Lime mortars - The role of carboxymethyl cellulose on the crystallization of calcium carbonate

Aerial lime-mortars are widely used in the conservation interventions, in which polymers could improve their mechanical strength. In this work, the effects of carboxymethyl cellulose (CMC) on the crystallization of calcium carbonate (CaCO3) in lime mortar have been studied in order to explore the mechanism of the improvement. The experimental results have shown that CMC molecules played as templates to control the morphology and size of CaCO3 crystals. Without CMC, the crystals appeared in the form of cylinder, while CMC addition changed the crystalline shape to be fusiform at the low concentration and spherical at the high concentration. The crystal size increased with CMC addition to the maximum value then declined, leading the lime mortar structure to be more compact, thus improving the compressive strength of lime mortar. These results might be attributed to the restraint effect of CMC molecules to slow down the growth rate and crystallinity of CaCO3 crystals. It was also found that CMC did not affect the polymorph of CaCO3 crystals, which is beneficial to maintain the compressive strength of lime mortar. (C) 2018 Elsevier Ltd. All rights reserved.