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A platform for research: civil engineering, architecture and urbanism
Analysis of setting mechanism of low-cement castables
The setting mechanism of the low-cement eastables was investigated by measurement of the relation between exothermal behaviors and the setting time, the analysis of concentration changes in the capillary water of the castables and the confirmation of surface film formation on alumina cement particles by colloidal silica. The conclusions are as follows: (1) The low-cement castables, when they are mixed with water, can be considered as a hydrophobic colloid consisting of superfine ceramic powder that is stabilized by deflocculant. Ca(2+) ions dissolve from the alumina cement into the mixing water. When the Ca(2+) concentration attains a threshold value, the stability of the colloid is lost and coagulation occurs. The setting of the castables occurs by this coagulation. (2) The role of the alumina cement in the eastables is as a source of Ca(2+)ions. Hardening (or hydration) of the alumina cement is an independent process that occurs after the setting of the castubles. (3) The dissolution rate of Ca(2+) ions is influenced by a surface film on the alumina cement particles. It is presumed that the diffusion process of Ca elements through the film determines the dissolution rate. The effect of NaHCO3 and colloidal silica on the delay of the setting time is considered to be by this film formation mechanism. (4) In the system containing STTP (sodium tripolyphosphat), the dissolved Ca(2+) ions react with tripolyphosphate ions. The chelate forms at the first stage and a precipitate forms at the later stage. After consumption of the tripolyphosphate ions by the reactions, the concentration of Ca(2+) ions increases and the aggregation occurs.
Analysis of setting mechanism of low-cement castables
The setting mechanism of the low-cement eastables was investigated by measurement of the relation between exothermal behaviors and the setting time, the analysis of concentration changes in the capillary water of the castables and the confirmation of surface film formation on alumina cement particles by colloidal silica. The conclusions are as follows: (1) The low-cement castables, when they are mixed with water, can be considered as a hydrophobic colloid consisting of superfine ceramic powder that is stabilized by deflocculant. Ca(2+) ions dissolve from the alumina cement into the mixing water. When the Ca(2+) concentration attains a threshold value, the stability of the colloid is lost and coagulation occurs. The setting of the castables occurs by this coagulation. (2) The role of the alumina cement in the eastables is as a source of Ca(2+)ions. Hardening (or hydration) of the alumina cement is an independent process that occurs after the setting of the castubles. (3) The dissolution rate of Ca(2+) ions is influenced by a surface film on the alumina cement particles. It is presumed that the diffusion process of Ca elements through the film determines the dissolution rate. The effect of NaHCO3 and colloidal silica on the delay of the setting time is considered to be by this film formation mechanism. (4) In the system containing STTP (sodium tripolyphosphat), the dissolved Ca(2+) ions react with tripolyphosphate ions. The chelate forms at the first stage and a precipitate forms at the later stage. After consumption of the tripolyphosphate ions by the reactions, the concentration of Ca(2+) ions increases and the aggregation occurs.
Analysis of setting mechanism of low-cement castables
Analyse des Abbindemechanismus von zementarmen Feuerbetonen
Maeda, Eizo (author) / Jono, Katsufumi (author) / Kanatani, Satoi (author) / Haraoka, Takashi (author)
2009
9 Seiten, 11 Bilder, 20 Quellen
Article (Journal)
English
Ansteifen (hydraulisch) , Abbindung , Wasserabbinden von Zement , Erhärten (Zementabbinden) , zementarmer Feuerbeton , hydrophobe Gruppe , Kolloid , Entflockungsmittel , Calciumion , Natriumphosphat , Polyphosphat , Koagulation , Chelatbildung , Chelat , kolloidale Kieselerde , Zirkoniumoxid , Zirkoniumsilicat , Calciumaluminatzement
A study of the setting mechanisms of low cement castables by exothermic profile
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