The research presented in this thesis studies the effects of foamed bitumen on the deformational behaviour and performance of pavement materials. The research was conducted in the laboratory and the field, using specific New Zealand materials. The aggregate used is a blend of a coarse aggregate imported from the Auckland region with a crushed dust from the Canterbury region. The bitumen selected for the study is an 80/100 bitumen grade, and the active filler was a Portland Cement, both commonly used for foamed bitumen stabilization in New Zealand. In the laboratory, samples of mixes with different foamed bitumen content were tested under various loading and stress conditions to investigate the effects of foamed bitumen on the deformational behaviour of the mix. The tests performed were: Indirect Tensile Strength (ITS), Indirect Tensile Resilient Modulus (ITM), Repeat Load Triaxial compression (RLT) and Monotonic Load Triaxial compression (MLT). Preliminary ITS and RLT tests conducted on mixes with 1% and 0% cement, at different foamed bitumen contents, indicated that mixes without cement performed poorly compared to the mixes with 1% cement. Therefore, the rest of the laboratory study was on mixes with 1% cement. ITS tests were conducted on 150 mm specimens prepared with 0% 1%, 2%, 3% and 4% bitumen content, with a common 1% cement. Results indicated that foamed bitumen increases the ITS values of the mix, up to an estimated optimum of 2.8% bitumen content. Similar trends were obtained with ITM tests, in which a diametrical load pulse was applied on 150 mm specimens, showing an estimated resilient modulus peak near to 2.8% bitumen content. RLT specimens were prepared at 0%, 2% and 4% bitumen content, at two compaction efforts, creating specimens at low and high bulk density. Permanent deformation RLT tests involved the application of seven stages of 50,000 load cycles each (4 Hz), with increasing deviator stress (from 75 kPa in the first stage, up to 525 kPa in the seventh stage) and at constant confining pressure of 50 kPa. Results of RLT permanent deformation tests indicated that the increase in the foamed bitumen content resulted in an increase in the permanent deformation of the material. MLT tests were conducted on specimens at 0%, 2% and 4% bitumen contents, at two compaction efforts, creating specimens of low and high bulk density, at confining pressures ranging from 50 kPa to 300 kPa, with a deformation rate of 2.1% per minute. Results indicated that the effect of foamed bitumen was a reduction of the peak vertical stress, or a reduction in the peak strength. The peak stresses obtained in MLT tests were plotted in stress diagrams, and the failure was approximated as linear function of the confining stress. The fundamental shear parameters (angle of internal friction and apparent cohesion) were estimated, and results indicated that foamed bitumen has no apparent effect in cohesion but does reduce the angle of internal friction. The reduction of the angle of internal friction explains the general trends observed in the laboratory, that on one hand the compressive strength decreases with increasing bitumen content, but on the other hand, the tensile strength increases up to an optimum. A full-scale experiment was carried out using an accelerated testing of foamed bitumen pavements at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF). In the full-scale experiments, the same materials that were tested in the laboratory (aggregates, bitumen, cement) were used to construct six different pavement sections, each with different contents of bitumen and cement. Three were constructed using foamed bitumen contents of 1.2%, 1.4% and 2.8% respectively, plus a common active filler content of 1.0% cement. Two more pavements were constructed adding cement only (1.0%), and foamed bitumen only (2.2%). In addition, one control section with the untreated unbound material was tested. Strains were collected using a 3D Emu soil strain system installed in each pavement section. The curing time between construction and pavement loading was approximately three months. The pavement response, such as surface deformation (rutting), surface deflections and strains were periodically recorded during the execution of the test. The strains were collected at different depths by using an array of Emu strain gauges. Deflections were recorded using both a Falling Weight Deflectometer (FWD) and CAPTIF Beam deflectometer, which is a modified Benkelmann beam. A total number of approximately 5.6 million equivalent standard axles were applied on the pavement sections. The rutting measured in the sections stabilised with foamed bitumen and cement was the lowest, showing that the addition of foamed bitumen significantly improved the performance of materials with 1% cement. The sections stabilised with cement only, foamed bitumen only, and the control untreated section showed large amounts of rutting and heaving by the end of the test. Deflection measurements showed that the effect of foamed bitumen content is a reduction of pavement deflections, with the lowest deflection measured in the section stabilised with 2.8% bitumen and 1% cement. The elastic pavement strains showed that foamed bitumen reduced the tensile strains in the basecourse but did not have a significant effect on vertical compressive strains. During the construction of pavements, material samples were taken for ITS and RLT testing. Results indicated that the highest ITS was measured in the section with 2.8% foamed bitumen content and 1% cement, and the ITS in the section without cement and foamed bitumen only was about 4-5 times lower than the ITS measured in specimens with cement. RLT specimens without cement performed poorly in comparison with the specimens with 1% cement. The specimens with 1% cement showed higher permanent deformation with increase in the foamed bitumen content, supporting the results from the previous laboratory study. To interpret and relate the results observed in the laboratory and the field, stress path analysis was used, in which the stress ratio of the foamed bitumen layers was calculated at different depths. The analysis showed that foamed bitumen content decreases the maximum stress ratio, hence reducing the proximity to failure and relative damage of the layer. Three-dimensional and two-dimensional finite element modelling of the CAPTIF pavements, were used to further investigate the stress and strain fields induced by the loading and to explain the pavement performance observed in the full-scale experiment.

Despite applications of foamed bitumen technology in pavement construction in various places around the world, there are still several aspects about this technology that are not clear. In addition, knowledge on foamed bitumen technology is mainly empirical and lacks scientific basis. This study addresses some of the aspects for foamed bitumen technology such as: Investigation of any effects in binder composition during the production process for foamed bitumen; assessment of the effect of bitumen source on foamed bitumen characteristics; development of a rational method to optimise foamed bitumen characteristics and conditions; evaluation of aggregate particle coating within foamed bitumen mixes; further improvements in the mix design procedure specifically the method of compaction and optimum bitumen content determination stages are suggested.  Fourier transform infrared spectroscopy techniques were used to investigate any changes in bitumen composition after the production process of foamed bitumen. Fourier transform infrared tests were done on foamed bitumen and neat bitumen specimens for two bitumens with similar penetration grades. Foamed bitumen characteristics of three bitumens were established by producing foamed bitumen at temperatures of 150ºC up to 180ºC and foamant water contents of 1, 2, 3, 4 and 5%. From the analysis of variation of foamed bitumen characteristics (maximum expansion ratio and half-life) at different temperatures a new method based on the equi-viscous bitumen temperature to optimize foamed bitumen conditions and characteristics was proposed. Rice density and surface energy concepts were used to evaluate aggregate particle coating with foamed bitumen. A granite aggregate divided into three different size fractions and three sets of foamed bitumen produced from three bitumen penetration grades were used. A gyratory laboratory compaction procedure for laterite gravels treated with foamed bitumen was established using the modified locking concept. Three laterite gravels with different chemical composition were mixed with foamed bitumen produced from one penetration bitumen grade. The resulting mixes were compacted up to 200 gyrations and the corresponding compaction curve defined in terms of height versus number of gyrations noted. In addition, the optimum moisture content requirements at the modified locking point were determined. 3D packing theory concepts, primary aggregate structure porosity and an indirect tensile strength criteria were employed to determine optimum bitumen content for foamed bitumen mixes.  Fourier infrared techniques revealed that foaming did not cause any changes in the bitumen chemistry, implying that the foamed bitumen production process may possibly be a physical process. Characterisation of foamed bitumen produced from three bitumen penetration grades showed that foamed bitumen characteristics (maximum expansion ratio and half-life) were mainly influenced by binder viscosity rather than the source. The equi-viscous temperature seemed to provide a suitable criterion at which foamed bitumen with optimum characteristics could be produced. Rice density results showed that aggregate size fraction, binder expansion ratio and viscosity influenced aggregate particle coating. For the coarser aggregate fraction, results revealed that binder coating seemed to be mainly influenced by temperature. Whilst for fine aggregate fraction the coating was mainly influenced by surface area. Surface energy results revealed that foamed bitumen exhibited better coating attributes than neat bitumen. A new laboratory compaction procedure for laterite gravels treated with foamed bitumen based on the modified locking point was developed. The modified locking point represents the state at which maximum aggregate particle interlock occurs when mixes are compacted in the field. It is based on the iii analysis of the rate of change for the gyratory compaction curve. The compaction curve in this case is defined in terms of compaction height versus number of gyrations. Gradation analysis beyond the modified locking point showed that aggregate particle breakdown occurred. Analysis of the optimum moisture at the modified locking point revealed that the moisture conditions were less than the aggregate optimum moisture conditions. It is recommended that this point be used to determine the optimal compaction characteristics of foamed bitumen mixes.  Aggregate structure porosity and an indirect tensile strength criteria can be used to determine the bitumen content that could be used in design of foamed bitumen mixes. This would reduce the amount of resources required since the bitumen content could be estimated prior to carrying out the actual laboratory work given that the aggregate grading is known. The aggregate structure can be divided (based on 3D packing theory) into oversize, primary, and secondary structures. The primary structure is mostly responsible for carrying loads whilst the secondary structure fills the voids within the primary structure and provides support to the primary structure. The aggregate size particles constituting the primary structure are deduced as a function of standard sieve sizes using the packing theory concepts. The minimum sieve size for the primary structure is proposed as 1 mm. The oversize structure consists of aggregate particles whose size is greater than the maximum size for the primary structure. The secondary structure consists of aggregate particles whose size is below the minimum size for the primary structure. The primary aggregate structure porosity can be used to establish the starting bitumen content; the bitumen content at which this porosity is 50% is chosen as the initial bitumen content. Indirect tensile strength values corresponding to 50% primary porosity are determined as well as the bitumen contents and compared against the recommended minimum values. / <p>QC 20161012</p>

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The pavement construction industry aims to reduce its Greenhouse Gas (GHG) emissions by investigating various energy efficient practices. The industry has focused on reducing energy consumption by producing Warm Mix Asphalt (WMA) surfacing materials that are workable at lower temperatures in relation to Hot Mix Asphalt (HMA), as a means to reduce carbon emissions. Half-Warm Foamed Bitumen Mixtures (HWF) is a relatively new material and is produced at temperatures below 100°C. This translates to large energy savings to overcome the latent heat of steam when exceeding 100°C. The characteristics of HWF mixes are a compromise between those of Foamed Bitumen Stabilised material (BSM-foam) and HMA characteristics. These include to a limited extent the improved tensile strength, particle coating and durability of HMA; and the shear strength of BSM-foam. The use of microwave technology as an efficient heating method to produce improved engineering properties of BSM-foam is proposed in this study. The benefits include energy saving due to its volumetric heating capability as well as rapid heating which improve productivity when using suitable materials. The aspect of recycling material brings forth further energy saving and emissions reduction when reusing materials. The portability of the in-plant recycling machines is an ideal candidate with logistical advantages to implement microwave generators to produce HWF mixes. This study is subdivided into four parts as it progressively investigates the potential to heat aggregates and produce HWF material. Firstly it investigates the heating potential of four aggregates, namely Hornfels, Quartzite, Eucrite, Granite and Reclaimed Asphalt (RA) at various moisture contents using a microwave apparatus. The second part discusses the thermodynamics of the preliminary investigation to provide insight into the third part, the Primary Investigation. The primary investigation evaluates the tensile strength and shear properties of two material blends by respectively implementing Indirect Tensile Strength (ITS) and monotonic triaxial tests on specimens. The two blends were a combination of RA and crushed hornfels. The fourth and final part evaluates the HWF properties in relation to those of the equivalent BSM-foam product by means of a pavement analysis. The highest laboratory production temperature achieved was depicted by the material properties, microwave power capability and production rates. This temperature was consistently recorded at 50°C which theoretically simulates an in-field production rate of approximately 25 tons per hour. ITS test results indicate 100% increase in tensile strengths and an increase in compaction density for the HWF mixes. Large reduction in moisture contents is also observed after curing in relation to BSM-foam. The benefits in improving a layer within a pavement structure have an effect on the pavement’s overall performance. This could assist in reducing the requirement for premium layers e.g. thickness of HMA within the structure, thereby further assisting energy conservation. The evaluation of the microwave heated HWF mixes can be considered economical if designed with a purpose to meet the thermal dynamic requirements of a material considering the microwaves volumetric potential. / AFRIKAANSE OPSOMMING: Die plaveisel konstruksie-industrie poog om hul kweekhuisgas (KHG) uitskeiding te verlaag deur verskeie energie doeltreffende metodes te ondersoek. Die industrie fokus op die vermindering van energie-verbruik deur middel van die produksie van Warm Mengsel Asfalt (WMA) oppervlak materiale wat werkbaar is in laer temperature in verhouding tot “Hete Mengsel Asfalt (HMA)” as `n metode om koolstof uitskeiding te verlaag. Half-Warm Skuim-Bitumen Mengsels (HWS) is `n relatief nuwe materiaal en word vervaardig onder 100 °C. Dit lei tot groot energie besparings en oorkom sodoende die latente hitte van stoom wanneer temperature van 100 °C oorskry word. Die karakter-eienskappe van HWS mengsels is `n kompromie tussen Skuim-Bitumen Gestabiliseerde materiaal (BSM-S) en HMA eienskappe. Dit sluit tot `n beperkte mate in die verbeterde spankrag, partikel bestryking; en die skeer krag van BSM-S. Die gebruik van mikrogolf-tegnologie as effektiewe verwarmingsmetode vir verbeterde ingenieurseienskappe van BSM-S word voorgestel in hierdie studie. Die voordele sluit in energie besparing as gevolg van die volumetriese verwarmingsvermoë sowel as snel verhitting wat produktiwiteit verbeter tydens die gebruik van gepaste materiale. Die gebruik van herwinde materiaal bring verdere energiebesparing en uitskeiding-vermindering mee. Die draagbaarheid van binne-aanleg herwinningsmasjinerie is ‘n ideale kandidate met logistieke voordele vir die installering van mikrogolf-opwekkers vir die produsering van HWS mengsels. Dié studie word onderverdeel in vier dele terwyl dit toenemend ondersoek instel na die potensiaal van hitte versameling asook die produksie van HWS stowwe. Eerstens ondersoek dit die verwarmingspotensiaal van vier versamelings naamlik horingsteen, kwartsiet, eukrite, graniet en Herwinde Asfalt (HA) teenoor verskeie vogskattings-mikrogolf aperate. Die tweede deel bespreek die termodinamika van die voorlopige ondersoek om insig te bied vir die derde deel, die primêre ondersoek. Die primêre ondersoek evalueer die rekbaarheid en skeereienskappe van twee materiaal-mengsels van ITS en monotoniese drieassige toetse onderskeidelik op verskillende monsters. Die twee mengsels was `n kombinasie van HA en gemaalde horingsteen. Die vierde en finale deel evalueer die HWS eienskappe in verhouding tot die van die ekwivalente BSM-S produk deurmiddel van `n sypad-analise. Die hoogste laboratoriumproduksie temperature wat bereik was, was uitgebeeld deur die materiaal-eienskappe, mikrogolf krag kapasiteit en produksiekoers. Hierdie temperature was deurlopend aangeteken teen 50 °C wat `n teoretiese voorstelling is van `n binneveld produksie tempo van ongeveer 25 ton per uur. ITS toets resultate wys `n 100 % verhoging in spankrag asook `n toename in kompakte vir die HWS mengsels. Groot afname in voginhoud is ook waargeneem na bewerking in verhouding tot BSM-S. Die voordeel verbonde aan die verbetering van `n lag binne `n plaveisel-struktuur, het `n impak op die plaveisel se algemene uithoubaarheid. Dit kan bydra tot `n verlaging in die vereiste binne die struktuur en verdere bydra tot energie besparing. Die evaluering van mikrogolf verhitte HWS stowwe kan as ekonomies beskou word wanneer dit doelgerig vervaardig word om te voldoen aan die termodinamika vereistes van `n materiaal, wanneer die mikrogolf volumetriese potensiaal in ag geneem word.

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.

Although foamed bitumen has been widely applied in pavement construction some of its aspects are still not yet understood. In this study, some of these aspects including: effects of the foaming process on binder chemistry, characterization of foamed bitumen and development of a rational method to optimize foam characteristics, evaluation of aggregate particle coating within foamed bitumen treated materials, and development of a gyratory compaction procedure for laterite gravels treated with foamed bitumen were addressed. The effects of the foaming process on bitumen chemistry were investigated using Fourier transform infrared spectroscopy techniques. Also, foam characteristics of three binders were established and a rational method to optimize foam characteristics proposed. Aggregate particle coating with foamed bitumen was studied using the concepts of surface energy and Rice density. In addition a gyratory laboratory compaction procedure for laterite gravels treated with foamed bitumen was established using the modified locking concept. Infrared techniques have shown that foaming does not cause any changes in the binder chemistry, suggesting that foaming may be a physical process. Further, foam characteristics are greatly influenced by binder viscosity. Also, the equiviscous temperature seems to produce foam with optimum foam characteristics. Rice density results showed that aggregate size fraction, binder expansion ratio and viscosity influenced aggregate particle coating. Surface energy results revealed that foamed bitumen exhibited better coating attributes than neat bitumen. A new compaction procedure for laterite gravels treated with foamed bitumen based on the modified locking point was developed. / QC 20110427

In this diploma thesis there are described the issues use of foamed bitumen as binder in asphalt mixtures. The thesis is divided into two parts, theoretical and practical. The aim of theoretical part was to elaborate an overview of technologies, which allow to reduce the temperature during the production and laying of asphalt mixtures. The aim of the practical part was to compare the selected empirical and functional parameters of two types of asphalt mixtures produced in two variants, with hot bitumen and foamed bitumen. Attention was paid mainly to stiffness and low temperature parameters.