Effect of zeolite calcination temperature on the carbonation degree and strength of steel slag compacts

Steel slag partially substituted with zeolite (SZ) is beneficial for further improving the compressive strength and carbonation degree, after a combined curing (hydration and carbonation) process, owing to the pozzolanic reaction. In this study, the effect of clinoptilolite-type zeolite calcinated at different calcination temperatures (200-800 degrees C) to modify the degree of the pozzolanic reaction is investigated. Moreover, the characteristics of SZ specimens after combined curing are also investigated. Additionally, the degree of the pozzolanic reaction and its mechanism in CHZ (Ca(OH)2 mixed with calcinated zeolite after 1 day (1d) of hydration) specimens are clarified and compared by various microscopy techniques. Compressive strength results revealed that the optimum calcination temperature was 800 degrees C. The compressive strength and carbonation degree of CSZ5-800 (steel slag specimen containing calcined zeolite (800 degrees C) after 1d of hydration followed by 2 h of carbonation curing) improved by 23.2 and 13.8 %, respectively, compared with that of the reference CSZ5-25. The porosity of CSZ5800 was 30.8 and 21.9 % higher than that of CSZ0-25and CSZ5-25, respectively. New minerals AFmc and C-S-H gel were detected by X-ray diffraction (XRD) and mass angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy in CHZ specimens. Notably, the C-S-H gel and AFmc content in CHZ-800 were 7 and 57.6 % higher than that of CHZ-25, respectively.