chapter  24
Ettringite-Based Cements
Pages 16

Alternative products were developed based on different chemical reactions. Long et a l. (1987) described a cement based on the formation of e t t r i n g i te from C4A3S v ia reaction (1), c a l l ed here type IV cement, which is currently used in some B r i t i sh mines. I ts composition is compared wiyh type II and I II cements in Table 3 and it has a close r e l a t i on to type K expansive cement. M i l ls (1984) described an attempt to avoid the use of the r e l a t i v e ly expensive HAC by returning to an accelerated OPC-based system involving a sl u r ry of OPC mixed with a second s l u r ry containing PFA and aluminium sulphate. An alternative solution based on mixing a special c l i n k e r, r i ch in C 2^A y a n (* C9S» w i t n a n OPC contained in a f i r st s l u r r y, with anhydrite, sodium carbonate (accelerator) and bentonite in a second slurry has been described by Longman and Drew (1985). E t t r i n g i te is formed by the reaction:

C 1 2 A 7 + 21 CS + 9 CH + 207 H = 7 C6 A S 3 H 3 2 (4)

2.3 Chemistry of type I I mine cements Eight laboratory methods of synthesising e t t r i n g i te were described by Berman and Newman (1960). One of these was the reaction between calcium sulphate solution and a solution of calcium aluminate obtained by shaking HAC with water. Since e t t r i n g i te dissolves incongruently in pure water, Berman and Newma n (1960) emphasised the need to have excess lime and also excess sulphate ions in solution at the completion of the reaction.