Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

João Monteiro; Vitor Silva; Paulina Faria

doi:10.3390/infrastructures6100143

Monteiro, João;Silva, Vitor;Faria, Paulina

2021-10-08 00:00:00

infrastructures Article Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries 1 1 1 , 2 , João Monteiro , Vitor Silva and Paulina Faria * Department of Civil Engineering, NOVA School of Science and Technology, NOVA University of Lisbon, 2825-516 Caparica, Portugal; jmds.monteiro@campus.fct.unl.pt (J.M.); vmd.silva@fct.unl.pt (V.S.) CERIS, Civil Engineering Research and Innovation for Sustainability, IST, 1049-001 Lisbon, Portugal * Correspondence: paulina.faria@fct.unl.pt Abstract: The interest in restoration and maintenance of old masonries towards their durability is nowadays combined with the concept of sustainability and the need to implement more suitable materials for building heritage interventions. This has led to the importance of having a better knowledge of air lime mortars, namely on the effect of pozzolanic additions, curing conditions and evolution at early stages. This study consisted in the characterization of mortars based on hydrated air lime and sand, with 1:2 (lime:sand) volumetric composition, with different weight percentages of substitution of lime by metakaolin (Mk): 0%, 10% and 20%. Mortar prisms were analyzed in three different curing environments: maritime (by the Atlantic Ocean), in laboratory humidity (95 5% relative humidity, RH) and standard (65 5% RH) conditioning. Tests were conducted to evaluate fresh and hardened properties of mortars, considering physical, chemical and mechanical performance at 28, 90 and 180 days. Results showed the viability of applying air lime-Mk mortars with curing conditions similar to the tested ones. In the standard curing, the mortar with 20% Mk revealed advantages in mechanical parameters. Concerning the behaviour towards water, Citation: Monteiro, J.; Silva, V.; improvements were shown at an early stage with the humid curing, while maritime curing beneﬁted Faria, P. Effect of Type of Curing and its behaviour for at least up to 6 months. Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries. Infrastructures 2021, 6, 143. Keywords: mortars; hydrated air lime; metakaolin; curing conditions; maritime natural exposure; https://doi.org/10.3390/ performance; ageing; masonries durability infrastructures6100143 Academic Editor: Maria do Rosário Veiga 1. Introduction Mortars have been used since ancient times. They are frequently used in renders, Received: 7 September 2021 being the sacriﬁcial coatings of many building facades. Their main purpose is to pro- Accepted: 1 October 2021 tect the substrate, namely the masonry walls, from exposure to external agents, such as Published: 8 October 2021 weather, pollution and impact actions [1]. By protecting the substrate, they contribute to the durability of the whole system. Publisher’s Note: MDPI stays neutral In Europe, the majority of historical mortars are lime-based and were used in con- with regard to jurisdictional claims in struction until at least the beginning of the 20th century, contributing vastly to the history published maps and institutional afﬁl- of construction [2]. After the invention of cement in the 19th century, and particularly with iations. the increase of scientiﬁc studies about hydraulic reactions, the development and techniques related to lime mortars were forgotten. The apparent advantages of Portland cement, such as higher strength and quicker hardening, contributed on a large scale to increasing their use. Copyright: © 2021 by the authors. However, with the need for restoration and maintenance of old renders and the ill- Licensee MDPI, Basel, Switzerland. omened effects of the use of Portland cement in architectural heritage, in the last decades, This article is an open access article many scientiﬁc studies have been carried out about promoting the re-use of air lime distributed under the terms and mortars, namely for heritage repair and conservation [2–4]. The requirements for mortars conditions of the Creative Commons to be used in conservation are quite different from those used in new construction, due to Attribution (CC BY) license (https:// compatibility criteria and also to reversibility when high cultural values are involved. creativecommons.org/licenses/by/ In these cases, it is intended to use mortars with high deformability and water vapor 4.0/). Infrastructures 2021, 6, 143. https://doi.org/10.3390/infrastructures6100143 https://www.mdpi.com/journal/infrastructures Infrastructures 2021, 6, 143 2 of 18 permeability, in order not to block moisture in the old masonries. Mortars should also have similar properties to the pre-existing mortars but lower than the substrate to avoid changing the original stress distribution [1]. Air lime-based mortars have positive environmental implications as compared with cement mortars due to their lower energy consumption for production, ﬁred at less than 900 C, and their contribution to CO balance by retaining and by carbonation when hardening the CO that was emitted from production [5]. They can be used in a wide variety of mixtures depending on their function, such as renders and plasters [6], repairing ornamental pieces and surfaces of historical buildings [7], bonding glazed tiles [8] and other use cases [4,9,10]. In new civil engineering applications and conservation, sometimes there is a need to improve air lime mortars, as they present slower setting and hardening, compared to cement ones. It is also notorious that their mechanical strengths are different from cement-based mortars [11]. Numerous studies have been carried out demonstrating that air lime mortars blended with pozzolans showed faster setting properties and an increase in their mechanical capacity and durability [12–14]. Pozzolans are ﬁne graded materials that, together with binders that contain calcium hydroxide, react in the presence of water and constitute hydrated compounds. Therefore, pozzolans can partially replace mortar binders, making mortars more durable and eco-efﬁcient. Examples of air lime–pozzolan mortars that are more than 2000 years old can be seen in several archaeological sites, both with natural pozzolans [12] and artiﬁcial pozzolans [15]. In these modiﬁed air lime mortars, it is important to understand the mechanisms of setting and hardening, as well as their chemical and mineralogical compositions [16]. The introduction of artiﬁcial pozzolans that result from waste generation can not only improve the characteristics of these mortars but also enhance the sustainability of the construction sector, through the recycling of materials [13]. Since metakaolin (Mk) has a high pozzolanic activity and is often used as a substitution of cement [17,18], it is interesting to evaluate the combination of this material with air lime. Previous research has shown some studies focusing on air lime-Mk mortars. In Table 1, a synthesis of some studies can be observed regarding air lime mortars, with substitutions of lime by Mk of up to 50%, with different volumetric proportions of the binder:aggregate and even with different curing cycles [19–28]. The majority of previous studies have assessed the inﬂuence of relatively high Mk contents on air lime mortars, which were mortars with binder:sand ratios of 1:3 (vol.), and the mortars were just assessed at younger ages. The curing conditions, namely temperature, relative humidity (RH) and salts exposure, should inﬂuence the kinetics of the hardening reactions and, subsequently, the mechanical strength [16]. The inﬂuence of natural exposure curing has rarely been assessed in previous studies of air lime–Mk mortars. Some research studies have mentioned the decrease in mechanical strength of air lime–Mk mortars after 3 months of age [19,20,27,28]. Therefore, the main objective of the present research was to evaluate the inﬂuence of curing conditions (near the Atlantic Ocean and with most probable contamination by salts, humidity and standard laboratory conditions) on the physic–mechanical characteristics of air lime-based mortars, with a binder:sand volumetric proportion of 1:2, when lime content replacement by Mk with percentages of 10 and 20% (vol.) occurs, after up to 6 months of the mortar ’s age. The aim was to increase knowledge on how these replacements and curing conditions may affect mortars performance at relatively early ages and how can it affect their future durability. Infrastructures 2021, 6, 143 3 of 18 Table 1. Synthesis of air lime mortars with incorporation of metakaolin, test methods and results. Study Mortars Analyzed Tests Results Consistency (EN 1015-3) 167–177 mm Binder(CL+Mk):Sand 1:2 with CL:Mk:sand (vol.) FStr (EN 1015-11) 0.08–1.07 MPa 1:0.5:3, 1:1:4, 1:1.5:5, submitted to dry and humid Faria [23] CStr (EN 1015-11) 0.36–8 MPa curing, tested at 60 d Op (EN 1936) 29–36% Consistency (EN 1015-3) 132–144 mm Ed (EN 14146) 729–6690 MPa Binder:sand 1:3 (vol.), with 0%, 30% and 50% FStr (EN 1015-11) 0.08–1.09 MPa substitutions of CL by Mk, submitted to Faria et al. [25] CStr (EN 1015-11) 0.13–2.82 MPa standard and humid curing tested at 28 d Op (EN 1936) 29–31% CS (EN 15801) 13.6–24.9 kg/m 2 0.5 CC (EN 15801) 0.84–1.43 kg/(m min ) Ed (BS 1881-209) 2.8–4.0 MPa Binder:sand 1:3 (vol.) with 0% and 20% of Mk, Andrejkovic ˇová et al. [20] FStr (EN 1015-11) 0.125–0.175 MPa submitted to weathering cycles, tested at 28, 90 CStr (EN 1015-11) 0.40–0.55 MPa and 180 d Binder:sand 1:3 (vol.) with 0% and 9% substitutions Consistency (EN 1015-3) 150 10 mm Cardoso et al. [22] of air lime by Mk, submitted to six different curing FStr (EN 1015-11) 0.05–0.15 MPa conditions, tested at 28, 90 and 365 d CStr (EN 1015-11) 0.1–0.6 MPa Consistency (EN 1015-3) 154–155 mm Binder:sand 1:3 (vol.), with 0% and 20% Ed (EN 14146) 2822–3691 MPa substitutions of Mk, cured under different FStr (EN 1015-11) 0.3–0.7 MPa Faria & Martins [24] conditions of RH and CO content and tested at CStr (EN 1015-11) 0.4–1.3 MPa 60 d for mechanical tests and 120 d for capillarity CS (EN 15801) 13.85–16.91 kg/m and drying 2 0.5 CC (EN 1015-18) 0.92–1.07 kg/(m min ) Consistency (EN 1015-3) 130–140 mm Binder:sand 1:3 (vol.), with 0%, 10%, 20% and Ed (EN 14146) 2.38–3.85 GPa 30% substitutions of CL by Mk, tested at 28, 90 Ferraz et al. [26] FStr (EN 1015-11) 0.22–0.36 MPa and 180 d CStr (EN 1015-11) 0.30–0.68 MPa Binder:sand 1:1, 1:2 and 1:3 (vol.), with 0%, 30% Consistency (EN 1015-3) 139–144 mm Gameiro et al. [19] FStr (EN 1015-11) 0.50–2.6 MPa and 50% substitutions of CL by Mk, tested at 28 CStr (EN 1015-11) 1–15 MPa and 90 d Binder:sand 1:1 (vol.), with 50% substitutions of Consistency (EN 1015-3) 152–150 mm Pavlík & Užáková, [27] CL by Mk, tested at 28, 90, 180 and 365 d CStr (EN 1015-11) 1.6–9 MPa Consistency (EN 1015-3) 133–148 mm Binder:sand 1:3 (vol.), with 0%, 10%, 15% and FStr (EN 1015-11) 1.69–2.93 MPa 20% substitutions of CL by Mk, tested at 28 and Arizzi & Cultrone [28] CStr (EN 1015-11) 2.36–9.12 MPa 120 d Op (not speciﬁed) 31–32% Consistency (NBR 13276) 195–210 mm Binder:sand 1:1, 1:2 and 1:3 (vol.), with 0%, 25% Ed (EN 14146) 6771–10485 MPa and 50% substitutions of CL by Mk, tested at 90 d FStr (EN 1015-11) 0.81–2.72 MPa Loureiro et al. [21] CStr (EN 1015-11) 2.02–12.63 MPa Porosity (EN 1936) 26–30% 2 0.5 Drying rate D1 (EN 16322) 0.0042–0.0051 kg/(m min ) 2 0.5 Drying rate D2 (EN 16322) 0.0391–0.0467 kg/(m min ) Notation: CL—air lime; CStr—compressive strength; Consistency—ﬂow table consistency; Ed—dynamic modulus of elasticity; FStr— ﬂexural strength; Op—open porosity; CS—capillary saturation value of samples with 40 mm 40 mm 80 mm; CC—capillary coefﬁcient; RH—relative humidity. 2. Experimental Programme To evaluate the inﬂuence of the replacement of the binder by Mk in air lime mortars, various tests were carried out on the fresh mortar and, after determined periods of cur- ing, on hardened specimens. The effect of three different curing conditions were tested, to assess the performance and expected durability of the mortars. 2.1. Materials All the mortars were prepared with an industrial powder hydrated air lime (CL), classiﬁed as CL90-S by EN 459-1 [29] and produced by Lusical, Lhoist group, Portugal. The same CL was also used in previous studies, such as Gameiro et al. [19] where the chemical composition can be seen, Andrejkovicov ˇ á et al. [20], Cardoso et al. [22], Faria & Mar- tins [24] and Faria et al. [25]. The aggregate was obtained by mixing three types of washed and calibrated silica sands with different granulometry (APAS 12, APAS20, and APAS30, from Areipor) with a volume ratio of 1:1.5:1.5, respectively. The particle size distribution of Infrastructures 2021, 6, 143 4 of 18 each sand and the sand mixture (S) can be seen in Figure 1. The Mk used in the modiﬁed mortars was an artiﬁcial pozzolana, Argical M 1200S, from IMERYS, and it was obtained from micronizing and calcining a kaolinitic clay. The chemical composition of the Mk that was used was assessed by Gameiro et al. [19]. The loose bulk density off all dry constituents of mortars, based on EN 1097-3 [30], is shown in Table 2. Table 2. Loose bulk density of mortars dry materials. Sands Air Lime (CL) Metakaolin (Mk) Material Mixture of Sands APAS12 APAS20 APAS30 Loose bulk density 0.361 0.294 1.412 1.405 1.388 1.463 [kg/dm ] Figure 1. Particle size distribution of each sand and the mixture of the three sands. 2.2. Mortars Preparation, Fresh State Characterization and Curing A reference mortar, named CL, with a volumetric binder:aggregate proportion of 1:2 was produced. Based on that proportion, two mortars were formulated with partial replacements of the lime with Mk: CL_10Mk and CL_20Mk (corresponding to substitutions of 10% and 20% in volume), as shown in Table 3. The water was added to ensure workability for the reference mortar to be able to be applied as a render by a skilled professional and kept constant for the other mortars. Table 3. Composition of mortars. Quantities Weight Volume Mk Mortar Sand (g) Water CL (g) Mk (g) (mL) CL:Mk:S B:S CL:Mk:S B:S (wt.% of CL) APAS12 APAS20 APAS30 CL 1:0:2 1:2 1:0:7.75 1:7.75 0 578.1 0.0 CL_10Mk 1:0.14:2.22 1:2 1:0.11:8.61 1:7.75 10 520.3 57.8 1129.6 1686 1665.6 1000 CL_20Mk 1:0.31:2.50 1:2 1:0.25:9.69 1:7.75 20 462.5 115.6 Notation: B = CL or CL + Mk (considering Mk included as binder). The mortar mixing procedure was based on the EN 1015-2 [31]. After cleaning and taring the trays, the components were placed from the coarsest to the ﬁnest granulome- try. After mixing the dry materials, they were manually homogenized and placed in a mechanical mixer. The water was then added in the ﬁrst 15 to 30 s and followed by 120 s of mechanical mixing. After this period, the process was interrupted to remove the materials Infrastructures 2021, 6, 143 5 of 18 which accumulated at the edges of the vat. The mechanical mixing process restarted with a duration of 30 s, concluding the kneading. Mortars in the fresh state were characterized by the ﬂow table consistency test, accord- ing to EN 1015-3 [32], bulk density following EN 1015-6 [33], air content according to EN 1015-7 [34] and water retention based on EN 1015-8 [35]. The mortar specimens were prepared in standardized prismatic metallic molds with 40 mm 40 mm 160 mm dimensions. The prismatic specimens were submitted to 3 distinct cures: maritime (m), humid (h), and standard (s) curing. The mortar specimens exposed to each curing are speciﬁed adding the type of curing (m, h or s) to its abbreviation in curved brackets. Standard curing corresponds to controlled conditions of (65 5)% RH and tem- perature of (20 2) C, guaranteed by a controlled environment room. Humid curing corresponds to RH and temperature conditions of (95 5)% and (20 2) C. This per- centage was reached with the use of a large vat containing water, where a support grid, for the specimens, had been installed. The vat was kept closed with a polyethylene cover to create this high RH environment. The maritime cure was performed in natural exposure at the Portuguese Laboratory for Civil Engineering (LNEC) Natural Exposure Station, located in Cabo Raso, Lisbon. This natural exposure station is located only about 25 m from the Atlantic Ocean, which implies a natural sprinkling of saltwater, with a high concentration of chlorides and contact with salt fog. This environment is very aggressive and frequent in Portugal and other countries bordering the Ocean. Small size ceramic tiles were placed on the top of each specimen, and on the periphery, wooden prisms (false specimens) were placed to ensure that similar exposure conditions existed for all prismatic specimens (Figure 2). Figure 2. Mortar specimens exposed at LNEC’s Natural Exposure Station in Cabo Raso, Lisbon, seeing organization and the Atlantic Ocean (a,b). 2.3. Hardened State Characterization The hardened state tests were carried out at 28, 90 and 180 days of the specimens’ lifespan. The dynamic modulus of elasticity quantiﬁes the mortar ’s rigidity; the lower it is, the better the mortar can support small substrate deformations without cracking. It was determined based on EN 14,146 [36], for natural stone, using a Zeus Resonance Meter. Four non-destructive tests were performed with each specimen, changing the prism posi- tion in the equipment. The ﬂexural strength test was performed using a universal machine Zwick Rowell model Z050, with a load cell of 2 kN and a speed of 0.2 mm/min, based on EN 1015-11 [37]. The carbonation test was performed with phenolphthalein, with one half of each specimen tested for ﬂexural strength at 90 days. It results in a chromatic variation of the surface when in contact with calcium hydroxide (Ca(OH) ), which is uncarbonated mortar), 2 Infrastructures 2021, 6, 143 6 of 18 acquiring a pink color. The carbonated (CaCO ) part does not change color. In this test, only a quantitative evaluation of the evolution of carbonation was made, in visual terms. The other half of each specimen was used in the compressive strength test, with the same equipment and using an apparatus that ensured a compressive area of 40 mm 40 mm, a load cell of 50 kN and a speed of 0.7 mm/min, also following the EN 1015-11 [37]. Small samples of each specimen were prepared of around 40 mm 40 mm 20 mm and used in the open porosity and dry bulk density tests. The samples were subjected for 24 h to 60 C, cooled and submitted to the open porosity and the bulk density tests based on EN 1936 [38] for natural stone, with a vacuum, hydrostatic weighing and water- saturated weighing. In the capillarity water absorption test, samples of 40 mm 40 mm 70 mm in size were used. The test was carried out based on EN 15,801 [39]. Before starting the test, the samples were kept for at least 48 h in an oven at a temperature of 60 C until they reached a constant mass value (corresponding to a variation of 0.1% mass within 24 h). The samples were removed from the oven and cooled at ambient temperature. They were wrapped in polyethylene ﬁlm to waterproof their lateral faces and only allow water to be absorbed by a unidirectional capillary raise from the button. The test took place in a tank with saturated ambient conditions. Inside, a tray was placed and levelled, with a plastic net at the base (which ensures that the base of the samples was in contact with the water), ﬁlled with water up to a height of 5 mm and weighted after deﬁned periods of time in contact with water. Water was added whenever necessary so that the height of the water remained constant. Capillary absorption curves were determined for each sample by weighing them until reaching an asymptotic value (Cs). For all mortars, the capillary coefﬁcient (CC) was also calculated. The drying capacity test started right after the capillarity test ended, with the same samples with lateral surfaces within the polyethylene ﬁlm. After the initial weighing for drying (the last for capillary absorption), the samples were moved to a waterproof surface where standard cure conditions were imposed (RH of (65 5)% and a temperature of (20 3) C), and they continued being weighted after deﬁned periods of time, with the top surface as the only drying area. The drying curves, with a mass decrease per drying area by time and by the square root of time, were calculated and allowed determination of the rates for two drying phases, D1 (the ﬁrst stage of drying) liquid front and D2 (the second stage of drying) including the moisture front [40], by the negative slope of the initial and intermediate linear segment, respectively, based on EN 16,322 [41]. 3. Results and Analysis 3.1. Characteristics of Fresh Mortars The results of the ﬂow table consistency, water retention, air content and bulk density of fresh mortars are shown in Table 4. Table 4. Flow table consistency, water retention, air content, and bulk density of fresh mortars. Mortar Flow (mm) Water Retention (%) Air Content (%) Fresh Bulk Density (kg/m ) CL 141 3 93.9 4.2 1952.2 CL_10Mk 134 3 92.4 4.3 1965.1 CL_20Mk 137 2 92.8 4.1 1961.7 Results obtained on the ﬂow table consistency show that, for the same ratio of wa- ter/binder (the binder being the sum of air lime and Mk), the replacement of lime by Mk seems to tend to reduce the ﬂow but without jeopardizing workability. That is not the case for instance when brick dust is added; that type of pozzolanic addition may have a great inﬂuence on fresh mortar behaviour because of the signiﬁcant water absorption during mortar preparation [13]. However, the reduction did not correspond to the Mk content. As expected for air lime mortars, good workability was obtained, even with a low ﬂow. Infrastructures 2021, 6, 143 7 of 18 Gameiro et al. [19], using the same air lime and Mk and binder:sand ratios of 1:1, 1:2 and 1:3 (vol.) but with 0%, 30% and 50% lime replacement (Table 1), achieved an average ﬂow of 138 5 mm, showing very similar results to those obtained in Table 4. Faria et al. [25] also obtained ﬂows of around 140 mm for 1:3 (vol.) binder:sand ratio and 0%, 30% and 50% Mk replacing lime. The same range of values of 140 mm for 1:3 (vol.) binder:sand ratio were achieved by Cardoso et al. [22], Faria & Martins [24] and Ferraz et al. [26], for 1:3 (binder:sand, in vol.), reached consistency ﬂows of around 155 mm, slightly higher than the other studies, possibly due to different water/binder ratios. Loureiro et al. [21], analyzing the consistency of air lime mortars with the addition of 0%, 25% and 50% of Mk (Table 1), obtained a higher consistency by using a different method, returning results not comparable. Pavlík & Užáková [27] also obtained values of around 150 mm for 1:1 (binder:sand, in vol.) with 50% substitution of Mk. Regarding the water retention, air content and bulk density, all mortars had very similar results, showing the low inﬂuence of 10–20% Mk replacing air lime. 3.2. Characteristics of the Hardened Mortars 3.2.1. Dynamic Modulus of Elasticity The results of the Dynamic modulus of elasticity test carried out at 28, 90 and 180 days are displayed in Figure 3. Figure 3. Dynamic modulus of elasticity (DME) of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. The modulus of elasticity increased from 28 to 90 days in the mortars CL and CL_10Mk, for all types of curing conditions. On the other hand, all CL_20Mk registered a decrease in the value of DME with increasing age. It is also notable that humid curing delayed the DME of the reference air lime mortar at 1 month, and both maritime and standard curing were more adequate for that mortar. On the contrary, maritime curing seemed to optimize the DME of mortars with 10% replacement by Mk (CL_10Mk) at young ages; however, there was a decrease of DME from 3 to 6 months, although this was not so signiﬁcant for the other curing conditions. Mortars with 20% Mk replacing lime achieved the highest DME at 1 month, decreasing after 3 and 6 months; however, DME was always higher for these mortars. Comparing the dynamic modulus of elasticity obtained in the present study with the results obtained by previous studies, it is possible to see that Andrejkovicov ˇ á et al. [20], for mortars with 20% Mk, obtained very similar results compared to those present in Figure 3. Based on Loureiro et al. [21], the contents of hydraulic products of the air lime–Mk mortars with 20% Mk in comparison to the CL mortars justify the increase of the DME by the Infrastructures 2021, 6, 143 8 of 18 improvement of the cohesion and bonding between the particles. However, this increase was not observed in mortars with 10% substitution (Figure 3), which suggests that a higher Mk content is necessary for the hydration products to compensate for the lime replacement. Comparing the results at 90 days with mortars tested at 60 days by Faria & Martins [24], the values were in the same range. In Faria & Martins [24] study, the higher values were registered in mortars with 20% replacement of CL by Mk, in conditions with high RH and accelerated curing with CO . Faria et al. [25], at 28 days (a short curing period when considering lime-based mortars) and with humid curing, obtained higher values of DME with percentages of 30% and 50% of Mk. Ferraz et al. [26], for mortars with 0% of Mk, obtained an upward trend in elasticity modulus values from 28 to 90 days, especially for 30% Mk substitution, which reached the highest value of 3850 MPa. However, in the present study, the maximum value was achieved with 20% Mk at 28 days, with nearly 5000 MPa of DME, and a decrease from 28 to 90 days occurred, contradicting the results obtained by Ferraz et al. [26]. 3.2.2. Flexural and Compressive Strength The ﬂexural and compressive strength tests performed at 28, 90, and 180 days can be seen in Figures 4 and 5, respectively. Figure 4. Flexural strength of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. It is possible to observe, in maritime and standard curing mortars, that the values of ﬂexural strength increased from 28 to 90 days and decreased from 90 to 180 days. Regarding humid curing, this trend was only seen in the mortar with 10% Mk. Both the maritime and the standard curing seemed beneﬁcial for the reference air lime mortars, particularly after 1 month. However, there was a decrease from 3 to 6 months that did not occur with the humid curing. This curing seemed to delay the initial ﬂexural strength of the reference and 10% Mk mortars. However, for the reference mortar, values drastically increased after 3 months. Mortars with 20% replacement of lime by Mk achieved the highest ﬂexural strength, particularly with the standard curing. Except for the reference mortar with humid curing, where ﬂexural strength increased with age, and the mortar with 20% Mk with humid curing, where it decreased with age, there was always an increase from 1 to 3 months and a decrease for 6 months. Gameiro et al. [19], for 30%, and Andrejkovicov ˇ á et al. [20], for 20% of lime substitution by Mk, also obtained a decrease of ﬂexural strength with age. This was possibly due to mortars’ shrinkage with microcracking and also due to the increase of the water/binder Infrastructures 2021, 6, 143 9 of 18 ratio. However, although there was a decrease in values, mortars with the presence of Mk, speciﬁcally with substitutions of 20% or more, always presented higher values of mechanical strengths over time, compared to reference mortars, which seemed to be induced by the occurrence of a pozzolanic reaction. Figure 5 shows the result obtained for the compressive strength, and the highest values were obtained with the mortars where Mk replaced 20% of lime, for all the cur- ing conditions and ages. However, the decrease with age was much less signiﬁcant for standard curing mortars in comparison to maritime and humid curing mortars. For the reference air lime mortar, the compressive strength increased with time from 1 to 6 months, achieving the highest results with standard curing. With maritime curing, the results at 1 month were higher in comparison to the humid curing. This behaviour was also present in Pavlík & Užáková [27], where these authors obtained a signiﬁcant decrease in compressive strength with the age for mortars of up to 365 days, with a binder:aggregate of 1:1 (vol.) and 50% substitutions of CL by Mk. However, the values obtained for these modiﬁed mortars were much higher than those obtained in reference mortars, showing one more time very signiﬁcant mechanical improvement with Mk substitutions with mortar age. This decrease in mechanical strength can be explained by the fact that lime mortars that were cured in highly humid conditions, with feeble access to CO , had a reduced carbona- tion rate. This uncarbonated lime in mortars that were in humid curing conditions justiﬁes the decrease in compressive strength. The same behaviour was registered by Arizzi & Cultrone [28] in all mortars, with the exception of 10% substitution of lime by Mk, when an increase in compressive strength was obtained from 28 to 180 days. Figure 5. Compressive strength of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. In general, Gameiro et al. [19], Andrejkovicov ˇ á et al. [20], Loureiro et al. [21], Faria & Martins [24] and Faria et al. [25] (Table 1) also obtained an increase of ﬂexu- ral and compressive strength with the increase of the percentage of lime substitution by Mk in all mortars. Nevertheless, Gameiro et al. [19] and Loureiro et al. [21], who performed tests on mortars with different binder:aggregate ratios, obtained a decrease of mechanical strength with the decrease of the binder:aggregate ratio, which could be induced, as in compressive tests, by mortars shrinkage with microcracking and also due to the increase of the water/binder ratio Faria et al. [25], for substitutions of 30 and 50%, concluded that humid curing proved to be unfavorable for mechanical characteristics compared to standard curing, and the same occurred in the present study for 10 and 20%. As in the compressive strength test, Infrastructures 2021, 6, 143 10 of 18 this behaviour could also be explained by the lack of contact with CO , causing a lower carbonation rate. Cardoso et al. [22] concluded that pure lime mortars (CL mortars) have much higher mechanical behaviour than 9% Mk mortars, of nearly more than 80%. In the present study, something similar was found, although in a smaller percentage, with CL and CL_10Mk. It seemed that too low percentages of lime replacement by Mk could have a beneﬁcial effect on the initial hardening period but could lead to mortars with reduced strength, with this behaviour being more visible in the ﬂexural strength tests (Figure 4). Unlike other studies, Ferraz et al. [26] stated that 10–30 wt.% Mk does not promote a signiﬁcant inﬂuence on ﬂexural and compressive strength, especially at 28 days of curing. It is noteworthy that for these authors, reference mortars with 0% Mk had a slight increase with age, but in mortars with Mk, there was also a slight decrease in mechanical characteristics from 90 to 180 days. 3.2.3. Carbonation The qualitative results for the carbonation of all mortars after 90 days of curing are presented in Figure 6. Analyzing the results, it could be concluded that carbonation was much faster for standard curing reference air lime mortar, followed by maritime curing mortars and humid curing mortars. This behaviour was also observed in mortars with 10% and 20% Mk replacing lime. It is feasible to say that in mortars with Mk, the highest carbonation occurred in standard curing and the lowest in humid curing. However, it is likely that pozzolanic reaction may have caused pH changes, which may have masked the results. Figure 6. Carbonation at 90 days of curing in maritime, saturation and standard conditions: (a) reference mortars CL (m), CL (h) and CL (s); (b) mortars CL_10Mk (m), CL_10Mk (h) and CL_10Mk (s); (c) mortars CL_20Mk (m), CL_20Mk (h) and CL_20Mk (s). 3.2.4. Open Porosity and Dry Bulk Density The obtained results for the open porosity of all the mortars after 28, 90 and 180 days of different types of curing are presented in Figure 8. It can be observed that the open porosity increased when Mk was incorporated into the mortars. Humid curing presented the highest average value across all ages, and the standard cure showed the lowest average value at 90 and 180 days. Open porosity also decreased in every mortar from 1 to 6 months, except for CL_10 Mk (m), which kept its value from 1 to 3 months. The mortars where Mk replaced 20% of lime registered the highest values, meaning that the total volume of interconnected pores was higher than the reference mortars (CL) and the mortars where Mk replaces 10% of lime. Loureiro et al. [21] also obtained similar results in the range of 28% for mortars with substitutions of 0% at 90 days. For 25 and 30% of lime substitution by Mk, results in the range of 27–29% were obtained, similar to those in Figure 8. Loureiro et al. [21] obtained the lowest values of porosity in the mortar only with air lime, similar to the results obtained in Figure 8, where CL (s) had the lowest value at 90 days of age. According to the same author, mortars with Mk were more cohesive than the air lime mortars but had a similar microstructure (in terms of void numbers) to the mortars without Mk. Infrastructures 2021, 6, 143 11 of 18 Faria et al. [25], for 25%, 30% and 50% of lime substitution by Mk, obtained results in the same range as those present in Figure 6, with porosity slightly increasing with the increase of Mk. However, Arizzi & Cultrone [28] declared that the pore system of mortars with and without Mk presented similar open porosity values in the range of 31%. Despite the presence of Mk generating a new family of pores, whose volume increases at increasing Mk amounts [42], reference mortars also have a low volume of pores in the same range of the radius [43], translating into minimal differences of porosity. Figure 7 presents the results of dry bulk density obtained in the present study. It was possible to identify a trend, where bulk density increased from 1 to 6 months in all of the analyzed mortars. The reference mortar showed higher values than mortars where Mk replaced 10% and 20% of the binder, as expected, since mortars CL_10Mk and CL_20Mk (regardless of the curing) obtained higher values in the open porosity test. The variation in porosity and bulk density does not explain the different mechanical results obtained for the tested mortars. Figure 7. Dry bulk density of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. Figure 8. Open porosity of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. Infrastructures 2021, 6, 143 12 of 18 3.2.5. Capillary Water Absorption The average capillarity curves of mortars at 28, 90 and 180 days of curing can be seen in Figure 9. At 28 days, both the maritime and standard curing for the CL mortar presented an increase in the initial rate, but in the total absorbed water absorption, they stabilized at lower values. Mortars with 20% replacement of lime by Mk, concretely CL_20 Mk (m) and CL_20 Mk (h), exhibited the opposite behaviour, presenting a slower absorption rate in the initial phase, but they stabilized at higher values of the total absorbed water. At 90 days and 180 days, it was also visible that mortars where Mk replaced 10% and 20% of the lime had a slower absorption in the ﬁrst phase, compared to the reference mortars (CL), and they also presented higher values of the total absorbed water. It was also veriﬁed in all ages that the mortars submitted to humid curing had an increase in the initial rate and lower values of the total absorbed water, compared to maritime and standard curing. As can be seen in Table 5, with the introduction of Mk, a decrease in the initial rate existed, shown by the capillarity coefﬁcient (CC), and so did an increase in the total absorbed water, shown by the Capillary saturation value (Cs). At 28 days, the reference mortars (CL) represented the worst cases of the capillarity coefﬁcient, due to the faster ratio of water absorption. At 90 and 180 days, an increase of the CC was visible in humid curing compared to the others. Higher asymptotic values were achieved in CL_10Mk (m) and CL_20Mk (m) at 90 days. Figure 9. The Capillary curves of mortars with 0, 10 and 20% Mk replacing air lime, after (a) 28 days; (b) 90 days; (c) 180 days in maritime, humid and standard curing conditions. Infrastructures 2021, 6, 143 13 of 18 Table 5. Capillary saturation value (Cs) and capillary coefﬁcient (CC) of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. 2 2 0.5 Cs (kg/m ) CC (kg/(m min )) Mortar (Curing) 28 Days 90 Days 180 Days 28 Days 90 Days 180 Days CL (m) 20.4 19.7 20.3 4.5 4.7 4.4 CL_10Mk (m) 23.4 23.7 24.2 3.6 4.2 4.4 CL_20Mk (m) 24.0 24.4 23.7 3.2 3.4 3.4 CL (h) 20.2 20.6 20.4 3.8 4.5 4.1 CL_10Mk (h) 23.7 22.6 23.6 3.6 3.8 3.8 CL_20Mk (h) 23.6 23.1 24.2 3.1 3.1 3.2 CL (s) 20.3 19.8 20.1 4.6 4.4 4.0 CL_10Mk (s) 21.6 23.0 22.6 4.0 4.0 4.0 CL_20Mk (s) 22.4 22.2 23.1 3.5 3.3 3.1 In general, similar results of Cs were obtained by Faria et al. [25] and Faria & Mar- tins [24], where the total absorbed water was higher for air lime mortars with Mk, and the capillary coefﬁcient was lower when Mk partially substituted the lime. With the exception of mortars with 20% substitution of lime by Mk and in conditions of humid curing, Faria & Martins [24] obtained a decrease of total capillary water absorption when Mk was used, contradicting the results presented in Table 5, for CL_20Mk (h). However, Faria & Mar- tins [24] and Faria et al. [25] presented lower values for CC, revealing slower absorption rates in the initial phase of drying. 3.2.6. Drying Is important to know how mortars lose the water that they have absorbed to better understand their future performance in terms of durability. A high drying capacity can improve a mortar ’s durability, avoid the appearance of fungi [44] and contribute to salts’ transport to the surface. The drying curves of phase 1 and phase 2 at 28, 90 and 180 days, are presented in Figure 10. Through the linear segments of the curves by time and by square root of time, it was possible to determine the ﬁrst drying rate (D1) and the second drying rate (D2), respectively, as shown in Table 6. D1 is normally associated with the release of water, in the ﬁrst drying stage, and D2 is related with the release of vapor in a more advanced drying phase. At 28 days, maritime curing seemed to induce mortars to have the highest drying rates of the 1st phase (D1), meaning an increase in the release of water, in comparison to humid and standard curing conditions. D2 seemed to increase with the addition of Mk at this early age. As an absolute value, the highest ratios of D2 were observed in CL_10Mk(h) and CL_10Mk(s), meaning an increase in the evaporation rate due to improved diffusion. However, mortars with 10% substitution showed inconstant results over time. Loureiro et al. [21], analyzing the drying rates of mortars with the same binder:aggregate ratio and 25% substitution of air lime by Mk (Table 1), achieved very different results when compared to those obtained in Table 6. According to the same author, mortars with a low binder content show a shorter D2, because that content may have favored the formation of larger pores, which results in a great loss of moisture during phase D1. 3.3. Application for New Construction and for Rehabilitation and Conservation Purposes According to the European standard for mineral binder renders and plasters, EN 998-1 [45], mortar CL_20Mk (s) may be classiﬁed as CS II, having a compressive strength between 1.5–5.0 N/mm at 28 days. Although air lime-based renders and plasters may not be adequate for cement-based walls, they are clearly adequate for eco-efﬁcient walls, such as contemporaneous rammed earth, cob, wattle and daub, earth blocks ma- sonry and straw bale masonry. To develop more sustainable mortars with properties that are compatible with the rehabilitation of old buildings, it is important to compare them with studies that present the characteristics that mortars must have for rehabilitation. Infrastructures 2021, 6, 143 14 of 18 Veiga et al. [1] recommend a range of values for mortars for old buildings at 90 days. The CL_20Mk (s) mortar presented results in the ranges adequate to be used as plastering and rendering mortars and as repointing mortars: ﬂexural strength of 0.2–0.7 N/mm for renders and plasters and 0.4–0.8 N/mm for repointing; compressive strength of 2 2 0.4–2.5 N/mm for renders/plasters and 0.6–3.0 N/mm for repointing; the dynamic mod- 2 2 ulus of elasticity of 2000–5000 N/mm for renders/plasters and 3000–6000 N/mm for repointing. However, the capillarity coefﬁcient (CC) was not within the recommended limits. To lower the CC value, the sand mixture should probably have an increase of ﬁner sand (APAS 30) or the introduction of a compatible hydrophobic admixture [46,47]. Figure 10. Drying curves of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions: (a–c) by time, showing the initial slope of drying phase 1 at each age; (d–f) by square root of time, showing the intermediate slope of drying phase 2 at each age. Infrastructures 2021, 6, 143 15 of 18 Table 6. Values of drying rates for the ﬁrst (D1) and second (D2) drying phases of mortars with 0, 10 and 20% Mk replacing air lime, after 28, 90 and 180 days in maritime, humid and standard curing conditions. Drying Rate, 1st Phase (D1) Drying Rate, 2nd Phase (D2) 2 2 0.5 Mortar (Curing) (kg/m h) (kg/m h ) 28 Days 90 Days 180 Days 28 Days 90 Days 180 Days CL (m) 0.144 0.162 0.178 1.710 1.335 1.326 CL_10Mk (m) 0.163 0.166 0.176 1.472 1.534 1.639 CL_20Mk (m) 0.138 0.193 0.173 1.822 1.695 1.473 CL (h) 0.123 0.183 0.112 1.075 1.736 1.374 CL_10Mk (h) 0.124 0.147 0.133 1.779 1.642 2.080 CL_20Mk (h) 0.116 0.141 0.183 1.910 1.840 1.606 CL (s) 0.098 0.167 0.143 1.033 1.399 1.262 Infrastructures 2021, 6, x FOR PEER REVIEW CL_10Mk (s) 0.113 0.176 0.112 1.759 1.960 2.066 16 of 18 CL_20Mk (s) 0.095 0.184 0.143 1.805 1.474 1.759 4. Conclusions This paper aimed to contribute to the existing knowledge on air lime mortars with a volumetric binder:aggregate ratio of 1:2, considering the effects of substitutions of lime by This paper aimed to contribute to the existing knowledge on air lime mortars with a Infrastructures 2021, 6, x FOR PEER REVIEW 16 of 18 metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions volumetric binder:aggregate ratio of 1:2, considering the effects of substitutions of lime by (maritime, humid and standard) for up to 180 days of age. The objective was to assess the metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions effect that (maritime, humid lime replacem and standar ent by these d) for up perc to 180entage days of s of Mk age. The may objective have on the morta was to assess the r’s Infrastructures 2021, 6, x FOR PEER REVIEW 16 of 18 This paper aimed to contribute to the existing knowledge on air lime mortars with a performance and future durability at these young ages and to assess if the different tested effect that lime replacement by these percentages of Mk may have on the mortar ’s perfor- volumetric binder:aggregate ratio of 1:2, considering the effects of substitutions of lime by curin mance g condit and futur ions c e durability an signific atant these ly inf young luence t ages he res andu to lts. The fo assess if llow the dif ing conc ferent tested lusions were curing Infrastructures 2021, 6, x FOR PEER REVIEW 16 of 18 metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions obtained: conditions can signiﬁcantly inﬂuence the results. The following conclusions were obtained: This paper aimed to contribute to the existing knowledge on air lime mortars with a (maritime, humid and standard) for up to 180 days of age. The objective was to assess the  AsAs the rep the replacement lacement level in level in air lime airmortars lime mortars increased, incre compr asedessive , compre andssive ﬂexural andstr fle engths xural vol effect that umetric blime replacem inder:aggregate ra ent by these tio of 1:2, perc consientage dering t s of Mk he effects of may ha subsve on the morta titutions of lime by r’s also increased. However, the 10% substitution (CL_10Mk) proved not to be optimized and strengths also increased. However, the 10% substitution (CL_10Mk) proved not to be metaThi kaoslin pa(per Mk) ai in perce med to contribute to the exi ntages of 10% and 20% sting know , subjecte ledge on d to diffe air rent lime mortars curing condit with a ions performance and future durability at these young ages and to assess if the different tested revealed optimized inconsistent and revea results. led in The consist lackent of res consistency ults. The in lacthe k of consi resultssmeant tency in t that, he res in most ults vol (mar umetri itime, h c bu inder:a mid an ggregate ra d standard ti ) fo o of r up 1:2, to consi 180 d der ay ing t s of h age. e effects of The obje subs ctivti e was t tutions of o asses lime by s the curing conditions can significantly influence the results. The following conclusions were cases, the properties of these mortars were worse than the reference ones (CL), which may meant that, in most cases, the properties of these mortars were worse than the Infrastructures 2021, 6, x FOR PEER REVIEW 16 of 18 metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions effect that lime replacement by these percentages of Mk may have on the mortar’s obtained: justify further investigation. reference ones (CL), which may justify further investigation. (maritime, humid and standard) for up to 180 days of age. The objective was to assess the performance and future durability at these young ages and to assess if the different tested From the studied percentages, it could be concluded that in air lime mortars with propor-  As the replacement level in air lime mortars increased, compressive and flexural  From the studied percentages, it could be concluded that in air lime mortars with effect that lime replacement by these percentages of Mk may have on the mortar’s curing conditions can significantly influence the results. The following conclusions were tions strengths of 1:2 (vol.), alsoonly incre replacements ased. However, the of 20% of 10% lime substi by Mk tution ( effectively CL_10Mk) impr proved not t oved the overall o be proportions of 1:2 (vol.), only replacements of 20% of lime by Mk effectively improved This paper aimed to contribute to the existing knowledge on air lime mortars with a performanc obtained: e and future durability at these young ages and to assess if the different tested behaviour. optimized and revealed inconsistent results. The lack of consistency in the results the overall behaviour. volumetric binder:aggregate ratio of 1:2, considering the effects of substitutions of lime by curing conditions can significantly influence the results. The following conclusions were  Standar As the rep d curing lacement level in at (65 5)% RHair had lime a positive mortars inﬂuence increased on,mechanical compressive str and ength fle param- xural meant that, in most cases, the properties of these mortars were worse than the Infrastructures 2021, 6, x FOR PEER REVI  EW St andard curing at (65 ± 5)% RH had a positive influence on mechanical stre 16 of ngt 18 h metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions obtained: eters strengths but a negative also incre inﬂuence ased. H on owever, the water behaviour 10% substi . tution (CL_10Mk) proved not to be reference ones (CL), which may justify further investigation. parameters but a negative influence on water behaviour. (maritime, humid and standard) for up to 180 days of age. The objective was to assess the  Humid As the rep curing,lacement level in close to saturated air RH, lime showed mortars a negative increa inﬂuence sed, compre in mechanical ssive and fle strength xural optimized and revealed inconsistent results. The lack of consistency in the results  From the studied percentages, it could be concluded that in air lime mortars with  Humid curing, close to saturated RH, showed a negative influence in mechanical effect that lime replacement by these percentages of Mk may have on the mortar’s tests, strengths mainly durinb also incre the ase initial d. Hoages wever, the of some 10% mortars, substitution ( but it C had L_10 superior Mk) proved not t performance o be proportions o meant that, in most ca f 1:2 (vol.), on ses, the properti ly replacements es of of 20% o these f lime by morta Mk rs were worse tha effectively imprn oved the strength tests, mainly durinb the initial ages of some mortars, but it had superior This paper aimed to contribute to the existing knowledge on air lime mortars with a performance and future durability at these young ages and to assess if the different tested related to water. This could be due to the hydration between calcium hydroxide and the optimized and revealed inconsistent results. The lack of consistency in the results referenc the overall be e ones havio (CL)u , wh r. ich may justify further investigation. performance related to water. This could be due to the hydration between calcium volumetric binder:aggregate ratio of 1:2, considering the effects of substitutions of lime by curing conditions can significantly influence the results. The following conclusions were Mk silicates, which is slow, competing with the carbonation of the calcium hydroxide itself,  From t meant tha he st t, in most ca udied percent ses, the properti ages, it could be conclu es of these ded t morta hat in rs were worse tha air lime mortarsn wit the h  Standard curing at (65 ± 5)% RH had a positive influence on mechanical strength hydroxide and the Mk silicates, which is slow, competing with the carbonation of the metakaolin (Mk) in percentages of 10% and 20%, subjected to different curing conditions obtained: which may be blocked by water layers at the mortar surface. proportions o reference ones f (CL 1:2 (vol.), on ), which may ly replacements justify further inve of 20% ostigation. f lime by Mk effectively improved parameters but a negative influence on water behaviour. calcium hydroxide itself, which may be blocked by water layers at the mortar surface. (maritime, humid and standard) for up to 180 days of age. The objective was to assess the  Curing As the rep by thelAtlantic acement level in Ocean, with airsalts lime contamination, mortars increa had seda, compre negativessive impact and on fle longer xural -  From the studied percentages, it could be concluded that in air lime mortars with the overall behaviour.  Humid curing, close to saturated RH, showed a negative influence in mechanical  Curing by the Atlantic Ocean, with salts contamination, had a negative impact on effect that lime replacement by these percentages of Mk may have on the mortar’s term mechanical strength values (tested up to 180 days) and a negative effect on water strengths also increased. However, the 10% substitution (CL_10Mk) proved not to be proportions of 1:2 (vol.), only replacements of 20% of lime by Mk effectively improved  Standard curing at (65 ± 5)% RH had a positive influence on mechanical strength strength tests, mainly durinb the initial ages of some mortars, but it had superior longer-term mechanical strength values (tested up to 180 days) and a negative effect performance and future durability at these young ages and to assess if the different tested behaviour, especially on drying. However, it will be important to continue assessing the optimized and revealed inconsistent results. The lack of consistency in the results the overall behaviour. perf paraorma meters b nce u rela t a nega ted to water. Thi tive influence on s could be due to the hydra water behaviour. tion between calcium on water behaviour, especially on drying. However, it will be important to continue curing conditions can significantly influence the results. The following conclusions were mortar ’s performance after further ageing and, if possible, on experimental rendered panels meant that, in most cases, the properties of these mortars were worse than the  Humi Standa d curi rd cur ng, cl ing at ose to satura (65 ± 5)% RH ted h RaH d, a showed a positive nega influence tive ion nfl uence i mechanic n mechani al strengt cal h hydroxide and the Mk silicates, which is slow, competing with the carbonation of the assessing the mortar’s performance after further ageing and, if possible, on obtained: and case studies. reference ones (CL), which may justify further investigation. st parengt rameters b h tests u, ma t a nega inly d tive uri in nb t fluence on he initiawater beh l ages of a som viour. e mort ars, but it had superior calcium hydroxide itself, which may be blocked by water layers at the mortar surface. experimental rendered panels and case studies.  From As the rep the present lacement level in study and in comparison air lime mortars with results incre fraom sed,literatur compre e,ssive mortars andwith flexural 20%  From the studied percentages, it could be concluded that in air lime mortars with  perf Humi orma d curi nce ng, cl related to water. Thi ose to saturated sR could be due to the hydra H, showed a negative infl tiuence i on between ca n mechani lcium cal  Curing by the Atlantic Ocean, with salts contamination, had a negative impact on  From the present study and in comparison with results from literature, mortars with Mk seem promising and should be further studied. strengths also increased. However, the 10% substitution (CL_10Mk) proved not to be proportions of 1:2 (vol.), only replacements of 20% of lime by Mk effectively improved strength tests, mainly durinb the initial ages of some mortars, but it had superior hydroxide and the Mk silicates, which is slow, competing with the carbonation of the longer-term mechanical strength values (tested up to 180 days) and a negative effect 20% Mk seem promising and should be further studied. optimized and revealed inconsistent results. The lack of consistency in the results the overall behaviour. perf Theorma Mk nce used rela was ted to water. Thi a commercial one, s could be due to the hydra and the production process tion between ca was not known. lcium on wat calcium e hydr r behoxide aviour, e itseslf, pec wih ally ich m on dry ay be in bg locked . However by w , i at t will be er layers import at the mort ant to ar cont surf inue ace. The Mk used was a commercial one, and the production process was not known. meant that, in most cases, the properties of these mortars were worse than the  However Stand,athe rd cur ﬁring ing at of the (65kaolins ± 5)% RH to prh oduce ad a p Mk ositdoes ive in not fluence surpass on the mechanic ﬁringa of l st air rengt lime h hydroxide and the Mk silicates, which is slow, competing with the carbonation of the  ass Curing by th essing the m e Atlantic Oc ortar’s pean, w erformiath salt nce aft s e contamin r furtheation, had r ageing an a negative impact d, if possible, on on However, the firing of the kaolins to produce Mk does not surpass the firing of air lime reference ones (CL), which may justify further investigation. parameters but a negative influence on water behaviour. (maximum 900 C) and may even be reduced by up to 50% (to 600 C). Furthermore, longer calcium -t hydr erm m oxide echanic itseal lf,st w rengt hich m h v aa y be lues b (t locked ested up by w toa 18 ter l 0 d aye ayrs s) at an td a neg he mort aar tiv su e rf effect ace. experimental rendered panels and case studies. (maximum 900 °C) and may even be reduced by up to 50% (to 600 °C). Furthermore, the  From the studied percentages, it could be concluded that in air lime mortars with  the kaol Humi ins d curi usedng, cl could ose to satura be residuested from RHother , showed a industries, negati such ve in as fluence i from washed n mechani sands. cal  on wat Curing by th er beha e Atlantic Oc viour, especiean, w ally on dry ith salt ings . However contamination, had , it will be import a negative impact ant to continue on  From the present study and in comparison with results from literature, mortars with kaolins used could be residues from other industries, such as from washed sands. proportions of 1:2 (vol.), only replacements of 20% of lime by Mk effectively improved Therst efor rengt e, the h te technical sts, mainl characteristics y durinb the in of it air iallime–Mk ages of mortars some mort may ars, b be associated ut it had s with uperior the longer-term mechanical strength values (tested up to 180 days) and a negative effect assessing the mortar’s performance after further ageing and, if possible, on 20% Mk seem promising and should be further studied. Therefore, the technical characteristics of air lime–Mk mortars may be associated with the ecological the overall be aspect havio of formulation ur. mortars with less embodied energy. Hence, there may performance related to water. This could be due to the hydration between calcium on water behaviour, especially on drying. However, it will be important to continue experimental rendered panels and case studies. The Mk used was a commercial one, and the production process was not known. ecological aspect of formulation mortars with less embodied energy. Hence, there may be  Standard curing at (65 ± 5)% RH had a positive influence on mechanical strength hydroxide and the Mk silicates, which is slow, competing with the carbonation of the assessing the mortar’s performance after further ageing and, if possible, on  From the present study and in comparison with results from literature, mortars with However, the firing of the kaolins to produce Mk does not surpass the firing of air lime ecological advantages of using air lime–Mk mortars, not only in the rehabilitation of parameters but a negative influence on water behaviour. calcium hydroxide itself, which may be blocked by water layers at the mortar surface. 20% experimental rendered Mk seem promising pan aned shou ls and ld be case studies. further studied. (maximum 900 °C) and may even be reduced by up to 50% (to 600 °C). Furthermore, the heritage buildings, but also as rendering and plastering mortars for new buildings.  Humid curing, close to saturated RH, showed a negative influence in mechanical  Curing by the Atlantic Ocean, with salts contamination, had a negative impact on  From the present study and in comparison with results from literature, mortars with The Mk used was a commercial one, and the production process was not known. kaolins used could be residues from other industries, such as from washed sands. In future work, it will be interesting to assess the effect of highly polluted strength tests, mainly durinb the initial ages of some mortars, but it had superior longer-term mechanical strength values (tested up to 180 days) and a negative effect 20% Mk seem promising and should be further studied. However, the firing of the kaolins to produce Mk does not surpass the firing of air lime Therefore, the technical characteristics of air lime–Mk mortars may be associated with the environments, namely with contact with SO2. performance related to water. This could be due to the hydration between calcium on water behaviour, especially on drying. However, it will be important to continue The Mk used was a commercial one, and the production process was not known. (maximum 900 °C) and may even be reduced by up to 50% (to 600 °C). Furthermore, the ecological aspect of formulation mortars with less embodied energy. Hence, there may be hydroxide and the Mk silicates, which is slow, competing with the carbonation of the assessing the mortar’s performance after further ageing and, if possible, on However, the firing of the kaolins to produce Mk does not surpass the firing of air lime ecolog kao Autho lins used rica Colntributio ad could be vantage ns: Conc s ofre eptual usin sidug es izati air from o l n, im Pe .F. other –M ; method k m ind ort ology, uastr rs, not ies, P. s F. on ; vali uch ly dati as inon t from w h , J.M e reh .; formal analysis, aashed bilita san tion o ds.f calcium hydroxide itself, which may be blocked by water layers at the mortar surface. experimental rendered panels and case studies. J.M.; investigation, J.M. and V.S.; resources, P.F.; data curation, J.M. and V.S.; writing—original draft (maximum 900 °C) and may even be reduced by up to 50% (to 600 °C). Furthermore, the herit Therefore age b,u til hdings e technica , but l ch also ar as act rende eristics o ring an f air l d p im last e–Mk ering m mort o ars m rtars fo ay r new b be assoc uiil at din ed g wit s. h the  Curing by the Atlantic Ocean, with salts contamination, had a negative impact on  From the present study and in comparison with results from literature, mortars with preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project ecological kaolins used aspect of form could be ulat resid ion ues mortar from s with other less em industr bodied en ies, such erg as y. Henc from w e, ther ashed e may sand be s. In future work, it will be interesting to assess the effect of highly polluted longer-term mechanical strength values (tested up to 180 days) and a negative effect 20% Mk seem promising and should be further studied. administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published ecolog Therefore ical, tad he t va ent chnica ages o l ch f usin aractg erist air l ics o ime f a –M ir lk m imeo –Mk rtars, not mortars m onlya i y nb t eh assoc e reh ia atbed ilitwit ation o h the f environments, namely with contact with SO2. on water behaviour, especially on drying. However, it will be important to continue version of the manuscript. The Mk used was a commercial one, and the production process was not known. ecological aspect of formulation mortars with less embodied energy. Hence, there may be heritage buildings, but also as rendering and plastering mortars for new buildings. assessing the mortar’s performance after further ageing and, if possible, on However, the firing of the kaolins to produce Mk does not surpass the firing of air lime ecolog Authorica Colntributio advantage ns: Conc s of eptual using izati airo l n, im Pe .F. –M ; method k mort ology, ars, not P.F. on ; valily dati inon th , J.M e reh .; formal analysis, abilitation of FundIn future ing: This research was work, it w funded by ill be interestin national fug nds from to assess the Portu the ef gufeese F ct of hi oundation f ghly pollute or Sciencd e experimental rendered panels and case studies. J.M.; investigation, J.M. and V.S.; resources, P.F.; data curation, J.M. and V.S.; writing—original draft ( and Technolog maximum 90y 0 °C by su ) apporting nd may the Civil even be reduced by Engineering Research and Innovation for Su up to 50% (to 600 °C). Furthermore, the stainability heritage buildings, but also as rendering and plastering mortars for new buildings. environments, namely with contact with SO2.  From the present study and in comparison with results from literature, mortars with preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project Unit—CERIS (project UIDB/04625/2020). kaolins used could be residues from other industries, such as from washed sands. In future work, it will be interesting to assess the effect of highly polluted 20% Mk seem promising and should be further studied. administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published Therefore Author Contributio , the technica ns: Conc l ch eptual aracte izati risto ics o n, P.fF. a;i method r lime–Mk ology, m P ort .Fars m .; validati ay on be, assoc J.M.; formal analysis, iated with the environments, namely with contact with SO2. Institutional Review Board Statement: Not applicable. version of the manuscript. J.M.; inv The Mk estigat ion, J used .M. was and V. a comm S.; resou ercial one, rces, P.F.; data and the pro curation, J.M duc.tion process and V.S.; writing was not kno —original draft wn. ecological aspect of formulation mortars with less embodied energy. Hence, there may be Informed Consent Statement: Not applicable. preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project However, the fi Author Contributio ring of ns: Conc the eptual kaoli izati ns to produce on, P.F.; method Mkology, does not P.F.; vali surp dati ass the on, J.M firing .; formal analysis, of air lime ecolog Funding: ica This l adresearch was vantages of f usin unded by g air natio lime n–M al fu k m nds from ortars, not the Portu ong ly u i ese F n th oe reh undation f abiliota r Scien tion o ce f administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published ( J.M. ma; inv xime um stig90 ation, J 0 °C.) M. an and V. d maS.; y even be reduced by resources, P.F.; data cuup ratio to 50 n, J.M % . and (to 600 V.S .°C) ; writing . Furthermore, the —original draft and Technology by supporting the Civil Engineering Research and Innovation for Sustainability herit Data Availa age bubil ildings ity Statement: , but alsoThe data as rende that rin support the findings of g and plastering mort this study are a ars for new bv uailab ildin le from the gs. version of the manuscript. preparation, r Unit—CERIS (p eview roject UIDB/0 and editing, J.M 4625/2020). . and P.F.; visualization, J.M.; supervision, P.F.; project kaolins used could be residues from other industries, such as from washed sands. corresponding author upon reasonable request. In future work, it will be interesting to assess the effect of highly polluted administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published Therefore, the technical characteristics of air lime–Mk mortars may be associated with the envi Fundronments, na ing: This research was mely wi f th conta unded by ct wi natio th nSO al fu 2. nds from the Portuguese Foundation for Science Institutional Review Board Statement: Not applicable. version of the manuscript. ecological and Technolog aspect of form y by supporting ulat the Civil ion mortar Eng s with ineerless em ing Research and Innovation for Su bodied energy. Hence, ther ste may ainability be Informed Consent Statement: Not applicable. Unit—CERIS (project UIDB/04625/2020). Author Contributions: Conceptualization, P.F.; methodology, P.F.; validation, J.M.; formal analysis, ecolog Funding: ica This l adresearch was vantages of f usin unded by g air natio lime n–M al fu k m nds from ortars, not the Portu ong ly u i ese F n th oe reh undation f abiliota r Scien tion o ce f J.M.; investigation, J.M. and V.S.; resources, P.F.; data curation, J.M. and V.S.; writing—original draft and Technology by supporting the Civil Engineering Research and Innovation for Sustainability herit Data Availa age bubil ildings ity Statement: , but alsoThe data as rende that rin support the findings of g and plastering mort this study are a ars for new bv uailab ildin le from the gs. Institutional Review Board Statement: Not applicable. preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project Unit—CERIS (project UIDB/04625/2020). corresponding author In future work, it w upon reasonable reque ill be interestin st. g to assess the effect of highly polluted Informed Consent Statement: Not applicable. administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published environments, namely with contact with SO2. Institutional Review Board Statement: Not applicable. version of the manuscript. Data Availability Statement: The data that support the findings of this study are available from the Informed Consent Statement: Not applicable. Autho corresponding author r Contributionsupon : Conc re eptual asonable reque ization, P.F. st. ; methodology, P.F.; validation, J.M.; formal analysis, Funding: This research was funded by national funds from the Portuguese Foundation for Science J.M. and Technolog ; investigation, J y by su .M.pporting and V.S.; the Civil resourcesEng , P.Fi.; neer data ing cu Research and Innovation for Su ration, J.M. and V.S.; writing—orig stainability inal draft Data Availability Statement: The data that support the findings of this study are available from the preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project Unit—CERIS (project UIDB/04625/2020). corresponding author upon reasonable request. administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published Institutional Review Board Statement: Not applicable. version of the manuscript. Informed Consent Statement: Not applicable. Funding: This research was funded by national funds from the Portuguese Foundation for Science and Technology by supporting the Civil Engineering Research and Innovation for Sustainability Data Availability Statement: The data that support the findings of this study are available from the Unit—CERIS (project UIDB/04625/2020). corresponding author upon reasonable request. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request. Infrastructures 2021, 6, 143 16 of 18 be ecological advantages of using air lime–Mk mortars, not only in the rehabilitation of heritage buildings, but also as rendering and plastering mortars for new buildings. In future work, it will be interesting to assess the effect of highly polluted environ- ments, namely with contact with SO . Author Contributions: Conceptualization, P.F.; methodology, P.F.; validation, J.M.; formal analysis, J.M.; investigation, J.M. and V.S.; resources, P.F.; data curation, J.M. and V.S.; writing—original draft preparation, review and editing, J.M. and P.F.; visualization, J.M.; supervision, P.F.; project administration, P.F.; funding acquisition, P.F. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by national funds from the Portuguese Foundation for Science and Technology by supporting the Civil Engineering Research and Innovation for Sustainability Unit—CERIS (project UIDB/04625/2020). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data that support the ﬁndings of this study are available from the corresponding author upon reasonable request. Acknowledgments: Acknowledgements are due to Duarte Vargas for the mortar testing campaign. Conﬂicts of Interest: The authors declare no conﬂict of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript or in the decision to publish the results. References 1. Veiga, M.D.R.; Fragata, A.; Velosa, A.; Magalhães, A.C.; Margalha, G. Lime-Based Mortars: Viability for Use as Substitution Renders in Historical Buildings. Int. J. Arch. Herit. 2010, 4, 177–195. [CrossRef] 2. Veiga, R. Air lime mortars: What else do we need to know to apply them in conservation and rehabilitation interventions? A review. Constr. Build. Mater. 2017, 157, 132–140. [CrossRef] 3. Botas, S.; Veiga, R.; Velosa, A.; Silva, A.S. Compatible Air Lime Mortars for Historical Tiled Facades: Bond and Mechanical Strength versus Tile–Mortar Interface Microstructure. J. Mater. Civ. Eng. 2020, 32, 04020112. [CrossRef] 4. da Fonseca, B.S.; Pinto, A.F.; Silva, D.V. 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Lime mortars with ceramic wastes: Characterization of components and their inﬂuence on the mechanical behaviour. Constr. Build. Mater. 2014, 73, 523–534. [CrossRef] 14. Mansour, M.S.; Kadri, E.-H.; Kenai, S.; Ghrici, M.; Bennaceur, R. Inﬂuence of calcined kaolin on mortar properties. Constr. Build. Mater. 2010, 25, 2275–2282. [CrossRef] 15. Borsoi, G.; Silva, A.S.; Menezes, P.; Candeias, A.; Mirão, J. Analytical characterization of ancient mortars from the archaeological roman site of Pisões (Beja, Portugal). Constr. Build. Mater. 2019, 204, 597–608. [CrossRef] Infrastructures 2021, 6, 143 17 of 18 16. Alvarez, J.I.; Veiga, R.; Martínez-Ramírez, S.; Secco, M.; Faria, P.; Maravelaki, P.N.; Ramesh, M.; Papayianni, I.; Válek, J. RILEM TC 277-LHS report: A review on the mechanisms of setting and hardening of lime-based binding systems. Mater. Struct. 2021, 54, 1–30. [CrossRef] 17. Elavarasan, S.; Priya, A.; Ajai, N.; Akash, S.; Annie, T.; Bhuvana, G. Experimental study on partial replacement of cement by metakaolin and GGBS. Mater. Today: Proc. 2020, 37, 3527–3530. [CrossRef] 18. Raheem, A.; Abdulwahab, R.; Kareem, M. Incorporation of metakaolin and nanosilica in blended cement mortar and concrete—A review. J. Clean. Prod. 2021, 290, 125852. [CrossRef] 19. Gameiro, A.; Silva, A.S.; Faria, P.; Grilo, J.; Branco, T.; Veiga, R.; Velosa, A. Physical and chemical assessment of lime–metakaolin mortars: Inﬂuence of binder:aggregate ratio. Cem. Concr. Compos. 2014, 45, 264–271. [CrossRef] 20. Andrejkovicov ˇ á, S.; Velosa, A.L.; Rocha, F. Air lime–metakaolin–sepiolite mortars for earth based walls. Constr. Build. Mater. 2013, 44, 133–141. [CrossRef] 21. Loureiro, A.; Paz, S.P.A.; Veiga, M.D.R.; Angélica, R.S. Assessment of compatibility between historic mortars and lime- METAKAOLIN restoration mortars made from amazon industrial waste. Appl. Clay Sci. 2020, 198, 105843. [CrossRef] 22. Cardoso, D.; Gameiro, A.; Silva, A.S.; Faria, P.; Vieira, R.; Veiga, R.; Velosa, A. Inﬂuence of curing conditions in lime-metakaolin blended mortars—A mineralogical and mechanical study. In Proceedings of the HMC2013—Historic Mortars Conference, University of West Scotland, Glasgow, UK, 11–13 September 2013. 23. Faria, P. Resistance to salts of lime and pozzolan mortars. In RILEM Proceedings pro067—International RILEM Workshop on Repair Mortars for Historic Masonry; Groot, C., Ed.; RILEM Publications: Paris, France, 2009; pp. 99–110. 24. Faria, P.; Martins, A. Inﬂuence of air lime type and curing conditions on lime and lime-metakaolin mortars. In Durability of Building Materials and Components Building Pathology and Rehabilitation; de Freitas, V.P., Delgado, J.M.P.Q., Eds.; Springer: Berlin Heidelberg, 2013; Volume 3, pp. 105–126. [CrossRef] 25. Faria, P.; Branco, T.; Carneiro, J.; Veiga, R.; Santos Silva, A. Argamassas com base em cal para a reabilitação de rebocos. In Proceedings of the 4º Congreso de Patología y Rehabilitación de Ediﬁcios. PATORREB 2012 Grupo, Santiago de Compostela, Spain, 12–14 April 2012. CD-ROM. 26. Ferraz, E.; Andrejkovicov ˇ á, S.; Velosa, A.L.; Silva, A.S.; Rocha, F. Synthetic zeolite pellets incorporated to air lime–metakaolin mortars: Mechanical properties. Constr. Build. Mater. 2014, 69, 243–252. [CrossRef] 27. Pavlík, V.; Užáková, M. Effect of curing conditions on the properties of lime, lime–metakaolin and lime–zeolite mortars. Constr. Build. Mater. 2016, 102, 14–25. [CrossRef] 28. Arizzi, A.; Cultrone, G. Comparing the pozzolanic activity of aerial lime mortars made with metakaolin and ﬂuid catalytic cracking catalyst residue: A petrographic and physical-mechanical study. Constr. Build. Mater. 2018, 184, 382–390. [CrossRef] 29. CEN. EN 459-1:2015. Building lime. Part 1: Deﬁnitions, Speciﬁcations and Conformity Criteria; CEN: Brussels, Belgium, 2015. 30. CEN. EN 1097-3:1998. 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Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

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ISSN: 2412-3811
DOI: 10.3390/infrastructures6100143
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Abstract

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Infrastructures – Multidisciplinary Digital Publishing Institute

Published: Oct 8, 2021

Keywords: mortars; hydrated air lime; metakaolin; curing conditions; maritime natural exposure; performance; ageing; masonries durability

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Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

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Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

Effect of Type of Curing and Metakaolin Replacement on Air Lime Mortars for the Durability of Masonries

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