## 1 Introduction  
Self-compacting lightweight concrete (SCLC) combines the unique advantages of self-compacting concrete (SCC) and lightweight aggregate concrete (LWAC), making it a versatile material for applications such as tall buildings and large-span structures. This combination reduces the self-weight of structures and improves their seismic performance, while maintaining the exceptional workability and mould-filling capability characteristic of SCC [1, 2]. SCC achieves compaction under its own weight without the need for vibration thanks to its high viscosity and cohesion, which also prevent segregation during handling and placement [3, 4, 5, 6]. Incorporating lightweight aggregates into SCC further enhances its properties by reducing density, lowering transportation costs, and improving onsite workability, as well as thermal and acoustic performance for building occupants [7].  
Several lightweight and recycled aggregates, such as expanded clay [8], dolomite [9], marble and granite [10], expanded polystyrene [11], ground granulated blast-furnace slag, and metakaolin [12], have been successfully used in SCLC. The performance of lightweight concrete depends heavily on the mineralogy, production methods, and porosity of the aggregates. These factors influence workability, mechanical strength, density, and thermal conductivity, as well as the transition zone between the aggregate and cement matrix [2, 13, 14]. While substantial research has explored the properties of SCLC using various aggregate types [14, 15, 16, 17, 18, 19, 20, 21, 22, 23], the development of sustainable alternatives remains a growing priority in the construction industry.  
In Brazil, the production of lightweight aggregates is largely limited to a single manufacturer in Sao Paulo, which uses clay as the sole raw material in a rotary kiln process. This geographical concentration hinders the widespread adoption of lightweight aggregates in regions far from the Southeast, such as the North and Northeast [24]. Simultaneously, the increasing scarcity of natural resources has driven the search for sustainable materials. Two promising byproducts generated in Brazil's Northeast--sugarcane bagasse ash (SBA) and schelite mining residue (SMR)--offer a viable alternative for producing artificial lightweight aggregates [25, 26].  
SBA, a byproduct of renewable energy production, is generated in significant quantities due to Brazil's extensive sugarcane industry, with the 2022/2023 harvest reaching 615.84 million tons, 45.6 million of which were from the northeast, representing an increase of 10.8% [25, 26]. This generates a substantial amount of bagasse ash, which is currently underutilized. Similarly, in the mining of scheelite (CaWO\({}_{4}\)) used for tungsten production, 99.2% of the extracted material becomes waste. In the municipality of Currais Novos, RN, approximately 10 million tons of this waste have already been accumulated, with 14 local mining companies contributing to this total. Previous studies have demonstrated the technical feasibility of using SBA and SMR for producing lightweight aggregates; however, their application in SCLC remains unexplored.  
This study represents a pioneering investigation into the development of SCLC incorporating unconventional lightweight aggregates produced from SBA and SMR. These aggregates, sourced from the northeast region, offer a sustainable alternative to traditional materials like expanded clay, which is widely used but regionally limited. By reducing CO\({}_{2}\) emissions, logistics costs, and delivery times, this work supports the use of industrial byproducts and promotes sustainable practices in civil construction. The fresh and hardened properties of SCLC produced with these novel aggregates, as well as their durability, are systematically evaluated. This approach advances sustainable waste management while contributing to the development of environmentally friendly construction materials tailored to regional needs.