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A study of the setting mechanisms of low cement castables by exothermic profile
Low cement castables have different allowable setting times depending on conditions during application such as atmospheric temperature, humidity, etc. In general, because of its time dependent property in the installation, the quantitative evaluation of allowable setting time is very important. According to previous reports it is clear that the setting time of low cement castables correlates with the time of the exothermic reaction generated by the fine powder part. Furthermore, the duration of the exothermic peak has also been shown to follow a linear relationship in an Arrhenius plot, indicating that the setting process obeys the thermal activation principle. It is well known that the hydration reaction in alumina cement does not obey the Arrhenius law. However, no thorough study has yet been made of the setting reaction in low cement castables with regard to the influence of cement types, additives and their amounts. The present paper focuses on dispersives and retardants for low cement castables and investigates the hydration mechanism from the viewpoint of the exothermic profile. The results have clarified the following: The exothermic peak time nearly coincided with the transition time to an elastic body. Two factors were considered for the reaction rate determination step of the setting time: the diffusion rate reaction and the dissolution rate. With an increase in the amount of dispersive, the activation energy increased as well, and the shift of the rate determining reaction was considered to shift to dissolution.
A study of the setting mechanisms of low cement castables by exothermic profile
Low cement castables have different allowable setting times depending on conditions during application such as atmospheric temperature, humidity, etc. In general, because of its time dependent property in the installation, the quantitative evaluation of allowable setting time is very important. According to previous reports it is clear that the setting time of low cement castables correlates with the time of the exothermic reaction generated by the fine powder part. Furthermore, the duration of the exothermic peak has also been shown to follow a linear relationship in an Arrhenius plot, indicating that the setting process obeys the thermal activation principle. It is well known that the hydration reaction in alumina cement does not obey the Arrhenius law. However, no thorough study has yet been made of the setting reaction in low cement castables with regard to the influence of cement types, additives and their amounts. The present paper focuses on dispersives and retardants for low cement castables and investigates the hydration mechanism from the viewpoint of the exothermic profile. The results have clarified the following: The exothermic peak time nearly coincided with the transition time to an elastic body. Two factors were considered for the reaction rate determination step of the setting time: the diffusion rate reaction and the dissolution rate. With an increase in the amount of dispersive, the activation energy increased as well, and the shift of the rate determining reaction was considered to shift to dissolution.
A study of the setting mechanisms of low cement castables by exothermic profile
Funakoshi, R. (author) / Matsue, T. (author) / Takahashi, N. (author) / Ishikawa, M. (author)
Journal of the Technical Association of Refractories, Japan ; 23 ; 286-289
2003
4 Seiten, 9 Bilder, 1 Tabelle, 9 Quellen
Article (Journal)
English
Abbindung , Additiv , Aktivierungsenergie , Aluminiumoxid , Arrheniusgleichung , Auflösungsgeschwindigkeit , Diffusionsgeschwindigkeit , exotherme Reaktion , feines Pulver , Feuchtigkeit , Gießschlicker , Hydratisieren , Reaktionsgeschwindigkeit , Retardiermittel , thermische Aktivierung , Umgebungstemperatur , Zement , zementarmer Feuerbeton
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