A novel type of controlled low strength material derived from alum sludge and green materials

[Display omitted] •Alum sludge can be recycled as fine aggregate into eco-friendly CLSM.•Alum sludge addition increased water demand and hindered CH formation.•PFA was a promising supplementary cementitious material for producing CLSM.•Addition of CaCl2 or TEA effectively shortened overlong stiffening time. The management and disposal of alum sludge generated from water treatment works is a worldwide issue. This study proposed an innovative method to utilize alum sludge as a partial replacement of recycled fine aggregate for producing controlled low strength material (CLSM). Various supplementary cementitious materials (SCMs) and accelerators were incorporated to produce CLSM with high flowability (>200 mm), relatively short stiffening time (