Crystallinity of Sodium silicate-activated Slag cured under electric field at ambient temperature

Abstract

Rapid urbanization creates an ever-increasing demand for infrastructure in today’s world. Due to the sizable CO2 emissions associated with the global production of ordinary Portland cement (OPC), alternative cementitious materials are being developed that exhibit comparable compressive strengths to OPC-based binders but with lower CO2 footprints to facilitate sustainable urbanization. In this regard, alkaliactivated materials (AAMs) have been identified as an effective alternative to OPC in the construction industry. Durability, defined as a material’s resistance to degradation processes like weathering, chemical attack, and abrasion, is controlled by the structure of the material. Crystalline materials are more resistant to heat and chemicals than amorphous materials of the same chemical composition. Thus, increasing durability of AAMs lowers global demand for construction materials, making AAMs a commercially viable, sustainable alternative to OPC. This research adopts a similar approach to elucidate if the application of electric field on sodium silicate-activated slag (SSAS) can alter morphology and induce crystallinity in predominantly amorphous gel-like structure of SSAS and thereby subsequently increase its durability. A.C. and D.C. potential fields were applied on SSAS pastes cured at ambient temperature for 24 hours after activation. Furthermore, some samples were doped with high-dielectric constant barium titanate (BaTiO3) which increases the propensity for crystallinity to elucidate its effect under electric field application. Additionally, D.C. current was passed through some samples to elucidate current’s effect on SSAS pastes. Mineralogical analysis of variously aged samples by means of X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) is reported. The results revealed that D.C. and A.C. voltage application does not have a significant impact on promoting formation of more crystalline phases in sodium-silicate activated slags. Yet, D.C. current application of 4 mA has been shown to produce seemingly more crystalline phases in pastes with and without addition of barium titanate. This finding has rather promising implications for alkali-activated slag’s long-term durability. Thus, future work is required to validate the obtained results and to characterize the impact of D.C. current on AAS pastes more quantitatively.