Investigation of the Critical Grinding Threshold and Microstructural Optimization of Iron Tailings in Cement-based Systems

The objective of this study is to investigate the effect of particle size distribution (PSD) on the performance of cement-iron tailings powder composite cementitious materials (CT-C-CMs). Nine groups of iron tailings powder (ITP) with varying PSDs were prepared by mechanical grinding to produce composite cementitious materials. Grey Correlation Analysis (GCA) shows a strong correlation between the diameter of ITP particles smaller than 51.8 μm and the compressive strength of the CT-C-CMs. Specifically, particles smaller than 12.7 μm significantly enhance strength at medium and late ages, whereas larger particles exert variable effects depending on curing age and ITP contents. Pore structure analysis indicates that CT-C-CMs containing up to 20% ITP exhibit reduced porosity and a refined pore size distribution. This is characterized by an increased proportion of harmless pores (<50 nm), resulting in improved matrix densification. Non-evaporable water (n-EW) measurements reveal a decrease in the degree of hydration with increasing ITP content, as most of the ITP remains unreacted, contributing primarily through filling and dilution effects. Optimal performance occurs when the ITP content does not exceed 20%, and the PSD is carefully controlled around a critical fineness threshold of approximately 12.7 μm. These findings clarify the mechanism of action of ITP in cement-based cementitious systems and offer practical guidance for the resource-efficient utilization of iron tailings as supplementary cementitious materials.