Crystallization and Colloidal Stabilization of Ca(OH)₂ in the Presence of Nopal Juice (Opuntia ficus indica): Implications in Architectural Heritage Conservation

Abstract

Hydrated lime (Ca(OH)) is a vernacular art and building material produced following slaking of CaO in water. If excess water is used, a slurry, called lime putty, forms, which has been the preferred craftsman selection for formulating lime mortars since Roman times. A variety of natural additives were traditionally added to the lime putty to improve its quality. The mucilaginous juice extracted from nopal cladodes has been and still is used as additive incorporated in the slaking water for formulation of lime mortars and plasters, both in ancient Mesoamerica and in the USA Southwest. Little is known on the ultimate effects of this additive on the crystallization and microstructure of hydrated lime. Here, we show that significant changes in habit and size of portlandite crystals occur following slaking in the presence of nopal juice as well as compositionally similar citrus pectin. Both additives contain polysaccharides made up of galacturonic acid and neutral sugar residues. The carboxyl (and hydroxyl) functional groups present in these residues and in their alkaline degradation byproducts, which are deprotonated at the high pH (12.4) produced during lime slaking, strongly interact with newly formed Ca(OH) crystals acting in two ways: (a) as nucleation inhibitors, promoting the formation of nanosized crystals, and (b) as habit modifiers, favoring the development of planar habit following their adsorption onto positively charged (0001) faces. Adsorption of polysaccharides on Ca(OH) crystals prevents the development of large particles, resulting in a very reactive, nanosized portlandite slurry. It also promotes steric stabilization, which limits aggregation, thus enhancing the colloidal nature of the lime putty. Overall, these effects are very favorable for the preparation of highly plastic lime mortars with enhanced properties.

Setting behavior and bioactivity assessment of calcium carbonate cements

“…9,10 However, there is still a lack of understanding about the interactions between organic materials and inorganic cements. For instance, polysaccharides, fatty acids (olive oil), and Nopal juice (a plant extract) have been used in traditional lime mortars to improve some of their properties 11 but in most cases they displayed a negligible impact on the mechanical strength. 12 Nevertheless, recent research has shown that the presence of organic molecules in chalk (a carbonate sedimentary rock) is key to understand its strength on geological time scales.…”

Tuning the Dimensionality of Nano Ca(OH)2 with Surfactants for Wall Painting Consolidation

“…To overcome the disadvantages of organic materials, inorganic materials have been developed because of their high compatibility and long‐term durability . Ca(OH) 2 is a representative inorganic material used in the conservation of cultural heritage . Compared to bulk particles, nanosized Ca(OH) 2 has good permeability and high reactivity with CO 2 , which can ensure fast carbonation, high carbonation degree, and effective consolidation .…”

“…Compared to bulk particles, nanosized Ca(OH) 2 has good permeability and high reactivity with CO 2 , which can ensure fast carbonation, high carbonation degree, and effective consolidation . Therefore, during the last two decades, researchers have developed various methods to obtained nanosized Ca(OH) 2 . However, drawbacks of synthesis methods (high energy, expensive, time‐consuming or complex operations) remain unresolved.…”

“…[7,8] Ca(OH) 2 is a representative inorganic material used in the conservation of cultural heritage. [9][10][11][12][13] Compared to bulk particles, nanosized Ca(OH) 2 has good permeability and high reactivity with CO 2 , which can ensure fast carbonation, high carbonation degree, and effective consolidation. [13][14][15][16][17] Therefore, during the last two decades, researchers have developed various methods to obtained nanosized Ca(OH) 2 .…”

“…[13][14][15][16][17] Therefore, during the last two decades, researchers have developed various methods to obtained nanosized Ca(OH) 2 . [9][10][11][12][13][14][15][16][17] However, drawbacks of synthesis methods (high energy, expensive, timeconsuming or complex operations) remain unresolved. Generally, homogeneous and heterogeneous synthesis are the primary methods used to prepare Ca(OH) 2 .…”