Lime-based mortars were widely used in the past as masonry mortars, rendering or plastering mortars. Until the XIX century mortars were based on air lime (calcium hydroxide). Sometimes pozzolans were added to air lime mortars in order to obtain hydraulic behaviour. In fact, in some applications with low contact with carbon dioxide or abundant contact with water, hydraulic behaviour was needed; otherwise air lime mortars would be unable or would take too long to carbonate. Only by the XIX century natural hydraulic limes appeared. These types of lime, made with calcium carbonate stone with some amount of clay, contain some amount of calcium hydroxide but will mainly form hydraulic compounds. Many ancient masonry walls made with lime mortars, with or without pozzolans, are still in use today. Several of these masonries need urgent repair with mortars that can assure their protection , mainly as repointing mortars or as rendering mortars. In order to gain insight to lime-based mortars characteristics, pure air lime and recently classified natural hydraulic lime mortars, as well as mortars with these types of lime but with different amounts of metakaolin, were exposed to different curing conditions. The objective of this work is to present their characterization. The type of lime, the use and quantity of a pozzolan as metakaolin, and the influence of curing conditions were studied in order to evaluate mortar capillary water absorption and drying, when compared to other mortar characteristics. Mortars were fabricated with binder:sand volumetric proportion of 1:3. The binders were a CL90 powder air lime from LUSICAL H100, a NHL3,5 natural hydraulic lime from SECIL and a NHL5 natural hydraulic lime from SECIL. These two last binders are new products, recently formulated and classified by the recent version of EN 459-1:2010 . The pozzolan was a metakaolin Argical M 1200 S from IMERYS (Mk). When metakaolin was used, a weight percentage of lime was replaced by the same weight of metakaolin. The percentage of lime substitution by metakaolin in the formulated mortars was then related with the hydroxide calcium available in each lime – 30% and 50% in air lime mortars, 10% and 20% in NHL3.5 mortars and 5% and 10% in NHL5 mortars (Table I). The used sand was a mixture of three calibrated washed siliceous sands. The mixture of the three sands was previously optimized to achieve a good grading curve. After demoulding, mortar samples were exposed to laboratorial humid (90% RH) and standard (65% RH) curing conditions and to natural maritime exposure (at Cabo Raso LNEC station). Mortar samples have been tested at the age of 28 days (some results have been presented elsewhere ) and are currently being tested at 90 days for mechanical resistance (dynamic modulus of elasticity, flexural and compressive resistance, resistance to sulphates attack) and for physical characteristic (open porosity, water capillary absorption and drying). These last characteristics will be particularly analyzed in this work. The main conclusions drawn regarding the testing at age of 28 days are: - the curing conditions were more important for NHL5 and for air lime mortars than for NHL3.5 mortars, and the variation was lower for physical characteristics; - the substitution of lime by metakaolin decreases (improves) the capillary coefficient of hydraulic lime mortars and increases (worsen) the capillary coefficient of air lime mortars; generally it had no influence on asymptotic value of capillary absorption; - mortars with NHL3.5 have shown drying conditions comparable to air lime mortars but the lime substitution for metakaolin slightly difficulted the drying of NHL3.5 in all curing conditions. Since the testing at age of 90 days is still under evolution, the corresponding results will only be ready for the poster presentation. Comparison among mortars will show the influence of the type of lime, the presence of the metakaolin partially substituting the lime, the curing conditions and the age of the samples. Characteristics are compared to the expected evolution with ageing  and to range values reported in literature [5,6] that point out the adequacy of the different mortars to different types of application on the repair of ancient masonries, as repointing and rendering mortars. The importance of physical characteristics of mortars as capillary suction and drying on masonry behaviour is highlighted.
Acknowledgments The authors wish to acknowledge Fundação para a Ciência e a Tecnologia for the financial support under projects METACAL (PTDC/ECM/100431/2008) and LIMECONTECH (PTDC/ECM/100234/2008), to companies LUSICAL, SECIL and IMERYS for the supply of air lime, natural hydraulic lime and metakaolin and to MSc students João Grilo, João Carneiro, Tiago Branco, Duarte Mergulhão e Rui Antunes who worked in the experimental campaigns.
References  C Groot, Developments on repointing of salt-laden historic masonry in the Netherlands, Proc. Int. Conf. on Rehabilitation of Ancient Masonry Structures, Lisbon, 4 May, 5-15 (2012).  CEN, Building lime. Part 1: Definitions, specifications and conformity criteria. EN 459-1: 2010.  P Faria, V Silva, J Grilo, J Carneiro, T Branco, D Mergulhão, R Antunes, Compatible natural hydraulic mortars for historic masonries (in portuguese), Proc. Int. Conf. on Rehabilitation of Ancient Masonry Structures, Lisbon, 4 May, 29-38 (2012).  A El-Turki, R Ball, S Holmes, W Allen, G Allen, Environmental cycling and laboratorial testing to evaluate the significance of moisture control for lime mortars, Construction and Building Materials 24, 1392-1397 (2010).  R Veiga, A Fragata, A Velosa, A Magalhães, G Margalha, Lime-based mortars: viability for use as substitution renders in historic buildings. Int. J. Architectural Heritage 4 (2), 177-195 (2010).  CEN, Specification for mortar for masonry. Part 1: Rendering and plastering mortar. EN 998-1: 2010.
|Publication status||Published - 1 Jan 2012|