Component Five: Effects of Organic Additives

Work Completed

Work at the University of Granada has found that the addition of nopal juice produces a high quality lime putty following lime slaking. The microstructural characteristics of such hydrated lime are somehow similar or even superior to those of aged lime putties: high surface area, and small particle size, which should theoretically affect reactivity and water retention, and may lead to easier and faster carbonation. This quality improvement is obtained readily, right after slaking in the presence of nopal extract, an important fact to consider in practical, economically feasible conservation interventions. This work will be published as "TEM Analysis of Lime Putties: Influence of Nopal Juice (Opuntia ficus indica) on portlandite crystals microstructure," by C. Rodriguez-Navarrro, E. Hansen, et al (forthcoming). At the GCI, this work is being complemented by studying the short-term effects of both organic and inorganic additives on the rheological and working properties of lime putties, and the long-term effects on the chemical stability of the additives, their effects on curing, and on strength development.

Future work

Based upon the interesting results of the nopal study, the University of Granada received a research grant from the European Union to study "The Effects of Organic Additives on the Nanostructure and Colloidal Behavior of Hydrated Lime. Applications in the Design of Mortars for Restoration." The short-term and long-term effect of traditional and modern organic additives on properties of lime putties and mortars will be studied at the GCI.

From Summary of Grant Proposal on Organic Additives:

"Applications of modern lime mortars have found problems connected to low durability and poor strength development. In general, they do not achieve the superior performance of ancient lime mortars, which has been ascribed to the past ubiquitous use of natural organic additives. However, the effects of such additives are poorly understood, which has prevented their current use. Here we plan to study the effects of a number of both natural and artificial additives (nopal extract, pectin, alcohols—ethanol, ethyleneglycol, and surfactants—lignosulfonates, carboxylates, and phosphonates) on the nanostructure Ca(OH)₂ (nanocrystals formation and aggregation) and the related colloidal behavior of hydrated lime pastes. Upon selection of the best additivies(s) (based upon their promotion of nanocrystals formation with plate-like morphology, imparting high colloidal stability, viscosity, plasticity, and reactivity) and best application procedures (additive concentration, addition before or after lime slaking), quartz sand/hydrated lime mortars (with additives) will be prepared, and their carbonation evolution, mechanical properties and durability will be studied. Ultimately, we aim at designing new conservation lime mortars, with superior physical-mechanical properties and durability."

Last updated: October 2007