Types of expansive cement

Probably a majority of practical expansive cements have depended on the modification of a Portland cement in such a way as to increase the formation of ettringite. Single expansive cement clinkers can be made, but it has been more usual to produce admixtures that are blended or interground with a normal Portland cement or clinker. Blending has the advantage that the 

Type S cements are Portland cements high in C3A and with suitable contents of calcium sulphate they have found little favour as they are too diHicLilt to control. The A1,0, has also been supplied in forms other than those mentioned above. Impure alunite [KAl3(S04),(0H)(,]. which occurs as a natural rock, has been used, either after calcination (V6) or uncalcined (W30). In the latter case it was mixed with Portland cement clinker, anhydrite and pfa or slag and was found to dissolve relatively slowly, thus suitably delaying the expansive reaction. 

The possibilities of using free lime or periclase as expansive agents have also been investigated. Kawano cl al. (K50) and Long (L49) described clinkers in which substantial proportions of free lime are present as inclusions in alite. In both ca.ses, the raw mix included anhydrite. Long investigated and described the processes by which this microstructure was formed. 

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As aforementioned expansive cements produced industrially are based on the formation of ettringite. The technologies differ orrly with the type of calcium alu-minates and of the matrix material. The types of expansive cements are shown in Table 9.3. Two types of matrix are used Portland cement and calcium aluminate cement. The following phases are r ed as the sotrrce of aluminum ions CjA, CA (as calcium aliuninate cement), C4A3S and the calcitrm aliuninate hydrates C AH or CAHjq. The second technology is the oldest one, and was implemented by Dossier in forties XXc [60]. 

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