Zakaria, Nur Mustakiza
(2020)
Characterisation of bitumen and asphalt mixture with recycled waste plastic (RWP) modified binder.
PhD thesis, University of Nottingham.
Abstract
Good bitumen properties are desirable nowadays to achieve longer service life. In order to enhance the quality of bitumen in term of its properties, many researchers began to focus on bitumen modifications particularly in modifying bitumen with polymer mainly from recycled waste plastic. Incorporating bitumen with polymer significantly improves and reduces asphalt pavement distresses. However, there are still some drawbacks which significantly limit its development namely inappropriate polymer and bitumen blend may result in poor storage stability that would affect the performance of asphalt mixture. Besides that, excessive hardening by adding more polymer in bitumen may increase the energy required during production which will increase the cost of the construction. Also, the modification procedure may need high shear and mixing temperature for some period that would change the rheological properties of Polymer Modified Bitumen (PMB) due to ageing. Moreover, the increasing amount of plastic waste material at the landfill is another vital concern. So, the main aim of this study is to re-use the recycled waste plastics as a modifier in bitumen to enhance the performance of asphalt mixture. Therefore, finding the optimal shear rate, modification temperature and the mixing time are essential to ensure the optimum blend of Recycled Waste Plastic (RWP) modified binder that is stable and better in performance could be produced. In this study, six types of recycled polymer and bitumen with penetration grade of 160/220 are used for the modification. Then, additional two binders namely control binder (penetration grade of 40/60) and SBS-modified bitumen were used to compare with the RWP-modified binders that gave significant improvement in terms of its performance.
There are three main phases involved in this study. It begins with Phase 1 (selection and incorporation of RWP in bitumen) for optimising the blending condition for each RWP, Phase 2 (binder test) is to identify the rheological properties of PMB and optimise the RWP concentration and lastly, Phase 3 (mixture performance test) is to determine the performance characteristics of asphalt mixture for each RWP with respect to fatigue cracking and rutting.
Phase 1: The potential of RWP to modify base binder were identified based on the melting point of RWP and the optimisation of the blending variables were done based on the softening point of the modified binders. Then, RWP that cannot be blended with base binder will be excluded from the testing programme.
Phase 2: At this phase, the binder tests for RWP-modified binders in terms of chemical, structural, rheological, performance and durability properties were carried out. The effect of ageing during blending of RWP-modified binder was analysed by means of Fourier Transform Infrared (FTIR) for the chemical approach. The structural property was assessed in term of the stability of RWP-modified binder at higher temperature storage. Then, the rheological characteristics for unaged and aged binders were investigated. The fatigue and rutting performance of binder were characterised. The fatigue testing was evaluated by means of the Linear Amplitude Sweep (LAS) test and the Double-Edged Notched Tension (DENT) test while the rutting testing involved the Multiple Stress and Creep Recovery (MSCR) test. Lastly, the durability of the binders against moisture damage was investigated using the Peel test.
Phase 3: This phase consists of performance of asphalt mixture. First, an aggregate of granite and typical dense gradation of 14mm was selected for designing all asphalt mixtures by using two binder contents. The stiffness, fatigue and rutting were evaluated and conducted using Indirect Tensile Stiffness Modulus (ITSM) test, Indirect Tensile Fatigue Test (ITFT) and Repeated Load Axial Test (RLAT). All these tests were carried out by means of the Nottingham Asphalt Tester (NAT) machine.
The result from the studies show that the RWP-modified binder can significantly improve the rheological properties and performance of the base binder. The improvement is highly dependent on the amount of RWP added and more pronounced at higher percentage of RWP added namely 7%. However, the RWP-modified binders are more susceptible to fracture but it could withstand higher strain levels due to higher viscosity values that make it stiffer. The improvement in moisture durability for all binders after conditioning show that the effect of stiffening is dominated in which ageing take place during the conditioning The result obtained from the asphalt mixture performance test show that the RWP-modified mixtures are better than conventional mixture in rutting performance but not in fatigue performance.
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