E_H-pH- and main element analyses of Blast Furnace Slag Cement paste pore solutions activated with sodium monofluorophosphate: Implications for carbonation and self-healing

Over the past decade, sodium monofluorophosphate (Na-MFP) gained attention as inorganic self-healing agent on Blast Furnace Slag Cement (BFSC) products. Recent experimental studies revealed the recovering effect of Na-MFP on the microstructure of carbonated BFSC pastes with respect to their frost-salt scaling durability. This study investigates the interactions between pore solution and hydration products of OPC and BFSC pastes that were carbonated and/or vacuum-impregnated with aqueous Na-MFP. Pore solutions of pastes were characterized through systematic E_H-pH- and main element analyses by inductively coupled optical emission spectrometry (ICP-OES). Solid hydration products were analyzed by X-ray powder diffraction (XRD). Results indicate that the impregnation of hardened carbonated cement pastes with aqueous Na-MFP results in a recovery of the initial pH of 98.85% and 79.81%, respectively. Analytical results give insight into hydration and carbonation under the influence of Na-MFP. Results are compared with literature and expose that the hypothesis of crystalline apatite formation in BFSC products must be revised.