Expansive cements calcium oxide-based

In the most widely used expansive cements the cementitious component consists of ordinary Portland cement, but other binders such as calcium aluminate cement may also be employed. Most commonly, the expansive stresses in the course of hardening are created by the formation of ettringite (C3A.3CS.32H). This phase is formed in the reaction of a constitnent containing alutninnm oxide with calcinm snlfate, calcinm oxide or hydroxide and water. Less common than expansive cements based on ettringite... 

EXPANSIVE CEMENTS BASED ON CALCIUM OXIDE HYDRATION... 

Expansive cements based on calcium oxide are in essence Portland cemerrts with a content of hard-burnt free lime in amounts high enough to produce the reqrrired expansion. In principle, such a cement may be produced either by btrming the cemerrt raw meal in a way that results in the desired free CaO content in clinker, or by adding to a cement with a normal (that is, low) free lime content additional amounts of caldrrm oxide in the form of hard-burnt lime. To produce a distinct expansion of a Portlarrd cement paste the free CaO contents must lie typically above about 2-3 wt%. 

Expansive cements based on calcium oxide are rarely used because of difficulties in controlling the extent and the kinetics of expansion. It has been suggested that expansive additives based on free CaO should be used to prevent early age thermal cracking in hardening concrete (Ebensperger and Springenschmidt, 1992). 

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