Concrete is the most heavily used construction material in the modern world, and given the current global trends towards sustainability there is a need for significant advances, particularly in the construction sector. Geopolymer concrete (GPC) is a recent development in construction materials demonstrating similar structural properties to that of Ordinary Portland Cement (OPC) based concrete, yet whilst at the same time addressing the environmental footprint of the industry and economic concerns. GPC makes use of hazardous waste from several manufacturing process, which has obvious economic and environmental benefits. This allows GPC to have a far lower, in some cases up to 80%, embodied energy and carbon content than traditional concrete.
In terms of structural properties, GPC can have a characteristic compressive strength of up to 90MPa, depending on curing conditions and mix design. For example, 30 to 40MPa is indicative of strength attainable within 3 to 4 days of pouring, yet for OPC based concrete this is roughly 5 days. However, academics have also put forward curing conditions can have a significant impact on these figures, with some studies showing 90MPa achievable in as little as 6 hours (Gourley et al. 2011). In addition, GPC has a higher tensile strength which in some applications may make steel reinforcement obsolete. GPC properties such as low shrinkage and improved acid, sulphate and fire resistance, give it improved durability. This therefore makes GPC a viable replacement for project applications such as sewerage systems, corrosive environments and radioactive and hazardous material containment.
TABLE OF CONTENTS
Geopolymer concrete mix
Strength and Durability
Curing and workability
Need for geopolymer concrete
Concrete is the most heavily utilised construction material on the global stage. A staggering one cubic metre is consumed per person per year, a trend that is almost certain to continue, if not accelerate (Turner & Collins 2013). Considering the enormous scale of its use, even small innovations have the potential to create widespread benefits. The traditional binder in concrete, Ordinary Portland Cement (OPC), presently contributes somewhere between five and seven per cent of global anthropogenic carbon dioxide, CO2, emissions (Chotetanorm et al. 2013; Turner & Collins 2013). Geopolymer concrete (GPC), which substitutes geopolymers in place of OPC as the binder, has an approximately 80% lower carbon footprint than traditional concrete. While the practice of using geopolymers as a binding agent has been known for over 60 years, it is only recently that developed has rapidly advanced, particularly in countries such as Australia (Gourley et al. 2011). With the current global attitude shifting towards a more sustainable future, innovation in traditional concrete offers the potential to reshape the fields of engineering and construction and address these concerns.
The geopolymer binder used in place of OPC in GPC can be sourced from industrial by-product material. The base material should be rich in Silicon (Si) and Aluminium (Al), and can react with an alkaline solution, creating a geopolymetric binder (Rahman & Sarker 2011). Fly ash, both low and high calcium content varieties, would therefore be an example of base material; however it could also be a combination of various materials, such as metakoalin and slag. Regardless, the basic reaction with the alkaline solution is similar, resulting in a compact, well cemented composite (Rahman & Sarker 2011). The Concrete Institute of Australia (CIA) released a document in 2011 stipulating a recommended practice for GPC, however this in itself is limited to low calcium fly ash sourced materials, noted as Class F (Gourley et...
References: Gourley, J.T. & Johnson, G.B. (2005). Geoploymer, Green Chemistry and sustainable
McLellan, BC, Williams, RP, Lay, J, Riessen, Av & Corder, GD 2011, 'Costs and Carbon Emissions for Geopolymer Pastes in Comparison to Ordinary Portland Cement ', Journal of Clearner Production, vol. 19, pp. 1080-90.
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