The interaction of pH, pore solution composition and solid phase composition of carbonated blast furnace slag cement paste activated with aqueous sodium monofluorophosphate

Blast Furnace Slag (BFS) is a waste product of industrial steel production and a common additive in the cement industry in Northern European countries. However, cementitious materials made from slag-rich cement, particularly CEM III /B, are very susceptible to carbonation. Recent investigations have shown that the surface application of aqueous sodium monofluorophosphate (Na-MFP) as pre- and post-carbonation treatment can improve the surface durability of cementitious materials with a high BFS content. Significant improvements have been observed in the micro-mechanical characteristics of concrete surface and frost salt scaling resistance. On the basis of previous studies we are investigating self-healing of blast furnace slag cement (BFSC) products treated with the inorganic self-healing agent Na-MFP from a mineralogical point of view. In this study we combine results of pore solution pH analyses and main element composition under the influence of Na-MFP with the presence of crystalline phases found in the solid aliquot of the samples. Pore solutions were investigated by inductively coupled optical emission spectrometry (ICP-OES). Solid-material investigation was performed by X-ray powder diffractometry, including Rietveld quantitative phase analyses. Our results show that the element concentration and the pH of the paste pore solutions have direct influence on the formation of crystalline and amorphous phases forming in the solid sample aliquot during carbonation and self-healing by Na-MFP. In this work we focus especially on the influence of sulfur in solution and the formation of ettringite. In addition we discuss, why the formation of the crystalline phosphate apatite does not occur in cementitious products after Na-MFP treatment.Structural EngineeringCivil Engineering and Geoscience

Si isotope fractionation between Si-poor metal and silicate melt at pressure-temperature conditions relevant to metal segregation in small planetary bodies

Experimental investigations of Si isotope fractionation between Si-bearing metal alloy and silicate phases have to date been limited to high pressure (1-7. GPa) and high temperature (1800-2200. °C) conditions at highly reducing conditions, to optimize applicability of results to early core formation processes in the Earth. Here, we assess the extent and mechanism of Si isotopic fractionation at conditions relevant to metal segregation in small (km-scale) planetary bodies, using samples obtained from an industrial-scale blast furnace of Tata Steel (IJmuiden, the Netherlands).During the low-pressure, high-temperature process of steelmaking inhomogeneous blast furnace burden consisting of pre- and untreated iron ore, iron silicates and coke is reduced to oxygen fugacities near the C-CO buffer, resulting in the segregation of a metal phase containing only ~0.3wt% Si. Seven sample sets, each comprising a metal alloy and a silicate slag, were taken during tapping of the blast furnace at tapping temperatures between 1400°C and 1600°C. We find large isotopic mass fractionation between metal and silicate, with