The structural use of alkali activated materials (Geopolymers)

[摘要] ENGLISH ABSTRACT: Alkali activated materials (AAMs), also referred to as geopolymer concretes, are a new generationof alternative construction materials, which are formed through the alkali activation ofclinker-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 lowcarbon 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 thefocus on the compressive strength and the elastic modulus, as well as the structural behaviourof 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 modulusof the activator; and the coarse aggregate content and size. Compressive strengths of up to67 MPa were obtained, while the elastic modulus was low in comparison with that typicallyfound for OPC concrete, with values between 10 GPa and 32 GPa. The mechanical propertieswere mainly influenced by calcium content, sodium hydroxide concentration and the activatormodulus.Large scale reinforced AAM beams were tested in bending in order to obtain the flexural behaviourof reinforced AAMs, while reinforcement pull-out tests were performed to determinethe bond behaviour between AAMs and the reinforcement. For both these tests, two AAMmixes were compared against two OPC mixes with similar strengths. It was found that it ispossible to use design codes, such as the EN 1992-1-1, (2004), for the ULS design of reinforcedAAM beams. However, attention has to be given to the low elastic modulus in order to reducethe large deflections of the AAM beams. The design codes also seem to be inadequate for thedeflection calculations of AAMs. Promising results were obtained in terms of the design bondstress of AAMs, as they were generally higher than that of the OPC-mixes. This indicates thatshorter 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 structuralmaterial, as there is still a number of issues, for example the low elastic modulus, that need tobe addressed. However, there is potential for AAMs as a structural material, if these problemsare solved.

[发布机构] Stellenbosch University