Combined effect of silica fume and fly ash as cementitious material on strength characteristics, embodied carbon, and cost of autoclave aerated concrete.

Aerated concrete (AAC) or lightweight concrete is primarily used for non-load bearing structures in construction work. Generally, it is produced with cement as a main binding ingredient, and the production of cement is blamed to contribute 7 to 8% of CO emission in the environment. In addition, the dumping of industrial wastes is also a great environmental concern. This research is an attempt to produce low-cost and sustainable aerated concrete utilizing silica fume and fly ash as partial substitution to cement without compromising the fundamental properties of aerated concrete. The current study was divided into two phases: in the first phase, the silica fume was substituted up to 20% with a variation of 5% in each mix. In the second phase, the fly ash was replaced with cement in three variations, i.e., 10%, 20%, and 30% containing an optimum proportion of silica fume obtained in phase 1. The aluminum powder was added at 0.4% by weight of binder to introduce aeration in concrete. Before testing, samples of aerated concrete were cured with steam in an autoclaving machine for 9 h at a pressure and temperature of 1.5 bars and 127 °C respectively and oven-dried at a temperature of 105 °C for 24 h after steam curing. From the experimental results, the highest compressive and split tensile strength of AAC was recorded when 15% of the cement was replaced with silica fume and 30% of the cement was replaced with fly ash combined. At this proportion the least density was also recorded which showed the lightweight of AAC without compromising the strength characteristics. In addition, the reduction of 42.64% and 32.4% of embodied carbon and cost was observed respectively.