Masters Degrees (Civil Engineering)

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Browsing Masters Degrees (Civil Engineering) by Subject "Aggregates (Building material)"

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    Potential for recycled concrete aggregate stabilisation with bitumen emulsion and foamed bitumen
    (2020-03) Mazibuko, Nokuthula Mandy Antonia; Rudman, Chantal; Jenkins, K. J.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Bitumen stabilisation is a technology used to improve the strength properties of any aggregate, which is also environmentally friendly. The method of stabilisation requires less energy in comparison to hot asphalt mixes and it causes less pollution when compared to cement stabilisation. The sustainability benefit of BSMs can be improved when recycled materials from construction demolition waste such as recycled concrete is used. The existing TG2 outlines the process to determine whether an aggregate is suitable to be stabilised with foamed bitumen or bitumen emulsion. This research aims to use the same process to determine whether RCA is a suitable aggregate for stabilisation with bitumen emulsion or foamed bitumen. In addition, the BSM classification of the resultant BSM with RCA is determined along with the performance properties of the mix design. The indirect tensile strength (ITS) was used to determine the suitable active filler for RCA stabilised with bitumen emulsion and foamed bitumen. Active fillers considered included 1% lime and 1% cement. Furthermore, the optimum bitumen content for the aggregate was determined and found to be 2.2% for both bitumen emulsion and foamed bitumen. The shear strength parameters and resilient moduli of the optimum mix designs made from foamed bitumen and bitumen emulsion were tested with the monotonic and dynamic triaxial test. The preliminary results indicate that RCA is a suitable aggregate for stabilisation with low viscosity bitumen. Moreover, the ITS results suggest that no active filler is required and a potential BSM 1 layer can be produced with 2.2% bitumen content. This indicates the potential of using this material considering economical relevance. Furthermore, the shear parameters obtained for both binders (bitumen emulsion and foamed bitumen) also indicates that the mix designs can be classified as a BSM 1. Additionally, a high resistance to moisture damage was achieved as shown by the retained cohesion ranging from 88.2 to 90%. Moreover, the resilient modulus analysis indicates a stress dependent behaviour, which can be modelled by existing models used for unbound granular materials. However, care should be taken when stabilisation is done with bitumen emulsion due to the high absorptivity of the mortar, which causes early breaking of the emulsion. Pre-soaking of the aggregate was required to manage this challenge. The pavement life analysis shows that, if the layer is used in the base layer with a G5 subbase a pavement life suitable for a Category B road is obtained. Therefore, the addition of bitumen improves the behaviour and performance of RCA and the results indicate that it can be successfully used in a base layer. Therefore, there is potential for the stabilisation of RCA with either foamed bitumen or bitumen emulsion.