Influence of durability properties on performance of bitumen stabilised materials

Twagira, Elias Mathaniya (Stellenbosch : University of Stellenbosch, 2010-03)

Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: In both developing and developed countries, to ensure sustained economic growth the quest for optimal roads performance is an extremely high priority. A global increase in the use of foamed bitumen and bitumen emulsion materials (BSMs) as a solution to roads maintenance, rehabilitation, and upgrading has become evident. This is driven by environmental policies aimed at conserving energy and limiting the exploitation of new borrows pits. It has therefore become imperative that BSMs are used optimally, and, in order to achieve this, practitioners need to understand the mechanisms that influence durability and long-term performance. The changes in the behaviour of materials and the failure mechanisms of BSM mixes are long-term phenomena. This implies that the study of the physicochemical and mechanical properties of the mixes is vital. Therefore, a fundamental understanding of the moisture damage and age-hardening characteristics, which are related to materials’ properties, is required. The main objective of this study is to advance BSM technology by assessing the influence of the selected materials on durability behaviour 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 of binder and mineral aggregates. The properties of bitumen (foamed bitumen or bitumen emulsion) and mineral aggregates were reviewed. This was followed by review into the colloidal behaviour of foam and emulsion and physicochemical and mechanical interaction with mineral aggregates. Factors influencing the interaction of BSMs were then identified. Finally, the fundamental theories on thermodynamics, hydrodynamics, and electrokinetics were used to describe the step-by-step process by which adhesive bonding and cohesion occur in BSMs. The mixture durability in terms of moisture damage was investigated. To achieve this aim, the physical and mechanical moisture-induced damage process was analysed. The test control parameters were established and a laboratory device to quantify these parameters designed. New moisture conditioning procedures were developed and demonstrated in this study. From the moisture induction simulation test (MIST) procedure, it became evident that pulsing water pressures into compacted and cured BSM mixes simulates the hydrodynamic effect that occurs in the field due to dynamic traffic loading. The different mix matrices typically applicable to the recycling processes – such as Hornfels-RAP and Quartzite crushed stone, stabilised with either foamed bitumen or bitumen emulsion and the addition of active filler (cement or lime) – were investigated. It was found that a new moisture-conditioning procedure using the MIST device and monotonic triaxial testing can distinguish those BSM mixes that are resistant to moisture damage from those that are less resistant. The validation of the MIST and monotonic test results was done using the APT device, which is the MMLS3 wet trafficking test. The results on both tests showed good correlations in evaluating and screening BSMs in terms of moisture susceptibility. Field temperature data was collected and a model to accurately simulate the curing of BSMs was identified and proposed for further investigation and validation. It was found from the field temperature data collected in this study that the temperature gradient on the study site varied according to the depth of the BSMs (that is, 10oC-17oC during winter and 17oC– 47oC during summer). Understanding the influence of the temperature conductivity and rate of evaporation is important for inferring moisture damage and age-hardening behaviour and proper selection of BSMs. The age-hardening behaviour of BSMs is linked to the durability properties and longterm performance of these materials. The fundamental characteristics associated with shortand long-term age hardening were investigated in this study. The short-term dimension involved assessing the age-hardening characteristics of the binder (foamed bitumen colloids and bitumen emulsion droplets) prior to the production of BSMs. The long-term study involved extracting and recovering the binder from the briquettes (made from different mixes) compacted in the laboratory and cores extracted from different field pavement sections which were in service for 8-10 years. The study found that the length of time bitumen is kept in circulation in the laboratory plant at elevated temperature (170oC–180oC) before making BSM-foam contributes to the ageing of the binder, especially after eight hours. The foaming process in itself was found not to alter the bitumen properties. It is recommended that a temperature range between 160oC- 165oC be used for the production of foamed bitumen with softer bitumen. This will not compromise its quality. In addition, the time of circulation of bitumen in laboratory plant should not be longer than three (3) hours. The rheological properties of the bitumen recovered from laboratory briquettes and cores from field pavement show that age hardening on foamed bitumen and bitumen emulsion during in-service life occurred. The ageing also seemed to be dependent on the effect of traffic, with trafficked areas (i.e. on-wheel path and inner-wheel path) experiencing more ageing than untrafficked areas (i.e. between-wheel path). However, the extraction and recovery process was found to be complex, and produce uncertain results. Although the results show that binders in BSMs undergo age hardening, its distinct behaviour in BSM performance was not obvious from the extensive tests carried out in this study. The last part of the study contains its conclusions and recommendations. The study provides an insight into fundamental material durability properties, and 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 apply a mix that is durable and long-lasting. The specific durability-related issues addressed in this study are substance for future research. This novel solution to the application of BSMs will benefit all parties involved in the development of pavement recycling technology.

AFRIKAANSE OPSOMMING: Om volgehoue ekonomiese groei te verseker in beide ontwikkelende en ontwikkelde lande, geniet die soeke na die optimale werkverrigting van paaie ’n baie hoë prioriteit. ‘n Wêreldwye toename in die gebruik van skuimbitumen en bitumen-emulsiemateriale (BSMs) as ’n oplossing vir padonderhoud, rehabilitasie en opgradering is merkbaar. Dit word meegebring deur die omgewingsbeleide wat die ontginning van nuwe leengroewe beperk en besparing van energie bevorder. Die korrekte gebruik van hierdie materiale vereis dat die meganismes wat die duursaamheid en langtermyn-werkverrigting daarvan beïnvloed, deeglik verstaan word. Die verandering in materiaalgedrag en falingsmeganismes van BSM materiale is langtermynverskynsels. Dit impliseer dat bestudering van die fisiochemiese en meganiese eienskappe van die mengsels uiters belangrik is. Dis dus voor die hand liggend hoe belangrik vogbeskadiging en verharding met tyd, wat verwant is aan materiaaleienskappe, is. Die hoofdoelwit met hierdie studie is om die vooruitgang van BSM tegnologie te versnel deur dit moontlik te maak om gekose materiale te evalueer op grond van hulle invloed op duursaamheid en langtermyn-werkverrigting in alle toepassingsfases (naamlik mengontwerp, konstruksie en dienstoestand). Hierdie studie begin met ’n uitgebreide literatuuroorsig oor fundamentele begrippe van die karakterisering van interaksie van die bindstof en die minerale-aggregate. Inligting oor bitumen (skuimbitumen en bitumen emulsies) en eienskappe van minerale aggregate is bestudeer. Dit is gevolg deur ’n studie van die fundamentele begrip van die kolloïdale gedrag van skuim en emulsie, asook fisiochemiese en meganiese interaksie met minerale aggregate. Faktore wat die interaksie van BSM-materiale beïnvloed is geïdentifiseer. Die basiese teorie van termodinamika, hidrodinamika en elektrokinetika is daarna gebruik om stap vir stap die proses en formulering van adhesie-binding en kohesie in die BSMs, wat in hierdie studie aangebied word, te beskryf. Die kwantifisering van mengsel-duursaamheid in terme van vogbeskadiging is ontwikkel. Om hierdie doel te bereik, is die fisiese en meganiese proses van beskadiging deur vogindringing geïdentifiseer. Die gekontroleerde parameters is bepaal en ’n laboratoriumapparaat is ontwerp om hierdie parameters te kwantifiseer. Nuwe vogkondisioneringsprosedures is ontwikkel en in hierdie studie gedemonstreer. Van prosedures van voggeïnduseerde sensitiwiteitstoetsing (Engels: moisture induction simulation test (MIST)) was dit duidelik dat pulsering van waterdruk in BSM materiale die hidrodinamiese effek naboots wat in die veld bestaan as gevolg van dinamiese verkeerslaste. Verskillende mengselmatrikse wat tipies is van hergebruik, soos byvoorbeeld hoornfels-hersikleerde asfalt produk (Engels: recycled asphalt product (RAP)) en vergruisde granietklip, met skuimbitumen of bitumenemulsie gestabiliseer en met byvoeging van aktiewe vulmateriaal (sement of kalksteen), is ondersoek. Daar is bevind dat nuwe vogkondisioneringsprosedures (soos bepaal deur MIST apparaat en drie-assige toets) kan onderskei tussen BSM materiale wat weerstandig is teen vogbeskadiging en dié wat minder weerstandig (vatbaar) is. Die geldigheid van die MIST en monotone toetsresultate is bepaal deur gebruik van die APT apparaat wat ’n MMLS3 nat verkeerstoets is. Die resultate van beide toetse toon goeie korrelasie in die keuring van BM materiale in terme van vogvatbaarheid. In hierdie ondersoek is veldtemperatuurdata versamel en die toepaslike model om verouderende BM lae akkuraat te simuleer is geïdentifiseer en voorgelê vir verdere ondersoek en verifikasie. Daar is uit veldtemperatuurdata bevind dat temperatuurgradiënt op die betrokke terrein gewissel het met die dikte van die BSM, naamlik 10oC-17oC gedurende die winter en 17oC-47oC gedurende die somer. Begrip vir die invloed van temperatuuroordragkoëffisiënt en verdampingstempo is belangrik by die afleiding van vogbeskadiging en verharding met ouderdom en die korrekte keuse van BSM materiale.Verouderingsverhardinggedrag van BSMs is verwant aan die duursaamheidseienskappe en langtermynwerkverrigting van hierdie materiale. Die basiese karakteristieke wat met kort- en langtermyn verouderingsverharding geassosieer word, is in hierdie studie ondersoek. Die klem op die kort termyn is geplaas op die verouderingsverhardingsgedrag van die bindstof (skuimbitumen kolloïdes en bitumen-emulsiedruppels) voordat BSMs vervaardig word. In die lang termyn evaluasie het die studie ekstraksie en herwinning van bindstof uit brikette wat in die laboratorium gekompakteer is (van verskillende mengsels) en uit kerns verkry vanaf verskeie plaveiselgedeeltes na 8-10 jaar diens ingesluit. Die ondersoek het bevind dat die tydsverloop waarin bitumen in sirkulasie gehou is by verhoogde temperatuur (170oC-180oC) in die laboratorium-aanleg voordat BSMs vervaardig is, veral indien na 8 uur, bydra tot die veroudering van die bindstof. Die skuimproses op sigself verander nie die bitumeneienskappe nie. Daar word aanbeveel dat temperature tussen die grense 160oC-165oC gehandhaaf word vir produksie van skuimbitumen met sagter bitumen sonder dat die kwaliteit benadeel word en dat die sirkulasietyd nie 2 tot 3 ure behoort te oorskry nie. Die reologiese eienskappe van die herwinde bitumen vanuit laboratoriumbrikette en kerns van plaveisels toon dat ouderdomsverharding van skuimbitumen en bitumen-emulsie tydens die diensleeftyd plaasvind. Die veroudering is skynbaar ook afhanklik van verkeerseffekte, met belaste areas (in wielspoor of binne wielspoor) wat ’n hoër mate van veroudering toon as onbelaste areas (tussen wielspore). Die ekstraksie- en herwinningsproses op sigself was egter bevind as baie kompleks met uiters onseker resultate. Dit het gelei tot onsekere gedrag in terme van ouderdomsverharding van die BSM bindmiddel (skuim of emulsie). Alhoewel resultate toon dat die bindmiddels ouderdomsverharding ondergaan het, is die BSM werkverrigting nie duidelik uit die uitgebreide toetse wat in hierdie studie uitgevoer is nie. Die laaste deel van die studie bevat gevolgtrekkings en aanbevelings. Die studie lewer insig in die fundamentele duursaamheidseienskappe van die materiaal, wat bydra tot verbetering van die huidige prosedure van seleksie, saamstelling en formulering van die mengmatriks vir BSMs. Verder voorsien dit ’n metode wat in die praktyk gebruik kan word om met vertroue duursame mengsels met lang diensbaarheidsleeftye te vervaardig. ’n Nuwe oplossing en vooruitgang in die toepassing van BSMs is daargestel tot voordeel van alle partye betrokke by die ontwikkeling van herwinningstegnologie.

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