Alkali activation of blast furnace slag using a carbonate-calcium carbide residue alkaline mixture to prepare cemented paste backfill

Abstract

The utilization of calcium carbide residue (CCR) as alkali activator is promising to reduce production cost and ensure production safety. In this study, CCR/carbonates system and Ca(OH)2/carbonates system were used to replace the NaOH and KOH to activated blast furnace slag developing cemented paste backfill (CPB), and the difference of reaction products was also investigated. Then, the fluidity and compressive strength of the CPB prepared by different alkali activators were studied. Finally, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR) were used to characterize the hydration products, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize pore structure of hardened specimens. Results indicate that at the same concentration of alkali activator, the CPB sample with mixed alkali activator showed lower fluidity but higher strength compared with the sample with single alkali activator. Due to the large amount of Ca+ and CO32– in the mixed alkali activator, the content of C-S-H in the CPB sample increased significantly and new hydration products, hydrotalcite and CaCO3 were observed. Using CCR as a replacement of Ca(OH)2 to prepare alkali activator could achieve a better fluidity but little lower compressive strength. Hence, the utilization of CCR could effectively reduce its storage problem and the cost of alkaline activator while maintaining the CPB performance simultaneously.