Long Term Stability and Microstructure of Steam Cured High Strength Concrete with Ettringite Based Additives.

In this paper the microstructure and long term stability of steam cured high strength concrete with anhydrite or ettringite based additive containing anhydrite (EBA) are discussed. Concrete in which anhydrite alone was incorporated craked after 1 year. However, the use anhydrite with the optimum size of crystal grains to control the solubility rate of anhydrite and the additives (EBA) developed by combination of anhydrite and silicious materials, made it possible to produce a high strength concrete which has no crack after the lapse of about 14 years to confirm that the concrete can be stabilized over a long period. The impact strength of the high strength concrete with anhydrite and blast furnace slag is smaller than that of the one with anhydrite and silicious materials.By adding EBA, anhydrite is decreased at the beginning of the reaction and at the same time AFt is increased. It is observed that larger needle like crystals of AFt grow in a pore. In addition, the hydration of alite is accelerated by EBA. So, the total pore volume of the hardened cement is remarkably decreased by incorporating EBA.