Utilization of solid waste high-volume calcium coal gangue in autoclaved aerated concrete: Physico-mechanical properties, hydration products and economic costs

摘要

Owing to the insufficient application of recycling methods, the overall amount of coal gangue (CG) has been increasing at a high rate in China. Therefore, development of an efficient method for the CG reuse in other fields has become a pressing issue. This study aims to discover an effective method for implementing an autoclaved process for the preparation of environmentally friendly and lightweight building materials, such as autoclaved aerated concrete (AAC), with the goal of reusing solid waste and reducing the environmental hazard associated with high-calcium coal gangue (HCCG). The chemical composition of HCCG before and after the treatment was analyzed. The effects of the substitution amount and fineness of HCCG on the physical-mechanical properties and hydration products of the AAC were studied. The results show that the incorporation of HCCG does not affect the slurry performance, a vital element in gas foaming, owing to its contribution to the heat and alkalinity of slurry. Moreover, with increasing HCCG content, both, the bulk density and compressive strength of the AAC increased; the best mix contained 8% cement, 58% HCCG, 31% sand, and 3% gypsum (corresponding to 599.4 kg/m(3) and 4.57 MPa). These characteristics were in good compliance with the requirements on AAC blocks GB 11968-2006 for B06, A3.5. In addition, an assessment of the safety associated with using HCCG in AAC was conducted, revealing that high-calcium coal gangue autoclaved aerated concrete (HCCG-AAC) can be regarded as a nonhazardous building product and the proposed autoclaved curing can actually solidify heavy metals. Finally, the favorable influence of using high-volume HCCG waste was discussed from the economic viewpoint, which indicates that using HCCG lowers the cost by 40%. The results of this study can provide a new resource utilization method for solid waste coal gangue; in addition, this study can also be used as a theoretical basis for the preparation of autocalved aerated concrete with other low calcium gangue or solid waste. (C) 2020 Elsevier Ltd. All rights reserved.