Theories of expansion in sulfoaluminate - type expansive cements: Schools of thought

Abstract This paper discusses the theories of expansion in sulfoaluminate - type expansive cements. There are two major schools of thought: the Crystal Growth Theory and the Swelling Theory. According to the first school, expansion is caused by the growth of ettringite crystals from the surfaces of the expansive particles or from the solution resulting in a crystallization pressure and, hence, expansive force. According to the second school, expansion is caused by water-adsorption and swelling characteristics of ettringite gel which forms by a through-solution mechanism. Observations supporting and contradicting the two schools are briefly reviewed.