Life cycle assessment of alkali-activated concretes under marine exposure in an Australian context

Abstract

Alkali-activated concretes have been shown to be an environmentally advantageous construction material as they utilize waste or by-products as precursors, such as fly ash and ground blast furnace slag. These concretes also have the ability to achieve strengths suitable for structural applications. However, each mix design of an alkali-activated concretes is unique and requires a detailed life cycle analysis to determine the environmental impact and cost viability. This study evaluates the feasibility of alkali-activated fly ash or fly ash geopolymer and alkali-activated slag concrete developed for application in Australia currently subject to long term site performance studies. This paper reports a detailed life cycle assessment analysis of these concretes to assess their environmental footprint. The paper considers three distinct allocation methods: baseline, mass, and economic allocation, with two system boundaries: manufacture and construction. The study shows AAS concrete has a lower environmental impact than an equivalent strength PC concrete in two impact categories, global warming potential and eutrophication, while acidification and human toxicity depend on the allocation method applied in the manufacturing stage. The global warming potential (100-years) of AAS is 5.25–35% less than PC concrete. The FAGP concrete has more negative impacts on the environment than PC-based concrete, regardless of which allocation method is applied. The report highlights alkaline activators and transportation of raw materials as the main environmental impact contributors to concrete manufacture. The global warming potential of FAGP is 22–34% higher than the equivalent PC concrete in the baseline method. For the construction stage boundary, machinery appliances for handling concrete and transportation only contributes a small environmental impact (<4%) compared with concrete manufacturing. Cost estimation for concrete production suggests that the cost of the alkali-activated concrete is competitive with the conventional concrete market, dependant on the proximity of the feedstocks and the cost of sodium silicate. Neglecting the transportation cost of feedstocks, the cost of AAS concrete can be 4.8% cheaper, whereas the cost of FAGP concrete is 2.7% more expensive than PC concrete.