Aging of Lime Putty: Effects on Traditional Lime Mortar Carbonation

Abstract

The influence of storing slaked lime under water for extended periods of time (i.e., aging) on Ca(OH) 2 crystal morphology, texture, and carbonation evolution of various lime mortars has been studied by the combined use of X-ray diffractometry, phenolphthalein tests, porosity measurements, electron microscopy, and ultrasonic wave propagation analyses. Mortars prepared using traditional aged lime putties (up to 14 years storage under water) show rapid, extensive carbonation, resulting in porosity reduction and ultrasonic speed increase. The aged hydrated lime mortar carbonation reaction (i.e., Ca(OH) 2 ؉ CO 2 ‫؍‬ CaCO 3 ؉ H 2 O) follows a complex diffusive path, resulting in periodic calcite precipitation as Liesegang rings. In this case, binder:aggregate ratios >1:4 result in crack development. Nonaged commercial hydrated lime mortars show slower carbonation and need a higher binder:aggregate ratio (1:3). The carbonation of nonaged lime mortars follows a normal diffusion-limited continuous path progressing from the mortar sample surface toward the core. Differences between aged and nonaged lime mortar carbonation evolution are explained considering Ca(OH) 2 crystal shape changes (from prisms to platelike crystals) and size reduction that occurs on aging of lime putty. Implications of these results on historic building conservation using traditional lime mortars are discussed.

Lime-pastes with different kneading water: Pore structure and capillary porosity

“…In fact, the precipitate of calcium carbonate as calcite or one of its polymorphic forms allows to an accumulation of crystals, very close as a consequence of the reported solid volume increase when portlandite transforms to calcite (11.8%) [18].…”

“…This reaction results in a calcium carbonate precipitation, due to the rapid supersaturation with respect to CaCO 3 in the solution existing in the mortar pores (which contains dissolved CO 2 and Ca(OH) 2 in the condensed water) [18].…”

“…Given that calcite crystals replace portlandite crystals, and commercial nonaged hydrated lime mortars carbonates as a closer-to-equilibrium diffusion limited system [18], microstructure of these carbonated lime-pastes must be uncomplicated. In fact, the precipitate of calcium carbonate as calcite or one of its polymorphic forms allows to an accumulation of crystals, very close as a consequence of the reported solid volume increase when portlandite transforms to calcite (11.8%) [18].…”

Masonry repair lime-based mortars: factors affecting the mechanical behavior

“…Also, at early ages (28 curing days) the degree of carbonation was negligible as the amount of Ca(OH) 2 , which changes slightly, shows in the TG results (Table 6). (1:3) radio is the most suitable mixture for repair mortars, due to its highest strength [3]; (ii) the occurrence of some cracks due to the shrinkage when the binder amount increase above of (1:3) ratio [7]; (iii) the low strengths mainly achieved by lime mortars [13,15]; (iv) the increment of strength when aggregate content increases [23]. Cement-based mortars also increase in strength when binder proportions are raised [1].…”

“…Other questions refer to the most suitable binder:aggregate ratio: Cazalla et al [7] suggest a new repair lime mortar with binder:aggregate ratios  1:4, because the mortar is more rigid and with fewer cracks than 1:3, but Moropoulou et al [3] suggest that 1:3 could be selected as the proper ratio for restoration syntheses. In any case, in the previously cited works, the small amount of samples studied hinders the establishing of significant conclusions.…”