Impact of attraction forces on AAB fresh properties

Abstract

The nature of interactions between inorganic particles plays a key role in determining their fresh behavior. Interactions in Ordinary Portland Cement (OPC) are well known and defined as “strong-short-range attraction”. Alkali-Activated Binders (AABs) have been developed since the 1930s, but their microscopical properties are not well characterized yet. Oscillatory rheology has proved a promising method to measure the nature of interactions between particles of inorganic materials (i.e. calcite). Following the same approach, OPC and AAB pastes are characterized and compared to calcite suspensions, considered as a model system for cement. In particular, the elastic properties (elastic modulus and critical strain amplitude at which the paste yields) are measured as a function of volume concentration of particles, in a range for which an “attractive gel-like behavior” is observed. The amplitude of this concentration range depends on the extension length of the interparticle forces, and on their nature. At first, we characterized the elastic domains (dominated by interaction forces) using a classic fractal model. Then, we extracted the fractal dimensions of the flocs formed upon self-assembly of the primary particles, using the method by Shi et al.. In this study, AAB is constituted by ground and granulated blast-furnace slag (GGBS), calcium hydroxide, and sodium carbonate as solid activators. The interstitial solution composition of the AAB is varied in order to obtain an overall Ca2+ concentration similar to the cement one. The effect of superplasticizers for different [Ca2+] is also analyzed. Results show that the nature of interactions in AAB is intermediate between cement and calcite pastes. This explains the difference in their fresh behaviors and opens the way for optimizing their properties by controlling the interstitial solution composition.