Comparison of Water-Isopropanol Replacement and Lyophilisation for Hydration Stop of Cementitious Suspensions

Abstract

For modern concrete technology, rheology is crucial for characterizing the properties of fresh concrete on the basis of physically defined parameters. These properties can be influenced by many factors, but have an effect on paste level predominantly. To obtain an understanding of influencing factors such as the underlying kinetics and mechanisms at the initial colloidal scale a time variant analysis of cementitious suspensions is needed. In this article, a method to stop the hydration process of cementitious suspensions at any time by gradual water-isopropanol replacement and lyophilisation is demonstrated. Therefore, three different methods for hydration stop are investigated, namely water-isopropanol exchange, lyophilisation as well as a combination of both, and compared to pristine (non-reacted) cement particles. Analysis of dried samples leads to the observation that direct lyophilisation leads to particles of similar size as the pristine cement particles. Water-isopropanol replacement as well as water-isopropanol exchange with subsequent lyophilisation, instead, leads to a very broad particle size distribution with larger particles, which might be attributed to secondary agglomerations of particles. We further investigate the three different hydration stop methods by evaluating the pore size distribution by means of nitrogen physisorption. Additionally, scanning electron microscopy (SEM) as an imaging method is used.