Pre-hydration as a technique for the retardation of Roman cement mortars

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.