RILEM TC 277-LHS report: additives and admixtures for modern lime-based mortars

Abstract

The scope of this collective paper produced in the frame of RILEM TC 277-LHS is to provide sound knowledge on the use of additives/admixtures in lime-based mortars, based on literature and practice. The most widely known additives/admixtures are systematically presented. Their main effects and testing of their performance have been properly tabulated. It is well known that a plethora of additives/admixtures are produced every year by chemical industries. However, when using them in lime-based mortars, compatibility and durability aspects are of primary importance. The introduction of additives/admixtures in lime mortars was imposed by the need to improve important properties of these composites in the fresh and hardened state, namely, workability, durability, early-age and long-term strength and to reduce defects, such as shrinkage and long setting time. In this review paper, the terminology proposed by EN 16572 is followed, designating additive as a constituent added in small quantity to the binder, and admixture as a substance in quantities at least 1% w/w added to the mix. The additives/admixtures are classified according to their action and their validation with specific testing methodologies highlights the dosage sensitivity and the need to develop further standardization. The combination of different additives proposed in several studies resulted as the most promising strategy to enhance the performance of lime mortars. However, recently developed additives and admixtures need to be further evaluated with reference to their compatibility with other mortar constituents, and their effects on the overall mortar and render durability need to be studied. Finally, adopting similar terminology for additives/admixtures in lime and cement-based mortars will facilitate better comparison and assessment issues.

The Influence of Animal Glue as an Additive on the Properties of Lime Architectural Grouts

“…An additive is defined as a constituent that is added to the binder, usually in a small amount of at least 1% weight/weight (w/w), to modify its preparation or its properties in the fresh/hardened state, and it is a substance other than the binder, aggregate, filler, or water [7]. The use of organic additives in lime mortars dates back to Greek and Roman times [8].…”

“…In addition, the influence of traditional organic additives on the physical and mechanical properties of lime mortars has also been studied [7,[12][13][14][15]. Ventolà et al [12] found that organic additives such as animal-bone glue, nopal, casein, and olive oil in lime mortars improved the mechanical properties and reduced porosity, and nopal also increased the carbonation rate.…”

“…It has been shown that the presence of traditional organic additives can affect the carbonation and hydraulic reactions in lime mortars and improves their mechanical properties [7]. Organic additives, such as hygroscopic animal glue, act as a moisture retainer and slow down the drying process, so that the carbonation process is facilitated by water and proceeds according to the following reaction (1) [13,14]: Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O + 74 KJ (1) In addition, the properties of lime grout can also be improved by changing the particle size distribution of the filler.…”

Characterisation of Czech Modern Mosaic Mortars

“…Organic compounds have been added to inorganic binders since the time of the first ancient civilizations in order to improve their mechanical workability, mechanical properties and durability. Various organic additives have been usednamely fats (both plant and animal), proteins (animal glue, egg proteins, casein of curdled milk), saccharides and polysaccharides (sugar, various gums and sizes) or more complex substances such as animal blood [40], [41].…”