic performance in airfield pavements, and to determine if a competitive market exists for geosynthetic inclusion in airfield pavements. The main body of this dissertation is a compilation of four complementary articles that build upon the primary components of the main objectives. Chapter 1 and Chapter 2 present an introduction and a literature review, respectively. Updates to the DOD design methodology are presented in Chapter 3, results of laboratory-scale and full-scale evaluations are presented in Chapter 4 and Chapter 5, respectively, and potential implications of geosynthetic inclusion in airfield pavements are presented in Chapter 6. Chapter 7 presents overall conclusions and recommendations. Overall, it was found that, while some geosynthetics can be beneficial in airfield pavements, more rutting than would typically be allowed on an operational airfield was required to realize a meaningful performance benefit. In cases where geosynthetics were included in an airfield pavement, it was found that an extension of service life rather than a reduction in aggregate thickness was more optimal in assigning a geosynthetic value. Finally, the results of this dissertation indicated that geosynthetic inclusion in airfield pavements did not yield the same benefit level as that documented in the literature for highway pavements.

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Current pavement performance prediction models are based on the parameters such as climate, traffic, environment, material properties, etc. while all these factors are playing important roles in the performance of pavements, the quality of construction and production are also as important as the other factors. The designed properties of Hot Mix Asphalt (HMA) pavements, known as flexible pavements, are subjected to change during production and construction stages. Therefore, most of the times the final product is not the exact reflection of the design. In almost any highway project, these changes are common and likely to occur from different sources, by various causes, and at any stage. These changes often have considerable impacts on the long-term performance of a project. The uncertainty of the traffic and environmental factors, as well as the variability of material properties and pavement structural systems, are obstacles for precise prediction of pavement performance. Therefore, it is essential to adopt a hybrid approach in pavement performance prediction and design; in which deterministic values work along with stochastic ones. Despite the advancement of technology, it is natural to observe variability during the production and construction stages of flexible pavements. Quality control programs are trying to minimize and control these variations and keep them at the desired levels. Utilizing the information gathered at the production and construction stages is beneficial for managers and researchers. This information enables performing analysis and investigations of pavements based on the as-produced and as-constructed values, rather than focusing on design values. This study describes a geo-relational framework to connect the pavement life-cycle information. This framework allows more intelligent and data-driven decisions for the pavements. The constructed geo-relational database can pave the way for artificial intelligence tools to help both researchers and practitioners having more accurate pavement design, quality control programs, and maintenance activities. This study utilizes data collected as part of quality control programs to develop more accurate deterioration and performance models. This data is not only providing the true perspective of actual measurements from different pavement properties but also answers how they are distributed over the length of the pavement. This study develops and utilizes different distribution functions of pavement properties and incorporate them into the general performance prediction models. These prediction models consist of different elements that are working together to produce an accurate and detailed prediction of performance. The model predicts occurrence and intensity of four common flexible pavement distresses; such as rutting, alligator, longitudinal and transverse cracking along with the total deterioration rate at different ages and locations of pavement based on material properties, traffic, and climate of a given highway. The uniqueness of the suggested models compared to the conventional pavement models in the literature is that; it carries out a multiscale and multiphysics approach which is believed to be essential for analyzing a complex system such as flexible pavements. This approach encompasses the discretization of the system into subsystems to employ the proper computational tools required to treat them. This approach is suitable for problems with a wide range of spatial and temporal scales as well as a wide variety of different coupled physical phenomena such as pavements. Moreover, the suggested framework in this study relies on using stochastic and machine learning techniques in the analysis along with the conventional deterministic methods. In addition, this study utilizes mechanical testing to provide better insights into the behavior of the pavement. A series of performance tests are conducted on field core samples with a variety of different material properties at different ages. These tests allow connecting the lab test results with the field performance survey and the material, environmental and loading properties. Moreover, the mix volumetrics extracted from the cores assisted verifying the distribution function models. Finally, the deterioration of flexible pavements as a result of four different distresses is individually investigated and based on the findings; different models are suggested. Dividing the roadway into small sections allowed predicting finer resolution of performance. These models are proposed to assist the highway agencies s in their pavement management process and quality control programs. The resulting models showed a strong ability to predict field performance at any age during the pavements service life. The results of this study highlighted the benefits of highway agencies in adopting a geo-relational framework for their pavement network. This study provides information and guidance to evolve towards data-driven pavement life cycle management consisted of quality pre-construction, quality during construction, and deterioration post-construction. / Civil Engineering

A majority of the primary roadways in the United States are constructed using hot-mix asphalt (HMA) placed over a granular base material. The strength of this pavement system is strongly influenced by the local environmental conditions. Excessive moisture in a granular base layer can cause that layer to lose its structural contribution by reducing the area over which loading may be distributed. Excessive moisture and fine particles can be transported by hydrostatic pressure to the surface layers, thus reducing the strength of the overlying HMA by contamination. Moisture in the surface HMA layers can cause deterioration through stripping and raveling. In addition, as HMA is a viscoelastic material, it behaves more as a viscous fluid at high temperatures and as an elastic solid at low temperatures. Between these two temperature extremes, a combination of these properties is evident. Thus, understanding the environmental effects on flexible pavements allows better prediction of pavement performance and behavior under different environmental conditions. As part of the ongoing pavement research at the Virginia Smart Road, instrumentation was embedded during construction to monitor pavement response to loading and environment; moisture content of the granular base layers and temperature of the HMA layers were among the responses monitored. The Virginia Smart Road, constructed in Blacksburg, Virginia, is a pavement test facility is approximately 2.5km in length, of which 1.3km is flexible pavement that is divided into 12 sections of approximately 100m each. Each flexible pavement section is comprised of a multi-layer pavement system and possesses a unique structural configuration. The moisture content of aggregate subbase layers was measured utilizing two types of Time-Domain Reflectometry (TDR) probes that differed in their mode of operation. The temperature profile of the pavement was measured using thermocouples. Data for the moisture content determination was collected and results from two probe types were evaluated. In addition, the differences in the moisture content within the aggregate subbase layer due to pavement structural configuration and presence of a moisture barrier were investigated. It was shown that the two TDR probe types gave similar results following a calibration procedure. In addition to effects due to pavement structure and subgrade type, the presence of a moisture barrier appeared to reduce the variability in the moisture content caused by precipitation. Temperature profile data was collected on a continuous basis for the purpose of developing a pavement temperature prediction model. A linear relationship was observed between the temperature given by a thermocouple near the ground surface and the pavement temperature at various depths. Following this, multiple-linear regression models were developed to predict the daily maximum or minimum pavement temperature in the HMA layers regardless of binder type or nominal maximum particle size. In addition, the measured ambient temperature and calculated received daily solar radiation were incorporated into an additional set of models to predict daily pavement temperatures at any location. The predicted temperatures from all developed models were found to be in agreement with in-situ measured temperatures. / Ph. D.

This thesis focused on using a detailed structural evaluation of seven (three flexible and four composite) high performance in-service pavements designated as high-priority routes to verify the applicability of the Mechanistic Empirical (M-E) models to high performance pavements in the Commonwealth of Virginia. The structural evaluation included: determination of layer thicknesses (from cores, GPR and historical data), pavement condition assessment based on visual survey, estimation of layer moduli from FWD analysis as well as material characterization. One of the main objectives of this study was to utilize the results from the backcalculated moduli in order to predict the performance of this group of pavement structures using the M-E Design Guide Software. This allowed a quick verification of the performance prediction models used by comparing their outcome with the current condition. The in-depth structural evaluation of the three flexible and four composite pavements showed that all the sites are structurally sound. The investigation also confirmed that the use of GPR to determine layer thicknesses and the comparison with a minimum number of cores is a helpful tool for pavement structural evaluation. Despite some difficulties performing the backcalculation analysis for complex structures, the obtained results were considered reasonable and were useful in estimating the current structural adequacy of the evaluated structures. The comparison of the measured distresses with those predicted by the M-E Design Guide software showed poor agreement. In general, the predicted distresses were higher than the distresses actually measured. However, there was not enough evidence to determine whether this is due to errors in the prediction models or software, or because of the use of defaults material properties, specially for the AC layers. It must be noted that although an in-depth field evaluation was performed, only Level 3 data was available for many of the input parameters. The results suggest that significant calibration and validation will be required before implementation of the M-E Design Guide. / Master of Science

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: With the depletion of high quality conventional materials for road pavements, the consideration of cement stabilisation for sub-base and base layer materials often provide a feasible solution to the road industry. Like all pavement material types, the design inputs should be determined using reliable test methods, which provide a good indication of the property of materials. Any evaluation should provide a better understanding of the engineering and behavioural properties of the materials. This should form the basis for ascertaining their suitability for use in the pavement structure. However, the road industry is dependent on strength testing of cement-stabilised materials as a means to ascertain material suitability for use. Strength alone does not offer reliable insight regarding the performance and durability of the stabilised layer. This is because a cement-stabilised layer may be very stiff but not strong enough to withstand the loading and endure adverse environmental conditions. Similarly, the stabilised layer may be prone to cracking emanating from shrinkage, which leads to performance and durability related distresses. A stabilised sub-base and base of the pavement structure experiences tensile stresses and strains under traffic loading. At laboratory level, the flexural beam test simulates to an acceptable degree the mode of stress to strain to which the pavement layer experiences. However, the test lacks a standard test protocol. This leads to inconsistencies while evaluating the same material type. Due to this fact, the formulation of a standard laboratory test procedure is necessary. Shrinkage cracking is one of the major causes of pavement failure. The manifestation of wide cracks leads to performance related distresses. Cracks provide zones for the infiltration of water into the underlying layers, an aspect that results in further deterioration of the pavement structure. However, the evaluation of shrinkage at laboratory level is not usually undertaken. Disregarding shrinkage evaluation stems from the fact that a number of guidelines consider it as a natural material characteristic. The road industry frequently depends on the use of low cement contents among other techniques as a means to mitigate shrinkage cracking in cement-stabilised layers. The selection of a mitigation measure usually lacks reliable data concerning the material’s shrinkage potential. Because of this, the requirement to evaluate shrinkage at laboratory level as part of a material property measure provides a good indication regarding the quality of material. Nanotechnology products such as the Nanotterra Soil® a polymer cement additive are purported to mitigate shrinkage cracking in cement-stabilised layers. However, their suitability for use remains unspecified and dependent on the stakeholders. With the development of a shrinkage method, the evaluation of shrinkage reducing products can be undertaken. This research proposes a flexural beam test protocol for cement-stabilised materials, comprising of a span-depth ratio of nine or greater as fitting to provide a reliable measure of the material’s flexural strength and elastic modulus. The developed shrinkage test method provides a good repeatability and is user friendly. The test provides a good indication of the shrinkage criteria of ferricrete and hornfels with and without the polymer. The efficacy of the polymer is dependent on the cement content in the mix and the type and quality of the material. The research provides insight pertaining to the characterisation of shrinkage, behavioural properties, and durability of cement-stabilised materials. Analysis of the shrinkage crack pattern reveals that use of the polymer lessens the development of tensile stress in a cement-stabilised layer. Equally, the application of the low cement contents for stabilisation may not result in cracking of the stabilised layer. This research contributes to a better understanding of cement-stabilised materials. / AFRIKAANSE OPSOMMING: Namate hoë kwaliteit konvensionele materiale uitgeput raak, word sementstabilisasie van stutlaag en kroonlaag materiale al hoe meer oorweeg en is dit ʼn geskikte oplossing vir die padbou-nywerheid. Soos vir alle padboumateriale moet die ontwerpeienskappe bepaal word deur middel van betroubare toetsmetodes wat ʼn goeie aanduiding van die materiaal se eienskappe sal gee. Enige evaluering moet ʼn beter insae in die materiaal se ingenieurseienskappe en gedrag oplewer. Dit moet dan die basis vorm om die materiaal se gebruik in ʼn padstruktuur te evalueer. Die padbou-nywerheidmaak grootliks staat op die toetsing van skuifsterkte van sementgestabiliseerde materiaal om die geskiktheid daarvan vir gebruik te bepaal. Sterkte op sigself lewer egter nie ʼn betroubare maatstaf van die materiaal se gedrag en duursaamheid nie. Dit is aangesien ʼn sementgestabiliseerde laag baie solied mag wees maar nogtans nie sterk genoeg om belasting te weerstaan en bestand teen omgewingstoestande te wees nie. Net so mag ʼn gestabiliseerde laag vatbaar vir kraakvorming as gevolg van krimping wees en dit kan lei tot duursaamheid-verwante en werkverwante skade. ʼn Gestabiliseerde stutlaag en kroonlaag in die plaveiselstruktuur is onderhewig aan trekspannings en vervormings as gevolg van verkeerslaste. Op laboratoriumvlak boots die balkbuigtoets die spanning en vervorming wat ʼn plaveisellaag ondervind tot ʼn aanvaarbaar hoë mate na. Die toets beskik nie oor ʼn standaard-toetsprosedure nie. Dit lei tot afwykings terwyl dieselfde materiaal evalueer word. Om hierdie rede is die ontwikkeling van ʼn standaard-laboratoriumprosedure nodig. Krimpkraking is een van die grootste oorsake van plaveiselswigting. Die onwikkeling van wye krake lei tot werksverwante skade. Krake veroorsaak areas vir die infiltrasie van water in die onderliggende plaveisellae wat verdere agteruitgang van die plaveiselstruktuur veroorsaak. Desnieteenstaande word ʼn evaluering van kraking op laboratoriumvlak selde gedoen. Dit spruit uit die feit dat ʼn aantal ontwerp-riglyne kraking as ʼn natuurlike materiaaleienskap beskou. Die padbounywerheid moet dikwels staatmaak, op onder andere, ʼn lae sementinhoud om krimpkraking te minimeer. Hierdie tipe benadering gaan dikwels mank aan betroubare inligting oor die materiaal se krimpingspotensiaal. Om hierdie rede is die ondersoek van krimping op laboratoriumvlak nodig as deel van die ondersoek van die materiaaleienskappe om die kwaliteit van materiale te bepaal. Minimeringstegnieke verander deurlopend. Die toepassing van nanotegnologieprodukte, soos Nanotterra Soil®, ‘n polimeersement bymiddel, wat na bewering krimpkraking in sementgestabiliseerde lae kan minimeer, kom voortdurend op die mark. Nogtans bly hulle geskiktheid ongespesifiseerd en afhanklik van die leweransiers. Indien ʼn krimptoetsmetode ontwikkel word, sal die effektiwiteit van krimpverminderingsmiddels getoets kan word. Hierdie navorsing stel die ontwikkeling van ʼn toetsprosedure vir ʼn balkbuigtoets voor met ʼn spanlengte tot diepteverhouding van minstens nege as betroubare maatstaf van ʼn materiaal se buigsterkte en modulus van elastisiteit. Die ontwikkelde krimptoetsmetode lewer ʼn goeie herhaalbaarheid en is gebruikersvriendelik. Die toets verskaf ʼn goeie aanduiding van krimpingskriteria van ferrikreet en horingfels met en sonder polimeer. Die effektiwiteit van die polimeer hang af van die sementinhoud in die mengsel asook die tipe en kwaliteit van die materiaal. Die navorsing verskaf insig aangaande die karakterisering van krimping, gedragseienskappe en duursaamheid van sementgestabiliseerde materiale. Die navorsing help mee om sementgestabiliseerde materiale beter te verstaan.

As the cost of designing and building new highway pavements increases and the number of new construction and major rehabilitation projects decreases, the importance of ensuring that a given pavement design performs as expected in the field becomes vital. To address this issue in other fields of civil engineering, reliability analysis has been used extensively. However, in the case of pavement structural design, the reliability component is usually neglected or overly simplified. To address this need, the current dissertation proposes a framework for estimating the reliability of a given pavement structure regardless of the pavement design or analysis procedure that is being used. As part of the dissertation, the framework is applied with the Mechanistic-Empirical Pavement Design Guide (MEPDG) and failure is considered as a function of rutting of the hot-mix asphalt (HMA) layer. The proposed methodology consists of fitting a response surface, in place of the time-demanding implicit limit state functions used within the MEPDG, in combination with an analytical approach to estimating reliability using second moment techniques: First-Order and Second-Order Reliability Methods (FORM and SORM) and simulation techniques: Monte Carlo and Latin Hypercube Simulation. In order to demonstrate the methodology, a three-layered pavement structure is selected consisting of a hot-mix asphalt (HMA) surface, a base layer, and subgrade. Several pavement design variables are treated as random; these include HMA and base layer thicknesses, base and subgrade modulus, and HMA layer binder and air void content. Information on the variability and correlation between these variables are obtained from the Long-Term Pavement Performance (LTPP) program, and likely distributions, coefficients of variation, and correlation between the variables are estimated. Additionally, several scenarios are defined to account for climatic differences (cool, warm, and hot climatic regions), truck traffic distributions (mostly consisting of single unit trucks versus mostly consisting of single trailer trucks), and the thickness of the HMA layer (thick versus thin). First and second order polynomial HMA rutting failure response surfaces with interaction terms are fit by running the MEPDG under a full factorial experimental design consisting of 3 levels of the aforementioned design variables. These response surfaces are then used to analyze the reliability of the given pavement structures under the different scenarios. Additionally, in order to check for the accuracy of the proposed framework, direct simulation using the MEPDG was performed for the different scenarios. Very small differences were found between the estimates based on response surfaces and direct simulation using the MEPDG, confirming the accurateness of the proposed procedure. Finally, sensitivity analysis on the number of MEPDG runs required to fit the response surfaces was performed and it was identified that reducing the experimental design by one level still results in response surfaces that properly fit the MEPDG, ensuring the applicability of the method for practical applications. / text

Mechanistic-Empirical  (M-E)  pavement  design  procedures  are  composed  of  a  reliable  response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. One of the main objectives of this study was to develop a response model based on multilayer elastic  theory   (MLET)  with  improved  computational  performance  by   optimizing  the   time consuming parts of the MLET processes. A comprehensive comparison of the developed program with  two  widely  used  programs  demonstrated  excellent  agreement  and  improved  computational performance.  Moreover,  the  program  was  extended  to  incorporate  the  viscoelastic  behaviour  of bituminous materials through elastic-viscoelastic correspondence principle. A procedure based on collocation of linear viscoelastic (LVE) solutions at selected key time durations was also proposed that improved the computational performance for LVE analysis of stationary and moving loads. A comparison  of  the  LVE  responses  with  measurements  from  accelerated  pavement  testing  (APT) revealed a good agreement. Furthermore the developed response model was employed to evaluate permanent deformation models  for  bound  and  unbound  granular  materials  (UGMs)  using  full  scale  APTs.  The  M-E Pavement  Design  Guide  (MEPDG)  model  for  UGMs  and  two  relatively  new  models  were evaluated  to  model  the  permanent  deformation  in  UGMs.  Moreover,  for  bound  materials,  the simplified  form  of  the  MEPDG  model  for  bituminous  bound  layers  was  also  evaluated.  The measured  and  predicted  permanent  deformations  were  in  general  in  good  agreement,  with  only small discrepancies between the models. Finally, as heavy traffic loading is one of the main factors affecting the performance of flexible pavement, three types of characterizations for heavy traffic axle load spectrum for M-E analysis and design of pavement structures were evaluated. The study recommended an improved approach that enhanced the accuracy and computational performance. / <p>QC 20140512</p>

abstract: The major challenge for any pavement is the freight transport carried by the structure. This challenge is expected to increase in the coming years as freight movements are projected to grow and because these movements account for most of the load related distresses for the pavement. Substantial effort has been devoted to identifying the impacts of these future national freight trends with respect to the environment, economic growth, congestion, and reliability. These are all important aspects relating to the freight question, but an equally important and often overlooked aspect of this issue involves the impact of freight trends on the physical infrastructure. This study analyzes the impact of future freight traffic trends on 26 major interstates representing 68% of the total system mileage and carrying 80% of the total national roadway freight. The pavement segments were analyzed using the Mechanistic Empirical Pavement Design Guide software after collecting the relevant traffic, climate, structural, and material properties. Comparisons were drawn between the expected pavement performance using current design standards for traffic growth and performance predictions that incorporated more detailed freight projections which themselves considered job growth and six key drivers of freight movement. The differences in the resultant performance were used to generate maps that provide a bird’s eye view of locations that are especially vulnerable to future trends in freight movement. The analysis shows that the areas of greatest vulnerability include segments that are directly linked to the busiest ports, and surprisingly those from Atlantic and Central states that provide long distance connectivity, but do not currently carry the highest traffic volumes. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2016