Inorganic Adhesives Research Articles

Experimental Assessment of NSM FRP Systems with Inorganic Adhesives for Concrete Strengthening

Abstract: This study explores the application of various inorganic resins in the Near-Surface Mounted (NSM) strengthening technique, aiming to provide alternatives to traditional organic resins. The research centers on sixty single lap-shear concrete blocks, employing four distinct adhesives—ordinary mortar, Ultra-High-Performance Concrete (UHPC), geopolymer, and polyester-silica—for bonding Carbon Fiber-Reinforced Polymer (CFRP) strips to the concrete blocks. Conducted under monotonic loading, the investigation assesses the bond characteristics between the inorganic resins and both CFRP composites and the concrete substrate. Interfacial behaviour, bond strength, and failure modes are meticulously analyzed, shedding light on the performance of each adhesive. The study reveals insights into the efficiency of the NSM system, emphasizing the significance of the bond between FRP composites and concrete for optimal strengthening. The findings underscore the limited research on NSM systems using inorganic resins, providing a foundation for further exploration in this domain.

Improving the performance of geopolymer-based wood adhesives using a green mechanochemical strategy

Geopolymers are a new type of inorganic polymeric cementitious material with excellent properties such as flame retardancy and thermal stability. In this work, an environmentally friendly geopolymer-based adhesive was prepared using a one-step mechanochemical method, and the geopolymer-based adhesive was used to develop a low-cost, aldehyde-free, and highly flame-retardant plywood. Mechanical ball milling generated high temperatures through the collision of the agate balls and the material, which facilitated the polymerization reaction of the geopolymer. This method increased the viscosity of the adhesive and enhanced the “riveting” of the mechanical interlocks between the geopolymer and the wood. When the solid-liquid ratio of the synthetic geopolymer was 2.2, the bonding strength of the plywood developed using the adhesive prepared by the mechanochemical method was 43.0% higher than that of the plywood developed using the electromechanical stirring method, reaching 0.735 MPa, while in compliance with the GB/T 9846-2015 (China) standard for Class II plywood. In addition, the geopolymer-based adhesive had excellent thermal stability, and its mass retention rate was as high as 86.8% after treatment at 800oC. Meanwhile, the geopolymer-based adhesive endowed the flammable plywood with flame-retardant properties, and the heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of the plywood were as low as 275.9 kW/m2, 27.4 MJ/m2 and 0.84 m2, respectively. Therefore, geopolymer-based adhesives show great potential in replacing traditional aldehyde-based adhesives in plywood production, providing a new idea for quick, green, and efficient preparation of inorganic adhesives with excellent bonding properties.

Experimental investigation into mechanical performance of novel inorganic-bonded bamboo composite columns under axial compression

Engineering wood and bamboo composites bonded by organic adhesives have gradually become an important component in studies of green and sustainable development in the field of civil engineering. As an alternative solution, studies on inorganic adhesives in bio-based composites have sparked widespread research interest. Herein, a novel bamboo-based composite prepared with an inorganic adhesive was proposed, which is named “inorganic-bonded bamboo composite” and abbreviated as InorgBam. The compressive mechanical property is experimentally investigated. Fifteen groups of columns with various slenderness ratios are tested to evaluate the load–bearing capacity and buckling behavior under axial compressive load. The load–lateral deflection curves and stress–strain curves of the InorgBam columns correlated to the slenderness ratios were obtained. Results show that the strength failure with crushing at the end and buckling failure are the two typical failure modes of the InorgBam column under axial compression. The Euler formula and Newlin–Gahagan approach are adopted for calculating the ultimate stress in cases involving strength failure and buckling failure, and the stability coefficient of the InorgBam columns is analyzed using the prediction methods in the existing codes for the design of timber structures. The stability coefficient calculated by using formulas in the current codes for timber structures is feasible for InorgBam columns, and a proposed formula for the stability coefficient in the present study can be finely applied to the design of InorgBam columns. This study has valuable reference in promoting the structural application of this bamboo-based biomaterials.

Performance Study of Diamond Powder-Filled Sodium Silicate-Based Thermal Conductive Adhesives.

With the development of miniaturized, highly integrated, and multifunctional electronic devices, the heat flow per unit area has increased dramatically, making heat dissipation a bottleneck in the development of the electronics industry. The purpose of this study is to develop a new inorganic thermal conductive adhesive to overcome the contradiction between the thermal conductivity and mechanical properties of organic thermal conductive adhesives. In this study, an inorganic matrix material, sodium silicate, was used, and diamond powder was modified to become a thermal conductive filler. The influence of the content of diamond powder on the thermal conductive adhesive properties was studied through systematic characterization and testing. In the experiment, diamond powder modified by 3-aminopropyltriethoxysilane coupling agent was selected as the thermal conductive filler and filled into a sodium silicate matrix with a mass fraction of 34% to prepare a series of inorganic thermal conductive adhesives. The thermal conductivity of the diamond powder and its content on the thermal conductivity of the adhesive were studied by testing the thermal conductivity and taking SEM photos. In addition, X-ray diffraction, infrared spectroscopy, and EDS testing were used to analyze the composition of the modified diamond powder surface. Through the study of diamond content, it was found that as the diamond content gradually increases, the adhesive performance of the thermal conductive adhesive first increases and then decreases. The best adhesive performance was achieved when the diamond mass fraction was 60%, with a tensile shear strength of 1.83 MPa. As the diamond content increased, the thermal conductivity of the thermal conductive adhesive first increased and then decreased. The best thermal conductivity was achieved when the diamond mass fraction was 50%, with a thermal conductivity coefficient of 10.32 W/(m·K). The best adhesive performance and thermal conductivity were achieved when the diamond mass fraction was between 50% and 60%. The inorganic thermal conductive adhesive system based on sodium silicate and diamond proposed in this study has outstanding comprehensive performance and is a promising new thermal conductive material that can replace organic thermal conductive adhesives. The results of this study provide new ideas and methods for the development of inorganic thermal conductive adhesives and are expected to promote the application and development of inorganic thermal conductive materials.

Dual-crosslinking network and pre-anchorage effect enable high-performance, low-cost, and eco-friendly geopolymer adhesive for the wood industry

Alkali-activated geopolymers have shown unique advantages in applying adhesive materials because of their low cost, flame retardancy, and environmental friendliness. However, the high brittleness of the single aluminosilicate network and the weak interfacial compatibility of the geopolymer system result in poor bonding performance, which severely limits their application in the adhesives industry. Herein, a geopolymer-PF resin adhesive (GPA) with excellent comprehensive performance was successfully prepared by crosslinking geopolymer and PF resin with numerous reactive sites for the strong hybrid dual network under hot-pressing. In addition, the introduction of PF resin can achieve an effective pre-anchorage effect on wood for strong mechanical locking due to the excellent wettability, water resistance, and dimensional stability of PF resin. The produced GPA exhibits high initial wet shear strength (0.94 MPa) and adhesion toughness (0.271 J), 236% and 450% higher than pure geopolymer. The GPA also demonstrated remarkable age-strengthen performance, with bonding strength increasing to 1.27 MPa after 28 d, exceeding the majority of reported inorganic, biomass, and PF adhesives. In addition, the GPA displayed desirable eco-friendly and flame-retardant properties with a low-cost and sustainable approach. The pre-anchorage and double network structure design provide a general strategy for strengthening and toughening geopolymers, a key step forward in today's high-performance, low-cost, and sustainable production of inorganic adhesives from industrial solid wastes and geological resources.

EXPERIMENTAL RESEARCH DETAILED INDICATORS OF CEMENT-STABILIZED SOIL COMBINED EVOCRETE ST ADDITIVE

Statement of the problem. Under the conditions of intensive development of the world road transport infrastructure, there is currently a shortage of high-quality road construction materials. One of the key solutions to address this problem is to use stabilized soil with inorganic binder to make the pavement construction. Results. The paper presents an overview of the study results in evaluating the ability to use stabilized soil with inorganic binders, and other inorganic adhesives combinations for pavement construction. The study also shows the different levels of indicators of cement-stabilized soil combined Evocrete ST additive. Conclusions. It can be seen that the effectiveness of using Evocrete ST additive with a content of 3-5 % combining cement to stabilize the soil. The study proposes to use cement-stabilized soil combined Evocrete ST additive to make different type of pavement constructions.

Vertically-oriented graphene-boron nitride skeletons using graphene oxide as inorganic adhesives for high-efficiency thermal conduction of polymeric composites with electrical insulation and compressibility

Polymer-based thermal interface materials (TIMs) with high thermal conductivity are in high demand for rapid heat transfer between electronic components. It is still challenging to achieve significant enhancement in thermal conductivity of polymeric composites while maintaining satisfactory electrical insulation and good compressibility. In this work, we have developed a vertically-oriented graphene-boron nitride (GNP-BN) skeleton using graphene oxide (GO) as inorganic adhesives through ice-templating method, and vacuum-infiltrated with polydimethylsiloxane (PDMS) to fabricate GNP-BN/PDMS composites. The 5.2 wt% GNP-BN/PDMS composites exhibited high-efficiency thermal conduction (through-plane thermal conductivity of 1.16 W m−1 K−1 and enhancement efficiency as high as 104.7%), satisfactory electrical insulation (volume resistivity of over 108 Ω cm), and good compressibility (compressive modulus as low as 1.47 MPa). Such high performance is mainly attributed to the high-efficiency heat transfer pathway, low interfacial thermal resistance between components, effective hindrance to long-distance electron transport, and easy deformation of porous skeletons. The GNP-BN/PDMS composites show great potential to be used as high-performance TIMs in the field of electronic devices.

Flexural performance of RC beams strengthened with inorganic adhesive bonded NSM CFRP bar

Organic adhesives (e.g. epoxy) have been widely utilized in near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) strengthening technique for reinforced concrete (RC) structural members. Their inevitable shortcomings, such as poor fire resistance, emission of toxic fumes, and incompatibility with concrete substrate, necessitate the advancement of eco-friendly inorganic adhesives. In this study, two types of inorganic adhesives, including ordinary Portland cement mortar (OPCM) and alkali-activated slag mortar (AASM), were adopted in the NSM CFRP bar strengthening method for RC beams. The inorganic adhesive type, bonding length, and additional anchorage device on CFRP bar were considered as parameters in the strengthening scheme. One control beam and four strengthened beams were fabricated and tested, followed by comparison of their failure modes, loading behaviour, and reinforcement strains. The results show that all the strengthened beams exhibit higher ultimate loads than the control beam. Comparing to the OPCM, the AASM is more effective in mitigating debonding of CFRP bar and enhancing the ultimate load of beams. Furthermore, it is essential to provide a sufficient bonding length for AASM bonded NSM CFRP bars to guarantee their strengthening effectiveness. The addition of anchorage device for CFRP bars can further enhance the synergistic action between CFRP bar and adhesive, leading to a further enhancement in flexural strength and CFRP bar strain. In addition, the flexural strengths of OPCM or AASM bonded NSM CFRP bar-strengthened beams can be accurately predicted by the equations provisioned in ACI 440.2R-2017.

Green and rapid fabrication of superhydrophilic and underwater superoleophobic coatings for super anti-crude oil fouling and crude oil-water separation

The development of surfaces with super anti-crude oil-fouling behavior and crude oil-water separation properties is still a global challenge owing to the high viscosity of crude oil. Herein, superhydrophilic and underwater superoleophobic surfaces were successfully prepared by a simple, green and environmentally friendly one-step dip coating method. In the whole process, microcrystalline cellulose with hydrophilic hydroxyl functional groups was introduced into the coating with the help of inorganic adhesives, water was the only solvent, and no other organic solvents or surface modifiers was added. Besides being highly resistant to low viscosity oils and achieving effective oil-water separation (more than 98.3% separation efficiency after 30 cycles), the surface effectively resisted crude oil adhesion and achieved high viscosity crude oil-water separation. In addition, the underwater oil contact angle can still reach 147.5° and 152.5° after 20 cycles of sandpaper friction tests and 50 cycles of finger pressure tests, respectively, which indicates excellent durability. Furthermore, the method can achieve excellent superhydrophilicity and underwater superoleophobicity on varieties of substrates (such as copper foil, aluminum sheet and glass), showing very extensive applicability. It is expected that such fabrication strategy can provide a low cost, green and environmentally friendly approach to construct a series of superhydrophilic and underwater superoleophobic surfaces to achieve super anti-crude oil-fouling and (crude) oil-water separation.

Highly improved mechanical and thermal properties of alkali silicate and graphene nanoplatelet composite adhesives

Inorganic adhesives have received increased attention due to their high temperature resistance, non-toxicity, and environment friendliness. However, poor adhesion strength of inorganic adhesives hinders their application. Further, graphene improves the mechanical and thermal properties of polymer composites. Herein, graphene nanoplatelets (GNP) with different specific surface areas were added into a mixed silicate (MS) containing different ratios of alkali silicates. The results revealed that lap shear strengths increased from 7.4 MPa with the unmodified MS to 9.42 MPa with the MS/GNP 750_10% composite. In addition, the GNP powder with the highest surface area (MS/GNP 750_10% composite) formed maximum interfaces with the silicate matrix, leading to effective load transfer and reduction in stress concentration sites. Hardness and modulus increased as the GNP surface area increased; unmodified MS had the highest values because GNP changed MS from brittle to ductile. In addition, at room temperature, thermal conductivity increased by 60% in the vertical direction and 173% in the horizontal direction in the MS/GNP 750_10% composite compared to the unmodified MS. Furthermore, at a higher temperature (100 °C), the thermal conductivity of the MS/GNP 750_10% composite increased by 273% in the vertical direction and 412% in the horizontal direction. • This study investigated the effect of the surface area of GNP powder on the properties of Alkali silicate based adhesives. • The lap shear strength increased from 7.4 MPa in the bare MS to 9.42 MPa in the MS/GNP 750_10%. • The thermal conductivity increased by 60% in the vertical and 173% in the horizontal direction in the MS/GNP 750_10%.

Flexural performance of textile reinforced mortar on reinforced concrete beams

The report focuses on the study of the flexural properties of Textile Reinforced Mortar on Reinforced concrete beams using two distinct forms of textile fibre, such as carbon textile fibre and basalt textile fibre, which are separately superimposed on the strain zone by changing the amount of textile fibre layers. Two kinds of adhesives had been used for bonding textile overlays to the Reinforced concrete beams, such as organic and inorganic adhesives. The fine grained cement binder used in Textile reinforced Mortar behaves as an inorganic adhesive and epoxy was used instead of the organic binder. The number of layers used in overlays varied to determine their effectiveness in order to improve the load carrying ability. Beams and cylinders were cast and, therefore, experimental investigations were carried out on reinforced beams and cylinders using textile reinforced fibres in the flexure and split tensile tests. It was found that for the specimens overlaid with 2 layers of basalt fibre, the flexural strength increases by up to 38% and split durability increases by up to 12%

Solar selective reflector materials: Another option for enhancing the efficiency of the high-temperature solar receivers/reactors

The cavity wall is an important part of a cavity receiver in determining the receiver efficiency. Using solar selective reflector (SSR) materials with low solar absorptivity and high thermal emissivity for the cavity wall design is one efficient way to improve the receiver efficiency. In this work, we present a systematic study of the optical and high-temperature stability performances of six different SSR materials: one refractory ceramic fiber based substrate material (Fiberfrax 140) and five metallic oxide coatings which are prepared by mixing metallic oxide powders of alumina, magnesium oxide and titanium dioxide with commercial inorganic adhesives. The thermal stability was studied by heating up and keeping the six candidate materials in atmospheric conditions at a temperature of 1250 °C for 200 h. The spectrum of hemispherical reflectance in the spectrum band 0.25–25 μm was measured for analyzing the optical performance of the candidate materials. The obtained results show that all the six materials studied have good solar selective reflection characteristics, i.e, low solar absorptivity and relatively high thermal emissivity. Especially, the alumina coated substrate material shows excellent performances both for thermal stability and solar selective reflection. The solar reflectivity can reach 94.6%.

Effect of Thermal Stress on Push-Out Strength of Rod-Cylinder Joints Bonded with Inorganic Adhesives

Effect of Thermal Stress on Push-Out Strength of Rod-Cylinder Joints Bonded with Inorganic Adhesives

Mechanically durable superhydrophobic surfaces by binding polystyene nanoparticles on fibers with aluminum phosphate followed by hydrophobization

Mechanically durable superhydrophobic surfaces on cotton fabrics were fabricated by binding polystyrene nanoparticles onto fibers with aluminum phosphate (AP) followed by coating with polydimethylsiloxane (PDMS) as low surface energy substance. Decoration of nanoparticles roughened the fabric surface and coating with AP made stable the roughening structures. The as-prepared fabric surfaces not only showed excellent stability to acid, alkali, salt, organic solvent and UV irradiation, but also could maintain their superhydrophobicity after abrasion of 2000 or laundering of 35 cycles. The combination of inorganic adhesives AP and organic PDMS greatly enhanced the mechanical stability of the superhydrophobicty of the cotton substrate. Meanwhile, the obtained superhydrophobic fabrics showed excellent self-cleaning property.

Determination of Particles and Minerals Content in Soft Clay Soil of the Mekong Delta Coastal Provinces, Southern Vietnam for Inorganic Adhesives Stabilization

The paper aims at investigating the content of particles and minerals of soft clay soil in the Mekong Delta coastal provinces, southern Vietnam, as well as improving soil stability using inorganic adhesives, i.e.lime and cement-based stabilization. To study the composition of soft clay soil, a series of different laboratory methods were carried out and revealed various characteristics related to mineral composition, pH value, soluble salt content, and grain particle composition of soft clay soils. The results demonstrated five soil subtypes, namely high – saline soil (S2), low-saline soil (S1), acid sulfate soil (A), acid sulfate - saline soil (S-A), soil without salt andacid sulfate content (S0- A0). The soft clay soil (C) included 5 subtypes, which were C-S2, C-S1, C-A, C-AS, and C-S0-A0, whereas the soft sandy clay soil (SC) included three subtypes, namely SC-S2, SC- S1, and SC-S0-A0. Analysis of the above results showed that the high - saline soil, acid sulfate soil, and acid sulfate - saline soil are not suitable for lime and cement stabilization. This observation was illustrated by the initial experiment of cement – soil mixture properties.

Improving the water resistance and adhesion strength of a mixed alkali silicate adhesive by optimizing the molar ratio and curing conditions

It is important to eliminate the use of organic adhesives that are harmful to humans and cause environmental pollution. Environmentally friendly, harmless inorganic adhesives are being actively studied. Here, we found that optimized curing was possible when the curing time was controlled via temperature adjustment. We first prepared basic alkali silicate solutions, containing sodium, potassium, and lithium silicate, and compromised them in terms of water resistance. Adhesive strength was measured according to ASTM D3165 using a universal testing machine. The target material, a stainless steel (SUS) specimen, was prepared as described by ASTM D3165. Moreover, to develop fast thermal curing, the effects of two parameters were investigated: curing time and temperature. The temperature range tested was 80–140 °C for 2–36 h; we assessed adhesive strength. The maximum shear strength was obtained after thermal curing at 80 °C for 36 h, 120 °C for 12 h, and 140 °C for 2 h. However, when thermal curing proceeded past the maximum shear strength, the shear strength decreased, attributable to a reduction in the adherent area.

Facile preparation of a superamphiphobic fabric coating with hierarchical TiO2 particles

A functional superamphiphobic fabric coating with hierarchical TiO2 composite particles and inorganic adhesives displays excellent mechanical robustness, good chemical stability and self-healing property by a simple spraying method.

Properties of Inorganic Adhesives according to Phosphate Type and Borax Ratio

Properties of Inorganic Adhesives according to Phosphate Type and Borax Ratio

Mineral-Enhanced Polyacrylic Acid Hydrogel as an Oyster-Inspired Organic-Inorganic Hybrid Adhesive.

Underwater adhesion is crucial to many marine life forms living a sedentary lifestyle. Amongst them, mussel adhesion has been mostly studied, which inspires numerous investigations of 3,4-dihydroxyphenylalanine (DOPA)-based organic adhesives. In contrast, reef-building oysters represent another important "inorganic" strategy of marine molluscs for adhesion by generating biomineralized organic-inorganic adhesives, which is still rarely studied and no synthetic analogues have ever been reported so far. Here, a novel type of oyster-inspired organic-inorganic adhesive based on a biomineralized polyelectrolyte hydrogel is reported, which consists of polyacrylic acid physically cross-linked by very small amorphous calcium carbonate nanoparticles (<3 nm). The mineral-enhanced polyelectrolyte hydrogel adhesive is shown to be injectable, reusable, and optically clear upon curing in air. Moreover, comparable adhesion performance to DOPA-based adhesives is found for the hydrogel adhesive in both dry and wet conditions, which can even be further enhanced by introducing a small amount of second large cross-linker such as negatively charged nanoparticles. The present mineral hydrogel represents a new type of bio-inspired organic-inorganic adhesive that may find a variety of potential applications in adhesive chemistry.

Strength Design for Heat Resistant Adhesive Joints using Inorganic Adhesives

Strength Design for Heat Resistant Adhesive Joints using Inorganic Adhesives