Rapid Hardening and Fast-Setting Cements

The classic approach to the cement strength development was to increase the alite and CjA content, as well as the fineness of cement. The increase of silica modulus to about 3 and use of some minor components, mainly barium and boron results in further cement properties enhancement. The rate of hardening of these cements [121-123] is increasing with their specific surface in the range 4,400-4,600 cm /g and with K2SO addition (1.5 %), according to Grzymek s patent [124]. 

At early seventies the new technology of rapidly hardening cements, with the fluorine stabilized Cj2A, phase, was developed. The two modifications of this 

Ghosh et al. [129] proposed to add the calcium aluminate cement to Portland cement, together with calcium chloride and anhydrite. This mixture has the properties of expansive cement with setting time of about 15 min and strength 20 MPa after 2 h, 40 MPa after 7 h and 70 MPa after 1 day. Further strength increase is shght. 

The rapid hardening cements are known, which are composed of C4A3S in the mixture with C2S, C AF, CJ2A7 and anhydrite. The hardening of these cements 

It is known, that the monoclinic tricalcium aluminate with alkalis in solid solution reacts with water slowly (see Chap. 2). Therefore this phase can be used as a source of aluminate ions in reaction of ettringite formation. The fast-setting cements are known which contain 35 % NCj A, apart from the high belite content of 57% or calcium orthosilicate phases belite and alite (C2S—38%, 038—21%) [1]. 

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