ReviewStructural performance of reinforced geopolymer concrete members: A review
Introduction
With the growing environmental and economic concerns associated with conventional concrete-based building materials such as reinforced concrete structures, researchers have been actively involved in exploring possibilities in using alternative materials to address these concerns. For instance, alternative concrete-making materials have been trialled in reinforced concrete structures such as recycled concrete aggregate [1], [2] and agriculture waste materials [3], among others, in an attempt to reduce the dependency on conventional concrete constituent materials, which are fast depleting. One of the primary environmental concerns from concrete-based building materials is the high amount of carbon dioxide emission, which arises during the manufacturing of cement. Approximately 5% of the global carbon dioxide emission is contributed by the cement industry. In recent times, a cement-less binder for producing concrete, termed as geopolymer concrete, is fast gaining popularity in concrete research work as the technology eliminates the need for cement. In order to produce geopolymer, a process termed as ‘geopolymerization’ is required which involves the reaction between aluminosilicate material and alkaline liquids. Common aluminosilicate material used for producing geopolymer is fly ash and slag, which are both industrial by-products and both of these materials have much lower carbon dioxide emission factor compared to cement. It was reported that the use of geopolymer could bring down the overall carbon dioxide emission by up to 64% in comparison with the use of cement [4]. Furthermore, in terms of economic consideration, due to the lower price of fly ash compared to cement, the price of fly ash-based geopolymer concrete could be as low as 10–30% cheaper compared to conventional cement-based concrete after taking into account the price of alkaline liquids [5].
While most of the research works on geopolymer concrete focus on micro-scale investigation, recent researchers on the use of geopolymer concrete extends to the investigation of the structural behaviour of geopolymer concrete in load-bearing members such as reinforced concrete beams, columns, slabs and more. The structural properties of the concrete members is one of the most vital component in effectively introducing such concrete for actual buildings and applications. The conformity of the performance of reinforced geopolymer concrete members with existing design provisions should be ascertained in order to evaluate the feasibility of using these design codes for geopolymer concrete members for the convenience of structural design engineers. In addition, practising engineers would also be able to produce a more realistic, safer and effective design of geopolymer structures in the long run based on knowledge and findings from research works, such as numerical models, empirical equations, appropriate assumptions and safety factors, among others. In view of the importance of the structural aspect of utilizing geopolymer concrete in reinforced concrete structures, this review summarizes and discusses the published findings of research works involving geopolymer concrete structures such as beams, columns, slabs and panels.
Section snippets
Reinforcing bar-concrete bond
The structural performance of reinforced concrete members depends on the bond between concrete and reinforcement, in which the mechanism of bond influences the embedded length of reinforcing bar and consequently the load-bearing capacity of structural elements, crack opening and spacing [6]. ACI 408R [7] considers the bond strength as one of the structural properties and the understanding of the behaviour is critical to the eventual development of analysis and design basis of the structural
Discussion and suggestions
Based on the literatures studies, it is clear that till date, most research on using geopolymer concrete in structural members were mainly focused in reinforced concrete beams and columns, as well as the steel-concrete bond interaction. Generally, most of the performance of these reinforced geopolymer concrete members were found to exhibit similar, if not enhanced load-bearing capacities compared to the corresponding conventional reinforced cement-based concrete members. Because of this, most
Field application
In Australia, reinforced geopolymer concrete application had been utilized for actual field application, by using both precast geopolymer concrete elements and casting in-situ of the geopolymer concrete. Examples of these include precast retaining wall, precast bridge decks and boat ramp (Fig. 10) using geopolymer concrete of grade 40 [70]. In 2013, being the first application of geopolymer concrete in multi-storey building, precast geopolymer concrete floor beams were utilized as structural
Conclusion
Based on the review of the performance of the structural properties of geopolymer concrete members, it is concluded that the geopolymer concrete members such as beams and columns could be designed using design codes for conventional reinforced concrete members as most of the codes gave conservative estimation of the ultimate load-capacity of the geopolymer concrete members. Moreover, the general behaviour and failure mode of reinforced geopolymer concrete members were similar with those of
Acknowledgements
This work is funded by the University of Malaya under the grant GC003D-15SUS: “Application of environmental-friendly building materials consisting of local waste materials for affordable housing”.
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