To investigate the application of iron tailings in cement-based materials as fine aggregate and mineral admixture, six iron tailings sands were selected from different places of origin, and the methods of acid and alkali activation were adopted to increase the activity of tailings powder. The strength of mortar was evaluated and the composition and microstructure were analyzed to explore the mechanism. The experimental results show that iron tailings sands had little adverse effect on the mortar strength, and there was a maximum increase of 13.2% in 28-day compressive strength compared with that of river sand mortar. The hardness values of all the iron tailings sand and the interfacial transition zone (ITZ) around them were higher than that of natural river sand, but their Ca/Si ratios in the ITZ was lower, indicating a chemical reaction occurred between the iron tailings and cement paste. Generally, the iron tailings sand with higher SiO₂ content and finer particles tend to have higher activity. In addition, the pozzolanic activity of iron tailings powder could be greatly promoted by chemical activation, especially by acid activation. The activity index of cement mortar with unactivated iron tailings powder was only 63% at 28 days, whereas that of acid-activated and compound-activated samples reached up to 93%, and the heights of the maximum heat flow peak of these samples were even higher than that of the control sample without iron tailings powder, and the time to reach the peak was in some advance, moreover their impedance parameters were close to the control sample.

In this study, we investigated the formation and evolution of the corrosion layers in alkali-activated mortar and ordinary Portland cement mortar exposed to sulfuric acid and acetic acid environments with different pH values, and explored the differences in the deterioration mechanisms. The experimental results indicated that ordinary Portland cement (OPC) mortars experienced more severe deterioration in terms of appearance, mass loss, and strength loss as compared with alkali-activated mortars exposed to an acetic acid environment, but their neutralization depths were smaller. Alkali-activated fly ash (AAF) mortar had a the relatively intact appearance but the greatest neutralization depth, which was due to its stable three-dimensional network but highly porous structure. To sum up, alkali-activated fly ash/slag (AFS) mortar had the best resistance to acid attack. In addition, the mortars exposed to acetic acid suffered greater deterioration than those exposed to sulfuric acid with the same pH values, which was mainly due to the highly porous corrosion layer formed in acetic acid, whereas crystallization of gypsum in sulfuric acid had a pore filling effect. However, for alkali-activated slag (AAS) and OPC mortars exposed to a sulfuric acid environment, extensive gypsum resulted in the formation of micro-cracks, and the corrosion layer of OPC mortar was more prone to fall off. OPC mortar also had the greatest resistance difference values of the continuously connected micro-pores before and after acid corrosion, followed by AAS, AAF, and AFS mortars, and these values for all the specimens were smaller in sulfuric acid. Furthermore, the gaps between acetic and sulfuric acid attacks increased with increased calcium content in binders, which were 7%, 13%, 21%, and 29% for AAF, AFS, AAS, and OPC mortars, respectively. Thus, it can be inferred that an appropriate amount of gypsum existed in the corrosion layer which could act as a barrier to some extent ina sulfuric acid environment.