This study investigated the role played by iron-filing in the strength and microstructural characteristic of high ordinary Portland cement (OPC) based paste and mortar at substitution levels that ranged from 0 to 15 wt.%. It was found that, iron-filing mainly comprised Fe2O3, reduced the workability, influence carbonation, early strength development and impacted the nature of the product formed especially if prepared within the w/c ratio of 0.25 and 0.35–0.4 for paste and mortar, respectively. Moreover, iron-filing also induced and enhanced belite hydration, and influenced the crack-bridging effect within the microstructural matrix, while substitution level less than 5 % affected not the early strength. Besides, iron-filing could also influence the formation of calcium ferrosilicate hydrate as revealed in the microstructural analysis or elemental analysis from energy-dispersive X-ray spectrometer. The 28-day strength of 114 MPa and 61 MPa were achievable in paste and mortar, respectively for iron-filing replacement level within 5–10 %, even substitution up to 15 % could perform better than the sample prepared with OPC only. The study promotes waste valorization and the use of iron-filing in mass-concrete production.