Life-cycle assessment of fly ash and cenosphere-based geopolymer material

Abstract

It was widely reported in the early 2000s that geopolymer technology exhibits superior mechanical properties and lower global warming potential (GWP) over the use of ordinary Portland cement (OPC). However, a major limitation observed in the sustainability evaluation is a lack of consideration of environmental impacts from the use of industrial waste. This observation led to the purpose of this study, which is to identify the key factors throughout geopolymer production that contribute to its sustainability performance. In this paper, two geopolymers made of fly ash (G-FA) and cenospheres (G-C) were examined by mechanical testing while their sustainability impacts on a cradle-to-grave approach were investigated. The industrial waste and transport modelling impacts were given special attention in the performed life-cycle assessment. After 28 days of curing, G-FA exhibited 64.56 MPa and 6.03 MPa of compressive strength and flexural strength, respectively. G-C, with34 of G-FA bulk density, achieved 19.09 MPa and 3.13 MPa, respectively, with no significant changes observed after 14 days of curing. By upscaling the inventories to 1 m3 of industrial production scale, geopolymers showed a GWP reduction up to 49.7% compared to OPC with natural aggregates and presented benefits on human health damage category by 23.7% (G-FA) to 41.6% (G-C). In conclusion, geopolymer mortars establish compressive strength and flexural strength that are adequate for construction applications and present sustainability benefits in GWP, which suggests them to be potential substitutions for OPC. However, the industrial waste treatment (i.e., preparation of fly ash) will deplete water bodies, and the sodium silicate induces significant environmental burdens during its manufacture, becoming the key factor to enhance the geopolymer’s sustainability.