Lime-based Mortars Research Articles

Recycled Aggregates Influence on the Mechanical Properties of Cement Lime-Based Mortars

The current framework for managing construction waste, guided by European Union regulations, calls for an integrated waste management system. However, the reuse of old plaster waste, particularly from deteriorated facades, remains underexplored. This study investigates the potential of repurposing old plaster waste as a substitute for aggregates and cement in mortars, with the aim of promoting environmental sustainability and resource efficiency. Three mortar mixes were analyzed: a control mix, a mix with 45% waste replacing aggregates, and a mix with 10% waste replacing cement. Results show that replacing 45% of aggregates with plaster waste led to a 30% reduction in flexural strength, while the 10% cement replacement increased flexural strength by 6%. Compressive strength dropped by 27% and 38% for cement and aggregate replacements, respectively. Despite these reductions, the waste replacement remained within acceptable limits for structural integrity. Further microscopic analysis revealed that the incomplete integration of portlandite particles from the waste contributed to non-uniform bonding and crystal formation, weakening the mortar’s structure. This research demonstrates the feasibility of reusing old plaster waste, offering a novel approach to reducing construction waste and promoting a circular economy. It contributes to filling the knowledge gap on the reuse of plaster mortars while aligning with sustainable construction goals.

Second Life for Recycled Concrete and Other Construction and Demolition Waste in Mortars for Masonry: Full Scope of Material Properties, Performance, and Environmental Aspects

This review presents the scope of current efforts to utilize recycled construction and demolition waste in mortars for masonry. More than 100 articles are divided into groups pertaining to the type of mortar, different binder systems, the type of construction and demolition waste (CDW), and its utilization specifics. Cement-based mortars dominate this research domain, whereas recycled concrete is the main material employed to replace virgin aggregates, followed by recycled masonry and recycled mixed waste aggregates. Such application in cement-based mortars could increase water demand by 20–34% and reduce strength by 11–50%, with recycled concrete aggregates being the most favorable. Natural aggregate substitution is disadvantageous in strong mortars, whereas weaker ones, such as lime-based mortars, could benefit from this incorporation. The extent of this topic also suggests possibilities for different recycled material use cases in mortars for masonry, although the available literature is largely insufficient to infer meaningful trends. Nonetheless, the most relevant knowledge synthesized in this review offers promising and environment-conscious utilization pathways for recycled concrete and other construction and demolition waste, which brings opportunities for further research on their use in mortars for masonry and industrial-scale applications.

Development and Characterization of Lime-Based Mortars Modified with Graphene Nanoplatelets

Materials for the conservation of cultural heritage must meet specific demands, such as high durability, service life, and compatibility with other materials used in the original building structures. Due to their low permeability to water and water vapor and their high rigidity, the use of Portland cement (PC) mortars, despite their high mechanical resistance and durability, does not represent an appropriate solution for the repair of historic masonry and structures. Their incompatibility with the original materials used in the past, often on a lime basis, is therefore a serious deficiency for their application. On the other hand, lime-based mortars, compared to PC-based materials, are more susceptible to mechanical stress, but they possess high porosity, a high water vapor transmission rate, and moderate liquid water transport. This study aims at the development of two types of lime-based mortars, calcium lime (CL) and hydraulic lime (HL). The modification of mortars was conducted with a carbon-based nanoadditive and graphene nanoplatelets (GNs) in three dosages: 0.1%, 0.3%, and 0.5% of the binder weight. The enhancement of CL mortars by GNs greatly increased mechanical strength and affected heat transport characteristics, while other characteristics such as porosity, water absorption, and drying rate remained almost similar. The application of GNs to HL not only enhanced the strength of mortars but also decreased their porosity, influenced pore size distribution, and other dependent characteristics. It can be concluded that the use of graphene nanoplatelets as an additive of lime-based composites can be considered a promising method to reinforce and functionalize these composite materials. The improved mechanical resistance while maintaining other properties may be favorable in view of the increasing requirements of building materials and may prolong the life span of building constructions.

Capsule controlled release of crystallisation inhibitors in mortars

Crystallisation inhibitors, such as sodium ferrocyanide (NaFeCN), are highly effective in mitigating NaCl-induced weathering in lime-based mortars; however, direct addition of NaFeCN in lime-mortars increases its susceptibility to leaching and rapid depletion, thus compromising long-term performance. Here, we present hydrogel-capsules for the controlled-release of NaFeCN within hydraulic mortars for the prolonged prevention of salt weathering. Capsules were prepared by complexing chitosan and calcium-alginate in different ratios containing different concentrations of NaFeCN. The release of NaFeCN from these capsules was measured in (1) simulated lime-mortar solution (2) from mortar specimens incorporated with calcium alginate (CA) and chitosan-calcium-alginate (Cs-CA) capsules using ultraviolet–visible light spectrophotometry and Inductive Coupled Plasma-Optical Emission Spectroscopy. Mortars containing Cs-CA capsules exhibited controlled-release of NaFeCN with four times lower effective diffusion coefficient, compared to incorporating NaFeCN directly in mortar. Conversely, mortar containing CA capsules (without chitosan) released NaFeCN rapidly. Thus, chitosan’s presence in CA is necessary for tuning NaFeCN release and the reason may be attributed to chitosan’s role in reducing CA’s permeability and chitosan’s electrostatic-attraction to ferrocyanide anions, slowing diffusion of the latter. In conclusion, using Cs-CA capsules can control the release of NaFeCN within mortar, providing a steady NaFeCN supply to prolong mortar’s resistance against salt damage.

Kaolinite plastic binder in mortars: Rheological and mechanical properties

Portland cement and hydrated lime-based mortars are widely used in civil construction for covering and laying walls, sealing or structural restoration. However, the binders used in the production of mortar are produced in a way that is harmful to the environment, highlighting the need for alternative binders. In this work, the use of kaolinite plastic binder in mortars was evaluated, replacing hydrated lime with the material at levels of 0%, 50% and 100%. The importance of this study is to evaluate the feasibility of using an alternative binder in Portland cement and hydrated lime-based mortars. Fresh state properties were evaluated, such as consistency, squeeze flow and density in the fresh state; in addition to properties in the hardened state, such as compressive strength, water absorption, x-ray diffraction (XRD) and scanning electron microscopy (SEM). The characterization results of kaolinite plastic binder (D10 = 0.00009 mm and D60 = 0.0004 mm) show that the material has a particle size closer to hydrated lime (D10 = 0.00001 mm and D60 = 0.0004 mm), than Portland cement and quartz sand, evidenced by parameters D10 and D60. Additionally, the kaolinite plastic binder presents moderate pozzolanicity, indicating the feasibility of being used in this type of application. The workability tests show that kaolinite plastic binder has the potential to improve the workability of the mortar. In dynamic tests (consistency) it was observed that the 100% kaolinite plastic binder composition is viable as it promotes an increase in spread from 253 to 265 mm. In static tests (squeeze flow) the composition with 50% kaolinite plastic binder showed the best spreading results, with values of 10.7 mm, while the compositions containing 0% and 100% showed spreading of 8.97 and 7.40 mm, respectively. This demonstrates the potential for using kaolinite plastic binder in mortars. The hardened state results, such as compressive strength and water absorption, were also satisfactory. Although the compressive strength values showed a reduction with the use of kaolinite plastic binder, the values reached 7.5 MPa after 28 days, which is compatible with the proposed application. Finally, it was observed from the results of XRD and SEM that the kaolinite plastic binder shows adhesion with the hydration products of the Portland cement in the mortar, promoting a reduction in ettringite and portlandite due to its moderate pozzolanicity. Based on these results, it is possible to conclude that kaolinite plastic binder is a viable substitute for hydrated lime in mortars.

Effect of acidic environment exposure on mechanical properties of TRM composites

With the increasing application of textile-reinforced mortars (TRMs) for the strengthening of existing masonry structures, knowing the long-term behavior of these composites is increasingly of great importance. In recent years, there has been a progressive research effort on the durability of TRM composites following different aging protocols, yet the durability of TRMs still necessitates comprehensive experimental studies for a better understanding of their behavior. On the other hand, there is also a lack of established aging methods, including acidic attack.The present study aims to leverage knowledge of the durability of TRMs when exposed to acidic attack. For this purpose, two different commercial fabrics made of glass and basalt fibers and a lime-based mortar have been used. In parallel, two aging conditions were also investigated considering 1000, 3000, and 5000 hours of exposure. Overall, a total number of 462 specimens were tested, including tests for the matrix, fabric, and composite. Compressive, flexural, and elastic modulus tests studied the variation in the mechanical properties of mortar, tensile tests focused on the textiles, and pull-out and single-lap shear tests were used for TRM composite’s behavior. To investigate possible changes in material behavior due to aging, mineralogical and chemical analysis including Optical Microscopy, SEM, XRD, and TGA were carried out.

Investigating the standard design and production procedure of heritage mortars for compatible and durable masonry restoration

Historic buildings ensure generational knowledge of past events, milestones, construction developments and evolution of materials, architectural designs, and practices throughout the centuries. It is indisputable that heritage buildings' survival against deterioration factors has proven the use of durable materials for their construction. However, they suffer inevitable decay due to ageing. Therefore, restoring the monuments to their original appearance and strength is always necessary for long-term survival. This paper discusses solutions for the design and development methods of new compatible restoration mortars for the architectural heritage, covering four significant aspects, namely: i) visual analysis of the heritage building in question, ii) experimental analysis of the original mortar samples for their physical, mineralogical and chemical properties, iii) characterization of the potential raw materials (available in the study area) that are close to the original, and iv) assessment of the new mortar durability. The mortars collected from the Castle of Good Hope, an important and ancient colonial edifice in the Western Cape Province (South Africa), were earth (samples SK7 to SK9) and hydraulic lime-based (SK1 to SK6), with 21–38 % porosity. The raw materials used on this monument include feldspar aggregates, possibly from the West Coast (Cape Town) and hydraulic lime for SK1, SK3 and SK5 mortars. For the restoration of the lime mortars (SK1, SK3 and, SK5), a hydrated lime-based mortar with a binder-to-aggregate ratio of 1:3, made of west coast sea sand and 5 % seashell additives, with a porosity of 24 %, has proved to be the most durable. The aesthetics for all the restoration mortars M1 to M9 is difficult to achieve considering the original material ageing factor, thus, the use of color-enhancing pigments is recommended.

Microstructural modifications of lime-based mortars induced by ceramics and nanoparticle additives

Lime-based mortars are one of the principal choices for building and restoration projects, owing to their unique qualities and material compatibility. Admixtures have long been incorporated to enhance the performance and durability of mortars, with ceramics being a traditional choice. More recently, the addition of nanoparticles has been explored as a means to further improve these properties. However, the effective optimization of the complex interplay between additives in lime-based mortars, which is crucial for enhancing their sustainability, remains an ongoing area of research. This study investigated the effects of red-clay ceramic aggregates (RCC) and nanoparticle-based solutions of Ca(OH)2 and SiO2 on the mineralogy, hydraulicity, surface properties, pore structure, and mechanical properties of lime-based mortars. The addition of nanoparticle-based solutions increased the carbonation reactivity, whereas the ceramic aggregates caused a more extensive conversion of portlandite to calcite on the external faces, indicating reduced porosity during the carbonation process. Pozzolanic reactions and the formation of new calcium silicate compounds were observed, along with improved compaction, smoother surfaces, and microcrack formation. The porosity increased with the addition of the ceramic aggregates, whereas the addition of nanoparticles significantly increased the number of pores in the mesoporous range. The specific surface area of the mortars increased with the inclusion of ceramic aggregates and nanoparticles, whereas the open porosity increased and the density and compressive strength decreased with the addition of nanoparticles and associated pozzolanic reactions that occurred with the inclusion of ceramic aggregates. These findings lay the groundwork for future improvements in the formulation of lime-based mortars to balance hydraulicity, surface characteristics, and mechanical performance while preserving porosity.

Effect of basalt fiber length on the behavior of natural hydraulic lime-based mortars

Abstract The number of studies aimed at the characterization of reinforced lime-based mortars for use in the rehabilitation of historic buildings is still very small. This fact contrasts with the growing interest of the industry in these products as substitutes for cement mortars, both for their constructive advantages (compatibility requirements) and their lower cost (economic and environmental). For this reason, this study investigates the effect of basalt fiber length on the physical, mechanical, and durability properties of reinforced natural hydraulic lime mortars and provides criteria for selecting optical blends to meet the various performance requirements for their use as building materials for traditional and contemporary structures. Specimens with 1% volume of basalt fibers and lengths of 6, 12, 18, and 24 mm have been tested. The results in fresh mortar show that increasing the fiber length decreases the consistency and bulk density, as well as increases the air content. Regarding the durability properties of hardened mortar, no direct relationship is observed between fiber length and the decrease in the water absorption coefficient of reinforced mortars. Nor is there a clear relationship between fiber length and the increase in Shore hardness and the decrease in adhesive strength in the reinforced mortars. On the contrary, for small lengths (up to 12 mm), there is a direct relationship between fiber length and the increase in other fundamental mechanical properties such as flexural and compressive strength. Based on the results obtained, a predictive model is proposed to determine the amplification factor of flexural and compressive strength as a function of fiber length.

Investigation of the Impacts of Nonpolar Amino Acids on Air Lime Mortars

ABSTRACT Natural protein-based additives have been frequently added to lime-based mortars to enhance their properties. However, the possible mechanism underlying this effect is not well understood. All proteins are built up by the basic units of amino acids, which may be viewed as a useful starting point for the research topic. The present study focused on the impacts of nonpolar amino acids on air lime mortars. The results obtained from the present study highlighted that some nonpolar amino acids (represented by glycine, alanine, valine and proline) decrease mortar water retention, decrease consistency, delay and prolong setting, increase compressive strength, and decrease water absorption. However, other nonpolar amino acids (such as leucine, isoleucine, phenylalanine and tryptophan) showed almost opposite results. The addition of all the nonpolar amino acids slowed mortar drying and carbonation, decreased the carbonation degree, inhibited calcite formation, and tended to form metastable calcium carbonate phases, such as vaterite. Studying the effects of single amino acids on lime mortars could contribute to the design of repair mortars with more specific requirements, and the results of the present study could open up a series of future topics to be investigated.

Effect of Alkaline Environment on the Bond Behavior of TRM Composites Through Single-lap Shear Tests

Textile Reinforced Mortars (TRM) are increasingly used for strengthening existing masonry structures, offering a sustainable solution. This system consists of textile fibers embedded in an inorganic matrix, typically cement or lime-based mortars, applied to the substrate’s surface. Although the mechanical properties of these composite systems have been extensively studied, there is still limited understanding of their long-term performance and durability. This study aims to enhance knowledge in this area by examining the bond behavior of TRM composites exposed to an alkaline environment using single-lap shear tests. For this purpose, single-lap shear specimens were constructed using clay brick as the substrate, a lime-based mortar, and two different fabrics—basalt and glass. These specimens were subjected to an alkaline solution to simulate accelerated aging conditions, with constant temperature and pH. The specimens were tested after 1000, 3000, and 5000 hours of exposure to evaluate their bond behavior compared to control specimens of the same age. Additionally, the effect of the alkaline environment on the material properties of the composite constituents was investigated. Elastic modulus tests were conducted on cylindrical mortar samples and compared to reference samples, displaying satisfactory resistance to alkaline conditions. The study identified and compared the strength, stiffness, and failure mode of each specimen to the reference stage, providing valuable design parameters for various field applications.

Material properties of building limes for pointing mortar for renovation and restoration of neo-Gothic churches in Sweden

During the neo-Gothic period of the 18th and 19th century, many churches in Sweden were built in brick and natural stone with a traditional lime-based mortar. Moisture- and salt related problems were common in these church buildings, already a few years after they were erected durability problems arose. Examples of these durability problems were internal salt precipitation, leaching of lime-based mortar and other moisture-related deterioration of mortar joints. When these neo-Gothic churches are repointed, this should be done with appropriate traditional lime mortars. However, since the introduction of cement as a material for mortars and renders, the knowledge on lime-based mortars has gradually decreased. Lime as a material for mortar, renders and plasters is still used, but only on a small scale and mostly for work on heritage buildings. There is a knowledge gap regarding material properties and workability of traditional limes. Therefore, the aim of this project was to determine the material properties of lime mortars used for restoration of churches built in brick or natural stone masonry.

Study of the influence of micro- and nano-cellulose on the growth and carbonation kinetics of portlandite crystals

Restoration of historical buildings contributes to the preservation of history and identity of the cities, but also, in the current climate crisis, an alternative solution to reduce the environmental impact of the construction sector, which is one of the main global contributors to green-house gas emissions and waste production. It can be also claimed that the most sustainable building is the one that has already been built. An important aspect to consider for the restoration of built heritage is the use of compatible materials, such as lime-based mortars, that should be preferred over cement. However, their slow setting and hardening (via carbonation), and, in some cases, poor durability prevent their full acceptance and widespread use. One course of action is to improve the quality of the binder via an innovative approach: inclusion of natural organic additives during the slaking process of CaO. This is expected to have a higher impact than their inclusion in the mortar’s mix design. In the present work the analysis of the growth of Ca(OH)2 crystals following their crystallization in the presence of micro- and nano-cellulose is studied, together with the morphological changes that these additives induce on portlandite crystals. Moreover, the study of the carbonation kinetics of the modified portlandite crystals gives insights on the effect that these additives have on the quality of the binder. The promising results highlight the potential of micro- and nano-cellulose as sustainable additives for lime-based binders. Furthermore, these additives can be obtained from industrial wastes, promoting a circular economy.

Carbonation process of commercial lime mortars vs cement-based mortars: Comparative analysis of textural differences, strength and durability

The present study analyses 5 commercially available mortars (Italian, German and Hungarian brands) under various conditions such as dry, water-saturated and freeze-thaw. Laboratory tests assessed specimens' physical properties and carbonation process 28 days after casting using EN guidelines. The workability, density, ultrasonic pulse velocity, water uptake, and strength parameters were measured. The bulk density of the studied mortars was between 1514-1840 kg/m3, indicating the variations in composition and porosity, and it correlates well with the measured P-velocities of 1939 m/s to 2649 m/s. The compressive strength of cubic standard test specimens was between 1.8 and 8.4 MPa, suggesting different mineralization and carbonation processes, clearly marking the presence of the Portland cement phase. A large scatter of physical parameters and various durability marks water-saturated and freeze-thaw-affected mortars. Carbonation and curing conditions can cause significant parameter differences in lime-based mortars. CO2 sequestration depends on mortar composition, textural and micro-fabric, and environmental conditions.

Influence of PLA impregnation on the performances of vegetable fibers for lime-based composites

In recent years, the application of inorganic lime-based Textile Reinforced Mortar (TRM) for repairing existing masonry structures has gained a relevant interest due to the strong compatibility between masonry elements and the strengthening composite. In addition, several research groups worldwide have recently focused on the possible use of natural fibers for replacing the traditional reinforcement (e.g., steel, fiberglass, basalt, PBO, aramid, carbon, etc.) generally employed for TRM composites. As a matter of fact, the natural fabrics (easily available and biodegradable) present comparable resistance to conventional fabrics, good compatibility with the lime-based mortars and elastic modules compatible with masonry elements. On the other hand, it has been also demonstrated that one of the most relevant aspects on their possible application is related their long-term and durability performances which can be mitigated with coating and impregnation treatments. In this context, the present paper presents the preliminary result of an experimental research aimed at investigating the influence of a biodegradable coating system (PLA - polylactic acid) applied to different types of natural fibers (made of flax and jute) on the resulting performances either from the physical and mechanical standpoint. The results demonstrate a significant improvement of the observed performance of natural fibers that can be more properly employed for the production of natural TRM composites.

Effect of Textile Architecture on the Durability of Flax Textile-Reinforced Mortars

This paper presents the preliminary results of an experimental programme on the tensile performance of flax-TRM systems subjected to accelerated ageing. Two layers of flax textiles of different architecture were embedded in a lime-based mortar and were conditioned in water for 2000h (~83 days), at controlled temperatures of 23oC and 40oC. Bare textiles were also conditioned in a lime solution for the same duration and temperature conditions to assess and decouple the deterioration mechanisms at the textile and composite scale. Both unconditioned and aged textiles and composites were subjected to direct tensile tests. The results show that the textile architecture affected primarily the short-term mechanical properties and the degree of composite action that can be achieved. Exposure to harsher environments resulted in similar strength retention rates for both textile types and equal to 60-70%, while the composite performance was found to be mainly affected by degradation mechanisms occurring at the textile reinforcement level, which may reduce the effective reinforcement ratio below critical values.

Green way of improving the thermal efficiency of mortars by the addition of biobased phase change materials

The thermal efficiency of air lime-based mortars was improved by directly integrating varying amounts (5 wt. %, 10 wt. %, and 20 wt. %) of a microencapsulated biobased phase change material (PCM) into the fresh mortars. This PCM is made of vegetable oils and other organic wastes from the agri-food sector. The mortar formulation was optimized by adding different chemical additives and mineral admixtures. The mortar formulation was meticulously designed to produce rendering mortars that are easily workable, crack-free, and fully adherent for use in building envelopes. Positive outcomes in thermal efficiency tests have demonstrated the ability of these materials to store thermal latent energy, offering an environmentally friendly alternative to enhance the thermal comfort of building inhabitants.

Tensile behavior of Textile Reinforced Mortars made with Flax fabrics

Nowadays, several industrial sectors are more and more motivated to develop and adopt sustainable solutions. In this context, the construction industry is not an exception: new materials, possibly obtained from renewable and locally available sources, are being worldwide developed and explored. As part of this common effort, special attention is being paid to an emerging class of materials generally referred to as bio-based composite systems. This study investigates the mechanical properties of a Textile-Reinforced Mortar (TRM) system produced with flax textiles embedded within a hydraulic lime-based mortar. The research also aims at analyzing the cracking patterns exhibited by the Natural TRM systems under investigation. The proposed analyses highlight the relevant mechanical response observed in the experimental results and allows to have a comprehensive overview of the feasibility of using natural textiles for strengthening existing structures.

Development and characterisation of lime-based mortars incorporating coffee-based products for integrated seismic and energy retrofitting

The current conditions of the built heritage claim urgent solutions to face the inadequacies of many aged constructions. Recent earthquakes and increasingly extreme climate events have undoubtedly shown that it is not possible to postpone effective interventions to properly handle such issues. However, current retrofitting strategies seem unable to address the critical deficiencies of existing buildings, which regard both energy and structural aspects. Indeed, ordinary interventions in the last few years focused on solving episodic deficits or single issues and missed the opportunity for an integrated refurbishment. Within this context, the study and development of new materials with enhanced properties are of primary importance, also looking at sustainable concerns. In this work, innovative lime-based mortars incorporating sustainable aggregates have been developed and experimentally characterised for future applications in integrated retrofitting solutions. More specifically, coffee grounds subjected or not to a thermal treatment have been employed to improve the thermal performance of the mortar matrices. This waste material is considerably abundant around the world and may answer to the increasing need for more sustainable and renewable resources against the employment of virgin raw materials involving higher environmental impact. In this way, the benefits of integrated retrofitting approaches are further combined with natural-based solutions. The aim is to foster similar studies and applications, showing the great potential and opportunities of such eco-friendly systems that are not being adequately exploited.

Mechanical characterization of Glass Fibre-Reinforced Air Lime-Based Mortars

The basic issue in determining the deformational properties of masonry is to conduct a comprehensive experimental characterization of the masonry components' materials, including their mechanical properties. This characterization process is even more important for new sustainable mortar solutions, especially in the context of strengthening and renovating existing masonry buildings, including historic structures. The work presents and discusses the mechanical tests carried out on a mixed cement-lime mortar based on air lime and reinforced with the addition of industrial glass fibres. Mechanical testing on prisms (40 × 40 × 160 mm) and cylinders (60 diameter × 120 mm height) demonstrated the beneficial impact of fibres in the mortar mixture analysed specifically in terms of improved compressive, flexural and splitting post-peak behaviour.