Towards Low‐Carbon Construction Materials: Sustainable Phosphoric Acid‐Based Geopolymer Incorporating Iron Tailings and Fly Ash With Improved Mechanical Properties

ABSTRACT Fly ash phosphoric acid–based geopolymers suffer from low strength. This study incorporated iron tailings (IOT) as a co‐precursor with fly ash to fabricate high‐early‐strength phosphate‐based geopolymers (IPAM). The effects of phosphoric acid (PA) concentration, liquid‐solid ratio (L/S), IOT content, and curing time on physical properties were investigated, and the geopolymerization mechanism was elucidated via XRD, FTIR, XPS, SEM, ICC and BET. The mechanically optimal mixture was 25% IOT, 60% PA concentration, and an L/S of 0.85. Compared to the control (0% IOT), this formulation reduced paste fluidity by 80%, shortened the setting time from 216 h to 0.4 h, and dramatically increased the 56‐day compressive strength from 0.14 MPa to 22.7 MPa. IOT incorporation increased pH but decreased electrical conductivity (EC), significantly reduced total porosity and water absorption, and transformed the supermacroporous (>100 nm) structure into a mesoporous (<50 nm) one. The geopolymerization process involves dissolution of IOT and fly ash, formation of amorphous gels (Al–O–P, Fe–O–P) and crystalline phases (CaHPO 4 ·2H 2 O, AlPO 4 , Fe 3 (PO 4 ) 2 ), and conversion of Ca(H 2 PO 4 ) 2 ·H 2 O to CaHPO 4 ·2H 2 O. IPAM with 25% IOT exhibited a CO 2 emission intensity of 16.0 kg/m 3 /MPa and energy consumption intensity of 76.3 MJ/m 3 /MPa. This work enhances understanding of IOT‐enhanced fly ash phosphoric acid‐based geopolymer mechanisms, which is essential for carbon reduction, environmental protection, and waste utilization.