The setting of Roman cement is so rapid as tomake the use of retardation essential inmost practicalmortars. This work reports an approach to retardation of Roman cementmortars by means of a pre-hydration process in which pre-determined amounts of water (de-activation water) are added to the cement prior to subsequentmortar formation.
It is shown that this process yields bothmonocarboaluminate and a carbonated AFm phase, the balance of which is modified by storage time; the belite phases are not affected. Increases in both de-activation water and pre-hydratedmix storage time yield a longer workable life and slightly lower strength of the mortar. An increase in de-activation water also yields an increase in shrinkagewhilst an increase in storage time results ina reduction in shrinkage. Other parameters such asmixing protocol and re-mixing affect workable life without compromising the strength.