Browsing by Author "Bredenkamp, Zaandre"
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- ItemThe performance properties of recycled concrete in road pavement materials(Stellenbosch : Stellenbosch University, 2018-03) Bredenkamp, Zaandre; Rudman, Chantal; Jenkins, Kim; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Due to a rise in population and industrialisation, the demand on infrastructure in developing countries have increased significantly. The world has been moving towards a more environmentally friendly and sustainable approach to provide the necessary infrastructure to sustain the economy. High quality natural aggregate is a finite resource with declining supply. It is therefore imperative that materials previously regarded as waste, should be recycled and reused. Large amounts of Concrete Demolition Waste (CDW) is created when old infrastructure is destroyed and this material placed in already constrained landfill sites. There has been a shift in perceptions of this material from being a waste to being a valued road construction material in recent years. Recycled Concrete and Masonry Aggregate are widely used in some developed countries, where good quality natural resources are scarce. However, in developing countries that have an abundance of good quality aggregate, but limited knowledge in the field of recycling, this material is often disregarded. Builders’ rubble that have been recycled, such as Recycled Concrete Aggregate (RCA), has shown to be an effective alternative material in structural pavement layers in other countries. In the South African industry, standards and guidelines towards the use of this material has not yet been developed and implemented. The experimental design developed for this study, incorporated two different types of RCA material, the Unexposed material used from the crushing process, and Exposed material that has been treated with the aim to promote rapid self-cementation. In this study, laboratory triaxial tests, which included monotonic and permanent deformation tests were performed. The self-cementing potential of the material was investigated by using two different types of material. These materials were tested at different curing times to investigate the effect on the durability of the material. It was found that RCA material, both Exposed and Unexposed, had large amounts of variability in terms of behaviour. The Exposed RCA more so than the Unexposed RCA. This can be attributed to the reduction in self-cementation potential and the variable dispersion of the cement particles left in the material after processing of the Exposed material. Both materials had very high shear strength parameter values (cohesion and friction angle). Results revealed that the shear parameters are not an indication of the material’s ability to withstand permanent deformation, as was shown for the Exposed RCA material. The Exposed material exhibited similar shear parameters to the Unexposed material. However, the Deviator Stress Ratio for the Exposed material, where stable behaviour in the permanent deformation tests was observed, was much lower than that of the Unexposed material. This suggests that the material relies not only on the matrix of aggregate interlock, but possibly also on the cementitious bonds for shear strength and resistance to permanent deformation. Using the results obtained from permanent deformation results, the best fit model could be identified. The critical parameters that influence the behaviour of RCA were identified as deviator stress ratio, moisture content and density. This has a direct effect on the magnitude of plastic strain in the material. The results from the permanent deformation tests were used to synthesise a transfer function for the Unexposed RCA material. This transfer function can be used to calculate the pavement life of RCA layers within a pavement structure. Pavement analyses were performed on pavement structures that include RCA as either a base or subbase. These results were compared to three typical South African pavement structures. The transfer function that was developed was used to calculate the life for the pavement layers consisting of RCA materials. Although the DSR at which the material performs at satisfactory levels of permanent deformation is lower than that of standard granular materials used in pavement construction, the analysis yielded favourable results. Results showed that RCA material delivered reliable and achievable results for the use of this material in a pavement layer when compared to these standard pavements.