Effects of curing temperature and supplementary cementitious materials on the interfacial transition zone (ITZ) of high-ferrite cement products

This study investigated the changes in three characteristics, including phase compositions, microstructure, and microhardness, in the interfacial transition zone (ITZ) of high-ferrite cement (HFC) products when subjected to different curing systems. In addition, we explored the underlying mechanisms through which supplementary cementitious materials (SCMs) influence the ITZ under steam curing conditions. The characterization was performed through the application of test techniques such as X-ray diffraction analysis, backscattered electron, scanning electron microscopy, energy dispersive X-ray spectrometry, and microhardness. The findings demonstrated that the increase in the curing temperatures promoted the HFC mortar to generate an excellent ITZ performance compared to Portland cement and ground granulated blast furnace slag (GGBFS) showed an improvement in steam-cured HFC-ITZ better than. Specifically, optimal enhancement of the ITZ in steam-cured HFC cement-based materials was achieved through the 40% replacement of GGBFS where the calcium hydroxide (CH) content and orientation growth were reduced while the hydration product formation was increased, resulting in declined porosity. Furthermore, the incorporation of 20% replacement of fly ash (FA) led to the decrease in the CH content and porosity of the ITZ. However, due to the lower reaction activity, unreacted FA persisted in the paste even after 28 days of curing. Additionally, the uneven distribution of hydration products resulted in diminished microhardness. On the other hand, a 40% replacement of FA marginally improved the properties of the ITZ. Finally, the test data and conclusions in the paper can provide some evidence for the application of GGBFS and FA in HFC and HFC-based concrete.