Browsing by Author "Nel, Christiaan Ludolph Marais"

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    Identifying Gradings and binder combinations for improving the grey water resistance of asphalt
    (Stellenbosch : Stellenbosch University, 2017-03) Nel, Christiaan Ludolph Marais; Jenkins, Kim Jonathan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Premature failure of asphalt surfacing was observed on roads in areas within and surrounding informal settlements in Cape Town. It was concluded that the main source of failure was as a result of grey water spillage onto these road surfaces. Mew Way, located in the Khayelitsha area on the Cape Flats, required treatment and surfacing at least every 5 years to address grey water related problems. This has prompted the City of Cape Town and SABITA to initiate the Grey Water Resistant Asphalt Study to investigate the influence of grey water on the performance of asphalt. As part of the Grey Water Resistant Asphalt Study, extensive laboratory experiments and testing were required to investigate the grey water resistance of asphalt. The University of Stellenbosch was approached by the Grey Water Research Group under the leadership of Mr A. Greyling, Technical Director at BVi Consulting Engineers (Pty) Ltd, to develop a research methodology for this unique study. This research methodology was executed at the University of Stellenbosch where all results and conclusions related to this study were reported. The Researcher, after initiating an extensive literature study and identifying factors for improving the grey water resistance of asphalt, developed primary and secondary research methodologies. The objective of the primary research methodology was to identify gradings and binder combinations to improve the grey water resistance of asphalt. This research methodology consisted of two phases. Phase 1 included moisture inducing simulating tests (MIST) for moisture conditioning purposes and indirect tensile strength (ITS) tests. Tensile strength ratio (TSR) results of binder combinations that were tested during Phase 1, indicated that the retained strength of asphalt mixtures after grey water MIST was significantly lower when compared to clean water MIST conditioning. Results also indicated that a medium graded asphalt mixture achieved greater strength after grey water MIST conditioning when compared to fine graded asphalt mixtures. The binder additive EVA contributed significantly to achieving greater asphalt mixture strength after grey water MIST conditioning. Phase 2 consisted of laboratory scale model mobile load simulating (MMLS) and ITS testing of asphalt briquettes subjected to trafficking under dry (no water) and wet (grey water) conditions. Results from Phase 1 assisted with setting up asphalt gradations and binder combinations for testing during Phase 2 of the primary research methodology. TSR results from Phase 2 did not show significant variations between the performance of medium and fine graded asphalt mixtures after being subjected to wet (grey water) MMLS3 trafficking. However, permanent deformation results indicated that medium graded asphalt mixtures with EVA and SBS modified binders produced significantly lower deformations when compared to virgin binder (50/70 penetration grade) combinations after being subjected to wet MMLS3 trafficking. A binder additive, ZycoTherm®, in combination with an EVA modified binder and Sasobit did not only assist in reducing the permanent deformation, but also significantly increased the strength of the asphalt. ITS, permanent deformation, texture and material loss results of Phase 2 were combined to establish a rating criteria for determining suitable grey water resistant asphalt mixtures for high and low volume roads. Medium graded asphalt mixtures may provide a suitable grey water resistant asphalt mixture for high volume roads, whereas fine graded asphalt mixtures may provide a suitable solution for low volume roads. Based on the results of the rating criteria, the following asphalt mixtures showed significant resistance to grey water: . EVA + 1%Sasobit® + Extra Lime (COLTO Medium Continuous Graded) . EVA + Extra Lime (COLTO Medium Continuous Graded) . EVA + 1%Sasobit® (COLTO Fine Continuous Graded) . EVA + 1%Sasobit® + 0.1%ZycoTherm® (COLTO Fine Continuous Graded) After completing laboratory scale MMLS trafficking during Phase 2 of the primary research methodology, trafficked asphalt briquettes were subjected to ITS testing. Each asphalt briquette had a diameter of 150 mm, and during the preparation of test specimens for laboratory scale MMLS trafficking, two opposite segments with parallel chords and each having a 19 mm mid-ordinate, had to be machined-off from each briquette with a dual saw. This was done to fit nine asphalt briquettes in a test bed specifically designed for executing the laboratory scale MMLS trafficking procedure. This led to the setup of a secondary research methodology for investigating the influence of these removed segments on the indirect tensile strength of the shaped asphalt briquettes. This investigation was accomplished through linear-elastic finite element modelling. Results of the secondary research methodology indicated that a decrease of up to 8% in the maximum tensile strength can be expected at the centre of a shaped asphalt briquette (with removed segments as described above) when compared to an unshaped asphalt briquette. Results also indicate that no significant changes occurred in compressive stresses due to the shaping of briquettes. This study provides insight on the development of grey water susceptible asphalt mixtures, which serves as a starting point for ensuring that durability and user specifications for roads exposed to grey water are met.