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

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.