Fatigue performance of seals

Cloete, Romei Christeline (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Thin bituminous surfacings, in particular sprayed seals, are used quite extensively in various countries because they provide a low cost alternative to conventional asphalt. Seals furthermore provide an acceptable wearing course which guards the underlying pavement layers from the harsh effects of traffic and the environment by preventing ingress of moisture. Seals also provide a safe road environment by offering adequate skid resistance and noise reduction during its lifetime. Evaluating the fatigue performance of thin surfacings is a challenging and complex task. Back calculation of the modulus of a thin surfacing layer has always been difficult because the deflections measured at various distances of the load centre and in the load centre contained little to no information on the deformation of the thin top layer itself. The main objective of this research study is to characterize the fatigue performance of various types of seals sampled from existing road pavements across South Africa, taking into account different variables such as ages, climatic zones and traffic history. The characterisation of the fatigue of these sampled seals was carried out by developing a bi-layer system consisting of the sampled seal and a fast-cast polyurethane composite beam and subjecting to flexural bending in the four point bending beam apparatus, following the guideline for fatigue testing of Hot Mix Asphalt (HMA). The test parameters and results are analysed in terms of fatigue and master curves obtained. It is understood that the apparatus affords an insight on the mechanism of fatigue failure of beam specimens by carrying out bending tests with alternating strain and stress amplitudes. The test approach yielded fatigue results for the composite system, which required a direct beam theory solution set-up in MATLAB, to extract the fatigue results of only the seals. It was found that the conventional fatigue test criterion of fifty (50) percent reduction in initial flexural stiffness was only applicable for Single Seals, after various fatigue criteria were investigated. For Cape Seals the fatigue criteria was defined as fourty (40) percent reduction in initial flexural stiffness, whereas for Double Seals this failure criteria was significantly lower at twenty (20) percent reduction in initial flexural stiffness. It was furthermore found that Single and Cape Seals imitated the behaviour of a uniform mix, similar to HMA and hence failed at a higher fatigue criterion. Double Seals however had a less uniform mix behaviour which subscribed to a reduced or lower fatigue criterion. The influence of the variables on the outcome of fatigue was investigated by considering the effect of the single variables, combination of variables and the interaction between variables. For Single Seals it was found that the thickness of the seal, the applied loading strain and the age provided most significance on the outcome of fatigue. Similarly, for Cape Seals, the thickness and age provided most significance, but with the added significance of climate. For Double Seals the environment of the seals provided most significance on the outcome of fatigue.

AFRIKAANSE OPSOMMING: Dun bitumineuse oppervlaktes, in besonder oppervlak seëls, word omvattend baie gebruik in verskeie lande, omdat hulle ‘n lae koste alternatief bied teenoor konvesionele asfalt oppervlaktes, oppervlak seëls voorsien ‘n aanvaarbare dra laag wat die onderliggende plaveisel lae beskerm teen die negatiewe gevolge van die verkeer en die omgewing deur die instroming van vog te voorkom. Seëls bied ook ‘n veilige pad omgewing deur voldoende slip weerstand te voorsien en geraas te verminder. Die evaluering van die vermoëings geaardheid van dun oppervlaktes is ‘n uitdagende en komplekse taak. Terug berekening van die oppervlak laag was nog altyd moeilik, want die gemeete defleksies op verskillende afstande vanaf die las middle punt en in die las middle punt vervat min tot byna geen inligting oor die vervorming van die boonste laag nie. Die hoof doel van hierdie navorsing studie is om die vermoëings geaardheid van verskillende tipes oppervlak seëls monsters wat uit bestaande paaie regoor Suid Afrika geneem was te kenmerk, met die inagneming van verskillende veranderlikes, soos ouderdom, klimaatsones en verkeer geskiedenis. Die kenmerk van die vermoëings geaardheid van hierdie seël monsters is uitgevoer deur die ontwikkeling van ‘n twee-laag stelsel wat bestaan uit die gemonsterde seël en ‘n vining-giet poliuretaan saamgestelde balk wat onderwerp was aan buig in die vier punt buig balk apparat, na aanleiding van die riglyn vir die vermoëings toets vir Warm Gemengde Asfalt. Die toets parameters en resultate was ontleed in terme van vermoëings en meester kurwes. Dit word verstaan dat dié apparaat ‘n insig bied oor die meganisme van mislukte vermoëings geaardhede van balk toets monsters deur hulle te onderhewing aan buig toetse met afwisselende vervorming en spanning amplitudes. Dié toets benadering het wel vermoëings resultate gelewer vir die saamgestelde stelsel en die toepassing van direkte balk teorië was nodig om slegs die resultate van die seëls te bekom. Daar was gevind dat die konvensionele vermoëings toets maatstaf van vyftig (50) present vermindering in die aanvanklike buig styfheid was net van toepassing vir Enkel Seëls, nadat verskeie vermoëings kriteria ondersoek was. Vir Kaapse Seëls was die vermoëings kriteria gedefiniëer as veertig (40) present vermindering in die aanvanklike buig styfheid, terwyl vir Dubbel Seëls was hierdie kriteria aansienlik laër op twinting (20) present vermindering in die aanvanklike buig styfheid. Dit was verder bevind dat Enkel en Kaapse Seëls ‘n meer eenvormige mengsel gedrag naboots, soortgelyk aan Warm Gemengde Asfalt en dus op ‘n hoër vermoëings maatstaf misluk. Dubbel Seëls het egter ‘n minder uniform mengsel gedrag wat by ‘n laer vermoëings maatstaf misluk. Die invloed van die veranderlikes op die uitslag van vermoëing was ondersoek deur die oorweging van die uitwerking van enkele veranderlikes, kombinasie van veranderlikes en die interaksie tussen veranderlikes. Vir Enkel Seëls was bevind dat die dikte van die seëls, die toegepaste vervorming las en die ouderdom die meeste betekenisvolle uitkoms van vermoëing gelewer het. Net so, vir Kaapse Seëls, het die dikte en ouderdom die meeste betekenisvolle uitkoms van vermoëing verskaf, maar met di bykomende belang van klimaat. Vir Dubbel Seëls het die omgewing van die seëls die meeste belang gedra, in terme van die uitkoms van vermoëing.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97944
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