Carbonation-hardening properties and ITZ microstructure of low-calcium CO₂ sequestration binder mortar

To produce high-strength prefabricated building materials and reduce their CO₂ emissions, a new low calcium CO₂ sequestration binder (LC-CSB) was prepared by calcination of industrial raw materials limestone and sandstone at 1275 °C. The physical and mechanical properties development of the LC-CSB mortar was investigated at different carbonation durations (5 min, 10 min, 30 min, 1 h, 8 h, 24 h). Moreover, the microstructure and micromechanical properties of the interfacial transition zone (ITZ) between carbonated LC-CSB paste and siliceous river sand aggregate were revealed by SEM and nanoindentation. The results showed that the compressive strength of the LC-CSB mortar reached 43.2 MPa after carbonation for 24 h. The ITZ was more easily carbonated than the LC-CSB paste, and the calcite crystals generated after carbonation will be enriched at the ITZ with the increase of carbonation duration, while the porosity was significantly reduced.