| Summary: | In this study, iron ore tailings (IOTs) are used as aggregates to prepare iron-ore-tailing-engineered cementitious composites (IOT-ECCs) to achieve clean production. Some mechanical indexes, such as compressive strength (<i>f<sub>cu</sub></i>), four-point flexural strength (<i>f<sub>f</sub></i>), axial compressive strength (<i>f<sub>c</sub></i>), deformation properties, flexural toughness, and stress–strain behavior, are studied. The mass loss, <i>f<sub>cu</sub></i> loss, relative dynamic modulus elasticity (RDEM), and deterioration mechanism after the sulfate freeze–thaw (F-T) cycle are discussed in detail. In addition, pore structure analysis is performed using nuclear magnetic resonance (NMR), while a scanning electron microscope (SEM) is utilized to study the micro-morphology. The results showed that under the 20–80% IOT replacement ratio, IOT-ECCs exhibited improvements in their mechanical properties, pore structure, and resistance to sulfate freeze–thaw (F-T). The most notable mechanical properties and sulfate F-T resistance were demonstrated by the IOT-ECC with 40% IOTs (namely, IOT40-P2.0). Meanwhile, IOT40-P2.0 exhibited good pore structure as well as the bonding interface of the PF and the matrix. The pore structure and compactness of the matrix of IOT-ECCs gradually deteriorated as the F-T cycle increased. The research results will promote the application of IOTs in ECCs.
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