New-generation refractory concretes. Interrelation between structure formation and strengthening

Abstract

A thermodynamic approach is used to consider the general regularities of structure formation in binding systems used in the technologies of new refractory concretes. The fundamental distinction in both the mechanism of structure formation and the kinetics of strengthening among different types of binding systems is determined by their colloidal-chemical activity. The main regularities of structure formation and strengthening of systems without chemical reactions are considered for clays and highly concentrated binder suspensions, and these regularities for systems with chemical reactions are considered for the binder system of low-cement refractory concretes. The importance of microsilica additions in concrete technologies is shown.Different aspects of the problem of structure formation in the technology of new refractory concretes and the resulting phenomenon of strengthening (especially in hardening and drying) have been considered in previous articles of this series [1 -8]. For the problem discussed here, as follows from [9][10][11], the most productive approach is a thermodynamical one.Thermodynamic treatment and some special features of the process of structure formation, Different kinds of new-generation concretes have characteristic structural features. The main factor determining important differences in the mechanisms of structure formation and the final properties of the materials is the nature of the interaction between the dispersed phase and the dispersive medium (the colloidalchemical activity of the system). For example, the hardening (structure formation) of low-cement refractory concretes (LCRC) or ceramoconcretes with magnesia composition is largely determined by hydration (chemical binding of the liquid), whereas in ceramoconcretes on highly concentrated binder suspensions (HCBS) with an acid or acid-amphoteric composition [12] the contribution of this factor is insignificant. The binding phase in concretes of the first type has a condensation-crystallization structure, whereas in the second type the condensation structure is dominant.Belgomd Technological Academy for Building Materials, Belgomd, Russia, 71From the standpoint of the thermodynamic theory of liquefaction, structure formation of a liquefied body is understood as an irreversible thermodynamic process in which the intensity of liquefaction depends on the action of internal or external sinks (sources) of moisture [9, p. 18].Analysis of isotherms of the structural and moisture condition (Fig. I) allowed the authors of [9,10] to develop a method for describing and investigating processes of structure formation in capillary-porous disperse materials, which occur with partial binding of the moisture. In this case, the driving force of structure formation O n is the difference in potentialswhich corresponds to the mass balance in the system considered, i.e., u = u~ + un + uo = u~ + rL = coast,where U~ is the discharge of mass (amount of chemically bound moisture); U n is the amount of strucmmUy bound moisture corresponding to the change i...