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Self flowing refractory castables : study of the hydraulic bond and ceramic matrix formation Esanu, Florin

Abstract

Refractories are enabling materials in that their primary function is to facilitate the production of other materials such as metals, glasses, petrochemicals, and cements. They have enabled the utilization of heat to make materials since the Bronze Age. Although, in recent years, a number of studies concerning the many complex variables that determine the rheologic, hydraulic and ceramic properties of Advanced Refractory Castables (ARC) have been performed, the fundamentals of free-flow and of transition from a hydraulic to a ceramic matrix are still only poorly understood. The aim of this study is to provide a scientific base for understanding the flow behavior of A R C and its influence on the formation of ceramic. For this purpose the flow behavior of a series of low, ultra-low and no cement ARC compositions was analyzed. A method for measuring the viscosity of the binding system of ARC was developed. This method allowed for the first time the study of a direct correlation between the rheology of the matrix and the flow of a castable, and therefore a precise and scientific base for determining the influence of different dispersant additives. The rheological parameters of ARC compositions for different amounts of water, silica fume purity, content and type of refractory aggregate were correlated with mechanical strength at high temperatures. Based on the experimental and theoretical work carried out in this study a thorough characterization of the rheology of self-flowing castable refractories was performed. The rheological conditions that allow the early formation of the hydraulic matrix were identified. A new concept of interaction (Flash Flocculation) between the binding system and the spray gunning admixtures was developed. This concept was materialized in a novel type of spray gunning admixture. Laboratory studies as well as a pilot scale experiment confirmed the superiority of the flash flocculating admixture over the setting accelerators, which are currently used as spray gunning admixtures.

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