Natural Hydraulic Lime Mortars Research Articles

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.

Toughness of Natural Hydraulic Lime Fibre-Reinforced Mortars for Masonry Strengthening Overlay Systems

Masonry structures are susceptible to damage and collapse due to seismic actions, a problem in many urban areas. To address this issue, researchers are studying the use of fibre-reinforced mortars as overlay strengthening systems. This study assessed the use of synthetic polyacrylonitrile (PAN) fibres as reinforcement of natural hydraulic lime mortar, focusing on their influence on fresh behaviour and mechanical properties. Natural hydraulic lime (NHL) was chosen for its compatibility with typical older ceramic and natural stone structural masonry and contemporary ceramic brick infill masonry substrates, as well as for the sustainability benefits. The study also assessed the contribution of the PAN fibres to toughness enhancement in the developed formulations. The fresh behaviour of fibre-reinforced mortar (FRM) was found to be adequate for applications with fibre volume fractions below 0.50%. The compressive and flexural strengths were affected differently by the increase in fibre volume fraction, with compressive strength decreasing and flexural strength increasing. The maximum compressive strength of 13.3 MPa was obtained for 0.25% of fibres, while for flexural strength a maximum of 6.70 MPa was achieved with 1.00% of fibres. The compressive and flexural toughness, related to the post-cracking responses, increased with the fibre fraction, and even for fractions as low as 0.25%, an important increment of the capacity to dissipate energy was achieved.

Innovative Thermal Renders Incorporating Oyster Shells for Sustainable Insulation

In accordance with current sustainable development objectives, it is intended to implement innovative and sustainable solutions at economic, environmental, and functional levels, boosting the construction sector to increasingly contribute to society. Expanded cork is an alternative to sand aggregate in improving the thermal insulating properties of renders. In addition, other materials can be incorporated as aggregates in an attempt to contribute to both the improvement of the physical characteristics that the render must fulfil as well as the improvement of thermal behaviour (if possible). In this sense, bio-based materials generated by the aquaculture sector, such as oyster shells, can contribute as a bio-based insulation material for thermal renders. In this study, thermal natural hydraulic lime mortars were produced from a mixture of expanded cork (EC) insulating aggregate and oyster shells (OSs). The percentages of replacing EC by OSs were 20, 30, 40, and 50%. The tests were carried out in fresh and hardened states. The studied mortars presented a thermal conductivity and compressive strength of 0.151 W/(m·K) and 0.63 MPa, respectively. The most interesting performance between thermal conductivity and compressive strength was for the composite with 50% of each bio-based material. The potential of incorporating oyster shells as a bio-based insulation material could contribute to a sustainable blue circular economy.

Leaching behaviour of a crystallisation inhibitor in mortars

This paper investigates the leaching behaviour of sodium ferrocyanide, a known crystallisation inhibitor of sodium chloride, which is added to mortars for mitigation of salt decay. Leaching and depletion of the inhibitor is a practical performance related issue that might over time, make the inhibitor less effective against salt decay. In this research, the inhibitor was added to natural hydraulic lime (NHL) mortars during the mixing stage. Leaching of the inhibitor from the hardened mortar was assessed experimentally in laboratory. Both diffusion- and advection-driven transport mechanisms were considered. Diffusion experiments were carried out in a tank leaching test setup. Capillary absorption and drying cycles were used as a driving force to study advection-driven transport. Quantification of the leached species was carried out using various analytical techniques, including UV-VIS spectroscopy, ICP-OES and ion chromatography. The results from the tank leaching test show a high effective diffusion coefficient of ferrocyanide ions, in the same order of magnitude as sodium chloride transport. The advection test shows accumulation of the inhibitor at the evaporative surface and depletion of the inhibitor in the inner layers with successive wet-dry cycles. Based on these results it can be inferred that the degree of inhibitor leaching is significant and needs to be minimised to prolong the positive effect of the inhibitor on mortar durability. Potential solutions to reduce inhibitor leaching are discussed.

Lightweight pumice mortars for repair of historic buildings –Assessment of physical parameters, engineering properties and durability

The subject of the presented research was an experimental analysis of physical, engineering and durability parameters of lightweight mortars intended for the repair of historical buildings. Compatibility criteria, the requirements of technical standards and guidelines, and last but not least, previously published research results dealing with the development of mortars for repair delicate historic structures were taken into account in the design of mortar composition. Crushed pumice of a similar grain size was used to lighten the reference lime-based mortar and natural hydraulic lime mortar with quartz filler. Replacement of quartz sand with pumice was 25, 50, 75 and 100% by volume. The use of pumice allowed the fundamental physical, mechanical, hygric, thermal and durability parameters of the lightweight mortars to be such that they met the standard requirements for repair mortars and the heritage conservation requirements for compatibility with the original materials of historic masonry. The main finding was the fact that by replacing sand with pumice, a significant increase in the porosity of the mortars was achieved, while maintaining sufficient mechanical strength due to the pozzolanic reaction of the pumice. Mortars based on natural hydraulic lime have become more resistant to frost and salt crystallization. The advantage of the developed mortars was their low thermal conductivity and high water vapor permeability, which made them suitable for use on damp masonry, which is a substantial scientific contribution of the manuscript.

Hygro-Thermo-Mechanical Analysis of Brick Masonry Walls Subjected to Environmental Actions

Masonry walls comprise an important part of the building envelope and, thus, are exposed to environmental effects such as temperature and moisture variations. However, structural assessment usually neglects the influence of these hygro-thermal loads and assumes ideal conditions. This paper presents a hygro-thermo-mechanical model and its application to simulate the impact of temperature- and moisture-related phenomena on the structural behavior of masonry walls. A fully coupled heat and mass transfer model is presented and a 2D finite element model is prepared to simulate the behavior of a brick masonry wall under various hygro-thermal scenarios. Two different mortars are considered: namely, cement mortar and natural hydraulic lime mortar. The results are evaluated in terms of temperature and moisture content distribution across the wall thickness. The hygro-thermal model is further extended to incorporate mechanical effects through the total strain additive decomposition principle. It is shown that the hygro-thermo-mechanical response of the brick masonry wall is a complex 2D phenomenon. Moreover, the environmental loads change the natural stress distribution caused by gravitational loads alone. Finally, the wall with cement mortar develops higher levels of stress when compared to the one with lime mortar, due to the dissimilar hygro-thermal behavior between the constituent materials.

On Mechanical Behavior of Metal Anchors in Historical Brick Masonry: Testing and Analytical Validation

The repair and strengthening of historical masonry buildings is a fundamental aspect in the conservation of the built cultural heritage. Temporary shoring or strengthening are often used and, usually, involve the introduction of new metallic elements. The connection between the original substrate and the new elements must be analyzed carefully to prevent further damage to the building. This paper presents a study on the mechanical behavior of metal anchors applied to brick masonry walls. An experimental campaign is developed, and a series of pull-out tests are carried out on masonry walls built in a laboratory with natural hydraulic lime mortar and low mechanical strength bricks. Two groups of tests are conducted, namely, with the actuator in the direction of the anchor axis and with the actuator inclined with respect to the fastener axis. Moreover, two types of anchoring systems are used, namely, adhesive (chemical and cementitious grout) and mechanical anchors. The experimental results are compared to predictive analytical formulas available in the literature for estimation of the ultimate load capacity, according to the type of failure. From the comparison between experimental and analytical values, it is proven that the analytical formulation originally developed for concrete substrates cannot be directly extrapolated to brick masonry cases, and specific predictive formulas should be developed. The presented research can be used to select the most efficient anchoring system for strengthening and retrofitting of historical brick masonry structures.

Natural Hydraulic Lime Mortars for Hot-Humid Climates: Effects of Oyster Shells as Seeding Compound

This study explored the effects of formulation modifications of natural hydraulic lime (NHL) mortars exposed to hot temperature and high humidity conditions. The modified mortars were seeded by oyster shell powder, partially replacing the sand. The mortar samples underwent a curing period of 56 days with five observation days. The pH, carbonation depth, flexural strength, compressive strength, sorptivity, and morphology were studied. The results indicated that seeded mortars were more successful at setting and hardening high humidity settings. In addition, curing the mortars at higher temperatures hastened the hydration reaction significantly. The data indicate that seeded mortars can improve performance in several areas, notably carbonation rate (25%-45%), flexural strength (16%-60%), compressive strength (20%-55%), and sorptivity (18%-25%). The experimental protocol shows that the hardened mortar pore system is affected by the water-binder ratio, hydration level, relative humidity, and carbon dioxide concentration. The hydration of mortar greatly influences its strength. Using oyster shell powder as an aggregate substitute increased the performance of the mortars by microstructure and capillarity development. This circumstance is significant in our comprehension of modified lime mortars and seeding compounds, especially in hot-humid environments.

Design of a smart lime mortar with conductive micro and nano fillers for structural health monitoring

Structural health monitoring is an essential tool for assessing the performance of buildings and infrastructure, especially after critical events or the application of structural interventions. When dealing with architectural heritage structures, both structural health monitoring instrumentation and intervention materials need to be as inconspicuous and unintrusive as possible, both in terms of mechanical compatibility and aesthetics. Therefore, the design of smart sensors based on construction materials used in conservation engineering promises to provide an acceptable integrated structural health monitoring and upgrading solution for historic structures. In this paper an experimental investigation of smart intervention materials for historic masonry structures is presented. The materials consisted of natural hydraulic lime mortars modified through the inclusion of electrically conductive micro- and nanofillers: graphite, carbon nanotubes and carbon microfibres. The fillers provide multifunctionality to the matrix material based on an enhancement of its piezoresistive characteristics. Further, they result in an improvement of the mechanical properties of the intervention material without compromising its mechanical and chemical compatibility with the original structure. The resulting materials were evaluated based on mechanical property improvement, piezoresistivity enhancement and ease of production.

Effectiveness of Flax-TRM composites under traction

The scientific research in the field of masonry structures is increasingly welcoming the adoption of innovative and sustainable rehabilitation techniques aimed at the safeguarding of the Built Cultural Heritage. Textile Reinforced Matrix (TRM) composites are the most widely investigated strengthening systems for ancient masonry structures, thanks to their high compatibility level with the material substrates in terms of fire resistance, chemical/physical aspects, reversibility property, little impact on dimensions, stiffness and weight. Nevertheless, in the last years, the growing concern on sustainability increased the interest in products with low environmental impact, for promoting circular economy approaches in the design of the structural interventions. In particular, efforts have been done to replace the most common composites with materials less harmful to the environment, such as natural fibres, for developing compatible and sustainable rehabilitation techniques for masonry structures. This paper presents the preliminary results of experimental tests conducted by the authors on specimens of TRM composites made with natural, vegetable, flax-fibre grids and natural hydraulic lime mortar. The mechanical characterization tests aimed at detecting the tensile behaviour of the natural TRM system compared to the results available in the literature on different vegetable-fibre composites and TRMs made with natural basalt fibres. The experimental tests highlighted the promising mechanical effectiveness of natural TRM systems under traction and offered a hint to further research aimed at improving their mechanical strength and stiffness.

Cyclic shear-compression tests on two stone masonry piers strengthened with CRM and FRCM

This paper discusses the results of an experimental campaign on Composite-Reinforced Mortar (CRM) and Fabric-Reinforced Cementitious Matrix (FRCM) jacketing for the retrofit of stone masonry structures. Two double-leaf natural stone masonry piers were built with the same materials and geometry, including portions of adjoining spandrels above and below. Then CRM was applied to both faces of one of the specimens, using a natural hydraulic-lime mortar, glass-fiber-reinforced polymer meshes, and helicoidal steel connectors. The other pier, instead, was retrofitted with FRCM on both sides, combining a glass-fiber-reinforced cementitious mortar, bidirectional PBO textiles, and PBO connectors. Both specimens were subjected to the same vertical overburden load and to a quasi-static cyclic shear-compression test in double-curvature conditions, up to failure conditions. Different collapse mechanisms were triggered by the two retrofit systems, with flexure dominating the CRM specimen and shear controlling the FRCM one. The displacement capacity was enhanced by factors of about 2.5 in flexure and 3.0 in shear, compared to typical values for unstrengthened piers.

RILEM TC 277-LHS report: lime-based mortars for restoration–a review on long-term durability aspects and experience from practice

For conservation interventions of historic masonry generally lime-based mortars such as pure air lime mortars, lime-pozzolan mortars, natural hydraulic lime mortars and ternary mortars (lime-pozzolan-cement) are used. The main reason is that their hygric and mechanical (strength and ductility) performance are easy to adapt to most existing historic masonry (compatibility requirements). Although the basic appropriateness of lime-based mortars for restoration is undisputed, there are also some limitations in the application of these mortars. In this report a review is given of the theoretical backgrounds and further of laboratory research developments in the field of lime-based binders and mortars over the past decades. Furthermore, practical experiences in positive and negative sense (damage cases) are elaborated. Drawbacks and points of attention are being dealt with, which are essential for a durable application of lime-based mortars for the conservation of historic masonry. In general, it is concluded that points of attention should be addressed through a thorough evaluation of their potential and through testing of their suitability. For these mortars, even more than for modern cement-based mortars, specifically, environmental exposure conditions and application conditions should be considered.

Sustainability development and performance evaluation of natural hydraulic lime mortar for restoration.

Many efforts have focused on the deterioration of historic buildings, and natural hydraulic lime mortar without admixture is less resistant to environmental agencies than a lime mortar with admixtures. A research study has been carried out to study the effect of carboxymethyl cellulose (CMC) and alccofine (AF) with the natural hydraulic lime mortars in improving the hydraulic properties, durability properties, and freeze-thaw resistance. The performance of lime mortars was evaluated with various additives. The experimental results indicated the combined effect of CMCs and AF in lime mortars' compression testing in different stages. In blended mortars, the early compressive strength was increased. Also, mixed mortar exhibits stronger freeze-thaw resistance with a long healing period. These findings indicate that AF and CMC combination played an essential role in lime mortar (LM) properties, which is generally advantageous for restoration and conservation purposes, especially in historic structures in cold regions.

Effect of ultrafine pozzolanic powders on durability of fabricated hydraulic lime

Fabricated hydraulic lime (FHL), prepared by fully mixing hydrated lime and hydraulic components containing activated Si/Al, shows quicker strength development and better water resistance than that of hydrated lime, and has the advantage of raw material supply to replace natural hydraulic lime (NHL) for the restoration of ancient sites. As ultrafine pozzolanic powders such as nano-SiO2, silica fume, slag, fly ash and circulating fluidized bed combustion ash can not only improve the hydraulic activity, but also be beneficial for the permeability of FHL paste in the ancient sites, this study investigated the influence of the above ultrafine pozzolanic powders on the durability of FHL, and obtained an optimal FHL through orthogonal test, and its durability was compared with NHL. The results showed that nano-SiO2 had a significant improvement on the water and sulphate resistance of FHL paste as well as its early compressive strength; silica fume greatly influenced the water resistance and later compressive strength; slag is the most important factor to improve the sulphate resistance of FHL; fly ash and circulating fluidized bed combustion ash had a smaller effect on the durability of FHL. The optimum FHL is composed of 1% nano-SiO2, 2% silica fume, 10% slag, 10% fly ash, 6% circulating fluidized bed combustion ash and 69% hydrated lime, which owned much better water and sulphate resistance than NHL mortar. The superior durability of FHL pastes was mainly due to the diversification of the internal hydration products and the close connection from XRD and SEM analysis. FHL with excellent durability proposed in this paper may have a positive impact on the restoration of ancient sites. In the future, the reinforcement effect of FHL prepared in this study on cultural relics sites will be discussed.

A sustainable production of natural hydraulic lime mortars through bio-amendment

This article examined the effect of a bioproduct suspension obtained from fermentation of biodiesel’s crude glycerol when used to formulate natural hydraulic lime mortars, as a fluid replacing the mixing water. The bioproduct was used either sonicated or non-sonicated and two volumes of mixing fluid were tested. The aim was to assess the advantages and drawbacks that could be achieved with a waste-based bioproduct, instead of petrochemical-based additions. The investigation revealed a positive effect on workability, producing mortars with a lower mixing fluid content, improving the mechanical performance. Finally, the bioproducts reduced the mortar water absorption by gravity and capillary.

Innovative and Eco-friendly Solutions for the Seismic Retrofitting of Natural Stone Masonry Walls with Textile Reinforced Mortar: In- and Out-of-Plane Behavior

The application of textile-reinforced mortars (TRM) on masonry walls constructed with natural stones was studied through a set of medium-scale experiments. Fourteen experiments were carried out in total, including in- and out-of-plane cyclic tests as well as two different strengthening configurations. The first consisted of a TRM made of a natural hydraulic lime (NHL) mortar, combined with a natural flax-fiber textile, while for the latter, a novel alkali-activated material (AAM) geopolymer mortar combined with basalt textile was employed. The use of such low-carbon footprint materials instead of conventional ones makes these systems environmentally friendlier, in line with the modern requirements for lowering CO2 emissions. Both solutions led to a substantial increase of the load-bearing capacity, up to 70% for both in- and out-of-plane experiments. Stiffness and energy dissipation characteristics of the masonry elements were improved as well. If some durability related issues of both configurations and feasibility ones of AAMs are addressed, they could provide good candidates for application in real-life structures.

Effect of a mixed-in crystallization inhibitor on the properties of hydraulic mortars

<abstract> <p>Porous building materials are often subjected to damage due to salt crystallization. In recent years, the addition of crystallization inhibitors in lime-based mortar, has shown promising results in improving durability of this material against salt decay. Lime-based mortars have low mechanical properties and slow setting. They are often replaced with hydraulic binders to overcome these limitations. However, the effect of crystallization inhibitors in mortars with hydraulic binders is still unknown. Incorporation of crystallization inhibitors in hydraulic mortars would widen the application field of this new technology. In this research, the possibility to develop hydraulic mortars with mixed-in sodium ferrocyanide, an inhibitor of sodium chloride crystallization, is explored. As an essential first step, the influence of this inhibitor addition on the properties of hydraulic mortars is investigated. Two common types of hydraulic binders, natural hydraulic lime (NHL) and ordinary Portland cement (CEM I), were studied; the inhibitor was added in different amounts (0%, 0.1% and 1% by binder weight) during mortar (and binder paste) preparation. Relevant mortar and binder paste properties, in fresh (hydration, workability, setting time) and hardened (mechanical strength, elastic modulus, pore size distribution, water absorption) state, were assessed using several complementary methods and techniques. The results indicate that the addition of ferrocyanide does not alter the studied properties of both NHL and CEMI-based mortar and binder pastes. These results are promising for the further development of hydraulic mortars with an improved durability with respect to salt decay.</p> </abstract>

A Sustainable Production of Natural Hydraulic Lime Mortars Through Bio-Amendment

A Sustainable Production of Natural Hydraulic Lime Mortars Through Bio-Amendment

Effect of loading frequency on the fatigue life in compression of natural hydraulic lime mortars

This paper focuses on the study of the influence of the loading frequency on the fatigue life in compression of natural hydraulic lime (NHL) mortars. For this purpose, fatigue tests were performed under three different loading frequencies: 0.05 Hz, 0.5 Hz, and 5 Hz. The maximum and minimum stresses applied in the fatigue tests were 85% and 20% of the compressive strength of the mortar, respectively, and the runout limit was set at around three days. It is observed that the NHL mortar is sensitive to the loading frequency; that is, for higher frequencies, more cycles are resisted by the specimens. Concerning the secondary strain of the fatigue creep curves, the Sparks and Menzies law was satisfied independently of the loading frequency. This law is useful to predict the number of cycles to failure of runouts if the secondary strain is known. In addition, given the high scatter of results, a probabilistic treatment is applied. Firstly, they were fitted to a two-parameter cumulative Weibull distribution function. Secondly, the results were fitted to a probabilistic fatigue model based on the initial distribution. With it, one can obtain the failure probability of the material for any given value of loading frequency. Finally, we observed an increase in the residual strength after fatigue in comparison to the static compression tests of around 40%. Through mercury intrusion porosimetry tests, it is concluded that a possible chemical curing of the material could have occurred induced by the cyclic loads.

High temperature resistant restoration mortar with fly ash and GGBFS

Nowadays, the development of sustainable building materials is of loom large in for the preserve resources and reducing CO2 emission and environmental pollution effects. Exposure to fire or other high temperatures of mortars produced with calcium-based binders (cement or hydraulic lime) adversely affects their mechanical properties. In addition, the effect of high temperature may cause a change in the pore structures, causing cracking and spalling. Protecting the integrity of historical buildings exposed to high temperatures is important for cultural sustainability. In this study, natural hydraulic lime (NHL) used as a binder in mortars was replaced with 15, 30 and 60% fly ash (FA) and granulated blast furnace slag (GBFS). In the mixtures, 1.5% (by volume) polypropylene fiber (PF) was also used. Test results reveal that while the mortars’ workability increased as the FA and GBFS content increased, PF decreased the flow diameters of the mortars. It has been determined that the paste content affects the porosity and water absorption rates of mortars. With the addition of FA content, paste content increased and porosity reduced. Compressive strength over 10 MPa was obtained by using 30% FA in 90-day lime mortars. As the addition of GBFS, the compressive and flexural strength were negatively affected. PF has reduced the porosity and water penetration depth of the mortars thanks to its micro filler effect. FA-based mixtures were more resistant to high temperatures than GBFS-based mixtures. Compressive strength was measured between 4.3 and 8.6 MPa after 600 °C temperature in FA-based mixtures. In fibrous mixtures, increment of mass loss was more with high temperature. C-S-H gels were observed in XRD and SEM analyzes of mortars exposed to high temperatures. PF was observed in stereomicroscope images of mixtures exposed to 200 °C. Since the porosity of the mortars is relatively high (19.7%–30.8%), the PF in the mixtures exposed to 200 °C did not melt completely but was damaged. As a result, it would be more appropriate to use 30% of FA and 15% of GBFS in NHL mortars.