Lime-based Mortars Research Articles

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanostructured lime-based materials for the conservation of calcareous substrates

Enhancement of Fly Ash Concrete By Hydrated Lime and Steel Fibres

Utilisation of fly ash as partial replacement for cement often results in low early strength of the concrete and adversely affects the popularity of fly ash concrete in the field. A theory suggests that effective pozzolanic reaction of fly ash particles is hindered due to unsatisfactory quantities of lime in most fly ash compositions, and that this is the cause of low early strength in fly ash concrete. This lack maybe overcome by addition of hydrated lime (calcium hydroxide), ie, the combination of lime (calcium oxide) and water. Steel fibres are already established enhancers of concrete and with existing studies pointing to benefits of their inclusion in fly ash concrete, the effect of these fibres in the proposed improved lime fly ash concrete mix would be of importance.This paper primarily investigates the improvements on fly ash concrete with addition of hydrated lime on properties such as compressive, tensile, flexural strengths and elasticity. The studies are carried out on two main mixes, one of Ordinary Fly ash Concrete (OFC), ie, with 30% substitution of OPC with fly ash alone, and the other mix of Lime Fly ash Concrete (LFC), ie, with 5% lime, 25% fly ash and rest OPC. Instances of study include material testing, mix design, casting and curing conditions, on fresh and hard concrete. Furthermore, drawing inspiration from ancient lime-based mortars, which utilized saline and lime water, for casting and curing purposes, the same is tested for this lime-included mix. Secondly, the above studies are repeated for additional inclusion of steel fibres to further improve the capabilities of this mix. Finally, the study is concluded by drawing inferences for results, by means of theorizing possible micro mechanics of the mix, expected chemical reaction of constituents and from SEM analysis of created concrete samples

Dry mixes for the restoration: basic principles of design

To ensure compliance with historic solutions as the primary binder of dry mixes for the restoration is air lime. To date, almost all of the advantages and disadvantages of the lime-based mortars are known, and this allows implementing a scientific approach to the goal of ensuring the maximum possible durability of masonries and finishing designs. This article covers the main problems and goals faced by professionals in the field of producing dry building mixtures that are the most technologically and economically appropriate for the restoration of the historical buildings and constructions. The use of modern mineral additives opens up new prospects for improving the properties of lime dry mixtures, for both new construction and restoration works of the objects of historical heritage.

Micromechanics-based simulations of compressive and tensile testing on lime-based mortars

The purpose of this paper is to propose a continuum micromechanics model for the simulation of uniaxial compressive and tensile tests on lime-based mortars, in order to predict their stiffness, compressive and tensile strengths, and tensile fracture energy. In tension, we adopt an incremental strain-controlled form of the Mori–Tanaka scheme with a damageable matrix phase, while a simple J2 yield criterion is employed in compression. To reproduce the behavior of lime-based mortars correctly, the scheme must take into account shrinkage cracking among aggregates. This phenomenon is introduced into the model via penny-shaped cracks, whose density is estimated on the basis of particle size distribution combined with the results of finite element analyses of a single crack formation between two spherical inclusions. Our predictions show a good agreement with experimental data and explain the advantages of compliant crushed brick fragments, often encountered in ancient mortars, over stiff sand particles. The validated model provides a reliable tool for optimizing the composition of modern lime-based mortars with applications in conservation and restoration of architectural heritage.

The Effect of Aggregate Type on the Properties of Lime Mortars

Lime mortars represent indispensable building materials that have been used for centuries in civil engineering. Considering the necessity of numerous restoration work on historical buildings, a research of the applicability and suitability of various types of plasters for repairing the historical plasters has been developed. This work presents the applicability of limestone aggregate and limestone fines to aerial lime-based mortars. The role of aggregates on the properties of lime mortars is examined in this paper by comparing pure quartz sand and limestone aggregate and its quantity in the mortar. It was found that limestone aggregate produced the comparable or higher mortar strengths than quartz aggregate and slightly increased porosity, water absorptive capacity and carbonation rate of the mortars. Partially replacement of aggregate by limestone fines has caused dramatic growth in strength, especially in mortars with high content of binder. The applied limestone aggregate is convenient to lime-based mortars and the addition of limestone fines contributes to better mechanical properties of lime mortars.

Influence of the Aggregate Type on the Properties of Dolomitic Lime-Based Mortars

Considering the requirement of numerous restoration work on historical buildings with dolomitic lime-based mortars, a research of the applicability and suitability of various types of plasters for repairing the historical plasters have been developed. This work presents the applicability of limestone aggregate and limestone fines to dolomitic lime-based mortars. The role of aggregates on the properties of dolomitic lime mortars was examined by comparing pure quartz sand and limestone aggregate and its quantity in the mortar. Limestone aggregate and limestone fines accelerated the carbonation reaction in the mortars, but the positive impact of limestone aggregates to strength properties of mortars was not observed. Mortars with limestone aggregate showed higher total porosity and water absorption than those with quartz aggregate. Similar results was obtained for mortars with limestone fines. It was found that limestone aggregate and limestone fines, used in this work, is not so suitable and applicable to the dolomitic lime-based mortar as to the aerial lime-based mortars.

Experimental and numerical analysis of reinforced stone block masonry beams using GFRP reinforcement

This paper deals with an experimental and numerical study of stone block masonry beams externally reinforced using glass fiber-reinforced polymers (GFRP) strips. This study is conducted in order to investigate their flexural behavior. Eight masonry beams with 1.024m span were loaded monotonically up to failure under four-point bending setup. All the tested beams have two courses of stone masonry units. Two unreinforced masonry beams were considered as the reference specimens. The remaining six beams were externally reinforced using hand-made GFRP strips with different layers of chopped glass strand mat (two, three and four layers).In the purpose to replicate ancient stone masonry structures, stone blocks were adopted and lime-based mortar was used to prepare beams. Typical load–displacement curves of the tested beams were compared and discussed.Finite element (FE) modelling analyses, considering the Drucker–Prager criterion, were performed using ABAQUS to predict ultimate loading capacity and the failure mode of the masonry beams. By comparing numerical results with experimental ones, over and above the effectiveness of GFRP strips as external strengthening for stone masonry beams, the proposed finite element model has been validated and can be used for numerical analysis of ancient masonry structures.

Valorization of brick waste by alkali-activation: A study on the possible use for masonry repointing

Alkali-activation of brick waste has recently been proposed as a sustainable route to develop pastes/mortars with tailored mechanical properties and pore system. In this study, the suitability of using pastes from brick waste alkali-activation for repointing existing masonries (i.e., filling the most external part of mortar joints, lost due to deterioration processes) was investigated. Five different formulations (having SiO2/Al2O3 molar ratio ranging from 1.4 to 0.4) and two different curing temperatures (room temperature and 50°C) were investigated. Open porosity and efflorescence formation were found to decrease for decreasing SiO2/Al2O3 ratio. Curing at high temperature generally favored geopolymerization and reduced efflorescence formation. Pastes with SiO2/Al2O3=0.8 and 0.9 exhibited open porosity and water vapor permeability fairly similar to those of historic lime-based mortars, thus proving to be potentially compatible with them. Further optimization of the mix design seems however necessary to reduce the formation of efflorescence.

An integrated experimental-numerical study of the performance of lime-based mortars in masonry piers under eccentric loading

The paper focuses on the performance of various lime-based materials, alternative to Portland cement mortars, intended for application in repairing historic structures when subjected to mechanical loading. Results of basic material tests indicate that the use of metakaolin as a pozzolanic additive produces mortars with superior strength and sufficiently low shrinkage. Moreover, mortar strength can be further enhanced by the addition of crushed brick fragments, which explains the longevity of Roman concretes rich in pozzolans and aggregates from crushed clay products such as tiles, pottery, or bricks. An integrated experimental-numerical approach was used to identify key mortar parameters influencing the load-bearing capacity of masonry piers subjected to a combination of compression and bending. The simulations indicate increased load-bearing capacities for masonry piers containing metakaolin-rich mortars with crushed brick fragments, as a result of their superior compressive strength.

Laboratory Investigations on Lime-Based Mortars with Glutinous Rice Water Under Freeze-Thaw Cycles

Laboratory Investigations on Lime-Based Mortars with Glutinous Rice Water Under Freeze-Thaw Cycles

Compressive Strength of Lime-Based Mortars Reinforced by Micro Glass Fibers

Glass fiber-reinforced lime-based mortars have been studied. Two different fiber reinforcement amounts were used as an addition to the mixtures. Compressive strength and post-cracking behavior of mortars were observed and compared with reference mixture without any reinforcement (marked R). The fibers were added in the amount of 1.8 kg/m3 (mortar samples MA) and 93.75 kg/m3 (mortar samples MB). Destructive compression tests were chosen to compare the performance of the individual mixtures. The maximum compressive strength reached during the testing was the highest for reference samples, while those samples together with MA exhibited the elastic-brittle behavior. Only MB had post-linear hardening behavior and after reaching the maximum compressive strength a slow softening was present.

Experimental Investigation of the Interface between Synthetic and Glass Fibers and Lime-Based Mortars

In this article, the cohesion between fiber reinforcement and lime-based mortar is experimentally investigated using so-called pullout test. The experiment is based on the progressive pulling out of the fiber from the matrix. Comparing the experimental load-displacement diagram with the theoretical curve from the analytical model, the micromechanical parameters describing the fiber-matrix interface are evaluated. In the study, several types of synthetic and glass fibers are considered as well as two types of lime-based mortars. The first one is pure lime, while the second one has lime-metakaolin matrix.

Study of natural hydraulic lime-based mortars prepared with masonry waste powder as aggregate and diatomite/fly ash as mineral admixtures

NHL-based mortars were prepared by using waste marble powder (WMP) as aggregate and introducing diatomite and fly ash to partially replace natural hydraulic lime (NHL). Physical property evaluation showed that compressive and flexural strength of mortars prepared with diatomite were greatly enhanced, fly ash addition had noticeable improvement on mortars' flexural strength. Diatomite had a more positive effect on mortars' compressive strength than fly ash and 20% mineral addition made mortars achieve better mechanical properties. Apparent density of prepared mortars was decreased after introduction of diatomite and fly ash. Acid and sulfate resistance properties of mortars were improved by the presence of mineral. Diatomite was more effective than fly ash in improving the sulfate resistance of mortars. Microstructure, ultrasonic velocity and thermal properties characterization suggest that the improvement of mortars' properties could be attributed to pozzolanic reaction between mineral admixtures and calcium hydroxide (Ca(OH)2) which mainly occurred during curing period at the range of 14–28 days.

Study on the effectiveness of PNS and LS superplasticizers in air lime-based mortars

Polynaphtalenesulfonate (PNS) and lignosulfonate (LS) were tested as superplasticizers in pastes and mortars of pure air lime and air lime with a pozzolanic additive, nanosilica (NS). LS showed a better plasticizing effect than PNS: the flowability of the samples with LS as well as the slump retention over time was larger. LS strongly hindered carbonation due to its ability to form Ca2+ complexes. In mortars with NS, PNS was seen to interfere with the C-S-H formation, resulting in lower mechanical strengths. Adsorption isotherms and zeta potential showed that PNS was more adsorbed than LS onto lime and C-S-H particles. PNS acted mainly through electrostatic repulsion owing to its high anionic charge density and flat adsorption. However, LS was more efficient as superplasticizer in air lime media, steric hindrance being the main mechanism responsible for avoiding flocculation. Furthermore, LS yielded high compressive strengths in mortars with NS.

Study of the effect of three anti-graffiti products on the physical properties of different substrates

To protect the surface of materials from the effects of graffiti paints, there are anti-graffiti products that prevent the penetration of these paints into the pore system of the substrates, making the substrates water- and oil-repellent, thus facilitating their removal. This paper presents a comparative study of three commercial anti-graffiti products (two sacrificial and one permanent) applied on three substrates, in order to evaluate the changes caused by these products on the physical properties of the substrates. Thus, the anti-graffiti products were applied on a Portuguese limestone and on painted and unpainted lime-based mortars. The experimental work was focused on various laboratory tests such as open porosity, capillary water absorption, water absorption under low pressure, water vapour permeability, drying behaviour and colour variations. The results have shown that these products introduced variations on the physical performance of the substrates, especially the water absorption, drying behaviour and water vapour permeability.

Effect of Biomass Waste Materials as Unconventional Aggregates in Multifunctional Mortars for Indoor Application

In order to decrease energy consumption in buildings, a new way to recycle materials coming from biomasses waste in mortars was studied. For this purpose, mortars with water/cement equal to 0.5 by weight and aggregate/cement equal to 3.5 by volume were considered. Cement was replaced by hydraulic lime and sand was substituted with two different types of spruce sawdust shavings (as it is and roasted), biomass bottom ash and biomass fly ash. The results show that mortar prepared with cement has obviously a better mechanical strength and 60% lower capillary water absorption. All unconventional aggregates increase the total porosity of lime mortars. Moreover, biomass fly ash and both spruce sawdust shavings based mortars can be classified as lightweight mortar. Regardless of porosity and lightness, biomass bottom ash improves up to 150% the mechanical performance of lime-based mortars. Concerning durability, bio-based lime mortars show in general nearly twice higher capillary water absorption with respect to the sand lime mortars whit the exception of spruce sawdust shavings and biomass bottom ash. Mortars can be classified as permeable to water vapour. As it is and roasted spruce sawdust shavings are able to increase three and two times the capacity of the mortar to be a hygroscopic buffer in terms of MBV values.

Mechanical Properties of Fiber Reinforced Lime-Based Mortars Evaluated from Four-Point Bending Test

In the study, the bending behavior of high-performance fiber reinforced lime-based mortars is experimentally investigated using four-point bending test. From the experimental data, the influence of the mortar’s composition on its stiffness, cracking strength and ultimate strength are investigated. It is also studied, whether the response has strain-softening or strain-hardening character and whether the material exhibits multiple cracking. Such behavior is very important for the durability of the material, because it allows carrying load during imposed deformations (due to thermal effects, movements of foundations, seismicity, etc.). The number of formed cracks is examined using digital image correlation method. The mortar composition is considered with two types of binder (pure lime, lime-metakaolin), with two types of polyvinyl alcohol fibers in four volume fractions (0.5÷2.0%). As the reference, we consider two sets of specimens made of plain mortar without fiber reinforcement.

Masonry wall panels retrofitted with thermal-insulating GFRP-reinforced jacketing

Today there is a need to provide thermally efficient walls, while at the same time to increase the mechanical properties of old unreinforced masonry walls that will not require large amounts of energy in the retrofitting or deconstruction processes. To address this problem, this paper gives the results of shear tests carried out on masonry panels made of solid bricks retrofitted with a new technique based on the use of glass fiber-reinforced polymers (GFRP) grids inserted into a thermal insulating jacketing. This was made of different low-strength lime-based mortars. Tests were carried out in laboratory and results were used for the determination of the shear modulus and strength of the wall panels before and after the application of the GFRP reinforcement. Retrofitted panels exhibited a significant enhancement in the lateral capacity when compared to the control panels. The thermal performance of the proposed mortars was also investigated both with and without GFRP. Low values of thermal conductivity were found, especially for the samples with GFRP; a reduction of the thermal transmittance value in the 34–45 % range was also obtained by applying 45 mm layer of coating in conventional masonry walls.

Effect of curing conditions and Ca(OH)2-treated aggregates on mechanical properties of rice husk and hemp concretes using a lime-based binder

This study dealt with the effect of two different processes on the mechanical performances of lightweight insulating plant-based concretes using hemp hurd or rice husk and a lime-based binder. The first process was a lime-water treatment of plant aggregates prior to incorporating them in the mix. The second one consisted in exposing concrete materials to moist curing and elevated temperature.Chemical and textural modifications of plant aggregates after treatment were investigated by infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Compression tests were conducted on concretes using raw or treated aggregates after 28days of curing under standard conditions (20°C–50%RH).Effect of high relative humidity (95%RH) and elevated curing temperature (50°C) was first studied on lime-based mortars. Binder hardening was investigated by means of thermogravimetric analysis (TGA) and back-scattered electron imaging (BSE) on polished cross sections. Then, the same curing process was performed on plant-based concretes and the transition zone between plant aggregates and binder was analyzed by SEM. Compression tests were conducted after 28days for both materials.Results show that lime-water treatment improved compressive strength of rice husk-based concrete but halved that of hemp concrete. As regards the impact of curing conditions, it was shown that compressive strength of hydraulic lime mortars after 28days can be strongly increased with moist curing and elevated temperature. However, plant-based concretes suffer from a high leaching of polysaccharides in the binder and from a transition zone between aggregates and binder of very poor quality when they are subjected to moist curing. This led to unchanged or even lower mechanical performances of plant-based concretes in the case of high RH and elevated temperature compared to 20°C–50%RH.

Experimental Analysis of Repaired Masonry Elements with Flax-FRCM and PBO-FRCM Composites Subjected to Axial Bending Loads

In the construction industry, the use of natural fabrics as a reinforcement for cement-based composites has shown great potential. The use of these sustainable composites to provide strengthening or repair old masonry structures that exhibit structural problems mainly due to a poor tensile strength of the mortar/brick joints is revealed to be a promising area of research. One of the most significant load conditions affecting the mechanical response of masonry structures occurs when axial bending loads are applied on the resistant cross-section. In this study, three different types of masonry elements were built using clay bricks and a lime-based mortar. After 28 days, the samples were subjected to concentric and eccentric compressive loads. In order to produce significant bending effects, the compressive loads were applied with large eccentricity, and a sudden failure characterized the behavior of the unreinforced masonry (URM) elements. The tested masonry specimens were repaired using fabric-reinforced cementitious matrix (FRCM) composites produced using bi-directional flax and polyparaphenylene benzobisoxazole (PBO) fabrics. The mechanical behavior of the URM and repaired samples was compared in terms of load-displacement and moment-curvature responses. Furthermore, the results achieved using flax-FRCM composites were compared with those of using PBO-FRCM composites.