Developing alkali-activated controlled low-strength material (CLSM) using urban waste glass and red mud for sustainable construction

Using industrial waste in controlled low-strength material (CLSM) offers many benefits and addresses waste management issues. However, identifying optimal CLSM design while balancing environmental impacts and engineering properties poses a notable challenge. Herein, new alkali-activated CLSM formulations based on urban waste glass and red mud (RM) are proposed for the first time with systematic investigations into the material properties and sustainability. The formulations involve the ternary blends of slag, glass powder (GP) and RM as the binders and crushed glass as aggregate. Our observations show RM has a clay-like texture with complex crystalline phases rich in Al and Fe. Increasing the proportion of RM to GP notably decreases the flowability, extends the setting time and impairs the mechanical properties. Nevertheless, red mud demonstrates a crucial role of reducing bleeding level especially for the mixtures with high proportions of glass aggregate. The standard leachate tests as per toxicity characteristic leaching procedure (TCLP) show the heavy metals leached from the CLSM are below the concentration limits and exhibit low mobility. The microstructural and thermodynamic analyses reveal the precipitation of calcium-(sodium-)aluminosilicate hydrate (C-(N-)A-S-H) as the major binding material. The reactive Fe and Al in red mud most probably contribute to the formation of hydrogarnet phases. Moreover, the suggested CLSM formations typically exhibit reduced carbon emissions and lower costs compared to the traditional CLSM produced with cement and fly ash, underlining their environmental sustainability and cost-effectiveness. This study provides a potential guideline for the flowable fill construction in the regions with bauxite producers.