Browsing by Author "Cloete, Romei Christeline"
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- ItemFatigue performance of seals(Stellenbosch : Stellenbosch University, 2015-12) Cloete, Romei Christeline; Jenkins, Kim J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.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.