Design and synthesis of macrocyclic ligands for specific interaction with crystalline ettringite and demonstration of a viable mechanism for the setting of cement

Cementitious materials are among those most widely used by mankind while being among the least well understood. The detailed physicochemical processes involved in the hydration and setting of cement slurries are very complex, and a clearly defined quantitative account is still lacking; indeed, even the composition of the cement powder itself is not known exactly. Still less has there been any understanding of the mechanism by which numerous known retarders of the cement setting process act. In this article, we detail the synthesis of novel macrocyclic organophosphonate retarders 1a and 2a which were developed by rational methods. Attempts to synthesise these compounds as phosphonate ester derivatives were universally unsuccessful, however direct modification of the parent hexaaza- (3) and trioxatriaza-18-crown-6 (5) derivatives was successful, to provide the phosphonic acids 1b and 2b respectively. Subsequent testing of these compounds showed their ability to inhibit the growth of crystalline ettringite and delay the setting of cement. These results support the hypothesis that the formation of crystalline ettringite is the rate determining step in the setting of cement.