Crystal development during carbonation of lime-based mortars in different environmental conditions

This study examines crystal development during the carbonation of lime mortars according to the additives used and curing conditions. Two types of samples were prepared, one with sand and the other one additionally including Roman ceramics. These mortars were cured: 1) by spraying with a carbonation accelerator product under laboratory conditions; 2) in a climate chamber under 20 °C, 60% relative humidity, and 1600 ppm CO2; and 3) under laboratory conditions as controls. Polarized light microscopy, SEM-EDS and XRD were used at 28, 90, 120 and 180 days to monitor the carbonation process. Observations indicate the development of different CaCO3 polymorphs, which appeared as metastable phases. The early nucleation of a well-defined calcite phase as the most stable CaCO3 polymorph was only identified in the chamber-cured samples. Differences in the pore network were observed depending on the composition and morphology of the mortar components and the environmental curing conditions. [Display omitted] •High CO2 and DiloCarb® treatment favour advanced carbonation and self-healing.•In the lime mortar without ceramics, channel type pores occur in the aggregate border.•In the lime mortars with ceramics, vug type pores are produced in the binder during kneading.•The formation of tabular CaCO3 polymorphs caused an increase in stress leading to microshrinkage cracks.•The use of a ceramic provoked dissolution and then re-precipitation of more stable polymorphs.