Decrease In Adhesion Strength Research Articles

Activation of muscle amine functional groups using eutectic mixture to enhance tissue adhesiveness of injectable, conductive and therapeutic granular hydrogel for diabetic ulcer regeneration

Herein, Polydopamine-modified microgels and microgels incorporated with superficial epoxy groups were synthesized and applied as precursors for the fabrication of four granular hydrogels. To enhance the tissue adhesiveness, a ternary deep eutectic solvent was synthesized to activate the muscle amine functional groups facilitating the formation of robust NC bonds at ambient conditions. At a certain shear rate of 10 s−1, hydrogel DMG displayed a viscosity of 9×103 Pa/s, representing the highest complex viscosity among the tested hydrogels primarily driven by quinone groups in PDA which enhanced reversible interactions, thereby increasing particle cohesion. Moreover, the intersection point escalating from about 4×103 to approximately 9×104 as the concentration of DMG increased from 0 % (for MG) to 70% (7D3MG) by weight. There was a decrease in adhesion strength from 0.45 ± 0.08 N in MG to 0.39 ± 0.16 N, 0.35± 0.18 N, and 0.33 ± 0.15 N for 3D7MG, 7D3MG, and DMG respectively, suggesting that MG was capable of forming numerous covalent bonds, thereby enhancing its adhesion to the substrate. The type of eutectic mixture affected the electrical conductivity and a very important point was the changes in resistance value with time. For MG catalyzed by [DES]AZG, the resistance increased only by 1.3 % (from 3.37 to 3.81 kΩ) at day 3 and 37.09 % (from 3.37 to 4.62 kΩ) at day 5. The 3D7MG hydrogel exhibited superior therapeutic efficacy toward diabetic wound regeneration. The proliferation index value for 3D7MG-[DES]AZG and 3D7MG-[DES]AG were calculated 42.3 % and 58.6 %, respectively, while the control group exhibited a lower value of 37.8 %.

INFLUENCE OF TANGENTIAL SLIDING ON THE CONTACT AREA OF A MACROSCOPIC ADHESIVE CONTACT

Influence of tangential force on the adhesive contact, in particular on the adhesive strength and the contact area have been a subject of investigation and discussions for many years. Depending on the system under consideration, both increase and decrease of adhesion strength due to shearing of an adhesive contact have been reported. The same is valid for change of the contact area. While it is generally accepted that the contact area decreases when applying tangential traction, also opposite behaviour is possible. In the present paper we study theoretically and experimentally the conditions under which the contact area may increase or decrease due to shear.

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.

New insights on bonding mechanism of FCC and BCC high entropy alloy microparticles upon supersonic impact using micromechanical adhesion test

Coating buildup in cold spraying (CS) relies on particle bonding upon impact, thus making it a significant area of study. High entropy alloys (HEAs) are a class of materials with superior work-hardening ability and resistance to softening, making their particle impact and bonding particularly important to understand for their cold sprayability. In this study, the splat adhesion strength is measured with a scratch test for FCC CoCrFeMnNi and BCC AlCrFeMnNi HEA microparticles deposited on mirror-polished SS304 substrates. Nanoindentation tests were conducted to estimate the tensile and shear strengths of the HEA powders. The results showed that particle deformation and jetting were dominant in the FCC HEA/SS304 system, while substrate deformation was dominant in the BCC HEA/SS304 system. Focused ion beam cross sections of particles confirmed that the FCC HEA had good bonding and underwent significant deformation and grain refinement at the substrate/particle interface, while the BCC HEA had limited bonding only in the sheared zone of the particles.In spite of the very limited deformation of BCC splats, their average adhesion strength was measured to be 451 ± 141 MPa, which is significantly higher than that of FCC splats, with an average value of 308.7 ± 69.3 MPa. Fracture surface analysis revealed that FCC splats consistently exhibit ductile fracture, regardless of whether it occurs at the particle, substrate, or interface. In contrast, for BCC splats, fracture was ductile when occurring at the interface and substrate sides, while it was cleavage when occurring on the particle side. These findings suggest that the toughness and shear strength of the bonding developed at the interface were higher than those of the particle. It was found that the flattening ratio (FR) of the particles decreases for both FCC and BCC HEA splats with an increase in particle size, resulting in a decrease in adhesion strength. Metallurgical bonding has been identified as the primary factor contributing to the adhesion strength of both FCC and BCC HEA splats. Particle penetration, indicative of mechanical interlocking, appears to have little or no effect on adhesion strength. However, it does positively influence the increase in adhesion energy of the splats.

Effect of Al content on in-situ formation of Al2O3 protective layer on Ni-Al coatings in high-temperature chloride molten salt

The microstructure, strength, toughness, and resistance to chloride molten salt corrosion of Ni-Al coatings with varying Al content were investigated. Increasing the Al content from 9.9 to 61.1 at.% resulted in a decrease in adhesion strength and toughness, while an increase in corrosion rate. Contrary to previous reports, it is noteworthy that Ni-Al coatings with the lowest Al content exhibited superior resistance corrosion due to the formation of an oxidation layer which effectively blocked corrosion. This protective layer was primarily in-situ formed through the reaction between crystalline water present in the molten salt and an appropriate amount of Al. The balance between Al and O content is precisely regulated, resulting in the in-situ formation of Al2O3 protective.

Improvement of corrosion resistance and adhesion of hydroxyapatite coating on AZ31 alloy by an anodizing intermediate layer.

The primary objective of this study is using an anodizing intermediate layer to improve corrosion resistance and adhesion of hydroxyapatite coated AZ31 alloy for applications in biodegradable implants. An anodizing intermediate layer was formed on the surface of AZ31 substrate at various anodizing voltage of 10, 20, 30, and 40 V respectively by anodizing process. HAp was grow on the surface of AZ31 substrate at 90°C and pH solution of 7.5 by chemical solution treatment method for 2 h. The coated samples were evaluated their corrosion behavior by Electrochemical measurements and biodegradation behavior by immersion test in Hank's balanced salts solution (HBSS) for 28 days via amount of Mg2+ ion released. While, their adhesion strength were evaluated by pull-off method. The amount of Mg2+ ions released of the samples was quantified by the Inductively coupled plasma mass spectrometry. An anodizing intermediate layer was successfully synthesized at various voltages by anodizing process and HAp coatings were prepared by chemical solution treatment method. The corrosion rate of hydroxyapatite coated AZ31 alloy with an anodizing intermediate layer decreased 4.4 times, while adhesion strength increased about two times compared to the HAp coated AZ31 specimen without an anodizing layer and achieved ~14.70, ~6.92 MPa, respectively. After immersion test in HBSS, the adhesion strength of HAp/AZ31-HBSS-specimen decrease to 45% because of large corroded areas with depth holes of hundreds of micrometers. The slighter decrease in adhesion strength of HAp/30V/AZ31-HBSS-specimen to 22% is due to the contribution of the anodizing intermediate layer. HAp coated AZ31 alloy specimen with the existence of a porous structure with an elliptical shape, uniform and high density of MgO on the surface at anodizing voltage of 30 V resulted in a significant increase in corrosion resistance and the adhesion strength of HAp coatings.

Investigation of surface properties of biocomposite materials modified by corona plasma treatment

Studies aimed at determining the features of printing on biocomposite polymer materials were carried out. It has been found that the untreated composite films have a low adhesion strength at the composite film-paint interface, the surface tension did not exceed 28 mN/m, and the contact wetting angle was greater than 80 degrees. When the surface is activated by the "corona" discharge method, the adhesion properties appear to a greater extent, and with an increase in the processing stress of the "corona" discharge, the adhesion strength also increases. Thus, in a 25 kV surface treatment, the surface tension for the test composites was estimated to be above 40 mN/m and the contact wetting angle was less than 45 degrees. For BHA based on LDPE and TPC of various bases (corn, pea, rice), adhesion strength was evaluated in the range from 2.9 to 3.5 N/cm2, for PCM based on LDPE and ORD - 29 N/cm2. The result of this work is an increase in surface tension due to the appearance of polar groups on the surface of composite films, in particular oxygen-containing C-O and C = O, as confirmed by Fourier IR spectroscopy. Although the adhesion strength at the film-paint interface is increased when the surface of the composite films is activated, it has been observed that for LDPE-based BHC and thermoplastic starch, the adhesion properties are not constant and decrease over time. After two weeks, adhesion strength was evaluated, on average, 1.4 N/cm2. Most likely, BHCs do not transition to the electret state when the surface is activated by "corona" discharge, and external factors such as temperature and humidity act, as a result of which the number of polar groups on the surface decreases. On the contrary, a slight decrease in adhesion strength from 29 to 27 N/cm2 was observed for PCM based on LDPE and OPD, which is due to the chemical nature of the starting components.

The effect of different strong acids and silica‐coating on resin Ti adhesion

The presence of Si on the Ti surface is quintessential for a strong, durable silane‐based adhesion utilized in several dental applications. Silica‐coating and silanization form durable ≡Si‐O‐Si≡ bonds, which might have a positive effect on resin‐Ti adhesion. This laboratory study studied the effect of strong acids, their blends, and silica‐coating on Ti and resin‐Ti bonding. One‐hundred sixty‐eight c.p. grade 2 polished Ti samples (10 mm × 10 mm × 1 mm), out of which 96 were etched with 9% and 12%HF, a blend of 35%HCl+85%H3PO4 and a blend of 69%HNO3+35%HCl at 60°C, each for 2 min. One half was silica‐coated (Rocatec™ Plus, 110 μm SiO2‐coated‐Al2O3). Sixty Ti samples were first silica‐coated, and then, 48 of them were etched with 9%HF, 12%HF, a blend of 35%HCl+85%H3PO4, and a blend of 69%HNO3+35%HCl at 60°C for 2 min. SEM, EDX, XPS, and Ra analyses were carried out. Polished Ti samples were controls. All silanizations were carried out with a blend of 0.3 vol% 1,2‐bis‐(triethoxysilyl)ethane+1.0 vol% 3‐acryloxypropyltrimethoxysilane. Multilink™ Automix self‐adhesive resin composite cement was used in adhesion testing, and the samples were artificially aged followed by enclosed‐mold micro‐shear test on day 1 and weeks 1, 4, and 8. Failure mode analysis and statistical analysis with one‐way/two‐way ANOVA (p < 0.05) were carried out. HF etching produced the highest surface roughness. XPS analysis identified after etching with HF a variety of Ti and Si ions: Ti4+, Ti3+, Ti2+, and Ti0 and, on the other hand, Si4+, Si3+, and Si2+. A gradual decrease in adhesion strength was observed after artificial aging. Adhesive and cohesive failures were observed.

Overcoming the adhesion paradox and switchability conflict on rough surfaces with shape-memory polymers

Smart adhesives that can be applied and removed on demand play an important role in modern life and manufacturing. However, current smart adhesives made of elastomers suffer from the long-standing challenges of the adhesion paradox (rapid decrease in adhesion strength on rough surfaces despite adhesive molecular interactions) and the switchability conflict (trade-off between adhesion strength and easy detachment). Here, we report the use of shape-memory polymers (SMPs) to overcome the adhesion paradox and switchability conflict on rough surfaces. Utilizing the rubbery-glassy phase transition in SMPs, we demonstrate, through mechanical testing and mechanics modeling, that the conformal contact in the rubbery state followed by the shape-locking effect in the glassy state results in the so-called rubber-to-glass (R2G) adhesion (defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state), with extraordinary adhesion strength (>1 MPa) proportional to the true surface area of a rough surface, overcoming the classic adhesion paradox. Furthermore, upon transitioning back to the rubbery state, the SMP adhesives can detach easily due to the shape-memory effect, leading to a simultaneous improvement in adhesion switchability (up to 103, defined as the ratio of the SMP R2G adhesion to its rubbery-state adhesion) as the surface roughness increases. The working principle and the mechanics model of R2G adhesion provide guidelines for developing stronger and more switchable adhesives adaptable to rough surfaces, thereby enhancing the capabilities of smart adhesives, and impacting various fields such as adhesive grippers and climbing robots.

Elevated temperature axial crushing performance of multi-walled tube-reinforced aluminum foam

In this study, the influence of temperature on axial crushing behavior of multi-walled tube-reinforced aluminum foams (MWTRF) were researched by means of experiment, numerical prediction and theoretical analysis. The results indicate that the peak force and energy absorption performance of the MWTRFs present noticeably higher than those of the sum of aluminum foam (AF) and empty multi-walled tube (EMWT) at high temperature. The axial crushing performance of glued MWTRF is higher that of unglued MWTRF. This advantage gradually decreases with the increase of temperature due to a decrease of adhesive strength. The reinforcing mechanism is that AF in MWTRF inhibits buckling and alters the crushing deformation mode of EMWT, significantly improving the crushing performance and energy absorption performance of MWTRF. In addition, compared with the competing materials, MWTRFs have the outstanding performance of energy absorption under high temperature in a map for material selection.

Optical Tracking of Surfactant-Tuned Bacterial Adhesion: a Single-Cell Imaging Study.

Probing the interfacial dynamics of single bacterial cells in complex environments is crucial for understanding the microbial biofilm formation process and developing antifouling materials, but it remains a challenge. Here, we studied single bacterial interfacial behaviors modulated by surfactants via a plasmonic imaging technique. We quantified the adhesion strength of single bacterial cells by plasmonic measurement of potential energy profiles and dissected the mechanism of surfactant-tuned single bacterial adhesion. The presence of surfactant tuned single bacterial adhesion by increasing the thickness of extracellular polymeric substances (EPS) and reducing the degree of EPS cross-linking. The adhesion kinetics and equilibrium state of bacteria attached to the surface confirmed the decrease in adhesion strength tuned by surfactants. The information obtained is valuable for understanding the interaction mechanism between a single bacterial cell and surface, developing new biofilm control strategies, and designing anticontamination materials. IMPORTANCE Studying the interfacial dynamic of single bacteria in complex environments is crucial for understanding the microbial biofilm formation process and developing antifouling materials. However, quantifying the interactions between microorganisms and surfaces in the presence of pollution at the single-cell level remains a great challenge. This paper presents the analysis of single bacterial interfacial behaviors modulated by surfactants and quantification of the adhesion strength via a plasmonic imaging technique. Our study provided insights into the mechanism of initial bacterial adhesion, facilitating our understanding of the adhesion process at the microscopic scale, and is of great value for controlling membrane fouling biofilm formation.

Adhesion strength of straw biomass ash: Effect of dolomite additive

A self-designed tester is used to study the ash adhesion strength of straw biomass and the effect of dolomite additive. TG-DSC, SEM-EDX, XRD and thermodynamic equilibrium are applied to analyze the thermal behaviors, mineral transformation and liquid phase formations of ash samples. The results indicate that the adhesion strength of rice straw ash appears at 600 °C, increases rapidly above 700 °C, and reaches 21.83 kPa at 1000 °C. The melting related to KCl causes the ash adhesion strength of rice straw at low temperature. The more viscous silicate melts result in a rapid rise in ash adhesion strength with increasing temperature. Dolomite additive can inhibit the melting of KCl and increase the appearance temperature of ash adhesion strength. Dolomite promotes the formation of high melting point minerals such as orthoclase, CaMgSi2O6, wollastonite, periclase and magnesium silicate in ash, reduces the liquid phase and controls the growth of ash adhesion strength. When the addition ratio is more than 5%, dolomite has a better inhibitory effect on the ash adhesion strength of straw. When 5% dolomite is added, the appearance temperature of ash adhesion strength increases by 200 °C, and the ash adhesion strength decreases by 58.54% at 1000 °C.

Influence factors and calculation model of the adhesion strength of clayey soil for EPB shield tunnelling

Abstract When earth pressure balance (EPB) shield tunnels are constructed through clayey ground, the soil adheres to the cutter, cutterhead and chamber bulkhead due to the high adhesion strength between the steel and the clay, thus clogging the shield. To investigate the influence of different factors on the adhesion strength, this study used montmorillonite, kaolin and mixtures of the two as test soils. The adhesion strength between the steel and clay is determined with a customized rotary shear apparatus. The results show that when the consistency index of the soil specimen is less than 1, the adhesion strength between the steel and clay increases with the consistency index. As the consistency index decreases, the effect of the normal pressure on the adhesion strength gradually weakened. As the contact angle of the shear plate increases, thus reducing the hydrophilicity, the adhesion strength decreases. When the soil specimens with different plasticity index values have the same consistency index value, the adhesion strengths are similar. The adhesion strength increases gradually with increasing surface roughness. Based on grey incidence analysis, the order of the factors affecting the adhesion strength is as follows: normal pressure > consistency index > contact angle > plasticity index ≈ surface roughness. The normal pressure, consistency index and contact angle all have important effects on the adhesion strength between steel and clay. However, because there are no large differences in the contact angle among the metal materials, the approximate adhesion strength can be calculated by considering the effects of only the normal pressure and consistency index. The measures that are effective for preventing EPB shield clogging are increasing the soil softness and decreasing the hydrophilicity of the cutterhead by applying new materials for the cutters and cutterhead.

Adhesion strength of electrodeposited Ni, Zn, and Fe coatings with copper substrates

ABSTRACT This paper presents the adhesive strength values of electrodeposited nickel, zinc, and iron coatings on copper substrates at various deposition parameters, including laser-assisted stimulation of the deposition process. One of the factors determined to be responsible for the adhesive strength of metal films with a metal substrate is the formation of a diffusion zone at the ‘coating-substrate’ interface. It is shown that an increase in adhesive strength is achieved due to the expansion of the diffusion zone and the formation of solid solutions. The decrease in adhesive strength at high overpotentials is associated with the release of hydrogen and the formation of intermediate phases.

Research of the influence of xanthan gum on rheological properties of dough and quality of bread made from sprouted wheat grain

The effect of microbial polysaccharide xanthan in the amount of 0.1-0.4% on the rheological characteristics of the dough from sprouted wheat grain and quality indicators of bread was studied. It was found that when xanthan gum is added, the dough's spreading and adhesion strength decreases, and the dough's resilience-elastic and plastic-viscous characteristics improve. Bread made from sprouted wheat grains with the addition of experimental dosages of xanthan has better structural-mechanical and physicochemical properties, as evidenced by higher indicators of crumb compressibility, specific volume, and moisture compared to the control sample. To obtain bread with the best quality indicators, it is recommended to use 0.3% xanthan.

INVESTIGATION OF THE ABILITY TO BIODEGRADABILITY OF POLYURETHANE FOAM COMPOSITE MATERIALS WITH ALBUCID AND THE DYNAMICS OF ALBUCID RELEASE IN VITRO

Studies of biodegradability of polyurethane foam (PUF) composite materials with albucid under the influence of biological medium 199 (BM 199) and saline solution for 2 weeks, 1, 3 and 6 months were conducted. IR spectroscopy, physical-mechanical tests, DSC and TGA before and after incubation in model mediums were investigated. It was found that the influence of BM 199 and saline solution on the structure and properties of composite materials with albucid is similar. According to the results of physical-mechanical studies under the influence of model mediums there are processes of biodegradation which are confirmed by a decrease in adhesive strength after incubation in BM 199 and saline solution. According to IR spectroscopy, biodegradation is accompanied by redistribution of hydrogen bonds of NH groups of the polymer matrix. The results of studies by the DSC method indicate a decrease of Tg and increase of ΔСР of PUF composites with albucid compared to the control, which is associated with increasing of segmental mobility of macromolecules under the influence of model mediums and due to the albucid release from polymer matrix. It was found that PUF and PUF composites with albucid in vitro remain heat-resistant materials, because after incubation in BM 199 and a saline solution there is an increase in T0 and Tmax by the TGA method. Studies of the dynamics of albucid release from the PUF matrix were carried out. It was found that the composite materials are capable to the prolonged release of the drug. The amount of released albucid is 36.0 % on the 60th day of the experiment, which does not exceed the therapeutic dose and has no toxic effects. Therefore, polyurethane foam composite materials with albucid can be proposed as promising materials for use as implants with prolonged action of albucid in ophthalmological surgery.

Preparation of a superhydrophobic coating based on polysiloxane modified SiO2 and study on its anti-icing performance

An anti-icing surface with superhydrophobic properties was designed by combining poly(methyl-3,3,3-trifluoropropyl siloxane) (PMTFPS) modified silica with a low surface free energy fluorine‑silicone resin. The hydrophobic silica particles were characterized using SEM, FTIR, and XPS. The hydrophobicity, wettability and wear resistance of the resulting coating were analyzed. The anti-icing and de-icing properties of the coatings were also characterized in terms of complete icing time and ice adhesion strength. The obtained SiO2-PMTFPS coating achieved a contact angle of 158.5° and a roll-off angle of 1°. Compared with tinplate sheets, icing time is delayed by 200% at −10 °C and 800% at −15 °C. Ice adhesion strength decreases by 91.8% compared with tinplate, making ice relatively easy to remove. After sandpaper abrasion and immersion in solutions with different pH and temperature, the coating is proven to exhibit good abrasion resistance and chemical durability in water solutions.

A strong underwater adhesive that totally cured in water

• A facilely synthesized isocyanate-modified PDMS underwater adhesive was developed. • The adhesive was totally cured in water and adhered various substrates. • The highest underwater adhesion strength reached 2.8 MPa for PET. • The underwater adhesion mechanism of the adhesive was proposed. Underwater adhesives have drawn enormous interests for biomedical and engineering applications. In this work, a strong underwater adhesive is developed by addition reaction between bis(3-aminopropyl) terminated polydimethylsiloxane (PDMS) and hexamethylene diisocyanate (HDI). The PDMS-based adhesive was totally cured in aqueous solutions and exhibited strong adhesion with various substrates. The highest underwater adhesion strength of the adhesive on polyethylene terephthalate (PET) substrate reached 2.8 MPa, which is comparable with those commercial glues that cured in air. Such strong underwater adhesion is mainly caused by the combination of chemical crosslinks, hydrogen bonds and other physical interactions. Further study reveals that increasing the curing temperature can decrease the mechanical strength of the adhesive, which leads to a decrease in adhesion strength. Moreover, increasing the salt concentration in aqueous solution would screen the electrostatic charges at the interface and impair the underwater adhesion. Besides, the tensile adhesion tests suggested that the underwater adhesion strength was enhanced by 3 times as the curing time extended from 3 h to 6 h. The increased adhesion is mainly caused by the enhanced mechanical strength of the polymeric adhesive as well as the increased interactions at the adhesive-substrate interface. In addition, the strong adhesion force of the adhesive is also demonstrated from the microscale by employing atomic-force-microscope force measurement. This work provides both practical and fundamental insights into developing underwater adhesives with strong adhesion.

Adhesive properties of thiol-acrylate-epoxy composites obtained by dual-curing procedures

Composite materials were prepared using a thiol-acrylate-epoxy dual-curing system filled with Boron Nitride (BN) agglomerates. The adhesive properties obtained with two different acrylate ratios (r a ) were tested to characterize differences and applicability of final thermosets. The effect of bondline thickness, BN wt% and curing procedure on the adhesive strength was evaluated for both acrylate ratios r a by means of lap-shear tests. Materials with viscous intermediate (r a = 0.2) results were observed to have the best performance reaching a maximum of almost 5 kN with 20 wt% of BN. On the other hand, materials with an intermediate gelled network (r a = 0.5) showed a high accuracy in dimension control but lower values of adhesive strength were obtained. A decrease of adhesive strength with the increase of thickness was found for both r a , while the increase of BN wt% lead to higher adhesive strength. The beneficial effect of dual-curing processing on the adhesive properties of liquid intermediate materials was also experimentally demonstrated.

Bond Properties of NHL-Based Mortars with Viscosity-Modifying Water-Retentive Admixtures

This article studies the influence of biopolymeric viscosity-modifying admixtures with water-retentive function on the physico-mechanical properties of natural hydraulic lime-based mortars and their adherence to the traditional fired-clay brick substrate. The use of admixtures increases the water/binder ratio, which in turn leads to a decrease in the strength of the mortars. The viscosity-modifying function improves the adhesive strength between mortar and pre-wetter brick by increasing the binder paste viscosity, while the water-retentive function along with increased water content may lead to a decrease in adhesive strength. On the contrary, water retention and increased water content are beneficial on a dry surface, while paste viscosity plays only a minor role. When subjected to temperature-varying cycles, the mortars are more prone to in-mortar failure during the pull-off test. The air-entraining function of some admixtures improves the frost resistance of the mortars; however, it would negatively affect the adhesive strength by incorporating pores into the contact zone between the mortar and brick substrate. This study showed that the use of some of the studied admixtures may improve the adhesion of mortar to the brick substrate.