Utilization of submicron autoclaved aerated concrete waste to prepare eco-friendly ultra-high performance concrete by replacing silica fume

Silica fume (SF), as the main submicron filler material in ultra-high performance concrete (UHPC), determines the bulk density and final mechanical properties of UHPC. With the rapid increase in the demand for UHPC in the construction industry, SF is gradually becoming a luxury material. In the present work, wet grinding technology was used to prepare an alternative submicron material to replace SF. Wet-grinded submicron autoclaved aerated concrete waste (WSA) was prepared, and UHPC was prepared with the replacement of SF by WSA under different replacement levels (up to 100%). The results showed that at the level of 100% WSA replacement, UHPC's hydration process was promoted, the 28-day compressive strength was the same, and the pore structure was refined. But the cost of WSA is only 41% of SF, indicating that it is possible to completely replace SF in UHPC using WSA. The results propose a new technical approach for the replacement of high-cost SF in UHPC, which is expected to achieve high value-added benefits for construction waste.