Utilization of solid wastes for aerated concrete preparation: Mechanical properties and microstructural analysis

Aerated concrete (AC) is a kind of lightweight concrete with low density, low thermal conductivity, high sound absorption and excellent processability that has attracted much attention. Recently, many solid wastes have been used to prepare AC to save costs and resources. Researchers have studied the effect of different solid waste utilizations on the performance of AC. However, a comprehensive analysis of the effects of solid waste incorporation on the performance of AC at both macroscopic and microscopic scales is limited. In fact, the addition of irregular, loose porous and different specific gravity solid waste can change the water requirement of the slurry, thus affecting the pore structure, dry density and even the strength of the AC. Additionally, the variation in waste dosing affects the Ca/Si ratio and the generation of tobermorite or C-S-H gel within AC. Therefore, this paper systematically reviewed the effects of solid waste addition on AC microscopic properties, such as pore structure, hydration product morphology and generation. Moreover, macroscopic properties, such as dry density, mechanical properties and workability, were also reviewed. The solid wastes were classified into calcareous, siliceous and calcium-silica materials, taking into account the aluminum. In the case of autoclave aerated concrete, high levels of sand substitution using siliceous materials had a negative effect on strength development, and the optimal substitution should be limited to 30 %. In addition, Al, Na and Mg can significantly affect the crystal morphology. In the case of foam concrete, highly reactive wastes had a positive effect on compressive strength and water absorption when replacing cement. The composite blending of solid wastes had better performance than single solid waste blending. This paper will be helpful in finding more suitable wastes to prepare AC in terms of practical operational considerations and cost savings.