Study of the hardening kinetics of a mineral binder using electrical and optical methods

Abstract

Hardening of mineral binders (cement, gypsum, lime, clay) is accompanied by the dissolution of minerals from the binder surface, their chemical interaction with water (the reaction of hydration and hydrolysis), and the formation of a solution saturated with respect to new hydrates. The reactions of minerals with water continue for some time even after saturation when water molecules are adsorbed by the solid phase of the binder. An «intermediate» colloidal system thus formed is characterized by the viscosity or plasticity depending on the water content in it. At the final stage, the processes of recrystallization and coalescence of the particles in a colloidal solution occur resulting in solidification and hardening of the solution and increased strength of the formed stone. We present the results of studying the hardening kinetics of the aqueous solution of a mineral binder using electrical and optical methods with high time resolution. Semi-aqueous gypsum was selected as a mineral binder. During hardening, the resistance and the capacitance of the samples were measured along with the visualization of the spatial structure of the solution. The mineral composition of water significantly affected the character of hardening. Noticeable fluctuations of the electrical parameters were detected in the experiments with mineral water. Optical measurements showed that solidifying solution is similar in structure to dendrites and fractal dimensionality of the structure almost remains the same during growth. It is also shown that at the initial stage the hardening proceeds by the logistics law. The results obtained can be used and recommended for practical application for determination of the kinetic parameters of hardening and in diagnostics of the structure of materials based on mineral binders.