Micro-reactors to Study the Reaction of Slag in Alkaline Media

Abstract

A micro-reactor approach to study the hydration of cementitious materials has been developed in our laboratory. The method involves milling gaps that are a few microns in dimension in grains using a Focused Ion Beam. These gaps are then filled with solution, leading to dissolution, nucleation, and growth in the gaps. Hydration is stopped at selected time intervals, and a Scanning Electron Microscope is used to image the gaps. Information is obtained about dissolution-growth kinetics and hydrate morphology. Using this technique, we were able to obtain significant insights into the factors influencing early age hydration of tricalcium silicate and alite, and the effect of selected chemical admixtures on the same. In this study, we present the use of micro-reactors to study the alkaline activation of slag. The effects of solution pH and of the nature of the alkaline solution on the alkaline activation are discussed. Additionally, the dissolution of slag is studied, and we show that it is strongly affected by the presence of calcium and aluminum in solution. Results are compared and contrasted with those obtained with tricalcium silicate and alite. Originality The micro-reactor approach is probably the only method that offers the possibility of obtaining information about both dissolution and growth processes. We present ways in which factors affecting dissolution and growth may be understood, something that is very difficult or impossible using other techniques. Applying the micro-reactor technique to alkaline activation offers a way to better understand the reaction and the factors influencing it. Additionally, although we only present results with slag here, this technique may be used to study geopolymerization of several precursors with various solution compositions.