Mortar Structure Research Articles

Evolution of the microstructure of lime based mortars and influence on the mechanical behaviour: The role of the aggregates

The pore structure of air lime mortars, formulated with aggregates of different mineralogy and grain size distribution, was evaluated with the aim of studying the influence of sand type on the microstructural modification over time and of establishing the relationship between these modifications and the mechanical behaviour.The microstructure of the mortars was determined by mercury intrusion porosimetry at 28, 90 and 360 days, and the results were compared with its mechanical characteristics, namely compressive strength, flexural strength and modulus of elasticity.A remarkable increase of mechanical strength over time was found for all mortars. An optimized grain size distribution of the sand (optimized compactness) proved to be favourable to air lime mortars compared with grain size distribution defined by standard EN 196-1, showing a good behaviour of the interlocked structure but also adequate porosity that favours lime carbonation.A relationship between the mechanical properties and the porous structure was also established: large volumes in the range of macropores tend to reduce the mechanical strength while gel pores, related with the presence of hydraulic compounds, are generally linked to an increase in strength. Overall, the assessment of the microstructure indicates that the packing density and the shape of the aggregates are the dominant parameters influencing the pore size distribution of macropores; however, the mineralogy and related characteristics also have an important impact on capillary porosity.

Design and characterisation of ternary cements containing rice husk ash and fly ash

This study explored the interaction between rice husk ash (RHA) and fly ash (FA) as partial (0%, 15% or 30%) additions in new ternary cements designed to reduce cement industry energy consumption and greenhouse gas (GHG) emissions by lowering their clinker content. To that end, the effect of the introduction of mixed RHA and FA on the pozzolanicity of the RHA-FA/lime system was assessed and its impact on the chemical, physical, rheological, mechanical, calorimetric and microstructural properties of the new ternary cements analysed. The joint use of these additions revealed mixture synergies, with an initial rise in FA pozzolanicity in the presence of RHA, although this effect declined over time. The inclusion of the RHA-FA mixture prompted changes in the pore structure of mortars that after 90d translated into 2% lower compressive strength than the control in mortars with 15% addition and a 19% decline in materials containing 30% waste. That notwithstanding, the new cements were European standard EN 197-1-compliant for cement types II/A-M, II/B-M and IV-A. Furthermore, the mortars prepared with 15% RHA-FA released 5.67% less total of hydration than OPC and the materials containing 30% of the addition 13.54% less than the reference. In light of the foregoing, the new cements were found to be apt for use in construction, particularly in structures where large volumes of concrete are needed, for the reduction of the thermal gradient lowers the likelihood of surface cracking.

The influence of CuO nanoparticles and boron wastes on the properties of cement mortar

In this study, compressive and flexural strength, thermal properties, and pore structure of mortars modified with two types of boron waste and different amounts of CuO nanoparticles were investigated. The binders were prepared with 3% of borogypsum or borax waste and nano-CuO at concentration up to 4%. The setting time, compressive and flexural strength at 3, 7, and 28 days, DTA/TG, XRD, BET, and water absorption tests were carried out, and optimal nano-CuO percentages were determined. It was observed that nano-CuO addition in the range 2%–2.5% can improve mechanical properties, reduce the amount of unreacted portlandite, increase water absorption resistance, and decrease the setting time for borogypsum-containing mortars. The optimum nano-CuO replacement ratio changes between 0.5%–1% for borax waste-containing mortars. The results showed that nano-CuO was able to promote hydration reactions, act as a nanofiller, and provide a kernel for nucleation reactions.

The influence of different aggregates on the behavior and properties of gypsum mortars

The structure, behavior and properties of gypsum mortars with different types of fine aggregates were studied. Investigation by scanning electron microscopy shows that the presence of aggregate particles significantly influences the shape and size of gypsum crystals in the interfacial transition zone. The porosity of the gypsum matrix in mortars is greater than the porosity of pure gypsum paste and the pore size distribution shifts towards smaller pores. The shape and size of crystals in the transition zone depends on the surface roughness of the aggregate particles. The grain surface roughness was measured by confocal laser scanning microscopy. The properties of mortars also depend on the grain surface roughness. The workability, setting times and thermal conductivity decrease with increasing grain surface roughness, while the strength and water vapor resistance increase.

Effects of tablet waviness on the mechanical response of architected multilayered materials: Modeling and experiment

The excellent mechanical properties that biological materials possess are greatly influenced by the geometrical properties of their small scale constituents. Nacre, also known as Mother of Pearl, is an organic-inorganic composite material that makes up the inner layer of seashells. Nacre is observed for its impressive combination of stiffness, strength, and toughness which can be attributed to its waviness and the layering pattern of the brick and mortar structure of ceramic and protein that allows nacre to exhibit great mechanical energy and dissipate it over a large volume. In this study, the effect of this waviness on a model architected multilayered material system is analyzed numerically and experimentally in order to understand its effects on the stiffness, strength, and toughness of nacre. 3-D printed composites with auxetic and nacreous structure were created and tested in tensile boundary conditions. Finite element analysis was used to study the stress distribution and mechanical response of these composites. Results from the finite element models and the mechanical tests results show that increasing the tablet’s waviness increases the stiffness, however, there is an optimum value of tablet waviness for the highest strength and tensile toughness. Increasing waviness level can improve the elastic modulus by about 23%, strength by about 65% and toughness by about 42%. Using the proposed modeling approach, more detailed studies can be done on the toughening mechanisms of composite multilayered materials. These results can be used as a guide to design super-tough composites with multilayered structures.

Influence of Waste Glass Powder Addition on the Pore Structure and Service Properties of Cement Mortars

At present, reusing waste constitutes an important challenge in order to reach a more sustainable environment. The cement industry is an important pollutant industrial sector. Therefore, the reduction of its CO2 emissions is now a popular topic of study. One way to lessen those emissions is partially replacing clinker with other materials. In this regard, the reuse of waste glass powder as a clinker replacement could be possible. This is a non-biodegradable residue that permanently occupies a large amount of space in dumping sites. The aim of this work is to study the long-term effects (400 days) of the addition of waste glass powder on the microstructure and service properties of mortars that incorporate up to 20% of this addition as clinker replacement. The microstructure has been characterised using the non-destructive impedance spectroscopy technique and mercury intrusion porosimetry. Furthermore, differential thermal analysis was also performed. Compressive strength and both steady-state and non-steady-state chloride diffusion coefficients have also been determined. Considering the obtained results, mortars with 10% and 20% waste glass powder showed good service properties until 400 days, similar to or even better than those made with ordinary Portland cement without additions, with the added value of contributing to sustainability.

Lime mortars – The role of carboxymethyl cellulose on the crystallization of calcium carbonate

Aerial lime-mortars are widely used in the conservation interventions, in which polymers could improve their mechanical strength. In this work, the effects of carboxymethyl cellulose (CMC) on the crystallization of calcium carbonate (CaCO3) in lime mortar have been studied in order to explore the mechanism of the improvement. The experimental results have shown that CMC molecules played as templates to control the morphology and size of CaCO3 crystals. Without CMC, the crystals appeared in the form of cylinder, while CMC addition changed the crystalline shape to be fusiform at the low concentration and spherical at the high concentration. The crystal size increased with CMC addition to the maximum value then declined, leading the lime mortar structure to be more compact, thus improving the compressive strength of lime mortar. These results might be attributed to the restraint effect of CMC molecules to slow down the growth rate and crystallinity of CaCO3 crystals. It was also found that CMC did not affect the polymorph of CaCO3 crystals, which is beneficial to maintain the compressive strength of lime mortar.

Experimental Study in the Modification of Mortar Samples with Incorporated Rice Husk

Abstract The aim of this work is to investigate the influence of rice husk (RH) on the properties of mortar. Two different RH were used as integral additives in the mortar samples: direct natural RH addition to the mortar and the use of pretreated RH. The results of such modification are described, taking into consideration the interaction between the RH and mortar. In addition, the physical properties, visual observation and microstructure of mortar prepared with different amount of modified RH were experimentally studied. The test results indicated that modification of RH enhanced the interaction between the RH and mortar because of the impurities removal and rougher surface. Comparing with the natural RH, the modification of RH increases the density and the mechanical properties. The addition of RH can increase the pore number of the mortar mixture, resulting in decrease in the density and mechanical properties of mortar. Morphology characterization results showed that the modification of RH results in an improvement in the interaction between the RH and mortar and further increase in RH content increases the number of pores in the mortar structure.

Influence of a Crystalline Additive on the Porosity of Cement Mortars

The pore structure of a material radically infuences its properties, such as strength, freeze-thaw resistance, capillarity or resistance to elevated temperatures. The character of the pore structure is also limiting for the intrusion of aggressive oxides into the material, which affects its service life. The paper describes how a crystalline additive influences the pore structure of cement mortars. It describes the effect of secondary crystallisation and the influence of the additon of PP fibers on the apparent porosity and the internal structure of the mortar. It also discusses the influence of aggressive conditions on the mortar’s pore structure.

Hydrophobisation of mortars containing waste polyurethane foam

This paper investigates the physical and mechanical properties of mortars modified with waste polyurethane foam (WPF) and the influence of hydrophobising agents on the physical characteristics. The sand was substituted with WPF (2-4 mm grain size) in the mortars which consisted of 5, 10 and 15% of foam, respectively. The contact angle of lightweight mortars was determined (θw) in the function of time, prior to and after the frost resistance test. The surface free energy characterizing the wettability and adhesion of mortars under normal conditions and following frost erosion was calculated with Neumann’s method based on the obtained data. The structure of mortars, adhesion of lightweight aggregate to cement paste and the structure of thin hydrophobic film were demonstrated by means of scanning electron microscopy. The mortars subjected to hydrophobisation process revealed a slight mass change caused by freezing and thawing processes: 0.1% for methyl silicone resin, 2.1% for alkyl-alkoxy-silane, and 9.2% for the samples which were not hydrophobized. On average, the contact angle of the standard mortars was 3 times lower than the one of hydrophobic material. The best results illustrating the efficiency of hydrophobisation were obtained for methyl silicone resin.

Structure and properties of masonry mortars based on ceramic microspheres

Modern requirements in the field of energy and resource saving determines the need to apply effective fencing structures. To ensure the thermal homogeneity of the structures erected with small-piece masonry elements (ceramic and light-weight concrete units etc.), it is necessary to use lightweight mortars. One of the most effective methods to obtain such mortars is the introduction of hollow ceramic microspheres as a filler into their composition. The purpose of this work is studying of the composition and structure of a cement masonry mortar with hollow ceramic microspheres and modifying additives in correlation with its properties. The methods of thermogravimetric analysis, scanning electron microscopy, X-ray diffraction and standard test methods for the masonry mortars were used. The effect of the structural characteristics of the composite on the properties of final product was analyzed. It is established that the microstructure of the modified mortar samples is more compact in compare with basic composition, and the surface of the microspheres is covered by the products of the chemical interaction of its walls with the cement matrix. The aforesaid research allowed to obtain the high-performance lightweight mortars with hollow ceramic microspheres.

The influence of type of cement on the degradation of microstructure and transport properties of cement mortars exposed to frost induced damage

The purpose of the study is to understand how the cyclic water freezing (0, 25, 50, 75, 100 and 150 freeze-thaw cycles) impacts microstructure and transport properties of cement-based materials. Tests were conducted on cement mortars with different water/cement ratios (w/c=0.45 and 0.40) and on two types of cement (CEM I and CEM III) without air-entraining admixtures. The changes of pore size distribution and open porosity were investigated by means of mercury intrusion porosimetry. Additionally, the relationship between intrinsic permeability and the water absorption coefficient of cement mortar samples was analysed. The water absorption coefficient and gas permeability were determined using capillary absorption test and the modified RILEMCembureau method. The evolution of transport coefficients with growing number of freeze-thaw cycles were determined on the same sample. It was also established that change of pore structure (a decrease of small pore volume <100nm and increase of larger pores >100nm) induces an increase of water transport parameters such as permeability and water absorption coefficient. The higher gas permeability corresponds to the higher internal damage. In particular, it is associated with the change of cement mortar microstructure, which indicates damage of narrow channels in the pore structure of cement mortars.

Pore structure of mortars containing limestone powder and natural pozzolan assessed through mercury intrusion porosimetry and dynamic vapour sorption

Pore structure characterization is a key aspect when studying the durability of cementitious materials. When supplementary cementitious materials (SCMs) are used changes in pore structure are expected, and the complexity of its analysis is increased. The purpose of this paper is to describe the pore structure variation of mortars with two types of SCMs: natural pozzolan from volcanic origin (NP), and limestone powder (LP). We tested mixes with cement replacements (in weight) of 20 % and 40% by NP, and 10 % and 20% by LP. To analyse the pore structure, two widely accepted and complementary techniques were applied: dynamic water vapour sorption (DVS) and mercury intrusion porosimetry (MIP). With the DVS data, the Barret-Joyner-Halenda (BJH) model was used for pore size distribution assessment. Calculations with the Dubinin-Radushkevich (DR) model were also made for the smallest pore size range. Tests were performed at 28 and 90 days. MIP and DVS allowed evaluating the effect of the studied SCMs on different pore size ranges. Both techniques provided comprehensive information over a wide range of pore sizes. The mix with 40 % of NP had the best evolution, showing a significant volume decrease in the mesopore range.

Steady-state O2 and CO2 diffusion in carbonated mortars produced with blended cements

The diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ , the porosity and the pore structure of mortars produced with a Portland cement and a range of blended cements containing limestone powder, microsilica, portlandite or slag were measured in the non-carbonated and the carbonated state. Additionally, the setup for measuring O2 diffusion was adapted to measure also the CO2 diffusion of the carbonated mortars. The diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ and the total porosity were increased in the mortars containing microsilica and slag, while they were decreased in the other mortars due to carbonation. Invariably, the pore structure became coarser in all samples. The relationship between diffusion coefficients $$D_{{{\text{O}}_{2} }}$$ and $$D_{{{\text{CO}}_{2} }}$$ in the carbonated mortars was always linear, with $$D_{{{\text{O}}_{2} }}$$ systematically higher by factor of 1.37. As this factor broadly agrees with what was found in the scant literature about CO2 diffusion, it could be used for estimating $$D_{{{\text{CO}}_{2} }}$$ of carbonated mortar and concrete based on measurements of O2 diffusion.

Polymer-clay nanocomposite coatings as efficient, environment-friendly surface pretreatments for aluminum alloy 2024-T3

Surface pretreatment coatings are a research area in continuous transformation. Moving away from the well-known chromium conversion coatings (CCC) toward an environment-friendly alternative is of great interest. Materials such as the aluminum alloy 2024-T3 (AA2024-T3) used in aircraft, for example, provide good mechanical performance but lack good corrosion resistance. Here, we present a polymer-clay coating made from branched polyethylenimine (BPEI) and montmorillonite (MMT) clay as a potential CCC substitute, and we examine this for the corrosion protection of AA2024-T3. This polymer-clay coating is applied by airbrushing an aqueous BPEI/MMT mixture onto any substrate. With this approach, application time is significantly reduced in comparison to other techniques (e.g. layer-by-layer assembly), and the structure of the polymer-clay coating is finely tuned by controlling the polymer-clay ratio. Results from electrochemical measurements and salt spray testing reveal good long-term (40d) corrosion protection of AA2024-T3 provided by a 1.8 μm thick coating with a 20:80 polymer-clay ratio. This polymer-clay ratio yields a highly ordered multilayered brick and mortar structure, where MMT (bricks) provides a physical barrier for the diffusion of corrosive agents/corrosion products within the coating, and BPEI (mortar) provides structural support and decelerates the corrosion process through surface buffering.

Ultrasonic pulse and resonance method–evaluation of the degree of damage to the internal structure of repair mortars caused by exposure to high temperatures

When the repair mortars for the repair of concrete structures are exposed to high temperatures, it results in irreversible changes in their internal structure. These changes can be evaluated both on the basis of the compressive strength and flexural strength, but their evaluation can also be made using dynamic non-destructive methods. The article presents the findings on the use of parameters from the measurement by ultrasonic pulse and resonance method. Changes in the internal structure of repair mortars were evaluated on the basis of the dynamic Young’s modulus of elasticity and relative dynamic modulus of elasticity. The said parameters very well characterize the changes in the internal structure of the repair mortars, and their values decrease with the increasing temperature. Changes in the internal structure of the repair mortars also reduce the compressive strength and flexural strength. The researchers confirmed the suitability of the ultrasonic pulse and resonance method for evaluating the degree of damage to the internal structure of repair mortars exposed to high temperatures.

Review on 3D Prototyping of Damage Tolerant Interdigitating Brick Arrays of Nacre

The complex hierarchal architecture of nacre has revolutionized the field of materials science and engineering due to its unparalleled properties of strength, stiffness, damage tolerance and toughness. The characteristics of interdigitating brick and mortar structure is attributed as a conspicuous architecture for its unique combination of properties, which is organized over multiple hierarchal level from macro to nanometer in size. Despite the development of adequate methodologies such as layer-by-layer and self-assembly, imitating these physical and morphological intricacies in “one step” is still a complex and complicated phenomenon. Therefore, additive manufacturing techniques such as 3D printing can be a plausible candidate for manufacturing futuristic design concepts of composite, inspired from naturally graded functionality. In this review article, we have outlined the possibility of utilizing 3D printing technology and its challenges for bionic prototyping of nacre structure in artificial materials.

Use of Carbon Nano-Fibers in Cementitious Mortar

Cementitious materials, especially those with higher compressive strengths, provide relatively low toughness, tensile strength and strain capacity, and are susceptible to cracking under load and restrained shrinkage effects. These drawbacks were overcome through development of multi-scale reinforcement systems comprising carbon nanofibers and microfibers for high-strength cementitious mortars. Multi-scale reinforcement of the high-performance mortar produced significant gains in the flexural strength and toughness, and abrasion and impact resistance. Microstructural investigations were also conducted in order to provide insight into the structure and failure mechanisms of high-performance cementitious mortars with multi-scale reinforcement.

Exceptionally strong, stiff and hard hybrid material based on an elastomer and isotropically shaped ceramic nanoparticles

In this work the fabrication of hard, stiff and strong nanocomposites based on polybutadiene and iron oxide nanoparticles is presented. The nanocomposites are fabricated via a general concept for mechanically superior nanocomposites not based on the brick and mortar structure, thus on globular nanoparticles with nanosized organic shells. For the fabrication of the composites oleic acid functionalized iron oxide nanoparticles are decorated via ligand exchange with an α,ω-polybutadiene dicarboxylic acid. The functionalized particles were processed at 145 °C. Since polybutadiene contains double bonds the nanocomposites obtained a crosslinked structure which was enhanced by the presence of oxygen or sulfur. It was found that the crosslinking and filler percolation yields high elastic moduli of approximately 12–20 GPa and hardness of 15–18 GPa, although the polymer volume fraction is up to 40%. We attribute our results to a catalytically enhanced crosslinking reaction of the polymer chains induced by oxygen or sulfur and to the microstructure of the nanocomposite.

Influence of fly ash on the pore structure and shrinkage characteristics of metakaolin-based geopolymer pastes and mortars

This study investigates the pore structure and shrinkage behavior of metakaolin-based geopolymer pastes and mortars containing 0–30% fly ash. Fly ash substitution decreases average reactivity of the solid precursors, resulting in a lower reaction rate and accompanying longer reaction time. Composition of the sodium aluminosilicate (N-A-S-H) gel formed in the geopolymers has been changed, and the continued reaction after hardening of the pastes generates a more compact binding gel phase with lower Al/Si ratio. Refinement of the pore structure entails a higher capillary tension developed in the binders to increase the autogenous shrinkage, but also restricts the water evaporation from the pore networks, resulting in a decreased drying shrinkage. The geopolymer mortars provide higher compressive strength and lower total shrinkage when compared with the pastes.