High-volume, ultra-low-density fly ash foamed concrete

Resource efficiency is a core criterion for the regulation of construction products and rightly promotes the most sustainable solution. This paper reports the development a low embodied carbon dioxide backfill material based on an ultra-low-density foamed concrete using a high volume of fly ash to replace Portland cement. This material builds on previously reported research on the underlying causes of instability in low-density foamed concrete mixes and demonstrates that, with the addition of a small amount of calcium sulfoaluminate (CSA) cement, stable ultra-low-density foamed concretes with density as low as 150 kg/m3 can be produced. A high volume of fly ash up to 70% of cement phase has been used, which reduced the average bubble size of the foamed concrete and increased the thickness of the bubble walls. The observed microstructure of fly ash foamed concretes was improved over the long term. The use of fly ash significantly reduced the embodied carbon dioxide of these mixes, which potentially has significant benefits for large-scale backfill and similar applications.