Solid waste-based low-carbon autoclaved aerated concrete: relationship between engineering properties and microstructure

A novel low-carbon autoclaved aerated concrete (AAC) was developed to enhance the high valuable use of solid waste in production, incorporating furnace slag, metro shield sand, and quartz tailings sand as 100% siliceous raw materials, constituting 60% of the total weight. In this study, comprehensive analyses were conducted on its engineering properties, including density, compressive, flexural, and splitting tensile strengths, and thermal conductivity. Advanced techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and high-resolution Industrial CT scanner (X-CT) were employed to examine AAC's material composition, hydration products, and pore structure characteristics at the microscale. The results indicated that the addition of 10% furnace slag resulted in a specific increase of 5.5% in compressive strength. However, escalating the furnace slag content to 30% proved detrimental to the toughness and dry shrinkage of AAC. The microstructure analysis indicates that the use of furnace slag can improve the connectivity and roundness of pores and reduce the probability of large pores (>0.01 mm3), which will reduce the risk of damage localization. Furthermore, furnace slag in AAC enhanced sustainability and cost-effectiveness compared to metro shield sand and quartz tailings sand. Based on the TOPSIS model, an optimal AAC mixture, considering engineering performance, economy, and sustainability, was derived by blending the three types of solid wastes.