Creep in carbonatable binders

Abstract

Non-hydraulic lime (also known as air lime) is an ancient carbonatable binder that has regained attention due to its carbon sink potential. Besides lower CO2 emissions during production, air lime also absorbs carbon dioxide during its hardening process. Yet, the challenge with non-hydraulic lime (and alternative binders in general) lies in the absence of data, standards, and replicable studies. For instance, air lime is often used in masonry mortars, where volume stability (shrinkage and creep) is required to ensure structural safety, but research on this issue remains scarce. Therefore, the objective of this study was to apply existing frameworks to experimentally measure the total creep (EN 12390–17:2019) of non-hydraulic lime-containing mortars. Four groups were analyzed, with non-hydraulic lime contents of 100 %, 67 %, 50 %, and 0 % (binder volume). Specimens were subjected to three different curing conditions and then loaded and monitored for up to 240 days. The results showed that (i) unlike Portland cement, non-hydraulic lime mortars needed more time to develop strength under natural environmental conditions; (ii) the phenolphthalein test did not accurately monitor the carbonation depth of air lime-rich mortars; (iii) air lime-rich systems showed less shrinkage, possibly due to carbonation-induced expansion; and (iv) air lime-rich groups exhibited greater creep strains, confirming their high deformability. These findings demonstrate that air lime-containing mortars exhibit a distinct time-dependent behavior, highlighting the need to adapt existing standards for more accurate and reproducible long-term performance assessments.