Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by Subject "Asphalt emulsion mixtures"

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    hiResilient response and performance of bitumen stabilized materials with foam incorporating reclaimed asphalt
    (Stellenbosch : Stellenbosch University, 2014-04) Dal Ben, Matteo; Jenkins, K. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The increased use of reclaimed asphalt (RA) in Bitumen Stabilised Materials (BSMs), shortcomings in the existing design guidelines and manuals and ongoing developments in the concepts and understanding of these materials require further research into the fundamental properties and behaviour of BSMs. The state-of-the-art of foamed bitumen techniques is reviewed in the literature study. Current best practices in the design of BSMs and pavements incorporating such materials are also included in this literature study. Shortcomings and areas for further improvement of the design practice have been identified. With new environmental legislation, the importance of BSM technology including RA as an environmentally-friendlier and more sustainable construction technique is set to increase in the coming years. Changes in the behaviour of materials and failure mechanisms of BSM mixes are long-term phenomena. This implies that the study of the physico-chemical and mechanical properties of the mixes with increasing amount of RA is vital. Therefore, fundamental understandings of moisture damage and thermo-physical characteristics, which are related to material properties, are required. The main objective of this study is to advance BSM technology by assessing the influence of the selected materials on durability behaviour, temperature distribution and long-term performance in all phases of application (i.e. mix design, construction, and in-service condition). This study begins with a comprehensive literature review of research dealing with the interactions between RA and mineral aggregates. The properties of RA and mineral aggregates were reviewed. This was followed by a review into the mechanical properties of BSM-foam mixes with high percentage of RA and its durability performance. Factors influencing the temperature gradient of BSMs were then identified. Achieving a better understanding of the fundamental performance properties and temperature influence on the behaviour of BSMs with high percentage of RA is one of the key factors of this research, with a view to using the extended knowledge for improvements to current mix design and structural design practices. Finally, the fundamental theories on thermo-conductivity and the mechanical properties of the BSM were used to create a relationship between temperature and mechanical properties in a pavement section. A laboratory testing programme was set up to study the properties and behaviour of BSMs and to establish links with the compositional factors, i.e. the type of binder used, the percentage of RA in the mix and the addition of a small amount of cement as active filler. BSMs were blended in three different proportions of RA and good quality crushed stone materials: 100% RA (with 2 % bitumen content), 50% RA and 50% G2 Hornfels crushed stone (with 2.1% bitumen content) and 100% G2 (with 2.3 % bitumen content). Tri-axial testing was carried out to determine shear parameters, resilient modulus and permanent deformation behaviour, while brushing testing was carried out to determine the possible durability performance of the BSMs. The mixture durability in terms of moisture damage was investigated. Temperature data were collected and a model to accurately simulate the temperature distribution in the BSMs was identified and proposed for further investigation and validation. It was found from the laboratory temperature data collected in this study that the temperature gradient varied according to the depth of the BSMs. A considerable part of the efforts of this study were dedicated to characterise and model the temperature distribution in a pavement section, taking into account the mechanical properties and performance of the BSMs at different temperature layers. The study provides an insight into fundamental mechanical performance, material durability properties, and the thermal capacity and conductivity of the BSM-foam mixes with high percentage of RA. This will assist in improving the current procedure for selection, combining and formulation of the mix matrices for BSMs. In addition, the study provides guidelines that will enable practitioners to confidently understand the relationship between temperature gradient and mechanical behaviours of BSM-foam pavement section. The specific durability-related issues addressed in this study are substance for future research.
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    Mix design considerations for cold and half-warm bituminous mixes with emphasis of foamed bitumen
    (Stellenbosch : Stellenbosch University, 2000-12) Jenkins, Kim Jonathan; Van de Ven, Martinus F. C.; Molenaar, Andre A. A.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The use of foamed bitumen and bitumen emulsion as binders for use in road rehabilitation is gaining favour globally. High-level road facilities through to unpaved roads requiring attention are being treated with these binders due to environmental, economic and practical benefits in the use of cold bituminous mixes. In addition, static and mobile plant with the capability of performing stabilisation using bitumenemulsion and foamed bitumen has become commercially available and widely utilised, as a result of development in recycling technology and lapse in patent rights on foam nozzles. An understanding of the behaviour and failure mechanisms of these cold mixes, as well as sound guidelines for the mix design procedures of cold mixes, especially foamed bitumen, and design guidelines for pavements structures incorporating these materials, are lacking however. Mix designs are carried out primarily on the basis of experience and pavement designs are empirically based. The main objective of this dissertation is to address the need for a fundamental understanding of foamed bitumen and foamed bitumen mixes, and in so doing to develop techniques for adjudicating mixes, optimising their composition and rationalising their design both as mixes and as layers in road pavements. At the same time the exploration of new applications for foamed bitumen and the possibilities for progressive related technology, is a priority. To commence, this study includes an appraisal of most of the literature available on foamed bitumen. This is followed by a fundamental investigation of the colloidal mass of foam that is produced when small quantities of cold water are added to hot bitumen. Factors influencing the quality of the foam are identified and a Foam Index is developed for characterisation and optimisation of the foam. The spatial composition of a cold foamed bitumen mix, including Interaction of the foam with moist mineral aggregate, is also addressed in this dissertation. In particular, the stiffening of the filler mastic using foamed bitumen as binder is analysed. Techniques of optimising the sand type and content in the mix are also developed and guidelines for desired aggregate structures for foam treatment are established. The temperature of the mineral aggregate has been shown to have a profound influence on the behaviour and performance of a foamed bitumen mix. This has been selected as a focal area of further investigation and the research has lead to the development of a new process called "The half-warm foamed bitumen treatment process" that can produce mixes with almost the quality of hot mix asphalt with up to 40% less energy consumption. Other processes developed in this research include the use of cold mix asphaltic blocks for construction of road pavements in developing areas. This technology enhances the use of a high labour component in road construction in an economically competitive manner. The dissertation provides details for mix design and construction of the cold mix blocks. Finally, the study includes models for the performance prediction of foamed bitumen mixes. In particular, foamed mixes that exhibit stress-dependent behaviour have been investigated and models established on the basis of triaxial testing and accelerated pavement testing for the prediction of permanent deformation of such layers under repeated loading. Practical applications of the research findings are summarised in Appendix F. This includes: • methods for optimisation of the foamed bitumen properties, • guidelines for the selection of the ideal aggregate structure for cold foamed mixes, • procedures for carrying out cold mix design in the laboratory (including mixing, compaction and curing), • procedures for manufacturing half-warm foamed mixes in the laboratory, • methods for manufacturing cold mix blocks, and • pavement design methods for road structures incorporating foamed mix layers. Appendix G outlines statistical techniques that are relevant to the design of experiments in pavement engineering including examples of applications of these procedures. The techniques are applied selectively in the relevant chapters of the dissertation.
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    PAVDAM - probabilistic and volumetric design of asphalt mixtures
    (Stellenbosch : Stellenbosch University, 2002-12) Smit, Andre de Fortier; Jenkins, K. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The dissertation presents a design procedure for HMA mixes based on probabilistic and volumetric approaches, hereafter referred to as PAVDAM. Central to PAVDAM is the use of an analytical model for estimating the voids in the mineral aggregate (VMA) of asphalt mixes. Validation of the mix design procedure was done through accelerated pavement testing (APT) with the Model Mobile Load Simulator (MMLS3) at the National Center for Asphalt Technology (NCAT) test track in Opelika, Alabama. In addition, the semi-circular bending (SCB) test was evaluated to serve as an analysis tool to augment the proposed mix design procedure. Non-linear finite element analyses using a quasi-isotropic material model were done using the CAPA-3D finite element system developed at the Technical University of Delft in the Netherlands to better characterise the tensile strength properties of specimens tested with the SCB. PAVDAM is partly based on performance related and analytical procedures such as the Stategic Highway Research Program (SHRP) Superpave and the Belgium Road Research Centre (BRRC) design method. The mix design system was developed based on gyratory compaction procedures. In this regard, the criteria relating gyratory compaction to design traffic as specified in Superpave are used. PAVDAM differs from other mix design methods in that a probabilistic approach is used to account for the variabilities associated with mixture components and properties during the manufacturing stage. It serves as a subset of the volumetric optimisation stage of the mix design process. The development of an analytical model to estimate the VMA of an asphalt mix was the central theme of the dissertation. The analytical model developed is based on modified Aim and Toufar (MAT) packing models developed under SHRP research and used in the concrete industry. The MAT packing models are based on the theory underlying the packing of monosized spheres and the combination of successive binary systems. These models were further refined for use in the asphalt industry. A probabilistic procedure based on the BRRC PRADO packing model is used to account for the influence of size ratio of the successive monosized binary systems. The result was a model that allows an estimation of the VMA of a mix from the gradation of the mix, the voids in the filler and the porosities of the individual aggregate fractions making up the mix. Research was undertaken to couple VMA estimates with gyratory compaction levels. This allowed estimates to be made of the optimum binder contents of mixes for different design traffic levels. The VMA of a mix is difficult to estimate accurately since it is difficult to quantify the factors influencing VMA such as gradation, particle shape, angularity, texture and rugosity. Furthermore, the influence of binder content and compaction must be taken into account. The MAT packing model underestimates the VMA of mixes compared to measured values. For this reason it is necessary to calibrate the model to allow more accurate estimations. More sophisticated models are required to more accurately estimate the VMA of mixes. It is recommended that the development of these be explored further. Asphaltic materials are inherently heterogeneous and there are a large number of factors that influence their volumetric properties. Because of this, Monte Carlo simulation techniques are used in PAVDAM to evaluate the combined effect of the variabilities of significant material properties. The dissertation expands on the different variabilities and the effects of variability on mixture volumetrics and mix design verification. The dissertation outlines the algorithms and procedures used in PAVDAM to estimate the binder content of a mix. In order to validate the PAVDAM model, analyses were done to determine the reliability of specific NCAT MMLS3 test section mixes in terms of densification in the field. A comparison of PAVDAM estimated and field binder contents allowed a ranking of the reliabilities of the different section mixes in terms of field densification at the design traffic level. This ranking compared favourably with that obtained from an analysis of actual densification trends monitored in the field under full-scale trafficking. Initial FEM analyses of the SCB using linear elastic isotropic modelling allowed the development of equations to characterise the tensile strength and modulus characteristics of specimens tested using the SCB. It was emphasized that these equations do not provide a realistic assessment of the strengths or moduli of asphaltic materials. The strengths and moduli of these materials are influenced by strain rates within the materials that cannot be assessed using a simple linear elastic approach. To address this, an alternative FEM analyses using CAPA-3D was undertaken. An approach was adopted to account for the influence of tensile and compressive strain rates on modulus. The analyses made use of a quasi-isotropic material model and it was shown to better characterise the tensile strengths of HMA materials using the SCB. The analyses also indicated that the tensile strengths determined using the equations initially developed based on a linear elastic approach result in strengths that are unrealistically high. It is recommended that further finite element research be done using non-linear material modelling to evaluate the very complex stress-strain conditions within an SCB specimen to better characterise fracture response. It is also recommended that the fatigue characterisation of HMA be explored based on strength tests using the SCB. PAVDAM represents a rational approach to mix design, a shift from experimental empiricism towards scientific fundamentalism. PAVDAM can be used to define the spatial composition of asphalt mixes. The influence of mix component variability may be addressed and reliability assessments of candidate gradations are possible during volumetric optimisation. Furthermore, changes in the volumetric properties of asphalt mixes may be investigated. As such, PAVDAM is a mix design management tool and can only be effective when used as part of a system that closely monitors variability and systematically refines the underlying packing model.