Browsing by Author "Louw, Joachim Paul"
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- ItemThe structural use of alkali activated materials (Geopolymers)(Stellenbosch : Stellenbosch University, 2017-03) Louw, Joachim Paul; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Alkali activated materials (AAMs), also referred to as geopolymer concretes, are a new generation of alternative construction materials, which are formed through the alkali activation of clinker-free binder materials, such as fly ash and slag. Compared to Ordinary Portland cement (OPC) concrete, the production of AAMs is associated with low energy consumption and low carbon dioxide (CO2) emissions, together with promising mechanical properties. The main goal of this study is to determine the structural use of a fly ash/slag based AAM, activated with sodium silicate and sodium hydroxide. The mechanical properties, with the focus on the compressive strength and the elastic modulus, as well as the structural behaviour of reinforced AAMs are investigated to achieve this goal. For the mechanical properties of AAMs, several of mix parameters were varied, which include: the type of activator; the calcium content; the activator concentration; the dosage; the modulus of the activator; and the coarse aggregate content and size. Compressive strengths of up to 67 MPa were obtained, while the elastic modulus was low in comparison with that typically found for OPC concrete, with values between 10 GPa and 32 GPa. The mechanical properties were mainly influenced by calcium content, sodium hydroxide concentration and the activator modulus. Large scale reinforced AAM beams were tested in bending in order to obtain the flexural behaviour of reinforced AAMs, while reinforcement pull-out tests were performed to determine the bond behaviour between AAMs and the reinforcement. For both these tests, two AAM mixes were compared against two OPC mixes with similar strengths. It was found that it is possible to use design codes, such as the EN 1992-1-1, (2004), for the ULS design of reinforced AAM beams. However, attention has to be given to the low elastic modulus in order to reduce the large deflections of the AAM beams. The design codes also seem to be inadequate for the deflection calculations of AAMs. Promising results were obtained in terms of the design bond stress of AAMs, as they were generally higher than that of the OPC-mixes. This indicates that shorter embedded lengths can possibly be used for AAMs. It can be concluded that the AAMs is still some time away from being used as a structural material, as there is still a number of issues, for example the low elastic modulus, that need to be addressed. However, there is potential for AAMs as a structural material, if these problems are solved.