A Surface energy-based expansion mechanism associated with delayed ettringite formation

A surface energy-based mechanism for expansion in cement systems susceptible to Delayed Ettringite Formation (DEF) is proposed. The volume change behavior of nanoporous materials filled with impregnants and exposed to water vapor (considered analogous to the DEF situation) is described. The relevance of expansion due to Bangham swelling and dissolution phenomena is explained. The role of microcracking in expansion due to DEF is discussed. It is suggested that it is not necessary to invoke classical ‘crystal growth’ theory to explain expansion due to DEF. It appears that both AFt precipitation and surface effects are occurring concurrently and influencing the volume stability of the material.