(515e) Effects of Organic Additives On Hydration At Silicate and Aluminate Particle Surfaces

Hydration and crystallization processes are often influenced by the presence of low concentrations of additives or contaminants. In many cases, this involves competitive adsorption of additive species and water at inorganic oxide surfaces, which can have significant effects on surface hydration that drastically affect the mechanical and rheological properties of these complicated mixtures. A technologically important example is the use of dilute concentrations (<1 wt%) of organic additives that adsorb at silicate and aluminate particle surfaces and thereby inhibit hydration reactions in cement-water slurries. This maintains the fluidity of the cement-water mixtures by preventing the formation of cross-linked silicate and aluminate species that are central to the development of overall mechanical strength in cements. To understand the effects of organic additives on the hydration of silicate and aluminate particles, it is important to establish the compositions and interactions of the additives and water with inorganic surface species. Such understanding can be obtained by using nuclear magnetic resonance (NMR) spectroscopy in conjunction with electron microscopy, X-ray diffraction, and X-ray fluorescence, which allow hydration processes to be monitored over different length scales. Specifically, molecular-level interactions of industrially relevant concentrations (~0.1 wt%) of organic additives, such as saccharides and phosphonates, adsorbed at inorganic oxide surfaces are determined by using state-of-the-art NMR techniques. The results establish that sucrose molecules adsorb non-selectively at both anhydrous and hydrated silicate sites, but selectively at anhydrous aluminate sites. By comparison, phosphonates adsorb non-selectively at anhydrous and hydrated silicate and aluminate sites. The molecular-level compositions, structures and site-specific interactions in hydrating cements correlate with their macroscopic properties, such as, compressive strength and slurry viscosity. The analyses shed insights on hydration processes in cement-water mixtures, their constituent inorganic oxide species, and the influence of industrially relevant additive concentrations on cement setting.