hiResilient response and performance of bitumen stabilized materials with foam incorporating reclaimed asphalt

Thesis (PhD)--Stellenbosch University, 2014.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.AFRIKAANSE OPSOMMING: Die toenemende gebruik van herwonne asfalt (Engels: reclaimed asphalt (RA)) in bitumen gestabiliseerde materiaal (Engels: Bitumen Stabilised Materials (BSMs)), tekortkominge in die bestaande ontwerpriglyne- en handleidings en deurlopende verbeteringe in die konsepte en begrip van hierdie material vereis verdere navorsing oor die fundamentele eienskappe en gedrag van BSM. In die literatuurstudie word die huidige stand van kennis van die ontwerp van skuimbitumentegnieke ondersoek. Die literatuurstudie dek ook die huidige beste praktyke in die ontwerp van BSM en plaveisels wat hierdie materiale insluit. Tekortkominge en areas van verdere verbetering in die ontwerppraktyke is geïdentifiseer. Onlangse omgewingswetgewing verhoog die belangrikheid van BSM tegnologie, insluitend RA, as ‘n meer omgewingsvriendelike en volhoubare konstruksie-tegniek. Hierdie faktor sal in die toekoms al hoe belangriker word. Die verandering in die gedrag van materiaal en die falingsmeganismes van BSM mengsels is langtermynverskynsels. Dit impliseer dat die studie van die fisio-chemiese en meganiese eienskappe van mengsels met toenemende verhoudings van RA van kardinale belang is’n Fundamentele begrip van die vogskade en temo-fisiese eienskappe, wat verwant is aan die materiale se eienskappe, word vereis. Die primêre doelwit van die studie is die bevordering van BSM tegnologie deur die invloed van die geselekteerde materiale op duursaamheid, temperatuurverspreiding en langtermyn gedrag in al die fases van toepassing (mengselontwerp, konstruksie en in-dienstoestand) te bepaal. Die verhandeling begin met ‘n omvattende literatuuroorsig van navorsing oor die interaksie tussen RA en mineraalaggregate. Die eienskappe van RA en die mineraalaggregate word bespreek. Dit word gevolg deur ‘n oorsig van die meganiese eienskappe van die BSM-skuimbitumenmengsels met ‘n hoë persentasie RA en die duursaamheidgedrag daarvan. Faktore wat die temperatuurgradient van BSM beïnvloed word dan aangetoon. ‘n Beter begrip van die fundamentele gedragseienskappe en die invloed van temperatuur op die gedrag van BSM met ‘n hoë persentasie RA is een van die sleutelfaktore van hierdie navorsing. Dit het ten doel om die uitgebreide kennis te gebruik om huidige mengselontwerp en strukturele ontwerppraktyke te verbeter. Laastens is die fundamentele teorie van termogeleiding en die meganiese eienskappe van BSM gebruik om ‘n verhouding tussen temperature en meganiese eienskappe in ‘n plaveiselsnit te ontwikkel. ‘n Laboratoriumtoetsprogram is opgestel om die eienskappe en gedrag van BSM te bestudeer en om verwantskappe tussen samestellende faktore soos die tipe bindmiddel gebruik, die persentasie RA in die mengsel en die toediening van klein hoeveelhede sement as aktiewe vuller te bepaal. BSM is in drie verskillende verhoudings van RA en goeie gehalte gebreekte klipmateriaal vermeng: 100% RA met 2 % bitumen, 50% RA en 50 % G2 Hornfels gebreekte klip met 2.1 % bitumen en 100% G2 met 2.3 % bitumen. Drie-assige druktoetse is gebruik om skuifsterkteparameters, elastiese modulus en permanente vervormingsgedrag te bepaal. Borseltoetse is gebruik om die duursaamheidgedrag van BSM te bepaal. Die mengsels se duursaamheid is ook in terme van vogskade ondersoek

Diagnostics on the Basis of the Frequency-Temperature Dependences of the Loss Angle Tangent of Heavily Moistured Oil-Impregnated Pressboard

The aim of this study was to perform precision measurements of the frequency-temperature dependences of the loss angle tangent of the liquid-solid composite with the FDS Dirana meter. The composite consisted of heavily moistered oil-impregnated pressboard. The moisturization of the pressboard occurred in a manner as close as possible to the process of wetting the insulation in power transformers to a moisture content of (5.0 ± 0.2) wt. %. This value of moisture content was chosen because exceeding this value can lead to transformer failure. The measuring temperature range was from 293.15 K (20 °C) to 333.15 K (60 °C), with a step of 8 K. The measuring frequency range was 0.0001 Hz to 5000 Hz. It was observed that the shape of the frequency dependence of the loss angle tangent for a moisture content of 5.0 wt. % does not depend on the value of the measuring temperature. An increase in temperature leads to a shift of the waveforms into the higher frequency region. This is associated with a decrease in the relaxation time, and its value depends on the activation energy. It was found that a good fit of the waveforms, simulated by Dirana, to the actual tgδ waveforms obtained at temperatures between 293.15 K (20 °C) and 333.15 K (60 °C) requires the introduction of temperatures, higher than the actual insulation temperatures, into the program. It was found that estimating the moisture content for different temperatures using Dirana soft-ware for insulating an oil-impregnated pressboard produced large discrepancies from the actual content. Better results were obtained after an adjustment requiring manual temperature correction towards higher, compared to measured, temperatures. The moisture content estimated after correction by the Dirana meter ranges from of 4.5 wt. % to 5.7 wt. % and increases almost linearly with increasing measuring temperature. The average moisture content estimated by the Dirana meter for all measuring temperatures is 5.1 wt. % and is close to the actual content (5.0 ± 0.2) wt. %. The uncertainty of the estimate is ±0.43 wt. % and is more than twice as high as the true value

Diagnostics on the Basis of the Frequency-Temperature Dependences of the Loss Angle Tangent of Heavily Moistured Oil-Impregnated Pressboard

The aim of this study was to perform precision measurements of the frequency-temperature dependences of the loss angle tangent of the liquid-solid composite with the FDS Dirana meter. The composite consisted of heavily moistered oil-impregnated pressboard. The moisturization of the pressboard occurred in a manner as close as possible to the process of wetting the insulation in power transformers to a moisture content of (5.0 ± 0.2) wt. %. This value of moisture content was chosen because exceeding this value can lead to transformer failure. The measuring temperature range was from 293.15 K (20 °C) to 333.15 K (60 °C), with a step of 8 K. The measuring frequency range was 0.0001 Hz to 5000 Hz. It was observed that the shape of the frequency dependence of the loss angle tangent for a moisture content of 5.0 wt. % does not depend on the value of the measuring temperature. An increase in temperature leads to a shift of the waveforms into the higher frequency region. This is associated with a decrease in the relaxation time, and its value depends on the activation energy. It was found that a good fit of the waveforms, simulated by Dirana, to the actual tgδ waveforms obtained at temperatures between 293.15 K (20 °C) and 333.15 K (60 °C) requires the introduction of temperatures, higher than the actual insulation temperatures, into the program. It was found that estimating the moisture content for different temperatures using Dirana soft-ware for insulating an oil-impregnated pressboard produced large discrepancies from the actual content. Better results were obtained after an adjustment requiring manual temperature correction towards higher, compared to measured, temperatures. The moisture content estimated after correction by the Dirana meter ranges from of 4.5 wt. % to 5.7 wt. % and increases almost linearly with increasing measuring temperature. The average moisture content estimated by the Dirana meter for all measuring temperatures is 5.1 wt. % and is close to the actual content (5.0 ± 0.2) wt. %. The uncertainty of the estimate is ±0.43 wt. % and is more than twice as high as the true value

Influence of Annealing on the Dielectric Properties of Zn-SiO₂/Si Nanocomposites Obtained in “Hot” Implantation Conditions

This paper presents the results of AC electrical measurements of Zn-SiO2/Si nanocomposites obtained by ion implantation. Implantation of Zn ions was carried out into thermally oxidized p-type silicon substrates with energy of 150 keV and fluence of 7.5 × 1016 ion·cm−2 at a temperature of 773 K, and is thus called implantation in “hot” conditions. The samples were annealed in ambient air for 60 min at 973 K. Electrical measurements of Zn-SiO2/Si nanocomposites were carried out before and after annealing. Measurements were performed in the temperature range from 20 K to 375 K. The measurement parameters were the resistance Rp, the capacitance Cp, the phase shift angle θ and the tangent of loss angle tanδ, as a function of the frequency in the range from 50 Hz to 5 MHz. Based on the characteristics σ(f) and the Jonscher power law before and after sample annealing, the values of the exponent s were calculated depending on the measurement temperature. Based on this, the conductivity models were matched. Additionally, the real and imaginary parts of the dielectric permittivity were determined, and on their basis, the polarization mechanisms in the tested material were also determined

DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation

In this study, the conductivity and permittivity of electrical pressboard—insulating liquid—water composites were investigated, and the electrical properties of the composites and water were analysed comparatively. Mineral oil and synthetic ester were used as insulating liquids. It was found that the presence of water caused an increase in the permeability of the composite in the frequency range below 100 Hz. The value of static permittivity determined by water in the content of 5 wt. % was approximately 15. To obtain this value caused by liquid water, its volume should be approximately five (oil) and four times (ester) higher than its actual content, respectively. The determined values of the activation energy of the DC conductivity of the composites were several times higher than the values of the activation energy of the conductivity of the liquid water. The experimental values of the dielectric relaxation times were many orders of magnitude higher than the dielectric relaxation times of water. This means that the experimental results obtained for the dielectric permittivity, the activation energy of conductivity and the dielectric relaxation times for moisture electrical pressboard impregnated by mineral oil or synthetic ester exclude the possibility of the presence of liquid water in the composites. It was found that the conductivity of the composites increased exponentially with increasing water content. Such dependencies are characteristic of hopping conductivity, caused by the quantum phenomenon of electron tunnelling between nanometre-sized potential wells. As the increase in conductivity is determined by the presence of water in the composites, therefore, the nanometre potential wells were single-water molecules or nanodrops

Comparative Measurements and Analysis of the Electrical Properties of Nanocomposites Ti<i>_x</i>Zr_1−<i>x</i>C+α-Cy (0.0 ≤ <i>x</i> ≤ 1.0)

In this paper, the frequency-temperature dependence of the conductivity and dielectric permittivity of nc-TixZr1−xC+α-Cy (0.0 ≤ x ≤ 1.0) nanocomposites produced by dual-source magnetron sputtering was determined. The films produced are biphasic layers with an excess of amorphous carbon relative to the stoichiometric composition of TixZr1−xC. The matrix was amorphous carbon, and the dispersed phase was carbide nanoparticles. AC measurements were performed in the frequency range of 50 Hz–5 MHz at temperatures from 20 K to 373 K. It was found that both conductivity and permittivity relationships are determined by three tunneling mechanisms, differing in relaxation times. The maxima in the low- and high-frequency regions decrease with increasing temperature. The maximum in the mid-frequency region increases with increasing temperature. The low-frequency maximum is due to electron tunneling between the carbon films on the surface of the carbide nanoshells. The mid-frequency maximum is due to electron transitions between the nano size grains. The high-frequency maximum is associated with tunneling between the nano-grains and the carbon shells. It has been established that dipole relaxation occurs in the nanocomposites according to the Cole-Cole mechanism. The increase in static dielectric permittivity with increasing measurement temperature is indicative of a step polarisation mechanism. In the frequency region above 1 MHz, anomalous dispersion—an increase in permittivity with increasing frequency—was observed for all nanocomposite contents