REGULATED-SET CEMENT

The reactions in the regulated-set cements containing Cjj A3CF2 (note mixed notation) as a principal phase resemble those in ordinary Portiand cements. Initial reaction rates are controlled by ettringite formation. Setting occurs with formation of the monosulfate, along with some transitory lower-limed calcium aluminate hydrates that convert to the monosulfate within a few hours. 

Regulated-set cement and jet cement are modified Portland cements in which the normal aluminate phase is replaced by CuA CaF, through the use of a raw mix containing CaF,. Uchikawa and Tsukiyama (U2I) gave chemical (Table 10.4) and phase compositions of two jet cements. Botli contained approximately 60% of alite, 20% of C, i A CaF,. 1% of belite and 5% of ferrite. Admixtures are required to control the rate of reaction of the C, 1 A CaFj and the nature of the products. One of the cements included a proprietary retarder based on citric acid, togetlier with 2"/o of CaC O, . The other contained 2.5% of hemihydrale. In each case, Na,S04 (T o) and anhydrite were also present. The specific surface areas were around 550 m kg . 

The ettringite that is formed exhibits distinet eementing properties, but may cause expansion at a different rate and to a different degree, depending on the Al source involved in the reaction. Cements that eontain significant amounts of calcium sulfate include expansive cements (see seetion 21), regulated set cement (see section 5.2), supersulfated cement (see section 8.4), sulfobelite cement (see section 4.2), and sulfoalite cement (see section 4.3). Limited amounts of ealeium sulfate are also present in Portland cement (see section 2) and blended eements (see section 7). 

This chapterprovides adescription ofthe hydration and engineering behavior of special cements including magnesium oxychloride and oxy sulfate cement calcium aluminate cement portland-calcium aluminate blended cement phosphate cement regulated set cement and gypsum. 

Jet Set or regulated-set cement is a modified portland cement composition capable of developing a high early set strength upon hydration. The cement consists essentially of portland cement and from about... 

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