Advanced characterisation of hot mix asphalt with recycled crushed glass

George, Theresa Bernadette (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.


ENGLISH ABSTRACT: Over the last few decades, the use of glass in pavement applications has been implemented by various countries in the international community. South Africa, however, on average generates roughly 900 000 tonnes of domestic waste glass each year and has made little use of this readily available raw material. More recently, with national policies mandating the reuse, recycling and minimisation of domestic waste, in addition with several economic and environmental benefits, it is expected that the use of alternative materials, e.g. recycled glass, in road construction will increase. Depending on the application, the uses of recycled glass in road construction vary widely. This study investigates the engineering performance of Hot Mix Asphalt (HMA) incorporating locally available recycled crushed glass for use in the wearing course of South African pavements. The study contributes to current research at the Council for Scientific and Industrial Research (CSIR) which aims to optimise the design, construction and maintenance of roads through the use of cost-effective and sustainable materials that include waste materials. A continuously-graded asphalt mix with a glass replacement ratio of 15% and 50/70 penetration grade bitumen was designed for a traffic level of 3 to 30 million E80s. The mix design was conducted according to the current method for traditional asphalt mixes in South Africa. The results indicate that the glass-asphalt mix conforms to the South African mix design criteria. Furthermore, the moisture susceptibility of the glass-asphalt mix was evaluated with and without the use of anti-stripping additives. The standard Tensile Strength Ratio parameter supported with a microscopic imaging technique and an analytical modelling method were used to evaluate and quantify the resistance of the glass-asphalt mix to moisture damage. Analysis of the results reveal that an antistripping additive is essential to meet moisture susceptibility criteria and alleviate stripping for the investigated source and grading of glass particles, at a glass content of 15%. The study also assesses and compares the stiffness and permanent deformation properties of the glass-asphalt mix to a traditional continuously-graded asphalt wearing course mix, typically used for road construction in South Africa. Selected mathematical models were used to effectively characterise the deformation and stiffness behaviour of the mixes. The glass-asphalt mix shows increased stiffness and improved resistance to permanent deformation at elevated temperatures. Additionally, a multi-layer linear-elastic analysis is used to assess the influence of temperature and loading frequency variation on the structural capacity of the glass-asphalt and HMA surfacing layers. The analysis reveals that the structural capacity of both surfacing layers are comparable at intermediate temperatures, for both high and low loading frequencies. The findings of this study reveal that improved performance could potentially be achieved with the use of recycled crushed glass in continuously-graded asphalt wearing course mixes in South Africa.

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