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Low density polyethylene (LDPE) when dispersed in asphalt cement through a high shear blending process produces asphalt concrete mixtures (Novophalt) with superior resistance to deformation at high service temperatures. The dispersion of LDPE within the asphalt results in rheological changes in the binder which not only significantly improve resistance to creep deformation but also improve mixture shear strength. The ratio of induced octahedral shear stress in a paving mixture to the octahedral shear strength of the paving mixture at the specific conditions of loading is used to demonstrate the ability of Novophalt to reduce deformation potential of asphalt pavements through improved shear strength. The results of the shear strength analysis are corroborated by creep deformation and accumulated permanent strain analyses.
"ASTM Publication Code Number (PCN) 04-011080-08. - "Sponsored by ASTM Committee D-4 on Road and Paving Materials."-- Foreword. - Includes bibliographical references and indexes. - Electronic reproduction; W. Conshohocken, Pa; ASTM International; 2011; Mode of access: World Wide Web; System requirements: Web browser; Access may be restricted to users at subscribing institutions.
This book provides innovative chapters on the growth of educational, scientific, and industrial research activities among chemists, biologists, and polymer and chemical engineers and provides a medium for mutual communication between international academia and the industry. It presents significant research and reviews reporting new methodologies an
This book provides innovative chapters on the growth of educational, scientific, and industrial research activities among chemists, biologists, and polymer and chemical engineers and provides a medium for mutual communication between international academia and the industry. It presents significant research and reviews reporting new methodologies and important applications in the fields of industrial chemistry, industrial polymers and biotechnology as well as includes the latest coverage of chemical databases and the development of new computational methods and efficient algorithms for chemical software and polymer engineering.
Since its creation in 1884, Engineering Index has covered virtually every major engineering innovation from around the world. It serves as the historical record of virtually every major engineering innovation of the 20th century. Recent content is a vital resource for current awareness, new production information, technological forecasting and competitive intelligence. The world?s most comprehensive interdisciplinary engineering database, Engineering Index contains over 10.7 million records. Each year, over 500,000 new abstracts are added from over 5,000 scholarly journals, trade magazines, and conference proceedings. Coverage spans over 175 engineering disciplines from over 80 countries. Updated weekly.
Low density polyethylene is a major part of the waste plastic stream. Its use as a recycled additive in hot mix asphalt concrete pavement extends back to the mid-1970's in Europe. Recent and extensive testing has demonstrated that waste or recycled polyethylene is as effective in modifying the hot mix asphalt concrete as is virgin polyethylene as long as the recycled polymer is free of metals and paper and the percentage of additional polymer does not exceed 17 percent. The resistance to deformation of hot mix asphalt concrete modified with approximately 5 percent low density polyethylene is significantly better than that of the unmodified mix. Results of uniaxial creep testing parameters, including creep modulus, slope of the steady state portion of the creep curve and time to tertiary creep, on a large number of mixtures are used to evaluate the influence of recycled polyethylene modification. Moderate and low temperature fatigue properties are also evaluated based on controlled stress and controlled deformation fracture fatigue testing.
Rutting potential in asphalt concrete pavements (ACP) over both flexible (granular), and rigid (PCC) pavements is investigated. A detailed analysis of the influence of ACP mixture stiffness, stiffness ratios between the ACP surface and the supporting base, ACP layer thicknesses, surface shear, realistic tire contact stresses, and degree of interlayer bonding is presented. The result of the analysis is presented in terms of octahedral shear stress contours.
Of the principal deteriorations encountered most in the flexible pavements, thepermanent deformations constitute a major problem in regard both the traffic safety and cost of repair. In order to remedy these adverse effects, it is essential that both the mix design proportions be revised and the quality of the ingredients of the mix ( the aggregates and the bituminous binder) be increased. Although it is possible to use aggregates with lower wearing ratios, their availibility is restricted by limited geologic formations to several rock types (basalt and granit). This restriction has drawn the attention of researchers to the second element of the asphalt mix, the bituminous binder and hence the idea of modifıed asphalt was born.The purpose of this study is to investigate the influence of the High Density Polyethylene (HDP) ,as a bitumen modifier, on the Marshall and Resilient characteristics of the modifıed asphalt concrete. The goal of asphalt modification is to develop mix design proportions which improve the performance of the pavement by decreasing the permanent deformations. Chapter 1 diagnoses that increasing heavy traffic loads and harsh climate conditions causes serious and unexpected early deterioration in road pavements. The components of the asphalt concrete with the HDP modifıed binder are explained in Chapter 2. The resilient modulus of asphalt conrete is defıned in Chapter 3 where it is emphasized that the resilient modulus has gained popularity as a means of evaluating the response of asphalt concrete to loads. In this study the resilient modulus has been determined by the diametrial resilient modulus test which is a nondestructive test and allows the testing of the specimen under different conditions to avoid specimen-to-specimen variations. In Chapter 4, a survey of past studies on the polymer modifıed asphalt concrete are given. Materials and Procedures are presented in Chapter 5 where the results of investigation on the effects of mixing temperature (145-155-165oC), mixing time (5-15-30 min.) and HDP content (0-2-4- 6-8) on the rheologic properties of the binder are presented. During the research, a plethora of Marshall and Resilient Modulus tests have been performed on the Marshall specimens and the effects of mixing time, mixing temperature and HDP content on the Marshall and Resilient characteristics have been determined. The Resilient Modulus tests have been perforıned at four test temperatures (5-25-40- 60oC) , each repeated for three different rise time values (30-60-l00ms). As a result, for a given mixing time and mixing temperature, while penetration and ductility decrease, viscosity and softening point increase proportionally with increasing HDP content. Marshall stability increases up to 4% HDP and decreases there on. The resilient modulus displays a similar trend. Mathematical models have been established for each resilient modulus test. Statistical evaluations has revealed good correlation between observed and predicted values.
Rutting is recognized to be the major distress mechanism in flexible pavements as a result of increase in tire pressures and axle loads. Rutting is caused by the accumulation of permanent deformation in all or some of the layers in the pavement structure. The accumulation of permanent deformation in the asphalt surfacing layer is now recognized to be the major component of rutting in flexible pavements. This is a consequence of increased tire pressures and axle loads, which subjects the asphalt surfacing layer nearest to the tire-pavement contact area to increased stresses. Thus the study of permanent deformation properties of asphalt mixtures has become the focus of research, which aim to mitigate or reduce rutting in flexible pavements. The research work reported in this thesis aims to contribute towards understanding of the material properties and factors affecting permanent deformation in asphalt mixtures, mechanisms of the permanent deformation, and methods of its prediction. The specific objectives of this research work include; review and evaluation of available models for permanent deformation of asphalt concrete mixtures, investigation of the effect of volumetric composition, loading and temperature conditions on the permanent deformation of asphalt concrete, and the identification and definition of simple measures of resistance to permanent deformation. To meet the objectives of the study a laboratory investigation is conducted on several asphalt concrete specimens with varying volumetric composition. Two testing procedures are adopted; the repeated load triaxial and triaxial creep and recovery tests. The tests were conducted at two temperature levels of 25 and 50oC under varying stress conditions. A review of literature on factors affecting permanent deformation and available models for prediction of the permanent deformation is also conducted. The literature review indicated that most of the research work done so far concentrated on evaluation of the effect on permanent deformation response of component material properties such as aggregate gradation, aggregate angularity and binder type (or grade). Most of the studies conducted on permanent deformation properties of asphalt mixtures were also found to be based on different testing procedures and methods of evaluation, which makes it difficult to compare them and draw firm conclusions. The literature also indicated that, as yet, there is no comprehensive model for deformation of asphalt concrete. Results of tests conducted in this study are analysed to investigate the effect of volumetric composition, particularly binder content and void content, and loading conditions on the permanent deformation response of the mixture. Both the binder content and void content are found to significantly influence the permanent deformation characteristics. The effect of loading conditions, i.e., the confining stress and the deviatoric stress, is also found to be significant. Throughout this study emphasis is placed on methods and parameters that are used to evaluate mixtures for their resistance to permanent deformation. The traditionally used parameters such as the slope and intercept of the power model are evaluated for their sensitivities to changes in volumetric composition. This evaluation is based on the premises that any measure of resistance to permanent deformation should be sensitive to changes in volumetric composition to be good enough. It is found that most of these parameters are not sensitive to changes in volumetric composition and therefore are not suitable for comparison of mixtures made from the same materials but with varying proportion of the components. Permanent deformation in asphalt concrete is caused by both densification and shear deformation. The mode of deformation in asphalt concrete pavements, for greater part of their service life, is considered to be the shear deformation. Therefore it is necessary to evaluate mixtures for their susceptibility to shear deformation. The shear deformation manifests itself in the form of large lateral deformation relative to axial deformation. It is found that one dimensional analysis, which does not take the lateral deformation into account may lead to misleading results regarding the resistance to permanent deformation of mixtures. Therefore parameters which include volumetric and lateral strain are proposed for use in evaluation of mixtures. Substantial effort is put into modelling the accumulation of permanent deformation under repeated loading. For this purpose two approaches were selected: the cyclic hardening model based on bounding surface plasticity concept and an elasto-viscoplastic model based on strain decomposition approach. The bounding surface plasticity approach is found to be a convenient method to model the accumulation of permanent deformation. It is demonstrated that deformations calculated using cyclic hardening model based on bounding surface plasticity fits the measured deformation quite well. The elasto-viscoplastic model, which is based on strain decomposition approach, provides a suitable method for analysis of creep and recovery test results. Deformations calculated using this model also fit the measured deformation quite well. Finally a new composite measure of resistance to permanent deformation is developed. The resistance index is based on strain decomposition approach and is simple to calculate. The index incorporates a parameter related to shear susceptibility of mixtures and is sensitive to changes in volumetric composition. It is believed that this index can be used to compare and select mixtures at mixture design stage. If its applicability to other materials is proved by further research, it can also be linked to performance related specifications, as a simple measure of performance with regard to rutting.