Roman cement mortar prepared by a multi-stage mixing process

Roman cement is the predecessor to modern Portland cement. Nowadays, it is a very promising product with lower CO2 emissions, frequently used to restore historical objects. However, there are still many practical problems as a setting that can be affected in several ways. One possibility is the multistage mixing of fresh mortar, a practical historical method that has not yet been scientifically investigated. This article presents an experimental study investigating the effect of multistage mixing on the properties of fresh and hardened mortar. The properties and structure of the mortar were compared with a reference mortar (retardened by citric acid). Multistage mixing affects fresh mortars with optimal consistency and a workability time of 120 minutes. The influence of mixing on the hydration process and structural formation is characterized by isothermal calorimetry and SEM. Comparison of reference and modified mixing mortars exhibits differences in hydration process, structure, and initial strength, but no significant effect at 90 days strength.