Optimizing mechanical performance and flow characteristics of alkaline fly ash/rice husk ash composite backfill: Insights from multi-factor analysis and engineering optimization

Abstract

In order to effectively dispose of agricultural waste rice husk ash and improve the mechanical properties of backfill, the properties of fly ash/rice husk ash composite backfill material were studied in the laboratory. The effects of fly ash, rice husk ash, straw fiber and NaOH content on the properties of composite backfilling materials were studied, and the ratio parameters of composite backfilling materials were optimized based on engineering examples. Our findings reveal that fly ash content significantly impacts slump, with its addition enhancing the flow performance of composite backfilling materials. Conversely, straw fiber, rice husk ash, and NaOH content were found to have non-significant effects on slump. We observed that with the increase of fly ash content from 5 % to 20 %, the compressive strength of the backfill firstly increases and then decreases, and the optimal content range is about 10 %. Moreover, increased rice husk ash and NaOH content effectively enhance the UCS. However, higher fly ash and straw fiber content were found to impede the strengthening effect of NaOH on UCS. Nevertheless, higher NaOH content was observed to augment the strengthening effect of rice husk ash content. Furthermore, when the content of fly ash and rice husk ash is 5∼10 % and 3–12 % respectively, rice husk ash and fly ash effectively reduce the size range of internal void structures, enhancing the microstructure density and mechanical properties of the composite backfilling material. Based on engineering example, we determined the optimal ratio parameters of the composite backfilling material to be: 20 % fly ash content, 9 % rice husk ash content, 0.4 % straw fiber content, and 2.5 % NaOH content. This study is helpful to promote the application of waste rice husk ash and straw fiber in mine filling, and provides theoretical guidance for the parameter design of backfilling materials.